1. Field Of The Invention
The present invention is directed generally to thermal energy storage devices.
2. Description of the Related Art
The Stirling engine was first described in an 1816 patent issued to a Scottish clergyman named Robert Stirling. Many variants of the Stirling cycle were implemented over the next century and applied to applications such as pumping water from mines, and powering ships. Stirling engines were even used as kerosene-fueled cooling fans available in early Sears catalogs. All such applications were later displaced by the advent of the electric motor and internal combustion (“IC”) engine.
Before Philips began to apply modern materials and thermodynamic analysis to the Stirling cycle in the 1940's, all Stirling machines operated with air at atmospheric pressure. The use of helium or hydrogen working fluid at significantly elevated charge pressure enabled major improvements in both efficiency and specific power. Philips, its licensees and others developed many versions of Stirling engines and coolers aimed at a wide range of applications, but outside of a few cryocooler applications, no significant commercialization has occurred. The primary reasons are the inherent life and reliability limitations imposed by the sliding seal in all kinematic Stirling machines (where piston and displacer motions are constrained by conventional crankshafts and related mechanisms), and the high cost that results from no engines having crossed the threshold from demonstration machines to high level production of an engine with comprehensive design for manufacture and assembly (“DFMA”).
A typical Stirling engine includes a hot heat exchanger and a cold heat exchanger. Heat is supplied to the hot heat exchanger at a high temperature Th and rejected to the environment at a low temperature Tc from the cold heat exchanger. A regenerator heat exchanger located between the hot heat exchanger and cold heat exchanger stores and delivers thermal energy to different parts of the cycle. In a two piston alpha configuration, a phase difference between two piston motions is used to extract net work from the cycle by having most of the gas in the hot region during the expansion phase (volume between the two pistons is increasing) and most of the gas in the cold region during the compression phase (volume between the two pistons is decreasing). Net positive cyclic work is applied to the pistons because cycle work output from expanding a hot gas is greater than negative cycle work input by compressing a cold gas. Inertia associated with the piston motions carries the engine through the compression work phase. Single acting alpha engines can only be implemented as kinematic machines since the resonant dynamic forces acting on free pistons cannot achieve a phase relationship that enables positive work output.
Beta and gamma Stirling engine configurations both use a single power piston, but add a displacer piston to shuttle working gas between the hot and cold ends. The displacer motion does not change total cycle volume (except at a second order level resulting from the physical diameter of the displacer drive rod), but creates a pressure wave within the cycle working gas by shuttling gas through the heat exchangers so that most of the gas alternates between the hot and cold regions. This pressure wave applied to the power piston generates net cyclic work that causes the piston to reciprocate. Beta and gamma engine configurations can be implemented as either kinematic or free piston engines. Free-piston engines utilize different resonant dynamics of a lightly loaded displacer (that shuttles gas only through the heat exchangers) and the heavily loaded power piston (that extracts work from the engine cycle) to resonantly tune the system to achieve the proper strokes and phase relationship between piston and displacer motions. The difference between beta and gamma engine configurations is that in beta engine configurations, the displacer and power pistons are constrained to the same diameter so they can reciprocate within the same cylinder. In contrast, gamma engine configurations offer more design flexibility with the piston and displacer in separate cylinders. These engines are inherently single acting.
Traditional kinematic Stirling engines extract power from the Stirling cycle via mechanical linkages. They are complicated and expensive to build, and require a lubricated crankcase, piston and rod seals, and mechanical bearings that restrict performance and limit life. Power output is difficult to vary in a kinematic design, generally being accomplished by a complex system that pumps the helium or hydrogen working fluid back and forth between the engine and a storage reservoir to change the average working pressure in the engine. By contrast, free-piston Stirling engines (“FPSE”), such as those available from Infinia Corporation of Houston, Tex. (“Infinia”), include an independently mounted displacer and a power piston that is directly coupled to a linear alternator, both using virtually infinite life flexure bearings and clearance seals that do not require lubricants. Power can be varied over a wide range of output levels, while maintaining high efficiency by using the engine controller electronics to vary terminal voltage and, therefore, piston stroke. Free-piston Stirling engines may be configured to have a simple mechanical configuration that delivers a highly efficient, low or no maintenance product.
As explained above, a Stirling engine is powered by thermal energy. For continuous operation, a Stirling engine typically requires a continuous supply of thermal energy at its hot end. The thermal energy is used to maintain the high temperature Th, of the hot end. However, some sources of thermal energy are not continuous. For example, solar energy is intermittent. Further, some thermal energy sources may supply more energy than is required to operate the Stirling engine. Thus, a need exists for devices configured to store thermal energy for later use by a Stirling engine or other thermal energy consuming devices. The present application provides this and other advantages as will be apparent from the following detailed description and accompanying figures.
The present application provides a thermal energy storage (“TES”) and transfer device for storing thermal energy generated by a thermal energy source and transferring it to a different physical location. The stored thermal energy may be used at a later time by a recipient structure or device such as a thermal energy driven power generation device or any other device requiring thermal energy (e.g., a Stirling engine or a steam turbine). The TES device may be described as a buffering means for thermal energy supplied by a thermal energy source before the thermal energy is provided to the recipient structure or device. Thus, the TES device may be used to introduce a delay period between the generation of the thermal energy and its consumption by a thermal energy driven power generation device. Alternatively, the TES device may be configured to provide thermal energy to a thermal energy driven power generation device without introducing a delay. As will be described below, the TES device may be adapted for use with various thermal energy sources as well as various recipient structures or devices, including various thermal energy driven power generation devices.
The thermal energy input portion 102 and the thermal energy output portion 104, are each configured to transfer heat through at least one heat transfer mode (e.g., conduction and/or convection). By way of a non-limiting example, the thermal energy input portion 102 and/or the thermal energy output portion 104 may be implemented as a simple conductor. Alternatively, the thermal energy input portion 102 and/or the thermal energy output portion 104 may be implemented as a heat pipe (described below) or similar structure.
Thermal energy (illustrated as arrow “A1”) is transferred to the thermal energy input portion 102 of the TES media 110 from a thermal energy source 130. The thermal energy source 130 may be external to the interior chamber 100 of the vessel 90 or alternatively, housed inside the interior chamber 100. The thermal energy source 130 may be implemented using any suitable heat source.
The thermal energy (illustrated as arrow “A1”) transferred to the thermal energy input portion 102 heats the TES media 110 housed inside the interior chamber 100. The TES device 10 includes one or more heat transporting members or means 140 configured to transfer heat via at least one heat transfer mode (e.g., conduction and/or convection). By way of a non-limiting example, the heat transporting means 140 may be implemented as simple conductors (e.g., solid rods of thermally conductive material).
Alternatively, the heat transporting means 140 may be implemented as one or more conventional heat pipes. Heat pipes transfer thermal energy from a hotter location to a cooler location. Heat pipes may be configured to perform this function even when a small difference in temperature exists between the hotter location and cooler location. At the hotter location, heat pipes have a hot interface and at the cooler location, heat pipes have a cold interface. Heat pipes also have a liquid tight interior void (e.g., a channel or chamber) that houses a working fluid defined by an outer sidewall constructed from a material having a high thermal conductivity. Inside the interior void, the working fluid is housed in a partial vacuum having a pressure near or below the vapor pressure of the working fluid. Thus, inside the interior void, a portion of the working fluid in a liquid phase and a portion of the working fluid in a gas phase. In other words, the working fluid is in a saturated phase that includes a saturated liquid and saturated vapor.
Inside the interior void, thermal energy is transferred from the hot interface to the cold interface via a process referred to as two-phase convection. Specifically, inside a heat pipe, at the hot interface, the working fluid evaporates to form a saturated vapor. The portion of the heat pipe in which the working fluid evaporates may be referred to as an evaporator. The evaporated working fluid flows as a gas toward the cold interface whereat it condenses back into a liquid. The portion of the heat pipe in which the working fluid condenses may be referred to as a condenser. The liquid working fluid then returns to the hot interface. By way of an example, the interior void of the heat pipe may include wicks that move the liquid working fluid by capillary action back to the hot interface whereat the working fluid may evaporate again. Alternatively, gravity or some other force may be used to return the liquid working fluid back to the hot interface whereat the working fluid may evaporate again. Thus, inside the interior void, the working fluid repeated cycles between the gas phase and the liquid phase as well as between the hot interface and the cold interface.
A heat pipe need not have any particular shape. For example, a heat pipe may have an elongated extruded shape (e.g., a hollow cylindrical shape), a non-elongated shape (e.g., a hollow disk shape), and the like. As is appreciated by those of ordinary skill in the art, a heat pipe may transport thermal energy along a single direction or multiple directions. In implementations that transport thermal energy in multiple directions, the hot interface and the cold interface may change physical locations on the heat pipe as the temperatures at the hotter location and/or the cooler location change. Thus, the flow direction of thermal energy through the heat pipe may change in response to changing temperatures at the hotter location and/or the cooler location.
In addition to transferring thermal energy via two-phase convention, a heat pipe may transfer thermal energy via conduction. For example, as mentioned above, the interior void of the heat pipe is defined by an outer sidewall constructed from a thermally conductive material. The outer sidewall will conduct thermal energy to surrounding media (e.g., the TES media 110) and/or structures (e.g., thermal energy output portion 104).
The heat transporting means 140 are illustrated as heat pipes 140A, 140B, 140C, 140D, and 140E, disposed inside the TES media 110. The heat pipes 140A—140E transfer thermal energy stored in the TES media to the thermal energy output portion 104 of the vessel 90. The heat pipes 140A—140E may be configured to transport thermal energy to the thermal energy output portion 104 from the TES media 110 and to transport thermal energy from the thermal energy output portion 104 to the TES media 110. In other words, the heat pipes 140A—140E may provide bidirectional thermal energy flow. The direction in which thermal energy flows may be determined based upon which of the thermal energy output portion 104 and the TES media 110 is hotter. If the thermal energy output portion 104 is hotter than the TES media 110, the heat pipes 140A—140E will transport thermal energy from the thermal energy output portion 104 to the TES media 110. On the other hand, if the TES media 110 is hotter than the thermal energy output portion 104, the heat pipes 140A—140E will transport thermal energy from the TES media 110 to the thermal energy output portion 104. Alternatively, the heat pipes 140A—140E may be configured to transport thermal energy in only a single flow direction from TES media 110 to the thermal energy output portion 104.
Optional conductive fins (e.g., fins 836 illustrated in
The TES device 10 may include sensors “HF1,” “HF2,” and “HF3.” The sensors “HF1,” “HF2,” and “HF3” are positioned in locations where the TES media freezes last as the thermal energy is extracted therefrom. The sensors “HF1,” “HF2,” and “HF3” are also positioned in locations where the TES media melts last as the thermal energy is stored therein. When the vessel 90 has a generally cylindrical shape, one or more sensors “HF1” are arranged inside the interior chamber 100 in a location adjacent the thermal energy input portion 102, one or more sensors “HF2” are arranged inside the interior chamber 100 in a location adjacent the thermal energy output portion 104, and one or more sensors “HF3” are arranged inside the interior chamber 100 along its central axis extending between the thermal energy input portion 102 and thermal energy output portion 104. The sensors “HF1,” “HF2,” and “HF3” are configured to measure temperature information and transmit that information. When the last region of TES media 110 to freeze, freezes or the last region of TES media to melt, melts, the temperature of the TES media 110 can be measured and the energy content of the TES media determined.
While not illustrated in
By way of yet another alternate embodiment, one or more of the heat transporting means 140 may be connected between the thermal energy input portion 102 and the thermal energy output portion 104. By way of a non-limiting example, the heat pipes 140A—140E may extend from the thermal energy input portion 102 to the thermal energy output portion 104. The heat pipes 140A—140E may be configured to transport thermal energy directly from the thermal energy input portion 102 to the thermal energy output portion 104 and to transport thermal energy directly to the thermal energy input portion 102 from the thermal energy output portion 104. In other words, the heat pipes 140A—140E may provide bidirectional thermal energy flow. As explained above, the direction in which thermal energy flows may be determined based upon which of the thermal energy input portion 102 and the thermal energy output portion 104 is hotter. If the thermal energy input portion 102 is hotter than the thermal energy output portion 104, the heat pipes 140A—140E will transport thermal energy from the thermal energy input portion 102 to the thermal energy output portion 104. On the other hand, if the thermal energy output portion 104 is hotter than the thermal energy input portion 102, the heat pipes 140A—140E will transport thermal energy from the thermal energy output portion 104 to the thermal energy input portion 102. Alternatively, the heat pipes 140A—140E may be configured to transport thermal energy in only a single flow direction, i.e., from the thermal energy input portion 102 to the thermal energy output portion 104.
