HIGH-TEMPERATURE LATENT HEAT STORAGE SYSTEM USING TRANSPORTABLE HEAT PIPES FOR VERSATILE INTEGRATION WITH EMERGING MICROREACTORS

Abstract

A heat pipe integrated thermal battery (“HITB”) is provided that may include a storage tank, a thermal storage medium within the storage tank, a guide tube extending within the storage tank and through at least one end of the storage tank, and a heat pipe configured to be movable within the guide tube. The heat pipe may be configured to discharge heat to and absorb heat from the thermal storage medium within the storage tank.

Description

TECHNICAL FIELD

Thermal energy storage systems are disclosed. More particularly, latent heat storage systems including a heat pipe integrated thermal battery and methods of using the heat pipe integrated thermal battery are disclosed.

BACKGROUND

With growing interest in the development of micro nuclear reactors and their application to microgrids, high-temperature thermal energy storage (“TES”) has received growing attention as a technology to reinforce the energy utilization and profitability of such reactors. TES offers the benefit of making heat a dispatchable energy asset. With an increasing interest/demand to connect micro nuclear reactors to microgrid(s), TES may help to maximize the energy utilization and profit of this class of new reactors. However, commercial-scale deployment of high temperature TES in the energy sector is difficult. Such challenges in deployment include the ability to interface the TES with other systems. This challenge also applies when combining high-temperature TES with advanced nuclear energy systems.

BRIEF SUMMARY

According to some embodiments, a heat pipe integrated thermal battery (“HITB”) may include a storage tank, a thermal storage medium within the storage tank, a guide tube extending within the storage tank and through at least one end of the storage tank, and a heat pipe configured to be movable within the guide tube. The heat pipe may be configured to discharge heat to and absorb heat from the thermal storage medium within the storage tank.

In some embodiments, a thermal energy storage system is provided. The thermal energy storage system may include a feed and drain tank comprising a heating element operable to melt a thermal storage medium to a molten state and a heat pipe integrated thermal battery (“HITB”) comprising a storage tank. The storage tank may be operable to hold the thermal storage medium such that latent heat of the thermal storage medium may be stored in the HITB. The thermal energy storage system may further include a thermal storage medium transport line connecting the feed and drain tank to the HITB and a pump configured to move the thermal storage medium from the feed and drain tank to the HITB and from the HITB to the feed and drain tank.

In some embodiments, a method for operating a heat pipe integrated thermal battery (“HITB”) is provided. The method may include charging the HITB and discharging the HITB. To charge the HITB a heat pipe may be moved through a guide tube to of the HITB to a charging position. Heat may be absorbed into the heat pipe from a first external system and transferred from the heat pipe to a thermal storage medium in a storage tank of the HITB.

To discharge the HITB, the heat pipe may be moved through the guide tube to a discharging position. Heat may be absorbed into the heat pipe from the thermal storage medium in the storage tank of the HITB and discharged from the heat pipe to a second external system.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system components/method steps, as appropriate, and in which:

FIG. 1A shows a schematic view of a heat pipe integrated thermal battery in a first operating state and FIG. 1B shows the heat pipe integrated thermal battery of FIG. 1A in a second operating state, according to embodiments of the disclosure;

FIG. 2 shows a schematic section view of the heat pipe integrated thermal battery;

FIG. 3 shows a schematic view of a thermal energy storage system incorporating the heat pipe integrated thermal battery;

FIG. 4 shows thermal resistance pathways involved in the heat transfer between a heat source or heat sink and the thermal storage medium of the heat pipe integrated thermal battery; and

FIG. 5 is a graph showing comparisons between a thermal resistant network model and Computational Fluid Dynamics (“CFD”) simulations that were performed for verifying the accuracy of a TRN model.

DETAILED DESCRIPTION

High temperature thermal energy storage (TES) systems that include a heat pipe integrated thermal battery (HITB) are disclosed. The HITB is configured to store latent heat by moving heat pipes within the HITB. The high temperature TES system may be coupled to an external thermal system that produces heat and operates at a temperature above about 150° C. The high temperature TES system may be easily coupled to the external thermal system without using complex interfacing mechanisms and without creating additional safety issues.

