Patent Application
20090077981
This disclosure relates generally to the field of cooling systems and, more particularly, to a topping cycle for a sub-ambient cooling system.
A variety of different types of structures can generate heat or thermal energy in operation. To prevent such structures from over heating, a variety of different types of cooling systems may be utilized to dissipate the thermal energy, including air conditioning systems.
According to one embodiment of the disclosure, a cooling system for a heat-generating structure comprises a heat exchanger, a first structure, a condenser heat exchanger, and a second condenser. The heat exchanger is in thermal communication with a heat-generating structure. The heat exchanger has an inlet and an outlet. The inlet is operable to receive fluid coolant substantially in the form of a liquid into the heat exchanger, and the outlet is operable to dispense fluid coolant at least partially in the form of a vapor out of the heat exchanger. The first structure directs a flow of the fluid coolant substantially in the form of a liquid to the heat exchanger. Thermal energy communicated from the heat-generating structure to the fluid coolant causes the fluid coolant substantially in the form of a liquid to boil and vaporize in the heat exchanger. The condenser heat exchanger receives a flow of the fluid coolant at least partially in the form of a vapor from the heat exchanger and transfers at least a portion of the thermal energy within the fluid coolant to a heat sink. The second condenser assists the condenser heat exchanger in transferring at least a portion of the thermal energy within the fluid coolant away from the fluid coolant. The second condenser is selectively activated when the heat sink reaches an undesirable temperature.
Certain embodiments of the disclosure may provide numerous technical advantages. For example, a technical advantage of one embodiment may include the capability to use a topping cycle in a sub-ambient cooling system. Other technical advantages of other embodiments may include the capability to compensate for circumstances in which a heat sink used in a cooling system reaches undesired levels. Yet other technical advantages of other embodiments may include the capability to allow cooling systems to operate in extremely hot environments and extremely cold environments. Still yet other technical advantages of other embodiments may include the capability to use a thermoelectric cooler (TEC) to selectively remove thermal energy from a sub-ambient cooling system. Still yet other technical advantages of other embodiments may include the capability to use a thermoelectric cooler (TEC) to both selectively remove thermal energy from a sub-ambient cooling system and selectively add thermal energy to the sub-ambient cooling system.
Although specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description.
For a more complete understanding of example embodiments of the present disclosure and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
It should be understood at the outset that although example embodiments of the present disclosure are illustrated below, the present disclosure may be implemented using any number of techniques, whether currently known or in existence. The present disclosure should in no way be limited to the example embodiments, drawings, and techniques illustrated below, including the embodiments and implementation illustrated and described herein. Additionally, the drawings are not necessarily drawn to scale.
Sub-ambient cooling systems (SACS) generally include a closed loop of fluid with an evaporator, a condenser, and a pump. The evaporator boils the liquid and feeds the liquid/vapor mixture to the condenser. The condenser removes heat (thermal energy) while condensing the vapor, and feeds the condensed liquid to the pump. The pump then returns the liquid to the evaporator to complete the loop. The evaporator absorbs heat (thermal energy) from a source such as hot electronics and the condenser transfers heat (thermal energy) to a cooling source such as the ambient air.
A SACS may be designed to transfer heat by forced, two-phase boiling from a higher temperature heat source to a lower temperature heat sink. In many cases, ambient temperature of air is a desirable heat sink. Referring to
As can be seen above, difficulties with a cooling system, such as a SACS, can arise when the available heat sink such as the ambient temperature is higher than the desired temperature of the heat source such as the hot electronics. Accordingly, teachings of some embodiments of the disclosure recognize a cooling system that compensates for circumstances when the heat sink (e.g., ambient temperature) reaches an undesirable level. Additionally, teachings of some embodiments of the disclosure recognize a cooling system that provides a second condenser that allows dissipation of thermal energy to a heat sink that has an undesirable desirable level. Additionally, teachings of some embodiments of the disclosure recognize a cooling system that provides a mechanism, which can compensate for both undesirably hot and undesirably cold conditions.