In embodiments in which the heat pipes 140A—140E are connected between the thermal energy input portion 102 and the thermal energy output portion 104, the heat pipes 140A—140E may pass through the TES media 110 or may be insulated therefrom. If the heat pipes 140A—140E pass through the TES media 110, at least a portion of the thermal energy transported by the heat transporting means 140 may be transferred to the TES media 110 and stored thereby. If the heat pipes 140A—140E are configured to provide bidirectional thermal energy flow. The direction in which thermal energy flows may be determined based upon which of the thermal energy input portion 102, the thermal energy output portion 104, and the TES media 110 is hotter. If the thermal energy input portion 102 is hotter than the thermal energy output portion 104 and the TES media, the heat pipes 140A—140E will transport thermal energy from the thermal energy input portion 102 through the TES media 110 to the thermal energy output portion 104. On the other hand, if the thermal energy output portion 104 is hotter than the thermal energy input portion 102 and the TES media 110, the heat pipes 140A—140E will transport thermal energy from the thermal energy output portion 104 through the TES media 110 to the thermal energy input portion 102. Alternatively, if the TES media 110 is hotter than both the thermal energy input portion 102 and the thermal energy output portion 104, the heat pipes 140A—140E will transport thermal energy from the TES media 110 to both the thermal energy output portion 104 and the thermal energy input portion 102.
Optionally, insulation (not shown) may be used to insulate the heat transporting means 140 and limit the amount of thermal energy transferred from the heat transporting means 140 to the TES media 110.
The thermal energy output portion 104 includes a heat delivery assembly 150 having an inside surface 145 spaced inwardly from an outside surface 160. The heat delivery assembly 150 may be implemented as a vapor chamber, heat pipe, and the like. The heat delivery assembly 150 includes a liquid tight internal chamber 165 at least partially defined between the spaced apart inside and outside surfaces 145 and 160. A two-phase compound or working fluid 167, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like, is housed inside the internal chamber 165. Inside the internal chamber 165, the heat delivery assembly 150 may condense and wick the working fluid 167 much like a conventional heat pipe (discussed above).
As mentioned above, one or more heat transporting means 140 are affixed to the inside surface 145 and configured to transfer thermal energy from the TES media 110 to the inside surface 145 of the heat delivery assembly 150. In particular embodiments, the heat pipes 140A—140E are in two-phase fluidic communication with the thermal working fluid 167 of the heat delivery assembly 150. The inside surface 145 is heated by the thermal energy originating from the heat transporting means 140 and/or the TES media 110. The heated inside surface 145 heats the working fluid 167 inside the internal chamber 165 of the heat delivery assembly 150. Then, the heated working fluid 167 heats the outside surface 160 of the heat delivery assembly 150. Thermal energy transferred to the inside surface 145 of the heat delivery assembly 150 by the heat transporting means 140 and/or the TES media 110 is comingled inside the internal chamber 165 of the heat delivery assembly 150 to produce a relatively uniform temperature and heat flux along the outside surface 160.
Thermal energy (illustrated as arrow “A2”) is transferred from the outside surface 160 to a recipient structure or device 170, such as a thermal energy driven power generation device. Thus, the outside surface 160 of the heat delivery assembly 150 is a heat-exchange surface. The recipient structure or device 170 may include any suitable device requiring heat energy. Non-limiting examples of suitable recipient structures or devices for use with the TES device 10 include an engine, a Stirling engine, a generator, a heat exchanger, and the like.
In alternate embodiments (not shown), the heat delivery assembly 150 may be omitted from the thermal energy output portion 104 of the vessel 90. In such embodiments, the thermal energy output portion 104 may include at least a portion of an outside surface of the interior chamber 100, which serves as a heat exchange surface. One or more of the heat transporting means 140 are affixed to the portion of the outside surface of the interior chamber 100 and transfer thermal energy from the TES media 110 to the portion of the outside surface of the interior chamber 100. The recipient structure or device 170 may be coupled to the portion of the outside surface of the interior chamber 100 and configured to receive thermal energy therefrom.
In embodiments in which the thermal energy source 130 is external to the interior chamber 100, the interior chamber 100 may include a heat receiving outside surface 180. In such embodiments, the outside surface 160 of the heat delivery assembly 150 and the heat receiving outside surface 180 are both heat-exchange surfaces. The outside surface 160 of the heat delivery assembly 150 can be configured in any manner appropriate for effecting an interface between the vessel 90 and the recipient structure or device 170. Similarly, the heat receiving outside surface 180 can be configured in any manner appropriate for effecting an interface between the vessel 90 and the thermal energy source 130. For example, one or both of these surfaces could be configured with fins, heat exchangers, heat exchangers that utilize a liquid, conduction means, and the like. Further, one or both of these surfaces may include a portion of one or more of the heat transporting means 140.
In particular embodiments described below, the outside surface 160 of the heat delivery assembly 150 is substantially planar. In such embodiments, the substantially planar outside surface 160 of the heat delivery assembly 150 may be configured to be coupled to a substantially planar or flat heater head of a Stirling engine.
The TES device 10 may be characterized as transferring thermal energy from a first location or region (e.g., the thermal energy source 130) to a second region (e.g., the recipient structure or device 170). Further, as mentioned above, because the transfer of thermal energy may be delayed by the TES media 110, depending upon the implementation details, particular embodiments of the TES device 10 may be used to buffer thermal energy as it is transferred between the first and second regions. The TES device 10 may be utilized as a thermal capacitor in any system requiring uniform application of heat flux from a non-uniform first region to the second region.
By way of non-limiting examples, the TES device 10 may be configured to perform one or more of the following functions:
The recipient structure or device 170 may be implemented as a prime mover configured to convert thermal energy to mechanical power, pneumatic power, hydraulic power, electrical power, and the like. Often, a prime mover will have a temperature range of peak efficiency. Because the TES device 10 can be operated with the TES media 110 in a saturated condition, latent heat can be delivered to the prime mover ideally isothermally at a desired temperature. If it is desirable to extract thermal energy stored in the TES media 110 for use with the prime mover, the sensible heat transfer could also be used once an appropriate temperature gradient is established.
The thermal energy source 130 may be implemented as a single heat source or multiple separate heat sources. For example, the TES device 10 may be configured for use with a single heat source, such as radiant solar energy or solar power. Alternatively, the TES device 10 may be configured for use with a multimode heat source that includes both solar power and heat developed from combustion. The thermal energy source 130 may be implemented using geothermal energy, or any other source of high-grade heat, alone or in a combination. Through application of ordinary skill in the art to the present teachings, the geometry of the TES device 10 could be altered to accommodate any thermal energy source or recipient structure or device requiring heat transfer.
The TES media 110 is a phase change material (“PCM”). Using latent heat of fusion of the phase change TES media 110 in the TES device 10 may improve the specific weight and volume relative to a TES device using a single-phase TES media. Thus, the TES device 10 may be incorporated in an integrated source/TES/sink module (e.g., an electrothermal system 300 illustrated in
There are many pure and eutectic salts, mostly alkali halides, with attractive properties for use as the TES media 110. Selection of the TES media 110 depends on matching its melting point to the application, namely, the temperature range desired at the heat sink. The TES device 10 may be configured to provide nearly isothermal heat transfer during the solidification phase of heat extraction. Also, depending on the acceptable operating temperature range of the heat sink, sensible heat may be extracted from the two-phase TES media 110 in its liquid and solid phases near its melting temperature. The TES device 10 may be utilized as a thermal capacitor in any system requiring uniform application of heat flux to a sink from a non-uniform source.
The TES media 110 serves two functions. First, the TES media functions as a heat transfer medium between the thermal energy input portion 102 and the thermal energy output portion 104. Second, the TES media 110 stores thermal energy and provides that stored thermal energy to the thermal energy output portion 104 when the thermal energy input portion 102 is not receiving thermal energy from the thermal energy source 130. The TES media 110 used may have a high melting temperature, and high latent heat of fusion. For example, eutectic salts may be used. By way of non-limiting examples, mixtures of LiF/NaF/MgF2, LiF/NaF, NaF/NaCl, and the like may be used. These mixtures have a relatively high heat of fusion and a melting temperature of about 1200° F.
While the above mentioned TES medias are suitable for this application, there are alternative materials available for achieving high energy storage. For example, Li, LiOH, LiH, LiF/CaF2, LiF, NaF, CaF2, and MgF2 may be used.
Particular implementations are configured such that the recipient structure or device 170 operates within a temperature range of about 1800° F. to about 900° F. For example, a Stirling engine may be configured to operate efficiently within this temperature range. In such implementations, lithium hydride (“LiH”) may be a desirable material because of its specific (fusion) energy and energy available over the designated temperature range of about 1800° F. to about 900° F. The heat of fusion of LiH is nearly three times that of the LiF/NaF/MgF2 eutectic. Moreover, its high heat capacity gives LiH an exceptionally high sensible heat addition over the temperature range of about 1800° F. to about 900° F.
On a volume basis, the above-mentioned TES medias are more balanced and somewhat equivalent. Of TES medias exhibiting a reasonable melting temperature, LiF appears to stand out as the best performing material for both energy density during fusion and over the temperature range of about 1800° F. to about 900° F. The heat of fusion per volume of LiH is not one of the top-performers in this case, owing to its low density, but LiH still provides the second best energy density over the temperature range of about 1800° F. to about 900° F., again due to its high heat capacity. The LiF/NaF/MgF2 eutectic rates fairly well in this case, offering almost the same performance as LiH. However, depending upon implementation details, single compounds such as LiH or LiF may be easier to prepare and implement.
Different values for the heat of fusion and melting temperature of LiF/NaF/MgF2 eutectic are known in the art: one based on thermochemical property data provided by Infinia Corporation of Houston, Tex. (“Infinia”); and another provided by an extensive NASA study. The thermochemical property data provides slightly better TES performance. Nevertheless, it is believed the chemical composition of the eutectics used to obtain these properties is the same.
If the interior chamber 100 of the vessel 90 has a volume of about 0.545 ft3. Table A1 below lists the material weights and available energies from various TES medias, including LiH, LiF, and the LiF/NaF/MgF2 eutectic. As shown in Table A1, by using LiH, the weight could be reduced by 50 lb in comparison to the LiF/NaF/MgF2 eutectic, without a significant change in energy storage.
Tables A2 and A3 below list additional properties of materials suitable for use as the TES media 110.
Fluoride salts (e.g., LiF, NaF, and MgF2) are reasonably safe to use and handle in most environments. These materials are inherently stable as indicated by their high melting temperature. They are not combustible, cannot explode, and have low reactivity at ambient conditions. A few of them are considered to be a moderate health hazard and/or moderately toxic, and thus require a reasonable amount of personal protection (e.g., goggles, gloves, lab smock, respirator or fume hood), when using. The fluoride salts can be irritants to the skin and airways, and should never be eaten (although NaF is a very minor ingredient in some toothpaste brands).
Table A4 below summarizes National Fire Protection Association (“NFPA”) and Hazardous Materials Identification System (“HMIS”) ratings given to LiF, NaF, MgF2, and LiH by most MSDS listings. Each rating system provides a score of 0-4 in three specific categories with “0” generally representing no special hazards and “4” used for severe or extreme hazard potential.
According to Table A4, the fluoride salts present a fairly low hazard overall. Further, shipping and general handling of the fluoride salts at room temperature does not appear to pose any special risks or measures. Many of the potential heath hazards associated with the fluoride salts (1-2 ratings) are due to applications where they are used/handled as a fine powder. Powders generally have higher hazards because of their high surface area (and thus reactivity) and the ease in which they can be inhaled and/or ingested. It is unlikely, however, that the TES media 110 would be in a powder form. As a thermal storage or heat transfer material, the TES media 110 may be most efficient when used as a continuous solid or liquid mass.
Another common warning for these materials is the possible release of hydrogen fluoride, hydrofluoric acid, or fluorine gases under circumstances such as extremely high temperatures (prompting decomposition) or exposure to water at high temperature. However, this cannot occur if the TES media 110 is stored in a water-free sealed container/vessel, and held below all but extreme (>2500° F.) temperatures, as would be the case for the TES media 110 used in the TES devices described herein (e.g., the TES device 10). However, it may not be crucial that the TES media 110 be completely dry before use to prevent the formation of the gases mentioned above. Naturally, corrosion of the vessel 90 should be limited and kept to a minimum.
LiH may be the most hazardous material mentioned above for use as the TES media 110. This is due to LiH's high reactivity with water, which results in the production of highly flammable hydrogen gas, and highly irritating lithium hydroxide (LiOH) and lithium oxide (Li2O) solids. By itself, however, LiH is very stable, and does not decompose unless heated above 1800° F. (where it breaks down to Li metal and H2 gas). Even then, the decomposition reaction is not exothermic, requiring continued energy input to sustain it. Note in Table A4 above, LiH is given a NFPA flammability rating covering a range of 0 to 4. This depends on the reporting source. Apparently some suppliers/manufacturers consider only whether the material itself is flammable (LiH is not flammable), or whether its potential water-reaction byproducts (hydrogen) are flammable (hydrogen is flammable). This inconsistency obviously leads to some confusion in MSDS interpretation.