The high temperature TES system including the HITB may be a latent heat storage system that enables flexible and robust integration with the external thermal system. The HITB may incorporate so called “transportable heat pipes” within the HITB to adjust the degree of thermal connection between a TES medium of the HITB and the external thermal system during use and operation of the high temperature TES system. The transportable heat pipes may be embedded heat pipes that provide a passive and flexible thermal connection between the TES medium and the external thermal system. The transportable heat pipes are configured to exchange heat between the TES medium of the HITB and the external thermal system. The transportable heat pipes are configured to be moved within (e.g., displaced within) guide tubes of the HITB, which provide a barrier between a fluid (e.g., a working fluid) of the external system and the TES medium surrounding the heat pipes.

The thermal connection between the HITB and the external thermal system may result in no separate heat exchanger or pump being required for thermal integration, providing a significant cost benefit. Safety issues that may arise from interconnecting disparate systems may also be reduced or eliminated. Also, there is no single failure of the high temperature TES system because individual heat pipes operate independent of each other. The high temperature TES system may be easily scaled up to include multiple modules.

FIG. 1A shows a schematic view of a HITB 100 in a first operating state and FIG. 1B shows the HITB 100 of FIG. 1A in a second operating state, according to embodiments of the disclosure. FIG. 2 shows a schematic section view of the HITB 100. Referring to FIGS. 1A-2, the HITB 100 may comprise a storage tank 110. The storage tank 110 shown in FIGS. 1A-2 comprises a cylindrical shape having a cylindrical outer wall 112, a planar first end 114 and a planar second end 116. The storage tank 110 may be insulated to retain thermal energy within the HITB 100. To this end, the storage tank 110 may further comprise an inner wall 118 and an insulating liner 119 between the inner wall 118 and the outer wall 112. In some embodiments, the walls, including the inner wall 118 and the outer wall 112, of the storage tank 110 may be formed from stainless steel, such as stainless steel 316. However, other materials may also be used depending on a particular application of the HITB 100. The insulating liner 119 may comprise a boron nitride ceramic coating.

The storage tank 110 may be configured to house (e.g., contain) a thermal storage medium 160. The thermal storage medium 160 may be formulated to exhibit a high heat capacity, high conductivity, high diffusivity, and high latent heat of fusion at an operating temperature of the HITB 100. The thermal storage medium 160 may also exhibit a solid-to-liquid phase change at a temperature around the operating temperature. By way of example only, the thermal storage medium 160 may comprise a metal alloy. The thermal storage medium 160 may include, but is not limited to, an aluminum alloy such as an aluminum-magnesium-zinc alloy. Other materials may also be used as a thermal storage medium 160 of the HITB 100. Such materials may be considered a “phase change material” (“PCM”) in that the material may undergo a solid-liquid phase change through a melting-solidification cycle at temperatures within a desired operating range for the HITB 100. For example, in addition to an aluminum-magnesium-zinc alloy discussed above, the thermal storage medium 160 may comprise molten salts, such as MgCl₂-NaCl, FLiNaK, or CaCl₂-NaCl. The thermal storage medium 160 may be formulated such that thermal energy is stored as latent heat of the PCM. Accordingly, the PCM used as the thermal storage medium 160 may be selected based on a target operating temperature for a given application.

The storage tank 110 may be formed of any suitable size for a particular thermal storage capacity. In some embodiments, the storage tank 110 may comprise a 30 kw-hour thermal storage capacity. For instance, the storage tank 110 may comprise a 60-cm diameter and a 60-cm length to provide the 30 kw-hour thermal storage capacity. However, this is merely exemplary and other dimensions of the storage tank 110 may be utilized based on a desired thermal storage capacity and a particular application.

The HITB 100 may further comprise a plurality of guide tubes 120 that are embedded within and extend through the storage tank 110. The guide tubes 120 may be oriented so as to be parallel with a longitudinal axis of the storage tank 110. The guide tubes 120 may have a length that is longer than a length of the storage tank 110 from the first end 114 to the second end 116. The guide tubes 120 may thus protrude out from at least one of the first end 114 or the second end 116 of the storage tank 110. In some embodiments, first ends 122 of the guide tubes 120 extend from the first end 114 of the storage tank 110 and second ends 124 of the guide tubes 120 extend from the second end 116 of the storage tank 110. The guide tubes 120 may be centered relative to the length of the storage tank 110 such that the lengths of the portions of the guide tubes 120 protruding from each end 114, 116 of the storage tank are substantially equal to one another. That is, a length of the portion of a guide tube 120 extending from the first end 122 of the guide tube 120 to the first end 114 of the storage tank is equal to a length of the portion of the guide tube 120 extending from the second end 116 of the storage tank 110 to the second end of the guide tube 120. However, the guide tubes 120 may be positioned at any desired location relative to the storage tank 110.

The guide tubes 120 may be supported by the storage tank 110 via a plurality of support members 123. The support members 123 may comprise a plurality of rods or struts that extend from the inner wall 118 of the storage tank 110. The support members 123, the guide tubes 120, and the storage tank 110 may be formed integrally (e.g., together) such as via an additive manufacturing process, casting, or other suitable manufacturing methods. Alternatively, the support members 123, the guide tubes 120, and the storage tank 110 may be formed separately and may be joined together using any suitable joining process such as welding or joining via one or more fasteners.

The guide tubes 120 may comprise a first end cap 126 disposed at a first end 122 of the guide tube and a second end cap 128 disposed at the second end 124 of the guide tube 120. The end caps 126, 128 may be configured to seal an inside of the guide tubes 120 from an external environment (e.g., an operating environment). In some embodiments, the end caps 126, 128 may be selectively removeable from the ends 122, 124 of the guide tubes 120 to provide access to the inside of the guide tubes 120.

The guide tubes 120 may comprise first fins 130 disposed adjacent to the first end 122 of the guide tubes 120 and may comprise second fins 132 disposed adjacent to the second end 124 of the guide tubes 120. The first fins 130 may be configured to facilitate heat transfer between the guide tubes 120 and fluid from the external thermal system providing a hot fluid supply source. The second fins 132 may be configured to facilitate heat transfer between the guide tubes 120 and another external thermal system, such as an industrial system providing a cold fluid supply source to be heated by the guide tubes 120.

The guide tubes 120 may be configured to support transportable heat pipes 140 within the guide tubes 120. The transportable heat pipe 140 within each guide tube 120 is configured and operable to receive heat from the external thermal system and to discharge heat to another external thermal system via the guide tubes 120. The transportable heat pipe 140 within each guide tube 120 is further configured and operable to receive heat from and discharge heat to the thermal storage medium 160 within the storage tank 110.

The transportable heat pipe 140 may include a working medium 170 within the transportable heat pipe 140. The working medium 170 with the transportable heat pipe 140 may be a liquid metal, such as sodium. However, other liquid metals may be used. By way of example only, the transportable heat pipe 140 may be a sodium heat pipe. The transportable heat pipe 140 may function as a passive heat transfer device. In some embodiments, the transportable heat pipe 140 may have a working temperature range of from about 400° C. to about 1000° C. The transportable heat pipe 140 may be configured to be replaceable, such as to be removable from the guide tubes 120 via the caps 126, 128, and to be placed into the guide tubes 120 via the caps 126, 128. Since the thermal storage medium 160 is separated from other fluids, no fluid exchange occurs between the working medium 170 and the thermal storage medium 160 or between the thermal storage medium 160 and fluids from external systems.

The HITB may comprise a heat pipe drive mechanism 150 that is configured and operable to move the transportable heat pipes 140 within respective guide tubes 120. The transportable heat pipe 140 may be moved between the first operating state (e.g., a charging position within the guide tubes 120) and the second operating state (e.g., a discharging position within the guide tubes 120) by the heat pipe drive mechanism 150. The heat pipe drive mechanism 150 may comprise a linear actuator 152 associated with each heat pipe 140. For example, the linear actuator 152 may comprise a worm gear stepper motor or other suitable linear actuator. Each linear actuator 152 may be configured and operable to move a respective heat pipe 140 within a respective guide tube 120. In some embodiments, each linear actuator 152 may be operated independent from other linear actuators 152. In some embodiments, the linear actuators 152 are controlled collectively. The linear actuators 152 may be any suitable linear actuator such as a hydraulic actuator, a pneumatic actuator, a mechanical actuator, or the like.