In the same way, the health hazard rating of 3 for LiH is due to the water reaction products of LiOH and Li2O, two very irritating and caustic substances to the skin and airways.
ARL has used LiH in experimental testing both as a hydrogen generating material and in a limited TES study. In both programs, LiH was used repeatedly in a solid and a molten state without incident. Primary precautions taken when handling LiH included keeping it away from water or humid ambient air, and avoiding the creation of LiH dust. Typically, LiH was handled/transferred inside an argon atmosphere glove box at the steam plant. When this was not practical, an argon purge was kept above open LiH containers, and respirators and protective gloves were worn when handling.
TES medias and materials are typically used in high-temperature, long-endurance applications. Thus, corrosion and durability of their containment vessel is certainly a critical issue. Although the data is far from complete, studies by NASA and Infinia show that common austenitic stainless steels hold up fairly well to molten fluoride salts, as does the some of the nickel-based Inconels and Hastelloys. The chromium component in these metals appears to be most vulnerable as CrF2 and CrF3 compounds are predicted to form at higher equilibrium concentrations than other metal fluorides. As already mentioned, the NASA study also showed the importance of removing residual water from the salts prior to loading in sealed vessels. This reduces the potential to make hydrogen fluoride at high temperature, a very reactive material to almost all materials including metals.
Investigations of LiH performed by ARL were conducted exclusively in 316 stainless steel vessels. Although total exposure time in the molten state was relatively short (hours), the vessels never showed any visual signs of surface degradation or weakening. The vessel 90 may be constructed from a stainless steel, such as 304 stainless steel, 316 stainless steel, and the like. However, the material used to construct the vessel 90 should be analyzed for corrosion and stress cracking as appropriate.
Alkali halide salts and salt eutectics offer many advantages when used as the TES media 110 in the TES device 10. Such salts have high latent heat of fusion and good sensible heat capacity, resulting in very high energy storage density. They are relatively benign to work with, can function through thousands of melt/freeze cycles without degradation, and cause negligible corrosive attack on conventional stainless steel containment. Depending upon the implementation details, it may also be possible to “recharge” the TES device 10 more rapidly than conventional electrochemical batteries by heating and re-melting the TES media 110 at a high heat transfer rate.
A challenge when designing a TES system (such as the TES device 10) is providing for effective heat transfer from the thermal energy source 130 to the TES media 110 (e.g., salt) and from the TES media 110 to the recipient structure or device 170, while maintaining the TES device 10 at a uniform temperature and avoiding large temperature gradients during the heat addition process and heat delivery process. The TES media 110 properties that create this challenge are its relatively low thermal conductivity when in the solid phase, and the higher density of the solid phase when compared to the liquid phase. For example, the solid phase may be about 20%-25% denser than the liquid phase.
As the liquid-phase TES media 110 (e.g., salt) is cooled by the recipient structure or device 170, the mass fraction of liquid TES media relative to solid TES media, will begin to change in the region best connected thermally to the recipient structure or device 170 via one or more of the heat transporting means 140. Earlier analyses have shown that, for particular embodiments, the TES media 110 should be no more than one to two inches from one of the heat transporting means 140. Heat pipes (e.g., the heat pipes 140A—140E) have been shown to offer adequate heat transport capability to effectively couple the TES media 110 to the recipient structure or device 170. This heat transport capability can be modified by the inclusion of optional conductive fins.
The latent heat of melting the solid TES media 110 at a fixed temperature is much larger than the sensible heat extracted from the liquid TES media over a particular temperature range (e.g., about 1800° F. to about 900° F.). This same principle is utilized for prior art trough TES systems. If a melting point near the peak efficiency temperature of the recipient structure or device 170 is used, most of the time the TES device 10 is operating at near optimum conditions for the recipient structure or device 170. The TES device 10 may serve as a thermal energy buffer that can maintain a relatively constant heat flux for the thermal energy output portion 104. With this relatively constant heat flux, undesirable “hot spots” can be prevented.
The TES media 110 may be selected based on the desired operating conditions of the recipient structure or device 170. For example, the TES media 110 selected may be based on the particular embodiment of the TES device in which the TES media is to be used.
Typical TES medias in the form of salts, or eutectic salts, have a low thermal conductivity. This poses a practical difficulty during operation of the TES device 10 because the TES media 110 is stored as a bulk material within the interior chamber 100 of the vessel 90. For both sensible and latent heat transfer, arrangements of prior art thermal energy transport structures can be ineffective at transferring heat into and out of the bulk TES media 110 uniformly. This problem may be compounded by TES medias that undergo a volumetric change when changing phase. Volumetric changes in TES medias in the range 30% are typical.
The poor thermal conductivity of many TES medias, volumetric changes caused by phase changes, means for adding or extracting heat from the TES medias, and voids present in solid or low quality TES medias have created challenges and poor heat transfer and overall performance in prior art TES devices that include thermal energy transport structures. Some prior art devices, such as the one described in U.S. Pat. No. 5,113,659 issued to Baker et al. on May 19, 1992, have tried to overcome these problems by storing TES media in small cells or canisters disposed about a thermal energy transport structure. However, this approach also has drawbacks. For example, the structure does not permit an appreciable amount of thermal capacitance or storage. Additionally, the introduction of an intermediary canister negatively affects heat transfer to the media due contact resistance and convection losses.
During steady-state operation, the heat transporting means 140 (e.g., the heat pipes 140A—140E) may each be considered ideally isothermal. Depending upon the configuration and arrangement of the heat transporting means 140, this can allow for uniform heat transfer to the bulk TES media 110 stored in the interior chamber 100 of the vessel 90 for purposes of adding or extracting latent or sensible heat. For uniform heat transfer to occur, the heat transporting means 140 (e.g., the heat pipes 140A—140E) may be configured to reduce or eliminate the presence of solid masses in the TES media 110 during certain modes of operation.
In certain circumstances, it is desirable for the TES media 110 to undergo a complete phase change. To transition the TES media 110 from a solid to a liquid, sensible heat is first transferred into the TES media 110. Then, latent heat is transferred into the TES media 110. Optionally, the liquid TES media 110 may be heated further by the addition of more sensible heat. Thus, to store thermal energy in the TES media 110, it may be necessary to transition all or a portion of the TES media from a solid to a liquid.
To extract all of the heat energy present in the TES media 110, it may be necessary to transition the TES media 110 from a liquid to a solid. This would require transferring the latent heat from TES media 110, which causes the phase change from liquid to solid. Then, remaining sensible heat may be extracted from the TES media 110 provided an appropriate temperature gradient exists. As is appreciated by those of ordinary skill in the art, before the latent heat is extracted, the liquid TES media 110 may be storing some sensible heat. When this is the case, the media is a single-phase liquid and not saturated. The sensible heat may be transferred from the single-phase liquid TES media 110 before the latent heat is extracted.
Some exemplary implementations of the TES device 10 will now be described.
In the TES device 200, thermal energy is transferred to the TES media 110 from the first and second thermal energy sources 208 and 210 in different directions (identified by arrows “A1” and “A3,” respectively). If the thermal energy source 210 is external to the interior chamber 100, the thermal energy source 210 may transfer thermal energy to the TES media 110 via a heat exchange surface 220. By way of non-limiting examples, different thermal energy sources may be used to add thermal energy to the TES device 200 along different planes, axes, or directions. The amount of thermal energy transferred into the TES device 200 from the thermal energy source 208 and/or the thermal energy source 210 may be controlled as needed. In
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The electrothermal system 300 includes a heat module 312 and a power module 314. In the embodiment illustrated, the heat module 312 is implemented as a Stirling engine 315, which may be configured to efficiently extract energy stored in the TES media 110. The heat module 312 may also receive thermal energy directly from the thermal energy input portion 102 and/or from one or more external thermal energy sources (not shown).
A Stirling engine converts heat or thermal energy into mechanical power by alternately compressing and expanding a fixed quantity of working fluid or other gas (i.e., hydrogen, helium, and air) at different temperatures. Thermal energy is supplied to a hot heat exchanger portion or heater head portion 315A of the Stirling engine 315 at a high temperature Th, and rejected to the environment from a cold heat exchanger portion 315B at a low temperature Tc. The working fluid is generally compressed in a colder portion 315C of the Stirling engine 315 and expanded in a hotter portion 315D resulting in a net conversion of heat into work. The functionality and components of Stirling engines are well known in the art and will not be described in further detail.
To convert mechanical movement to electrical power, the Stirling engine 315 may be coupled to or integrated with the power module 314. For example, the Stirling engine 315 may include a displacer 316 and a working fluid 318 in fluid communication with a power piston 320, which is part of the power module 314. The power piston 320 of the power module 314 may be connected to a conventional linear electrodynamic system 322 through a shaft 323 coupled to a mover 324. The linear electrodynamic system 322 further includes a stator 326 and a paired electrical line 328 to furnish or receive electrical power. Movement of the mover 324 relative to the stator 326 creates an electrical current that may be carried by the paired electrical line 328 to power one or more external electrical devices 330. Several alternate Stirling engine configurations are known in the art, and the present disclosure is not limited to use with any particular implementation of the Stirling engine.
Once the Stirling engine 315 is started, control may be accomplished by controlling the engine's output. For example, if as in
The electrothermal system 300 includes one or more sensors 327A, 327B, and/or 327C configured to sense temperature information from which heat flux may be determined. The sensors 327A, 327B, and/or 327C are positioned at locations where thermal energy is delivered to or received from the TES device 10.
The sensors 327A are placed on the heater head portion 315A of the Stirling engine 315 in a sufficiently cool location or safe zone (i.e., one that allows high sensor reliability) may be used to provide feedback to a stroke regulator or controller 329. Alternatively, the sensors 327A may be placed on the outside surface 160 of the heat delivery assembly 150. The sensors 327A collect temperature information that provides a proxy for heater head temperature. Carnot efficiency for the Stirling engine 315 increases as the temperature of the heater head portion 315A increases. If thermal energy available to the heater head portion 315A is held constant, as stroke increases, the temperature of the heater head portion 315A is drawn down or decreases. On the other hand, if thermal energy available to the heater head portion 315A is held constant, as stroke decreases, the temperature of the heater head portion 315A increases.
The sensors 327A transmit temperature information to the controller 329, which the controller 329 uses to determine a stroke setting. The controller 329 may determine a stroke setting that is optimal for a given operational parameter. The controller 329 is coupled to the mover 324 and configured to determine its stroke and thereby the temperature of the heater head portion 315A.
The heater head portion 315A of the Stirling engine 315 is connected to the outside surface 160 of the heat delivery assembly 150 of the TES device 10. The outside surface 160 of the heat delivery assembly 150 transfers thermal energy to the heater head portion 315A of the Stirling engine 315, which drives the displacer 316 and the power piston 320 and generates an electrical current in the electrical line 328.
The electrothermal system 300 includes a concentrator 340, such as a parabolic dish or mirror that concentrates solar energy on an absorber 350. The concentrator 340 may be mounted on a chassis/stand 360 and positioned by a tracking drive 362. By way of a non-limiting example, the concentrator 340 may be a modified or unmodified 3-kW solar dish sold by Infinia. The absorber 350 may be a component of the thermal energy input portion 102 of the TES device 10. For example, the absorber 350 may be the heat receiving outside surface 180 of the TES device 10. Alternatively, the absorber 350 may be another structure configured to transfer absorbed solar energy to the thermal energy input portion 102 of the TES device 10.
Optionally, the electrothermal system 300 may include a solar thermal receiver 370 adjacent the thermal energy input portion 102 of the TES device 10 configured to receive radiant solar energy from the concentrator 340. The receiver 370 may include a receiver plate 373 having an aperture 374 formed therein configured to reduce losses of the solar energy concentrated on the absorber 350. As mentioned above, the absorber 350 may be the heat receiving outside surface 180 of the TES device 10. Alternatively, the absorber 350 may be a component of the receiver 370. By way of a non-limiting example, the electrothermal system 300 may be constructed by modifying a 3-kW commercial Dish Stirling Concentrated Solar Power (“CSP”) system sold by Infinia to incorporate the TES device 10 between the receiver 370 and the Stirling engine 315.
Referring to
If the heater head portion 315A is too hot, the decision in decision block 2620 is “YES” and at block 2630, the controller 329 directs the Stirling engine 315 to increase its stroke thereby cooling the heater head portion 315A. In turn, the heater head portion 315A will cool the thermal energy output portion 104 of the TES device 10.