The heat pipe drive mechanism 150 may be configured to move the transportable heat pipes 140 through the guide tubes 120 to various positions within the guide tubes. In FIG. 1A, the HITB 100 is shown where the heat pipe drive mechanism 150 has driven the heat pipes 140 within the guide tubes 120 to a position adjacent to the first end 122 of the guide tubes 120 (e.g., the first operating state or charging position). In this position, at least a portion of the heat pipe 140 is adjacent to the fins 130 of the guide tube 120 and at least a portion of the heat pipes 140 extends beyond the first end 114 of the storage tank 110. Thus, the heat pipe 140 may be configured and operable to receive thermal energy from a hot fluid supply source 192 from an external thermal system via the interface between the heat pipe 140 and the guide tube 120 to transfer the heat to the thermal storage medium 160 in the storage tank 110 of the HITB 100. In some embodiments, the heat pipes 140 may facilitate heat transfer from the hot fluid supply source 192 via the working medium 170 while in the first operating state as shown in FIG. 1A. In some embodiments, the transportable heat pipes 140 may be moved to be within the thermal storage tank 110 (e.g., moved to a position within the guide tube 120 between the first end 114 and the second end 116 of the thermal storage tank 110) such that heat stored in the transportable heat pipe 140 from the hot fluid supply source 192 of the external thermal system may be transferred to the thermal storage medium 160. In this manner, heat may be transferred from the external thermal system to the thermal storage medium 160 of the HITB 100.

In FIG. 1B, the HITB 100 is shown where the heat pipe drive mechanism 150 has driven the heat pipes 140 within the guide tubes 120 to a position adjacent to the second end 124 of the guide tubes 120 (e.g., the second operating state or discharging position). In this position, at least a portion of the heat pipe 140 is adjacent to the fins 132 of the guide tube 120. The transportable heat pipes 140 may be moved out of the thermal storage tank 110 (e.g., moved to a position within the guide tube such that at least a portion of the heat pipes 140 extends beyond the second end 116 of the storage tank 110) such that the heat pipes 140 are exposed to the external thermal system that functions as a cold fluid supply source 194, enabling heat transfer from the thermal storage medium 160 to the external thermal system. Thus, the heat pipe 140 may be configured and operable to discharge thermal energy to the cold fluid supply source 194 from an external system via the interface between the heat pipe 140 and the guide tube 120. In some embodiments, the heat pipes 140 may facilitate heat transfer to the cold fluid supply source 194 via the working medium 170 while in the second operating state as shown in FIG. 1B.

In addition to the positions of the heat pipes 140 relative to the respective guide tubes 120 shown in FIGS. 1A and 1B, the heat pipes 140 may be moved to any desired other position within the guide tubes 120. For example, the heat pipes 140 may be moved to a position at least partially or fully within the storage tank 110 to discharge heat to or absorb heat from the thermal storage medium 160.

A portion of the heat pipe drive mechanism 150 may be configured to extend through the caps 128 of the guide tubes 120 to interface with and move the transportable heat pipes 140. The caps 128 may provide a dynamic seal with the heat pipe drive mechanism 150 to maintain a predetermined environment within the guide tubes 120. For example, an inert gas may be provided in the guide tubes 120 to reduce contamination and corrosion within the guide tubes 120 and to the heat pipes 140. In some embodiments, the caps 128 may be replaced with or may be incorporated into a component of the heat pipe drive mechanism that seals the second ends 124 of the heat pipes 140.

While the heat pipe drive mechanism 150 shown in FIGS. 1A and 1B interfaces at the second end 124 of the guide tubes 120, the heat pipe drive mechanism 150 is not limited to this configuration. The heat pipe drive mechanism 150 may also interface at the first end 122 of the guide tubes 120 or at both ends 122, 124 of the guide tubes. Because the transportable heat pipes 140 are configured to move along and within the guide tubes 120, the thermal storage medium 160 of the HITB 100 does not directly interface with a working fluid (e.g., a working medium 170) of the transportable heat pipes 140. The walls of the guide tubes 120 may provide a barrier between the working medium 170 of the transportable heat pipes 140 and the thermal storage medium 160 to prevent any potential safety issues that may arise in the event of a wall failure of a transportable heat pipe 140.