At decision block 2640, whether the new cooler temperature of the thermal energy output portion 104 is less than the temperature of the TES media 110 is determined. If the new cooler temperature of the thermal energy output portion 104 is less than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2640 is “YES” and at block 2650, the heat transporting means 140 will transport stored thermal energy from the TES media 110 to the thermal energy output portion 104. In turn, the thermal energy output portion 104 will transfer the received thermal energy to the heater head portion 315A. Thus, the heater head portion 315A receives thermal energy previously stored in the TES media 110. Then, the method 2600 returns to block 2610.
If the new cooler temperature of the thermal energy output portion 104 is not less than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2640 is “NO,” and the method 2600 advances to decision block 2655.
At decision block 2655, whether the new cooler temperature of the thermal energy output portion 104 is greater than the temperature of the TES media 110 is determined. If the new cooler temperature of the thermal energy output portion 104 is greater than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2655 is “YES” and at block 2660, the heat transporting means 140 will transport stored thermal energy from the thermal energy output portion 104 to the TES media 110 for storage. This will cool the thermal energy output portion 104 and cause the heater head portion 315A to transfer thermal energy to the thermal energy output portion 104 thereby cooling the heater head portion 315A. Then, the method 2600 returns to block 2610.
If the new cooler temperature of the thermal energy output portion 104 is not greater than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2655 is “NO,” and the method 2600 returns to block 2610.
If the heater head portion 315A is not too hot, the decision in decision block 2620 is “NO,” and the method 2600 advances to decision block 2675. At decision block 2675, the controller 329 determines whether the heater head portion 315A is too cool based on the temperature information received from the sensors 327A.
If the heater head portion 315A is too cool, the decision in decision block 2675 is “YES,” and at block 2680, the controller 329 directs the Stirling engine 315 to decrease its stroke thereby heating the heater head portion 315A. In turn, the heater head portion 315A will heat the thermal energy output portion 104 of the TES device 10.
At decision block 2685, whether the new hotter temperature of the thermal energy output portion 104 is greater than the temperature of the TES media 110 is determined. If the new hotter temperature of the thermal energy output portion 104 is greater than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2685 is “YES” and at block 2688, the heat transporting means 140 will transport thermal energy from the thermal energy output portion 104 to the TES media 110 for storage thereby. This will cool the thermal energy output portion 104 and cause the heater head portion 315A to transfer thermal energy to the thermal energy output portion 104 thereby cooling the heater head portion 315A. Then, the method 2600 returns to block 2610.
If the new hotter temperature of the thermal energy output portion 104 is not greater than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2685 is “NO,” and the method 2600 advances to decision block 2690.
At decision block 2690, whether the new hotter temperature of the thermal energy output portion 104 is less than the temperature of the TES media 110 is determined. If the new hotter temperature of the thermal energy output portion 104 is less than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2690 is “YES” and at block 2695, the heat transporting means 140 will transport stored thermal energy from the TES media 110 to the thermal energy output portion 104. In turn, the thermal energy output portion 104 will transfer the thermal energy to the heater head portion 315A. Thus, the heater head portion 315A receives thermal energy previously stored in the TES media 110. Then, the method 2600 returns to block 2610.
If the new hotter temperature of the thermal energy output portion 104 is not less than the temperature of the TES media 110 inside the interior chamber 100 of the vessel 90, the decision in decision block 2690 is “NO,” and the method 2600 returns to block 2610.
If the heater head portion 315A is not too cool, the decision in decision block 2675 is “NO,” and the method 2600 returns to block 2610. The sensing performed in block 2610 may be performed periodically or at random intervals.
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Referring to
The flux sensors transduce heat flux using measuring temperature. This is used to establish a thermal gradient to measure heat transfer. For certain embodiments, the sensors 327A, 327B, and 327C may be located so that they are not operated over-temperature. While exemplary locations for the sensors 327A, 327B, and 327C have been illustrated, through application of ordinary skill in the art to the present teachings alternate locations may be determined that are also suitable for determining the difference in the rate of heat transfer into and out of the TES device 10 and such embodiments are also within the scope of the present teachings.
Further, as explained above, the TES device 10 includes sensors “HF1,” “HF2,” and “HF3” that sense temperature information inside the interior chamber 100 of the vessel 90. The sensors “HF1,” “HF2,” and “HF3” may be coupled to the controller 329 and configured to transmit temperature information to the controller 329. The sensors “HF1,” “HF2,” “HF3,” 327A, 327B, and/or 327C may be communicatively connected to the controller 329 via wired and/or wireless connections.
As mentioned above, when the last region of TES media 110 to freeze, freezes or the last region of TES media to melt, melts, the temperature of the TES media 110 can be measured and the energy content of the TES media determined. These points in time may be used as starting time for a method 2800 illustrated in
At first block 2810, the sensors 327A, 327B, and/or 327C sense temperature information and transmit that temperature information to the controller 329 (see
In block 2830, the sensors “HF1,” “HF2,” and “HF3” sense temperature information inside the interior chamber 100 of the vessel 90, transmit that temperature information to the controller 329 (see
At decision block 2840, the controller 329 determines whether the amount of thermal energy stored in the TES device 110 (calculated in block 2820) exceeds a predetermined threshold value. If the amount of thermal energy stored in the TES device 110 exceeds the predetermined threshold value, the decision in decision block 2840 is “YES,” in block 2850, the controller 329 directs the Stirling engine 315 to increase its stroke to cool the heater head portion 315A to below the temperature of the TES media 110 (determined in block 2830). In turn, the heater head portion 315A will cool the thermal energy output portion 104 of the TES device 10.
Then, in block 2860, the heat transporting means 140 will transport stored thermal energy from the TES media 110 to the thermal energy output portion 104. In turn, the thermal energy output portion 104 will transfer the thermal energy to the heater head portion 315A. Thus, the heater head portion 315A receives thermal energy previously stored in the TES media 110. Then, the method 2800 returns to block 2810.
If the amount of thermal energy stored in the TES device 110 is less than the predetermined threshold value, the decision in decision block 2840 is “NO,” and in block 2870, the controller 329 directs the Stirling engine 315 to decrease its stroke to heat the heater head portion 315A to above the temperature of the TES media 110 (determined in block 2830). In turn, the heater head portion 315A will heat the thermal energy output portion 104 of the TES device 10. Then, the heat transporting means 140 will transport thermal energy from the thermal energy output portion 104 to the TES media 110 for storage thereby. Then, the method 2800 returns to block 2810.
The predetermined threshold value may be based at least in part on a quantity of thermal energy required to operate the Stirling engine 315 for a predetermined period of time. For example, the predetermined threshold value may be set equal to the amount of thermal energy required to operate the Stirling engine 315 for a predetermined amount of time (e.g., 2 hours, 3 hours, 4 hours, 6 hours, etc.).
The thermal energy input portion 102 of the TES device 400 includes a heat receiving assembly 404. In the embodiment illustrated, the heat receiving assembly 404 includes the absorber 350 and an internal wall 406 spaced inwardly from the absorber. The heat receiving assembly 404 may include an internal chamber 407 housing a working fluid 408, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the internal chamber 407 of the heat receiving assembly 404 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 404 functions as a conventional heat pipe. The heat receiving assembly 404 may be implemented as a heat pipe, a vapor chamber, and the like. Alternatively, the heat receiving assembly 404 may be configured to transfer thermal energy only by conductance.
The TES device 400 includes two separate sets of annular, or cylindrical shell-shaped heat transporting means 410A and 410B. The first set of heat transporting means 410A interleave with the second set of heat transporting means 410B in an alternating arrangement. The first set of heat transporting means 410A is spaced apart from the second set of heat transporting means 410B with TES media 110 disposed therebetween. However, in alternate embodiments, a single set of cylindrical shell-shaped heat transporting means (not shown) may connect the thermal energy input portion 102 directly to the thermal energy output portion 104.
The first set of heat transporting means 410A extends from the thermal energy input portion 102 of the TES device 400 into the TES media 110 but stop short of the thermal energy output portion 104. Solar flux concentrated by the concentrator 340 (see
The thermal energy output portion 104 of the TES device 400 includes a heat delivery assembly 450 substantially identical to the heat delivery assembly 150 (see
The second set of heat transporting means 410B extends from the thermal energy output portion 104 of the TES device 400 into the TES media 110 but stop short of the thermal energy input portion 102. The second set of heat transporting means 410B are illustrated as a plurality of concentrically arranged annular shaped heat pipes 432A to 432C. Each of the annular shaped heat pipes 432A to 432C has an internal channel 434 defined between a first heat conducting annular sidewall 436 space apart from a second heat conducting annular sidewall 438. Each of the internal channels 414 has an open end portion 440 in communication with the internal chamber 465 of the heat delivery assembly 450 of the thermal energy output portion 104 of the TES device 400. Thus, the working fluid 467 may travel within and between the internal channels 434 of the second set of heat transporting means 410B and the internal chamber 465 of the heat delivery assembly 450.
In the embodiment illustrated, the outside surface 460 of the heat delivery assembly 450 includes a portion of the heater head portion 315A of the Stirling engine 315 (see
The heater head portion 315A may be welded or brazed to the TES device 400 so the weight of the TES device 400 may be structurally supported by the Stirling engine 315. The heater head portion 315A may include a braze lip or weld lip 472 that may be weldable to the vessel 90 of the TES device 400. In other words, in the embodiment illustrated, the thermal energy output portion 104 of the TES device 400 is integrally formed with the heater head portion 315A of the Stirling engine 315 (see
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The TES device 400 can be configured to provide a high performance thermal storage system that successfully transports the heat to and from the phase change TES media 110 so that the latent heat of fusion and sensible heat can be stored over a wide range of temperatures. The TES device 400 may be configured to provide several hours of Stirling engine operation on demand. The TES device 400 may be configured so that it increases the size and weight of the commercial 3-kW Infinia solar heat drive by no more than a desired amount. The electrothermal system 300 (see
The Stirling engine 315 (see
Alternatively, the thermal capacity of the concentrator 340 may be increased to increase the amount of thermal energy supplied to the TES device 400. The amount of thermal energy supplied to the TES device 400 may be adequate to provide for sufficient thermal energy in the TES media 110 and at the same, provide sufficient thermal energy to operate the Stirling engine 315 at full output for the day. For example, assuming a nominal 10-hour daily operating period, the effective area of the concentrator 340 implemented as a solar dish sold by Infinia may be increased 40% to provide adequate thermal energy for simultaneous engine operation and TES storage. Such an increase in effective area may be achieved by increasing the diameter of the solar dish from its current diameter of about 4.8 m to a new diameter of about 5.7 m.
The TES media 110 may be implemented using a combination of environmentally benign salts that undergo a phase change at operating temperatures, and small quantities of either sodium or potassium metals within the vessel 90. The salts may include KF/NaF and/or NaF/NaCl eutectic mixtures in quantities of approximately 10 to 1000 lbs. These salts may be sealed inside the vessel 90 for the life of the TES device 400. Should a breach occur in the vessel 90, the salts are unreactive but fluoride poisoning can occur if consumed internally. Appropriate precautions would be taken to insure that exposure was minimized. While sodium and potassium in the metallic form are considered very reactive, the TES device 400 may be configured to use a small amount (e.g., approximately 30 grams) of these substances to effect the heat transfer.
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As mentioned above, the TES device 10 may be configured without pump loops that pump the TES media 110. In such embodiments, the TES device 10 will not experience the same maintenance issues associated with prior art centralized trough and power tower electrothermal systems. Multiple electrothermal systems 300 may be collocated in an array (not shown). For example, two to thousands of the electrothermal systems 300 may be aggregated into an array (not shown). Because the TES device 10 does not include any pumps or pump any fluids, problems associated with high temperature pumps and frozen loops will not render multiple electrothermal systems 300 within an array nonoperational. Should a problem occur, only one electrothermal system 300 in the array will experience issues, allowing the remaining electrothermal systems to continue operating. Thus, if only one electrothermal system 300 in an array is rendered nonoperational, the nonoperational electrothermal system will have little impact on the overall power production of the array.
Maintaining optical accuracy of the concentrated solar energy on the heater head portion 315A of a Stirling engine 315 can be expensive because the heater head portion needs to be heated uniformly to avoid hot spots that cause thermal stress. By incorporating the TES device 10 between the heater head portion 315A and the receiver 370, the heater head portion 315A is decoupled from the receiver 370, allowing more variability of the solar flux at the receiver 370 and/or absorber 350 without causing thermal stress on the heater head portion 315A. Further, the TES device 10 stores the heat and delivers it to the heater head portion 315A of the Stirling engine 315 uniformly. This lowers the optical accuracy requirements of the concentrator 340 and may reduce costs related to the concentrator 340, the chassis/stand 360, the tracking drive 362, the heater head portion 315A, as well as a variety of other subsystems of the electrothermal system 300 relative to prior art electrothermal systems.