To aid in the heat transfer between the guide tubes 120 and the respective transportable heat pipe 140 within each guide tube 120, a thermal interface 180 may be provided. The thermal interface 180 may be a heat conducting sleeve disposed between an outside surface of the transportable heat pipe 140 and an inside surface of the guide tube 120. The thermal interface 180 may be configured to remain fixed relative to one of the guide tube 120 or the transportable heat pipe 140. A lubricant may be provided to facilitate relative movement between the thermal interface 180 and the other of the guide tube 120 or the transportable heat pipe 140. The lubricant may include, but is not limited to, a boron nitride lubricant, a copper grease lubricant, or other suitable high temperature lubricant.

In some embodiments, the thermal interface 180 may be provided to remain fixed to an inside surface of each guide tube 120 such that the transportable heat pipe 140 is moveable through the thermal interface 180. The thermal interface 180 may extend along an entire length of the guide tube 120 or along a portion or portions of the guide tube 120. For example, the thermal interface 180 may be provided at portions of the guide tube at which heat transfer is to be facilitated, such as extending within the guide tube 120 along the lengths at which the fins 130 and 132 are provided. The thermal interface 180 may also be provided along the guide tube 120 at one or more portions within the storage tank 110. In some embodiments, the thermal interface 180 may be configured so as to be absent at and adjacent to the first end 114 and the second end 116 of the storage tank. In this manner, heat transfer may be facilitated between the external systems and the transportable heat pipe while preventing inadvertent heat transfer between an external system and the thermal storage medium 160 within the storage tank 110 via the thermal interface 180 within the guide tube 120.

In other embodiments, the thermal interface 180 may be provided to remain fixed to the transportable heat pipe 140 and is thus configured to move through the guide tube 120 with the transportable heat pipe 140. The thermal interface 180 may extend along an entire length of the heat pipe 140 or may extend along a portion or portions of the transportable heat pipe 140. For example, the thermal interface 180 may extend from ends of the transportable heat pipe 140 such that when the transportable heat pipe 140 is moved adjacent to one of the ends 122, 124 of the guide tubes 120, the thermal interface 180 is aligned to be adjacent to the one of the fins 130, 132. In some embodiments, the thermal interface 180 may be configured such that when the thermal interface 180 is aligned with one of the fins 130, 132, the thermal interface 180 does not extend through the ends 114, 116 of the storage tank 110. In this manner, inadvertent heat transfer between an external system and the thermal storage medium 160 within the storage tank 110 via the thermal interface 180 within the guide tube 120 may be prevented.

The thermal interface 180 may comprise a porous metal, such as a metal sheet or a metal foam. In some embodiments, the porous metal may comprise a mesh sheet of copper, bronze, stainless steel, or nickel that is formed into a sleeve to surround the transportable heat pipe 140 within the guide tube 120. The porous metal may provide a conductive thermal contact between the guide tube 120 and the thermal interface 180 and a conductive thermal contact between the thermal interface 180 and the transportable heat pipe 140 while allowing for thermal expansion and contraction of the thermal interface 180, the guide tubes 120, and the transportable heat pipes 140 in changing operating temperatures.

Modifications to the HITB 100 are also possible. For example, in FIGS. 1A and 1B, the HITB 100 is shown with the guide tubes 120 extending from both ends 114, 116 of the storage tank 110. It was described above with reference to FIGS. 1A and 1B that when the transportable heat pipes 140 are moved to the first end 122 of the guide tubes 120, the transportable heat pipes 140 absorb heat from a hot fluid supply source 192 from an external thermal system, and that when the transportable heat pipes 140 are moved to the second end 124 of the heat pipes 140, the transportable heat pipes 140 discharge heat to a cold fluid supply source 194 of an external thermal system. However, this is not intended to be limiting. The HITB 100 may be configured such that the transportable heat pipes 140 discharge heat when at the first end 122 of the guide tubes 120 and absorb heat when at the second end 124 of the guide tubes. Furthermore, the HITB 100 may be configured such that the guide tubes 120 extend out of only one of the ends 114, 116 of the storage tank 110. For instance, a portion of the guide tubes 120 extending out of only one of the ends 114, 116 of the storage tank 110 may facilitate both absorption of heat to and discharge of heat from the transportable heat pipes 140, depending on with which external thermal system the HITB 100 is interfaced.

FIG. 3 shows a schematic view of a thermal energy storage system incorporating the heat pipe integrated thermal battery. In FIG. 3, a thermal energy storage system 20 may comprise one or more HITBs, such as one or more HITBs 100 described above with reference to FIGS. 1A-2. The thermal energy storage system 20 may comprise a feed and drain tank 202. The feed and drain tank 202 may be configured to store a thermal storage medium (such as thermal storage medium 160 discussed above) when the HITB 100 is not in use.

The feed and drain tank 202 may comprise inlets/outlets to provide access to the feed and drain tank 202. For example, the feed and drain tank 202 may comprise a fluid inlet/outlet 204 which may be operable to allow fluid such as a gas to enter or exit the feed and drain tank 202. The feed and drain tank 202 may also comprise an ingot inlet 206. The ingot inlet 206 may comprise a port through which a metallic ingot may be inserted into the feed and drain tank 202 to load the feed and drain tank 202 with the thermal storage medium (e.g., thermal storage medium 160).

The feed and drain tank 202 may also comprise a thermal storage medium inlet/outlet 208. The thermal storage medium inlet/outlet 208 may be configured to drain the thermal storage medium (e.g., thermal storage medium 160) from the feed and drain tank 202 to fill the HITB 100 or to receive the thermal storage medium from the HITB 100, as will be described in more detail below. The feed and drain tank 202 may comprise heating elements 210. The heating elements 210 may be operable to melt the metallic ingot into a molten state for use as the thermal storage medium of the HITB 100.

The thermal energy storage system 20 may further comprise a thermal storage medium transport line 212 that extends between the feed and drain tank 202 and the HITB 100. The thermal storage medium transport line 212 facilitates transport of the thermal storage medium between the feed and drain tank 202 and the HITB 100. The thermal storage medium transport line 212 may comprise a valve 214 that controls the flow of thermal storage medium between the feed and drain tank 202 and the HITB 100. The HITB 100 may comprise an inlet/outlet 216 that connects the thermal storage medium transport line 212 to the HITB 100, allowing the thermal storage medium to enter into and exit from the HITB 100.

The thermal energy storage system 20 may comprise a vacuum pump 218. The vacuum pump 218 is operable to create a pressure difference within the thermal energy storage system 20 to move the thermal storage medium between the feed and drain tank 202 and the HITB 100. A HITB vacuum line 220 may connect the vacuum pump 218 with the HITB 100 at a vacuum inlet/outlet 222. The HITB vacuum line 220 may comprise a valve 228 that controls the application of the vacuum to the HITB 100 via the HITB vacuum line 220.

A feed and drain vacuum line 230 may connect the vacuum pump 218 with the feed and drain tank 202 via the fluid inlet/outlet 204. The feed and drain vacuum line 230 may comprise a valve 232 that controls the flow through the feed and drain vacuum line 230. An inert gas flushing line 234 may connect to the feed and drain vacuum line 230 to provide an inert gas to the feed and drain tank 202 to remove air from the system to prevent oxidation. The inert gas may comprise, for example, argon. The inert gas flushing line 234 may comprise a valve 236 to help control the flow through the inert gas flushing line 234.

The thermal energy storage system 20 may also comprise a HITB venting line 238 that connects the HITB 100 at a venting outlet 240 to the fluid inlet/outlet 204 of the feed and drain tank 202. The HITB venting line 238 may comprise a valve 242 to control the flow through the HITB venting line 238. The HITB venting line 238 may protect against an overpressure condition in the HITB 100 such as during a filling operation of the HITB 100.

As mentioned above, the thermal energy storage system 20 may facilitate filling and draining of a thermal storage medium into and out of the HITB 100. To fill the HITB 100 with a thermal storage medium, such as thermal storage medium 160 discussed above with reference to FIGS. 1A-2, one or more ingots of metallic material to be used as a source of the thermal storage medium may be loaded into the feed and drain tank 202 via the ingot inlet 206. The heating elements 210 may heat the one or more ingots into a molten state within the heat and drain tank 202.