Because the heater head portion 315A may be heated uniformly by the TES device 10, the entire electrothermal system 300 may be operated at higher heat flux than prior art electrothermal systems. Without the TES device 10, the heater head portion of a Stirling engine may characterized as operating at an average temperature, but some spots along the heater head portion 315A will be about 500° C. others will be about 650° C. Thus, if one were to try to increase the average temperature to about 650° C. some portions of the heater head portion 315A would be hotter than 650° C. Those portions are referred to as “hot spots.” If hot spots are minimized, the temperature of the entire heater head portion 315A can be maintained at a uniform temperature (e.g., about 650 C), which may increase power output and efficiency. By way of a non-limiting example, initial calculations related to the impact of incorporating the TES device 10 in the electrothermal system 300 have determined an overall system cost reduction of as much as 20%.
Solar TES is typically associated with trough TES systems and central receiver TES systems. Trough TES systems include several candidate approaches with widely varying stages of development. The LUZ SEGS I trough, using the primary mineral oil heat transfer fluid (HTF) in hot and warm tanks, provided 3 hours of daily direct energy storage capacity between 1985 and 1999. The 10-MW Solar 2 central receiver system demonstrated the viability of molten salt TES in the late 1990's. These and most other direct and indirect solar TES systems use sensible heat capacity stored in the liquid state, are relatively inefficient with typical solar to electric efficiencies of 15-20%, require complex pumping systems, and typically require large installations with plant sizes in the tens or hundreds of MW to be economically viable. Molten salt systems should avoid salt freezing. The entire system should be shut down with any freezing or when a component within the TES requires maintenance or fails. Phase change materials, which provide a large increase in energy storage density by utilizing the latent heat of fusion, are typically used only for low temperature storage in space heating and water heating applications.
In contrast, the electrothermal system 300 uses a PCM (the TES media 110) that is closely integrated with the Stirling engine 315 and the solar energy absorber 350 (and optionally, the receiver 370). The vessel 90 of the TES device 10 may be hermetically sealed and maintenance free. The TES device 10 may be characterized as a passive heat transport system that does not require insulated pumps, fittings, or other components to transport hot fluid. The TES device 10 is unaffected by ambient temperature levels or melt-freeze cycles. The electrothermal system 300 may be incorporated into an array of like electrothermal systems 300. In such an array, any problem that develops will negatively affect only a single electrothermal system 300.
Utilization of the latent heat of fusion in a TES device greatly improves the specific weight and volume relative to single phase TES systems and enables the practical use of an integrated receiver/TES/engine module.
Lithium salts generally have the best energy storage density but are also relatively quite expensive. Therefore, a non-lithium NaF/NaCl alternative is illustrated for comparison. While the NaF/NaCl alternative provides only about half the total volumetric storage capacity of LiH, the NaF/NaCl alternative still provides about five times the volumetric storage capacity of the liquid-phase NaNO3/KNO3 salt used in a “high temperature” advanced trough TES test loop by ENEA in Spain, in which the salt tanks operate at 270° C. and 550° C. There are many pure and eutectic salts, mostly alkali halides, with attractive properties that may be used to implement the TES media 110.
The KF/NaF phase equilibrium depicted in
Implementation challenges include low TES media thermal conductivities and a large volume increase during melting. With the variable orientation angle of a solar tracking system, heat transfer to and from the TES media 110 should be available in all regions of the vessel 90 for all orientations of the vessel, with sufficient heat transfer area between the heat transporting means 140 (e.g., the first and second sets of heat transporting means 410A and 410B illustrated in
The size of the TES device 10, the receiver 370, the concentrator 340, and other components of the system 300 may be determined based on operating parameters, such as a duration over which the Stirling engine 315 is to operate on power extracted from the TES media 110 after the thermal energy source 130 (see
The TES device 400 (see
The thermal energy input portion 102 of the TES device 800 includes a heat receiving assembly 804 including the heat receiving outside surface 180 of the thermal energy input portion 102, an internal wall 806 spaced inwardly from the heat receiving outside surface 180, and an internal chamber 807 at least partially defined between the heat receiving outside surface 180 and the internal wall 806. The heat receiving assembly 804 may be implemented as a vapor chamber, heat pipe, and the like. The internal chamber 807 of the heat receiving assembly 804 may house a working fluid 808, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the internal chamber 807 of the heat receiving assembly 804 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 804 functions as a conventional heat pipe transferring thermal energy via two-phase convention with or without conduction. In particular embodiments, the input energy portion 102 may transport thermal energy via conduction alone.
The TES device 800 includes two separate sets of heat transporting means 810A and 810B. The first set of heat transporting means 810A a spaced apart from the second set of heat transporting means 810B with TES media 110 disposed therebetween. The first set of heat transporting means 810A are distributed within the interior chamber 100 between the second set of heat transporting means 810B.
The first set of heat transporting means 810A extends from the internal wall 806 of the heat receiving assembly 804 into the interior chamber 100 housing the TES media 110 but stops short of the thermal energy output portion 104. Thermal energy transferred to the heat receiving assembly 804 of the thermal energy input portion 102 is transported into the TES media 110 by the first set of heat transporting means 810A, which are illustrated as being a plurality of elongated cylindrically shaped heat pipes 812. Each of the heat pipes 812 has an internal channel 814 and in particular embodiments may contain a plurality of radially outwardly extending conductive fins 816. In particular embodiments, the optional fins may be oriented at a clocking angle that would provide optimal heat transfer to and from the TES media. A closed end portion 820 of each of the internal channels 814 abuts the internal wall 806 of the heat receiving assembly 804. Thus, the working fluid 808 may travel inside the heat receiving assembly 804 but not within the internal channels 814 of the first set of heat transporting means 810A. In particular embodiments, the first set of heat transporting means 810A may be in fluidic communication with the internal chamber 807 of the heat receiving assembly 804. In particular embodiments, the first set of heat transporting means 810A may be in conductive communication with the heat receiving assembly 804.
The thermal energy output portion 104 of the TES device 800 includes a heat delivery assembly 850 substantially identical to the heat delivery assembly 150 (see
The second set of heat transporting means 810B extends from the inside surface 145 of the heat delivery assembly 850 of the thermal energy output portion 104 into the interior chamber 100 for housing the TES media 110 but stops short of the thermal energy input portion 102. The second set of heat transporting means 810B are illustrated as being a plurality of elongated cylindrically shaped heat pipes 832. Each of the heat pipes 832 has an internal channel 834 and a plurality of radially outwardly extending fins 836. A closed end portion 840 of each of the internal channels 834 abuts the inside surface 851 of the heat delivery assembly 850. Thus, the working fluid 867 may travel within the heat delivery assembly 850 but not within the internal channels 834 of the second set of heat transporting means 810B. In particular embodiments, the second set of heat transporting means 810B may be in fluidic communication with the internal chamber 865 of the heat delivery assembly 850. In particular embodiments, the second set of heat transporting means 810B may be in conductive communication with the heat delivery assembly 850.
The thermal energy input portion 102 of the TES device 900 includes a heat receiving assembly 904 including the heat receiving outside surface 180 of the thermal energy input portion 102, an internal wall 906 spaced inwardly from the heat receiving outside surface 180, and an internal chamber 907 at least partially defined between the heat receiving outside surface 180 and the internal wall 906. The heat receiving assembly 904 may be implemented as a vapor chamber, heat pipe, and the like. The heat receiving assembly 904 may house a working fluid 908, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the interior of the internal chamber 907 of the heat receiving assembly 904 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 904 functions as a conventional heat pipe.
The thermal energy output portion 104 of the TES device 900 includes a heat delivery assembly 950 substantially identical to the heat delivery assembly 150 (see
The TES device 900 includes a single set of spaced apart heat transporting means 910 that are distributed within the interior chamber 100 housing the TES media 110 (see
The heat transporting means 910 are illustrated as being a plurality of elongated cylindrically shaped heat pipes 912. Each of the heat pipes 912 has an internal channel 914 and a plurality of radially outwardly extending fins 916. A first closed end portion 920 of each of the internal channels 914 abuts the internal wall 906 of the heat receiving assembly 904 and a second closed end portion 922 of each of the internal channels 914 abuts the inside surface 951 of the heat delivery assembly 950. Thus, the working fluid 908 may travel inside the heat receiving assembly 904 but not within the internal channels 914 of the heat transporting means 910 and the working fluid 967 may travel within the heat delivery assembly 950 but not within the internal channels 914 of the heat transporting means 910. In particular embodiments, the heat transporting means 910 may be in fluidic communication with the internal chamber 907 of the heat receiving assembly 904 and/or the internal chamber 965 of the heat delivery assembly 950. In particular embodiments, the heat transporting means 910 may be in conductive communication with the heat receiving assembly 904 and/or the heat delivery assembly 950.
The interior chamber 100 of the vessel 90 of the TES device 1000 includes a central portion “C1” surrounded by a perimeter portion “P1.” The vessel 90 includes an annular shaped interior insulated channel 1002 extending along the perimeter portion “P1” of the interior chamber 100. The interior insulated channel 1002 may be segregated from the remainder of the interior chamber 100 by a continuous sidewall or divider 1005. The TES media 110 (see
The thermal energy input portion 102 of the TES device 1000 includes a heat receiving assembly 1004, including the heat receiving outside surface 180 of the thermal energy input portion 102, an internal wall 1006 spaced inwardly from the heat receiving outside surface 180, and an internal chamber 1007 at least partially defined between the heat receiving outside surface 180 and the internal wall 1006. The heat receiving assembly 1004 may be implemented as a vapor chamber, heat pipe, and the like. The heat receiving assembly 1004 may house a working fluid 1008, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the internal chamber 1007 of the heat receiving assembly 1004 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 1004 functions as a conventional heat pipe.
The TES device 1000 includes a first set of spaced apart heat transporting means 1010A and a second set of spaced apart heat transporting means 1010B. Each of the heat transporting means of the first and second sets 1010A and 1010B are spaced apart from one another and distributed within the interior chamber 100. The heat transporting means of the first and second sets 1010A and 1010B may be spaced apart from one another and distributed within the interior chamber 100 to optimize heat transfer to and from the TES media 110. The first set of heat transporting means 1010A reside inside the interior insulated channel 1002 and the second set of heat transporting means 1010B reside outside the interior insulated channel 1002.
The thermal energy output portion 104 of the TES device 1000 includes a heat delivery assembly 1050 substantially identical to the heat delivery assembly 150 (see
Each of the first set of spaced apart heat transporting means 1010A extend between the thermal energy input portion 102 and the thermal energy output portion 104. In the embodiment illustrated, the first set of spaced apart heat transporting means 1010A extend from the internal wall 1006 of the heat receiving assembly 1004 through the insulated interior channel 1002 of the interior chamber 100 to the inside surface 1051 of the heat delivery assembly 1050 of the thermal energy output portion 104. The insulated interior channel 1002 limits the amount of thermal energy that can be transferred from the first set of spaced apart heat transporting means 1010A to the TES media 110 (see
The first set of heat transporting means 1010A are illustrated as being a plurality of elongated cylindrically shaped heat pipes 1012. Each of the heat pipes 1012 has an internal channel 1014. A first closed end portion 1020 of each of the internal channels 1014 passes through the internal wall 1006 of the heat receiving assembly 1004 to dispose at least a portion 1020A of the first closed end portion 1020 of each of the internal channels 1014 inside the internal chamber 1007 of the heat receiving assembly 1004. A second closed end portion 1022 of each of the internal channels 1014 passes through the inside surface 1051 of the heat delivery assembly 1050 to dispose at least a portion 1022A of the second closed end portion 1022 of each of the internal channels 1014 inside the internal chamber 1065 of the heat delivery assembly 1050. Thus, the working fluid 1008 may travel inside the internal chamber 1007 of the heat receiving assembly 1004 but not within the internal channels 1014 of the first set of heat transporting means 1010A and the working fluid 1067 may travel within the internal chamber 1065 of the heat delivery assembly 1050 but not within the internal channels 1014 of the first set of heat transporting means 1010A.
The second set of heat transporting means 1010B extends from the inside surface 1051 of the heat delivery assembly 1050 of the thermal energy output portion 104 into the central portion “C1” of the interior chamber 100 housing the TES media 110 but stops short of the internal wall 1006 of the heat receiving assembly 1004 of the thermal energy input portion 102. The second set of heat transporting means 1010B are distributed within the central portion “C1” of the interior chamber 100 outside the insulated interior channel 1002. The second set of heat transporting means 1010B may be distributed within the central portion “C1” of the interior chamber 100 in such a way as to optimize the performance of the TES module 1000.
The second set of heat transporting means 1010B are illustrated as being a plurality of elongated cylindrically shaped heat pipes 1032. Each of the heat pipes 1032 has an internal channel 1034. Optionally, the heat pipes 1032 may include a plurality of radially outwardly extending fins (not shown). A closed end portion 1040 of each of the internal channels 1034 passes through the inside surface 1051 of the heat delivery assembly 1050 to dispose at least a portion 1040A of the closed end portion 1040 of each of the internal channels 1034 inside the internal chamber 1065 of the heat delivery assembly 1050. Thus, the working fluid 1067 may travel within the heat delivery assembly 1050 but not within the internal channels 1034 of the second set of heat transporting means 1010B.
After thermal energy has been transported to the thermal energy output portion 104 by the first set of heat transporting means 1010A, the second set of heat transporting means 1010B transport a portion of the thermal energy not being used by the recipient structure or device 170 (see
The interior chamber 100 of the vessel 90 of the TES device 1100 includes a central portion “C2” surrounded by a perimeter portion “P2.” The vessel 90 includes an interior insulated channel 1102 in its central portion “C2.” The TES media 110 (see
The thermal energy input portion 102 of the TES device 1100 includes a heat receiving assembly 1104 including the heat receiving outside surface 180 of the thermal energy input portion 102, an internal wall 1106 spaced inwardly from the heat receiving outside surface 180, and an internal chamber 1107 at least partially defined between the heat receiving outside surface 180 and the internal wall 1106. The heat receiving assembly 1104 may be implemented as a vapor chamber, heat pipe, and the like. The internal chamber 1107 of the heat receiving assembly 1104 may house a working fluid 1108, such as sodium, helium, mercury, zinc, indium, ammonia, alcohol, methanol, water, steam, air, and the like. As is appreciated by those of ordinary skill in the art, the internal chamber 1107 of the heat receiving assembly 1104 may contain a wicked structure that provides substantially identical functionality to that provided by a wick in a conventional heat pipe (described above). In this particular embodiment, the heat receiving assembly 1004 functions as a conventional heat pipe. The TES device 1100 includes a first set of spaced apart heat transporting means 1110A and a second set of spaced apart heat transporting means 1110B. Each of the heat transporting means of the first and second sets 1110A and 1110B are spaced apart from one another and distributed within the interior chamber 100. The heat transporting means of the first and second sets 1110A and 1110B may be spaced apart from one another and distributed within the interior chamber 100 to optimize heat transfer to and from the TES media. The first set of heat transporting means 1110A reside inside the interior insulated channel 1102 and the second set of heat transporting means 1110B reside outside the interior insulated channel 1102.
The thermal energy output portion 104 of the TES device 1100 includes a heat delivery assembly 1150 substantially identical to the heat delivery assembly 150 (see
Each of the first set of spaced apart heat transporting means 1110A extend between the thermal energy input portion 102 and the thermal energy output portion 104. In the embodiment illustrated, the first set of spaced apart heat transporting means 1110A extend from the internal wall 1106 of the heat receiving assembly 1004 through the insulated interior channel 1102 of the interior chamber 100 to the inside surface 1151 of the heat delivery assembly 1150 of the thermal energy output portion 104. The insulated interior channel 1102 limits the amount of thermal energy that can be transferred from the first set of spaced apart heat transporting means 1110A to the TES media 110 (see
The first set of heat transporting means 1110A are illustrated as being a plurality of elongated cylindrically shaped heat pipes 1112. Each of the heat pipes 1112 has an internal channel 1114. A first closed end portion 1120 of each of the internal channels 1114 passes through the internal wall 1106 of the heat receiving assembly 1104 to dispose at least a portion 1120A of the first closed end portion 1120 of each of the internal channels 1114 inside the heat receiving assembly 1104. A second closed end portion 1122 of each of the internal channels 1114 passes through the inside surface 1151 of the heat delivery assembly 1150 to dispose at least a portion 1122A of the second closed end portion 1122 of each of the internal channels 1114 inside the heat delivery assembly 1150. Thus, the working fluid 1108 may travel inside the internal chamber 1107 of the heat receiving assembly 1104 but not within the internal channels 1114 of the first set of heat transporting means 1110A and the working fluid 1167 may travel within the internal chamber 1165 of the heat delivery assembly 1150 but not within the internal channels 1114 of the first set of heat transporting means 1110A.
The second set of heat transporting means 1110B extends from the inside surface 1151 of the heat delivery assembly 1150 of the thermal energy output portion 104 into the portion 1103 of the interior chamber 100 housing the TES media 110 but stops short of the internal wall 1106 of the heat receiving assembly 1104 of the thermal energy input portion 102. The second set of heat transporting means 1110B are distributed within the portion 1103 of the interior chamber 100 outside the insulated interior channel 1102.
The second set of heat transporting means 1110B are illustrated as being a plurality of elongated cylindrically shaped heat pipes 1132. Each of the heat pipes 1132 has an internal channel 1134. Optionally, the heat pipes 1132 may include a plurality of radially outwardly extending fins (not shown). A closed end portion 1140 of each of the internal channels 1134 passes through the inside surface 1151 of the heat delivery assembly 1150 to dispose at least a portion 1140A of the closed end portion 1140 of each of the internal channels 1134 inside the heat delivery assembly 1150. Thus, the working fluid 1167 may travel within the heat delivery assembly 1150 but not within the internal channels 1134 of the second set of heat transporting means 1110B.
After thermal energy has been transferred to the thermal energy output portion 104 by the first set of heat transporting means 1110A, the second set of heat transporting means 1110B transport a portion of the thermal energy not being used by the recipient structure or device 170 (see
Thus, the TES devices 1000 and 1100 illustrated in
The TES subassembly 1210 has a housing 1220 defining a hollow interior region 1222 configured to store the TES media 110 (see
The housing 1220 has an open end portion 1226 configured to receive the combustor subassembly 1212, which may be affixed therein. By way of a non-limiting example, the combustor subassembly 1212 may be non-removably affixed to the housing 1220 using conventional metal bonding techniques known in the art. The combustor subassembly 1212 extends into the hollow interior region 1222 configured to store the TES media 110 (see
Opposite the open end portion 1226, the housing 1220 has a closed-end portion 1228. A heat delivery assembly 1230 that performs the function as the heat delivery assembly 150 (see
In the embodiment illustrated, the heat delivery assembly 1230 has been implemented as a heat pipe. The heat delivery assembly 1230 includes an interior sidewall 1232 spaced apart from an external sidewall 1234 with an internal chamber 1235 at least partially defined therebetween. In this embodiment, the thermal energy output portion 104 includes the heat delivery assembly 1230 and its interior and exterior sidewalls 1232 and 1234. The interior sidewall 1232 has a perimeter portion 1233 adjacent the housing 1220. Optionally, the interior sidewall 1232 includes a plurality of spaced apart through-holes 1240. The external sidewall 1234 may include the heater head portion 315A.
The external sidewall 1234 may include a ring shaped transition member disposed about the heater head portion 315A. The housing 1220 may be welded or brazed to the perimeter portion 1233 of the interior sidewall 1232 and the ring shaped transition member. The optional heater head portion 315A and/or ring shaped transition member may include weld lips (not shown) that may be used to weld the housing 1220 thereto. The interior sidewall 1232 and optionally exterior sidewall 1234 include one or more fill ports 1236.
The TES subassembly 1210 includes a plurality of heat transporting means 1258 illustrated as hollow cylindrically shaped heat pipes 1260 that extend from the interior sidewall 1232 toward the combustor subassembly 1212 and into the TES media 110 (see
The TES media 110 (see
External devices, such as the recipient structure or device 170 (see
The combustor subassembly 1212 will now be described. As mentioned above, the combustor subassembly 1212 is disposed inside the open end portion 1226 of the housing 1220 and extends into the hollow interior region 1222 configured to store the TES media 110 (see
The combustor subassembly 1212 includes an internal combustor chamber 1280 configured to be disposed inside and at least partially surround by the TES media 110 (see
To channel the combustion products away from the internal combustor chamber 1280, the combustor subassembly 1212 includes a first plurality of flow passages 1290, and one or more annular exhaust passageways (e.g., an inner annular exhaust passageway 1294A and an outer annular exhaust passageway 1294B) disposed inside the hollow interior region 1222 of the housing 1220 of the TES subassembly 1210 and extending through the TES media 110 (see
By way of a non-limiting example, the inner annular exhaust passageway 1294A may be approximately 7 inches from the center of the internal combustor chamber 1280 and the outer annular exhaust passageway 1294B may be approximately 12 inches from the center of the internal combustor chamber. The inner and outer annular exhaust passageways 1294A and 1294B have exit apertures 1296A and 1296B, respectively, through which combustion products may exit the combustor subassembly 1212 of the TES device 1200.
The combustor subassembly 1212 illustrated also includes a second plurality of flow passages 1300 that interconnect the inner and outer annular exhaust passageways 1294A and 1294B. The second plurality of flow passages 1300 are disposed inside the hollow interior region 1222 of the housing 1220 of the TES subassembly 1210 and extend through the TES media 110 (see
The combustion products exit the internal combustor chamber 1280 through the outlets 1284 flow through the TES subassembly 1210 of the TES device 1200 along radial or annular combustion gas flow paths. Specifically, each of the first plurality of flow passages 1290 connects the outlets 1284 of the internal combustor chamber 1280 to the inner annular exhaust passageway 1294A. The first plurality of radially extending flow passages 1290 transport the combustion products radially outward away from the internal combustor chamber 1280 and into the inner annular exhaust passageway 1294A. This approach may be configured to offer excellent heat transfer characteristics that can be manufactured in a straightforward manner with mostly loose tolerances and simple integration. In the embodiment illustrated, the first plurality of flow passages 1290 are implemented as an array of rectangular cross-section ducts. The total cross-sectional area of the first plurality of flow passages 1290 may be approximately equal to the cross-sectional area of the internal combustor chamber 1280.
A portion of the combustion products flowing radially outwardly through the first plurality of flow passages 1290 flows into the inner annular exhaust passageway 1294A and exits the inner annular exhaust passageway through the exit aperture 1296A. The remainder of the combustion products continue radially outward through the second plurality of flow passages 1300, enter and travel through the outer annular exhaust passageway 1294B, and exit the inner annular exhaust passageway through the exit aperture 1296B.
The first and second plurality of flow passages 1290 and 1300 may be configured so that the pressure inside the inner and outer annular exhaust passageways 1294A and 1294B adjacent the second plurality of flow passages 1300 is substantially equal. For example, in the embodiment illustrated, the combustor subassembly 1212 includes twice as many flow passages 1300 in the second plurality as in the first plurality of flow passages 1290. Each of the second plurality of flow passages 1300 has the same cross-sectional area as each of the first plurality of flow passages 1290. This arrangement causes the pressure inside the inner and outer annular exhaust passageways 1294A and 1294B adjacent the second plurality of flow passages 1300 to be substantially equal.
The average combined cross-sectional flow area of both the inner and outer annular exhaust passageways 1294A and 1294B may be substantially equal to the cross-sectional area of the internal combustor chamber 1280. Each of the inner and outer annular exhaust passageways 1294A and 1294B may taper, becoming larger near the exit apertures 1296A and 1296B. For example, adjacent the second plurality of flow passages 1300, the inner and outer annular exhaust passageways 1294A and 1294B may have a maximum width of about 0.10 inches and at the exit apertures 1296A and 1296B, the inner and outer annular exhaust passageways 1294A and 1294B, respectively, may each have a minimum width of about 0.02 inches. The combustion products enter each of the inner and outer annular exhaust passageways 1294A and 1294B at a temperature of about 1500 K (1227 C), and exit the combustor subassembly 1212 through the exit apertures 1296A and 1296B at a temperature of about 1000 K (727° C.). Heat transfer effectiveness is approximately proportional to the inverse of the width of the inner and outer annular exhaust passageways 1294A and 1294B. By tapering the inner and outer annular exhaust passageways 1294A and 1294B, the sidewalls “S2,” and “S3” of the inner and outer annular exhaust passageways 1294A and 1294B may have an approximately uniform temperature and heat flux along their portion of the combustion gas flow path as the temperature difference driving the heat transfer decreases.
The combustor subassembly 1212 illustrated includes three washer-shaped flat disk sections 1270A, 1270B, and 1270C. The disk section 1270A closes off the space between the internal combustor chamber 1280 and inner exit aperture 1296A. The disk section 1270B closes off the space between the inner and outer exit apertures 1296A and 1296B. The disk section 1270C closes off the space between the outer exit aperture 1296B and the outer cylindrical housing 1220. The combustor subassembly 1212 may be constructed mainly from sheet metal parts that are individually straightforward to fabricate. Such components may be brazed or welded together to produce a rugged combustor subassembly 1212. As mentioned above, the housing 1220 may include the weld lip (not shown) at its open end portion 1226 that may be welded or brazed to the disk section 1270C along its perimeter.