In the molten state, the thermal storage medium may flow through the thermal storage medium transport line 212 from the feed and drain tank 202 to the HITB 100. The flow may be caused by applying a vacuum via the vacuum pump 218 to the HITB 100. For example, the valve 214 of the thermal storage medium transport line 212 may be opened to allow flow of the thermal storage medium through the thermal storage medium transport line 212. The valve 232 of the feed and drain vacuum line 230 may be closed and the valve 228 of the HITB vacuum line 220 may be opened such that when the vacuum pump 218 is activated, a vacuum is applied to the HITB 100 at the vacuum inlet/outlet 222. The thermal storage medium may then flow through the thermal storage medium transport line 212 from the feed and drain tank 202 to the HITB 100 to fill the HITB 100 with the thermal storage medium. During filling, gas from the HITB 100 may be vented back to the feed and drain tank 202 via the HITB venting line 238. The valve 236 of the inert gas flushing line 234 may be opened as needed to equalize pressure in the thermal energy storage system 20. Once filled, the HITB 100 may be separated from the thermal energy storage system 20 and moved away from the thermal energy storage system 20 to be used as described above with reference to FIGS. 1A-2.

When the HITB 100 is no longer in use, it may be desirable to return the thermal storage medium to the feed and drain tank 202. The HITB 100 may be reattached to the thermal energy storage system 20 to move the thermal energy storage medium from the HITB 100 back to the feed and drain tank 202. To facilitate this, the valve 214 of the thermal storage medium transport line 212 may be opened to allow flow therethrough. The valve 232 of the feed and drain vacuum line 230 may be opened and the valve 228 of the HITB vacuum line 220 may be closed such that when the vacuum pump 218 is activated, a vacuum is applied to the feed and drain tank 202 at the fluid inlet/outlet 204. The thermal storage medium may then flow through the thermal storage medium transport line 212 from the HITB 100 to the feed and drain tank 202 to drain the HITB 100 of the thermal storage medium. As needed, valves 236, 232, and 228 may be opened to allow inert gas to flow to the HITB 100. The thermal storage medium may be stored in the feed and drain tank 202 for later use in the HITB 100.

As mentioned above, the thermal energy storage system 20 including the HITB 100 may be coupled to one or more external thermal systems. For example, the HITB 100 may be coupled to external thermal systems to absorb heat from the external thermal systems for storage and later use. Such external thermal systems may be configured to produce heat at a high temperature, such as at a temperature greater than or equal to about 150° C. The external thermal system may, for example, be configured to produce heat at a temperature between about 500° C. and about 600° C. By way of example only, the external thermal system may be a nuclear reactor, such as an advanced nuclear reactor (e.g., a micro nuclear reactor), a solar power plant, or an industrial heat plant. The HITB 100 may be further coupled to other external thermal systems to discharge heat stored in the HITB 100. Such external thermal systems may comprise power generation systems, chemical processing systems, hydrogen production systems, or other industrial applications.

To obtain a system-scale insight into the transient thermal behavior of the HITB during its cyclic operation of charge and discharge modes, a thermal resistant network (TRN) model has been developed. The TRN model was designed to evaluate the transient temperature history through each component and performance parameters such as melting completion time of a storage medium and charge/discharge periods for a given system sizing. The thermal resistance pathways involved in the heat transfer between the heat source (or heat sink) and the storage medium are presented in FIG. 4. Here, the transient temperature at each thermal component node (i.e., T₁-T₁₃) is determined by the following transient heat conduction equation:

$\begin{array}{c}{\rho }_i{c}_{p,i}{V}_i\frac{{\mathrm{dT}}_i}{\mathrm{dt}}=Q_{i,1}-Q_{i,2}\\ =\frac{T_{i,1}-T_i}{R_{i,1}}-\frac{T_i-T_{1,2}}{R_{i,2}}\end{array}$

• • Q_i,1: Heat entering through the interface (I,1) to component ‘i’
  • Q_i,2: Heat coming out through the interface (i,2) from component ‘i’
  • T_i,1: Temperature at the interface (i,1)
  • T_i,2: Temperature at the interface (i,2)

FIG. 5 shows a comparison between the TRN and CFD simulations that was performed for verifying the accuracy of the TRN model. The TRN model developed is currently used to investigate the thermal performance, effect of key design parameters (e.g., heat pipe performance, thermophysical properties of storage medium), and design optimization.

The embodiments of the disclosure described above and illustrated in the accompanying drawing figures do not limit the scope of the invention, since these embodiments are merely examples of embodiments of the invention, which is defined by the appended claims and their legal equivalents. Any equivalent embodiments are intended to be within the scope of this disclosure. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternative useful combinations of the elements described, may become apparent to those skilled in the art from the description. Such modifications and embodiments are also intended to fall within the scope of the appended claims and their legal equivalents.