The heat flows that melt and super-heat the TES media 110 (see
Heat transferred across the sidewalls “S2” and “S3” heats and melts adjacent regions of the TES media 110 (see
In the embodiment illustrated, the heat pipes 1260 each extend into the combustor subassembly 1212 and have a closed-end portion 1320 terminating inside the combustor subassembly 1212. When the internal combustor chamber 1280 is operating (i.e., during a heating cycle), the closed-end portions 1320 of the heat pipes 1260 in the TES media 110 (see
In the embodiment illustrated, the heat pipes 1260 are arranged in a pattern of concentric rings that include a first ring “R1A” that extends into the combustor subassembly 1212 between the internal combustor chamber 1280 and the inner annular exhaust passageway 1294A, and a second ring “R2A” that extends into the combustor subassembly 1212 between the inner and outer annular exhaust passageways 1294A and 1294B. Thus, each of the rings “R1A” and “R2A” is adjacent to and receives thermal energy from at least one of the internal combustor chamber 1280, the inner annular exhaust passageway 1294A, and the outer annular exhaust passageway 1294B.
By way of a non-limiting example, the first ring “R1A” may include eight heat pipes 1260 located at approximately 45 degree intervals at about 4.5 inches from the center of the housing 1220, and the second ring “R2A” may include 16 heat pipes at approximately 22.5 degree intervals at about 9.5 inches from the center of the housing 1220. An optional third ring (not shown) may include 20 heat pipes at approximately 18 degree intervals at about a 13.5 inches from the center of the housing 1220. These spacing intervals were selected to provide approximately two inch on-center spacing between the heat pipes 1260 within the TES media 110 (see
However, please note, this spacing is not provided near the center of the housing 1220 inward of the internal combustor chamber 1280. The exception in this central region does not pose a problem because as the TES media 110 (see
When the TES device 1200 is constructed, the TES media 110 (see
Optionally, an appropriate quantity of heat pipe working fluid 1242 (e.g., sodium) may be added through the filler port (not shown) in the ring shaped transition member. Then, the filler port (not shown) is sealed by inserting a plug (not shown) in the filler port. The plug may be affixed inside the filler port using any method suitable for affixing the plug 1238 in the filler port 1236.
It may be desirable to add heat pipe wicks (not shown) to the components in contact with the heat pipe working fluid. The heat pipe wicks (not shown) may be formed in the interior of the heat pipes 1260 by a knurling process. The heat pipe wicks may include a screen or granular wicking material added to the other components.
Effectiveness of Stirling engines (e.g., the Stirling engine 315 depicted in
By way of a non-limiting example, the TES device 1200 may be incorporated into an undersea vehicle and used to power the vehicle. In such embodiments, the internal combustor chamber 1280 may be configured to burn JP5, JP8, JP10, and the like. The use of strategic hydrocarbon fuels such as JP5, JP8, or JP10 in unmanned undersea vehicles (“UUVs”) is of interest to the U.S. Navy because of the potential for very large range travel when used with compact oxygen storage/generation, or for snorkeling. This is especially the case when high efficiency energy converters such as fuel cells or Stirling engines are used. An additional benefit is that the vehicle may go to near the surface of the water to run the combustor subassembly 1212 at a lower exhaust pressure (and therefore higher efficiency) to thermally “charge” the TES media 110 (see
The TES subassembly 1210 has a housing 1520 defining a hollow interior region 1522 configured to store the TES media 110 (see
The housing 1520 may be substantially similar to the housing 1220 (see
The TES subassembly 1510 also includes a heat delivery assembly 1530 that functions in a manner substantially similar to that of the heat delivery assembly 1230 (see
The heat delivery assembly 1530 is defined between an interior sidewall 1532 spaced apart from an external sidewall 1534. In this embodiment, the thermal energy output portion 104 includes the heat delivery assembly 1530 and its interior and exterior sidewalls 1532 and 1534. The interior sidewall 1532 and optionally exterior sidewall 1534 include one or more fill ports (not shown) substantially similar to the fill port 1236 (see
The TES media 110 (see
The combustor subassembly 1512 includes an internal combustor chamber 1580 configured to be disposed inside and at least partially surround by the TES media 110 (see
To channel the combustion products away from the internal combustor chamber 1580, the combustor subassembly 1212 has a plurality of flow passages 1590, and one or more annular exhaust passageways (e.g., an annular exhaust passageway 1594) disposed inside the hollow interior region 1522 of the housing 1520 of the TES subassembly 1510 and extending through the TES media 110 (see
The flow passages 1590 are substantially similar to the first flow passages 1290 (see
The flow passages 1590 connect the outlets 1584 of the internal combustor chamber 1580 to the annular exhaust passageway 1594. The radially extending flow passages 1590 transport the combustion products radially outward away from the internal combustor chamber 1580 and into the annular exhaust passageway 1594. The combustion products travel through the annular exhaust passageway 1594, and exit the annular exhaust passageway through the exit aperture 1596. As the combustion products travel through the annular exhaust passageway 1594, the combustion product heat the heat conducting sidewalls “S4” and “S5.”
The combustor subassembly 1512 includes an annular shaped heat pipe 1598 having a pair of spaced apart heat conducting sidewalls “S6” and “S7.” The sidewall “S7” is adjacent the sidewall “S4” of the annular exhaust passageway 1594. The sidewall “S7” may be spaced apart from or in face-to-face engagement with the sidewall “S4.” The sidewall “S7” receives thermal energy from the sidewall “S4” and transports that thermal energy into the TES media 110 (see
The heat pipes 1560 each extend from the heat delivery assembly 1530 into the combustor subassembly 1512 between the flow passages 1590 and each have a closed-end portion 1600 terminating inside the combustor subassembly 1612. When the internal combustor chamber 1580 is operating (i.e., during a heating cycle), the closed-end portions 1600 of the heat pipes 1560 adjacent the combustor subassembly 1512 transfer heat from the internal combustor chamber 1580 to the heat delivery assembly 1530. When the internal combustor chamber 1580 is not operating (e.g., during a cooling cycle), the entire length of each of heat pipes 1560 may transfer heat from the TES media 110 (see
In the embodiment illustrated, the heat pipes 1560 are arranged in a pattern of concentric rings that include a first ring “R1B” that extends into the combustor subassembly 1512 between the internal combustor chamber 1580 and the annular shaped heat pipe 1598, and a second ring “R2B” that extends into the combustor subassembly 1512 between the annular shaped heat pipe 1598 and the housing 1520. The heat pipes 1560 of the first ring “R1B” extend between the flow passages 1590. Thus, each of the rings “R1B” and “R2B” is adjacent to and receives thermal energy from at least one of the internal combustor chamber 1280, the annular exhaust passageway 1594, the annular shaped heat pipe 1598, and the flow passages 1590.
A working fluid (not shown) may be disposed inside the heat pipes 1560 and/or the annular exhaust passageway 1594. It may be desirable to add heat pipe wicks (not shown) to the components in contact with the heat pipe working fluid. The heat pipe wicks may be formed in the interior of the heat pipes 1560 by a knurling process. The heat pipe wicks may include a screen or granular wicking material added to the other components.
The TES subassembly 1710 has a housing 1720 defining a hollow interior region 1722 configured to store the TES media 110 (see
The housing 1720 has an open end portion 1726 to which the combustor subassembly 1712 is coupled. The open end portion 1726 includes a weld lip 1727 and the combustor subassembly 1712 includes a corresponding weld lip 1728. The combustor subassembly 1712 may be coupled to the housing 1720 by welding the weld lip 1728 to the weld lip 1727.
The TES subassembly 1710 includes a heat delivery assembly 1730 that functions in a manner substantially similar to that of the heat delivery assembly 1230 (see
The heat delivery assembly 1730 is defined between an interior sidewall 1732 spaced apart from an external sidewall 1734. In this embodiment, the thermal energy output portion 104 includes the heat delivery assembly 1730 and its interior and exterior sidewalls 1732 and 1734. The interior sidewall 1732 and optionally exterior sidewall 1734 include one or more fill ports 1735 substantially similar to the fill ports 1236 (see
The TES media 110 (see
Turning to
Each of the branching channels 1734 has a first substantially linear portion 1734A, a branching portion 1734B, a second substantially linear branched portion 1734C, and a third substantially linear branched portion 1734D. The branching portion 1734B connects the first substantially linear portion 1734A to the second and third substantially linear branched portions 1734C and 1734D.
The hollow regions 1732 are defined between the second and third substantially linear branched portions 1734C and 1734D as well as between adjacent branching channels 1734. Each of the first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D has an exit aperture 1736 formed in an outside portion 1738 of the combustor subassembly 1712.
The combustor subassembly 1512 includes an internal combustor chamber 1780 configured to be disposed inside and at least partially surround by the TES media 110 (see
The branching channels 1734 are configured to direct all of the combustion products away from the internal combustor chamber 1780. The first substantially linear portions 1734A each connect one of the outlets 1784 of the internal combustor chamber 1780 to the branching portion 1734B. The combustion products flow from the outlets 1784 into the first substantially linear portions 1734A. The outlets 1784 and/or the branching channels 1734 may be configured such that equal amounts of the combustion products flow into each of the branching channels 1734. At least a portion of the combustion products flow through each of the first substantially linear portions 1734A toward the outside portion 1738 of the combustor subassembly 1712 and exit the combustor subassembly 1512 through the exit aperture 1736 of the first substantially linear portions 1734A.
The branching portion 1734B connects the first substantially linear portion 1734A to the second and third substantially linear branched portions 1734C and 1734D. A remainder of the combustion products flow from each of the first substantially linear portions 1734A into the branching portion 1734B connected thereto. Then, the remainder of the combustion products flow from the branching portion 1734B into the second and third substantially linear branched portions 1734C and 1734D. The branching channels 1734 may be configured such that equal amounts of the combustion products flow into each of the second and third substantially linear branched portions 1734C and 1734D. Finally, the remainder of the combustion products flow through the second and third substantially linear branched portions 1734C and 1734D toward the outside portion 1738 of the combustor subassembly 1712 and exit the combustor subassembly 1512 through the exit apertures 1736 of the second and third substantially linear branched portions 1734C and 1734D.
Thus, the branching channels 1734 may be characterized as directing the combustion products radially outward away from the internal combustor chamber 1780 and out the exit apertures 1736. The combustion products heat the TES media 110 (see
Each of the branching channels 1734 may be configured to conduct substantially identical amounts of thermal energy from the combustion products into the TES media 110. The second and third substantially linear branched portions 1734C and 1734D may be configured to conduct substantially identical amounts of thermal energy from the combustion products to the TES media 110. The first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D may be implemented as balanced heat exchangers configured to deliver substantially identical amounts of thermal energy from the combustion products to the TES media 110. Further, the first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D may be configured to provide more thermal energy to portions of the TES media 110 located closer to the perimeter portion of the vessel 90 whereat the volume of TES media 110 increases.
The heat pipes 1760 each extend from the heat delivery assembly 1730 into the hollow regions 1732 of the combustor subassembly 1712. Each of the heat pipes 1760 has a closed-end portion 1790 terminating inside one of hollow regions 1732 of the combustor subassembly 1712. When the internal combustor chamber 1780 is operating (i.e., during a heating cycle), the closed-end portions 1790 of the heat pipes 1760 adjacent the combustor subassembly 1712 transfer heat from the internal combustor chamber 1780 to the heat delivery assembly 1730. When the internal combustor chamber 1780 is not operating (e.g., during a cooling cycle), the entire length of each of heat pipes 1760 may transfer heat from the TES media 110 (see
A working fluid (not shown) may be disposed inside the heat pipes 1760. It may be desirable to add heat pipe wicks (not shown) to the components in contact with the heat pipe working fluid. The heat pipe wicks may be formed in the interior of the heat pipes 1760 by a knurling process. The heat pipe wicks may include a screen or granular wicking material added to the other components.
In the combustor subassembly 1812, each of the branching channels 1734 includes the first substantially linear portion 1734A, the branching portion 1734B, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D. The branching portion 1734B connects the first substantially linear portion 1734A to the second and third substantially linear branched portions 1734C and 1734D. The hollow regions 1732 are defined between the second and third substantially linear branched portions 1734C and 1734D as well as between adjacent branching channels 1734. Each of the first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D has an plurality of exit apertures 1820 formed in an outside portion 1822 of the combustor subassembly 1812.
Inside at least a portion of the first substantially linear portion 1734A, the second substantially linear branched portion 1734C, and the third substantially linear branched portion 1734D, each of the branching channels 1734 may include a filler member 1830 adjacent the plurality of exit apertures 1820 that at least partially fills the interior of the branching channel. The filler member 1830 illustrated includes grooves 1832 aligned with each of the exit apertures 1820 to provide a flow path for the combustion products away from the outlets 1784 of the internal combustor chamber 1780 and toward the outside portion 1822 of the combustor subassembly 1812.