Claims

1. A heat pipe integrated thermal battery (“HITB”) comprising: a storage tank;a thermal storage medium within the storage tank;a guide tube extending within the storage tank and through at least one end of the storage tank; anda heat pipe configured to be movable within the guide tube, the heat pipe being configured to discharge heat to and absorb heat from the thermal storage medium within the storage tank.

2. The HITB of claim 1, further comprising a heat pipe drive mechanism configured to move the heat pipe within the guide tube.

3. The HITB of claim 1, wherein the guide tube comprises fins on a portion of the guide tube that extends outside the storage tank.

4. The HITB of claim 1, wherein the guide tube comprises an end cap allowing access within the guide tube.

5. The HITB of claim 1, further comprising a thermal interface within the guide tube, the thermal interface being between an inner surface of the guide tube and an external surface of the heat pipe.

6. The HITB of claim 5, wherein the thermal interface comprises a sleeve disposed against the inner surface of the guide tube.

7. The HITB of claim 6, wherein the sleeve comprises a porous metal.

8. The HITB of claim 1, wherein the storage tank comprises a cylindrical tank comprising an inner wall, an outer wall, and an insulating liner between the inner wall and the outer wall.

9. The HITB of claim 8, wherein the inner wall and the outer wall comprise stainless steel and wherein the insulating liner comprises a boron nitride coating.

10. The HITB of claim 1, wherein the thermal storage medium comprises a metal alloy and wherein heat stored in the thermal storage medium is stored as latent heat of the metal alloy.

11. The HITB of claim 10, wherein the metal alloy comprises an aluminum alloy.

12. The HITB of claim 1, wherein the guide tube protrudes from a first end of the storage tank and protrudes from a second end of the storage tank opposite the first end of the storage tank.

13. The HITB of claim 12, wherein when the heat pipe is moved to a first end of the guide tube, the heat pipe is configured to absorb heat and to transfer heat to the thermal storage medium, and wherein when the heat pipe is moved to a second end of the guide tube, the heat pipe is configured to absorb heat from the thermal storage medium and release heat from the guide tube.

14. A thermal energy storage system comprising: a feed and drain tank comprising a heating element operable to melt a thermal storage medium to a molten state;a heat pipe integrated thermal battery (“HITB”) comprising a storage tank, the storage tank operable to hold the thermal storage medium such that latent heat of the thermal storage medium may be stored in the HITB;a thermal storage medium transport line connecting the feed and drain tank to the HITB; anda pump configured to move the thermal storage medium from the feed and drain tank to the HITB and from the HITB to the feed and drain tank.

15. The thermal energy storage system of claim 14, further comprising a HITB venting line connecting the HITB and the feed and drain tank, the HITB venting line being configured to vent gas from the HITB to the feed and drain tank.

16. The thermal energy storage system of claim 14, further comprising: a HITB vacuum line connecting the pump to the HITB, the HITB vacuum line comprising a first valve; anda feed and drain vacuum line connecting the pump to the feed and drain tank, the feed and drain vacuum line comprising a second valve,wherein when the first valve is opened and the second valve is closed, a vacuum is applied to the HITB to move the thermal storage medium from the feed and drain tank to the HITB via the thermal storage medium transport line, andwherein when the first valve is closed and the second valve is opened, a vacuum is applied to the feed and drain tank to move the thermal storage medium from the HITB to the feed and drain tank.

17. A method for operating a heat pipe integrated thermal battery (“HITB”) comprising: charging the HITB, the charging comprising: moving a heat pipe through a guide tube of the HITB to a charging position;absorbing heat into the heat pipe from a first external system and transferring heat from the heat pipe to a thermal storage medium in a storage tank of the HITB;discharging the HITB, the discharging comprising: moving the heat pipe through the guide tube to a discharging position;absorbing heat into the heat pipe from the thermal storage medium in the storage tank of the HITB and discharging heat from the heat pipe to a second external system.

18. The method of claim 17, further comprising: prior to charging, filling the HITB with the thermal storage medium from a feed and drain tank.

19. The method of claim 17, further comprising: emptying the thermal storage medium from the HITB to a feed and drain tank.

20. The method of claim 17, wherein heat stored in the thermal storage medium is stored as latent heat of the thermal storage medium.