A portion 1840 of each of the branching channels 1734 adjacent to the filler member 1830 allows the combustion products to flow radially from one of the outlets 1784 of the internal combustor chamber 1780 into the first substantially linear portion 1734A, from the first substantially linear portion 1734A into the branching portion 1734B, and then from the branching portion 1734B into the second and third substantially linear branched portions 1734C and 1734D.
The rate of flow of the combustion products through the exit apertures 1820 may be determined at least in part by the size of the grooves 1832. Thus, the grooves 1832 may be configured to limit the outward flow of the combustion products from the combustor subassembly 1812. Further, the size of the exit apertures 1820 may be used to control the flow of combustion products from the combustor subassembly 1812. In the embodiment illustrated, the exit apertures 1820 increase in size radially away from the internal combustor chamber 1780.
The TES device 2000 includes a heat delivery assembly 2030 substantially similar to the heat delivery assembly 150 (see
The TES device 2000 includes a plurality of heat pipes 2040 that extend from the heat delivery assembly 2030 through the TES media 110. Each of the heat pipes 2040 may have at least one fin 2020 that extends toward the internal combustor chamber 2010. The heat pipes 2040 and fins 2020 are heated by the thermal energy transferred to the TES media 110 across combustor boundaries (e.g., across a sidewall of the internal combustor chamber 2010). The fins 2020 may contact the internal combustor chamber 2010 to be heated directly by the internal combustor chamber.
The TES device 2000 also includes one or more heat pipes 2042 that extend between the heat delivery assembly 2030 and the internal combustor chamber 2010 and transport thermal energy from the internal combustor chamber 2010 directly to the heat delivery assembly 2030. Fins 2050 extend from the heat pipe 2042 into the TES media 110. Thermal energy is transferred from the heat pipe 2042 into the TES media 110 by the fins 2050.
Two types of models were developed to model the behavior of the TES device 2000. In both models, the TES media 110 modeled was a eutectic salt storage medium. The first model is a first-order model created using the MatLab Simulink environment. This model breaks the internal combustor chamber 2010 into three main sections, a combustion section, a mixing section, and a flow return section, and uses a lumped parameter model for the TES media 110. This model may be used to evaluate the effects of the internal combustor chamber 2010 and TES size; number, size, and thermal characteristics of heat transfer fins and/or heat pipes; the thermodynamic properties of different TES medias; and combustor power on combustor efficiency and the time required for thermal charge up.
The second model employs a finite volume representation of the internal combustor chamber 2010 and the TES media 110 and uses CFD to couple the chemical reaction with the heat transfer of the internal combustor chamber 2010 to the phase change behavior of the TES media 110. This model may be used to evaluate specific elements of the combustor design, as well as the specific placement of the internal combustor chamber 2010, Stirling engine fins, and heat pipes 2040 and 2042 to guarantee uniform volumetric energy transfer from the internal combustor chamber 2010 to the TES media 110 and thence to the Stirling hot side (e.g., the heater head portion 315A depicted in
The following is a basic equation for modeling bulk transient behavior of the TES media 110:
where the fin thermal efficiency (“ηFin”) is modeled by the following expression:
ηFin=[(hFinPFin)/(kFinAFin]−1/tan h[(hFinPFin)/(kFinAFin)1/2LFin] (2)
The temperature of the TES media is related to the enthalpy by the following expression:
If hTES<=CP
then TTES=hTESCP
If CP
then TTES=TMP
If CP
then TTES=(hTES−hFG
Energy is transferred to the TES media 110 directly from the body of the internal combustor chamber 2010 and the fins 2020. As mentioned above, the internal combustor chamber 2010 was broken up into three virtual sections; the combustion section, the mixing section, and the return passage section. The combustion section contains the energy addition due to the chemical reaction, and the mixing section accounts for the temperature reduction caused by the addition of recycled combustion products for cooling. The return section refers to a designer specified number of reverse flow passages that redirect the combustion products out of the TES media 110. The term “thermal element” (“TE”) refers to the solid combustor housing associated with each section, and is modeled thermally by the following equation:
V
TEρTE
C
P
TE
dT
TE
/dt=A
C
Int
h
C
TE(TC−TTE)+hComb
The combustor gas temperatures are obtained from a steady flow 1st-law energy balance. A transient formulation was not used because it was assumed that the time scale associated with the change in gas temperature is very fast relative to that of the combustor walls or the TES media 110. For the combustion zone section the following equation was used:
m
O2
C
P
O2(TIN
Where
h
RAD=σε(TTE+TRad)(TTE2+TRad2) (6)
The CFD modeling of the Stirling engine heat source is accomplished via the CFD code CFDS-FLOW3D. This code has been used extensively by ARL for over 15 years, and has been modified at ARL to model the burning of hydrocarbon fuels such as JP5, JP8 and JP10; as well as to perform melting and freezing simulations. CFDS-FLOW3D has been used for the current application to model the heating of a phase-change TES storage medium via the burning of a hydrocarbon/oxygen in an attached combustor. The model incorporates chemical reaction, conjugate heat transfer through the internal combustor chamber 2010 to the TES media 110, phase change in the TES media, and extended surface heat transfer submodels. The model is run in a transient mode, so that the amount of energy stored in the TES media 110 increases with time.
Model results for the behavior of the internal combustor chamber 2010 and the TES media 110 are illustrated in
Plateaus 2110 in the combustion temperature indicate periods during which the internal combustor chamber 2010 (see
The top portion of
The results of
Calculations were also performed using lithium hydride (“LiH”) as the TES media 110. This material was chosen for its superior energy storage qualities and in particular its large heat of fusion and specific heat on a mass basis. LiH has the following properties:
Thus, the melting point of LiH is about 962 K, which is slightly less than that of the LiF/NaF/MgF2 eutectic, which is about 966 K. The specific heat and latent heat of fusion of LiH exceed those of the LiF/NaF/MgF2 eutectic by factors of 4.3 and 4.1, respectively. The energy density of LiH (between about 960 K and about 1240 K) is also greater, though only 1.03 times that of the LiF/NaF/MgF2 eutectic. The principal benefit of the LiH relative to the LiF/NaF/MgF2 eutectic is its low density. The solid/molten specific gravities of LiH and LiF/NaF/MgF2 are 0.82/0.55 and 2.8/2.0, respectively. Ballasting requirements for the LiH system are less stringent. The temperature and power flow characteristics indicate that the LiH media yields a 20% increase in duration (which for a vehicle means an increase in travel range) relative to the LiF/NaF/MgF2 eutectic.
The previous calculations were made using a thermostat controller that maintains the TES media 110 in a two-phase state. Additional energy would be available if the TES media 110 were heated to a temperature well into its liquid state. To employ this method of operation, a controller (not shown) may be used by the Stirling engine 315 (see
The boiling point of the LiF/NaF/MgF2 eutectic is not well known, but assumed to be approximately equal to 1950 K (based on the boiling point of LiF). It is not reasonable to heat the TES media 110 to near this temperature because of the danger of damaging the internal combustor chamber 2010, heat transfer surfaces (e.g., fins 2020), and the TES media storage tank 2015. If the maximum temperature of the TES media 110 is limited to about 1600 K, the increase in range relative to the two-phase eutectic system was approximately equal 43% (still less than that observed with LiH).
In the model, the internal combustor chamber 2010 was one inch in diameter and 4 inches long. Combustion products exited the internal combustor chamber 2010 via exhaust ducts similar to those illustrated in
Returning to
When the TES media 110 was LiF—NaF—MgF2, as a starting condition, the TES media was initially at a uniform temperature of 900 K. Thus, the analysis began assuming that the TES media 110 had previously experienced a number of heating/cooling cycles. The TES media 110 quickly reached melting temperature, but the melting process was slow due to the heat of fusion. When the TES media 110 is at its melting point, energy added by the internal combustor chamber 2010 is absorbed by the phase change of the TES media 110 from a solid to a liquid. Thus, a molten volume of the TES media 110 increases and a solid volume decreases as the TES media melts.
An analysis of the release of energy stored by the LiF—NaF—MgF2 eutectic to run the Stirling engine 315 (see
Heat transfer was via eight heat pipes 2040 located at the outer radius of the LiF—NaF—MgF2 eutectic. The heat pipes 2040 extended down the entire length of the TES media storage tank 2015 inside the solid TES media 110. A copper fin 2020 extended down from each heat pipe 2040 toward the center of the TES media 110 (or to the stainless steel wall of the internal combustor chamber 2010). It was assumed that each of the heat pipes 2040 was an excellent conductor, and its temperature along the entire length of the TES media 110 was assumed to be 800 K. The phase change from a liquid to a solid releases stored thermal energy from the TES media 110.
When the TES media 110 was LiH, the geometry and combustor flow rates were the same as those used above in the LiF—NaF—MgF2 eutectic analysis. It was assumed for a starting condition that the TES media 110 (i.e., LiH) was at a uniform temperature of 900 K. The energy release analysis proceeded as described above for the LiF—NaF—MgF2 eutectic. While the energy storage on a volume basis is roughly equivalent for the two materials, it is noted that the thermal conductivity of the LiH is almost a factor of two lower than that used for the LiF—NaF—MgF2 eutectic. This may make the fins 2020 attached to the heating pipes 2040 less effective conduits of energy out of the TES media 110, and will tend to reduce the rate of heat extraction from the TES media. This results in the lower rates of cooling.
Exemplary TES devices 10, 200, 400, 500, 800, 900, 1000, 1100, 1200, 1500, 1700, 1800, and 2000 have been described as having various numbers and configurations of thermal energy heat transporting means for transporting thermal energy to and from the TES media 110. As discussed above, these heat transporting means may be implemented as hollow tubes, elongated cylinders, annular channels formed between a pair of sidewalls, radially outwardly extending channels, and the like. Further, the various heat transporting means may include conductive fins from increasing the amount of surface area forming the interface between the heat transporting means and the TES media 110.
As discussed above, the TES media 110 resides inside a relatively large vessel (e.g., the vessel 90). Thus, the heat transporting means, which traverse the inside of the vessel, help ensure that no portion of the TES media 110 is more than a predetermined distance (e.g., about one to two inches) away from a thermal energy heat transporting means. This arrangement helps ensure that thermal energy is (1) effectively distributed within the bulk TES media 110 and (2) effectively extracted from the bulk TES media 110. Those of ordinary skill in the art appreciate that alternate configuration of heat transporting means beyond those explicitly presented herein may be used to achieve this result and are therefore within the scope of the present teachings.
Further, in all of the exemplary embodiments, except the TES device 200, the thermal energy input portion and the thermal energy output portion have been depicted as being located at opposite ends of the TES device. Many of these TES devices have been depicted as having an elongated cylindrically shaped vessel. In such embodiments, the heat transporting means have been illustrated as extending substantially linearly between the opposite ends of the TES device to define a thermal energy flow direction along the longitudinal axis of the elongated cylindrically shaped vessel. As is appreciated by those of ordinary skill in the art, the heat transporting means can be configured such that thermal energy is not transferred axially along the longitudinal axis. For example, through application of ordinary skill in the art to the present teachings, a TES device may be configured for off-axial heat transfer into or out of the TES media. Such non-symmetrical configurations of heat transporting means can be placed, or oriented, as desired between the thermal energy input portion and the thermal energy output portion. Also, the overall shape of the vessel of the TES device can be altered depending upon system needs. While cylindrical configurations have been shown, other extruded shapes such as squares, rectangles, triangles, ovals, trapezoids, or any other closed perimeter could be used.
The exemplary TES devices 10, 200, 400, 500, 800, 900, 1000, 1100, 1200, 1500, 1700, 1800, and 2000 have also been described as having a heat delivery assembly (e.g., the heat delivery assembly 150) at their thermal energy output portions. In particular embodiments, the heat delivery assembly includes a working fluid that may also circulate within the interior of at least a portion of the heat transporting means. The heat delivery assembly helps reduce hot spots and temperature gradients at the thermal energy output portion of the TES device by combining the individual thermal energy contributions of the individual heat transporting means transferring thermal energy to the heat delivery assembly before that thermal energy is transferred to an external device. Those of ordinary skill in the art appreciate that alternate configuration of heat delivery assembly beyond those explicitly presented herein may be used to achieve this result and are therefore within the scope of the present teachings.
The foregoing described embodiments depict different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations).
Accordingly, the invention is not limited except as by the appended claims.
The present application claims the benefit of U.S. Provisional Patent Application No. 61/079,787, filed Jul. 10, 2008, which is incorporated herein by reference in its entirety.
The invention described herein was made under federally sponsored research and development with Department of the Navy contract no. N00014-07-M-0409 and may be manufactured and used by or for the United States Government for governmental purposes without the payment of any royalties thereon.
Number | Date | Country | |
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61079787 | Jul 2008 | US |