The cooling system 10 of
The structure 12 may be arranged and designed to conduct heat or thermal energy to the heat exchangers 23, 24. To receive this thermal energy or heat, the heat exchanger 23, 24 may be disposed on an edge of the structure 12 (e.g., as a thermosyphon, heat pipe, or other device) or may extend through portions of the structure 12, for example, through a thermal plane of structure 12. In particular embodiments, the heat exchangers 23, 24 may extend up to the components of the structure 12, directly receiving thermal energy from the components. Although two heat exchangers 23, 24 are shown in the cooling system 10 of
In operation, a fluid coolant flows through each of the heat exchangers 23, 24. As discussed later, this fluid coolant may be a two-phase fluid coolant, which enters inlet conduits 25 of heat exchangers 23, 24 in liquid form. Absorption of heat from the structure 12 causes part or all of the liquid coolant to boil and vaporize such that some or all of the fluid coolant leaves the exit conduits 27 of heat exchangers 23, 24 in a vapor phase. To facilitate such absorption or transfer of thermal energy, the heat exchangers 23, 24 may be lined with pin fins or other similar devices which, among other things, increase surface contact between the fluid coolant and walls of the heat exchangers 23, 24. Additionally, in particular embodiments, the fluid coolant may be forced or sprayed into the heat exchangers 23, 24 to ensure fluid contact between the fluid coolant and the walls of the heat exchangers 23, 24.
The fluid coolant departs the exit conduits 27 and flows through the vapor line 61, the condenser heat exchanger 41, the expansion reservoir 42, a pump 46, the liquid line 71, and a respective one of two orifices 47 and 48, in order to again to reach the inlet conduits 25 of the heat exchanger 23, 24. The pump 46 may cause the fluid coolant to circulate around the loop shown in
The orifices 47 and 48 in particular embodiments may facilitate proper partitioning of the fluid coolant among the respective heat exchanger 23, 24, and may also help to create a large pressure drop between the output of the pump 46 and the heat exchanger 23, 24 in which the fluid coolant vaporizes. The orifices 47 and 48 may have the same size, or may have different sizes in order to partition the coolant in a proportional manner which facilitates a desired cooling profile.
A flow 56 of fluid (either gas or liquid) may be forced to flow through the condenser heat exchanger 41, for example by a fan (not shown) or other suitable device. In particular embodiments, the flow 56 of fluid may be ambient fluid. The condenser heat exchanger 41 transfers heat from the fluid coolant to the flow 56 of ambient fluid, thereby causing any portion of the fluid coolant which is in the vapor phase to condense back into a liquid phase. In particular embodiments, a liquid bypass 49 may be provided for liquid fluid coolant that either may have exited the heat exchangers 23, 24 or that may have condensed from vapor fluid coolant during travel to the condenser heat exchanger 41. In particular embodiments, the condenser heat exchanger 41 may be a cooling tower.
The liquid fluid coolant exiting the condenser heat exchanger 41 may be supplied to the expansion reservoir 42. Since fluids typically take up more volume in their vapor phase than in their liquid phase, the expansion reservoir 42 may be provided in order to take up the volume of liquid fluid coolant that is displaced when some or all of the coolant in the system changes from its liquid phase to its vapor phase. The amount of the fluid coolant which is in its vapor phase can vary over time, due in part to the fact that the amount of heat or thermal energy being produced by the structure 12 will vary over time, as the structure 12 system operates in various operational modes.
Turning now in more detail to the fluid coolant, one highly efficient technique for removing heat from a surface is to boil and vaporize a liquid which is in contact with a surface. As the liquid vaporizes in this process, it inherently absorbs heat to effectuate such vaporization. The amount of heat that can be absorbed per unit volume of a liquid is commonly known as the latent heat of vaporization of the liquid. The higher the latent heat of vaporization, the larger the amount of heat that can be absorbed per unit volume of liquid being vaporized.
The fluid coolant used in the embodiment of
Water boils at a temperature of approximately 100° C. at an atmospheric pressure of 14.7 pounds per square inch absolute (psia). In particular embodiments, the fluid coolant's boiling temperature may be reduced to between 55-65° C. by subjecting the fluid coolant to a subambient pressure of about 2-3 psia. Thus, in the cooling system 10 of
In particular embodiments, the fluid coolant flowing from the pump 46 to the orifices 47 and 48 through liquid line 71 may have a temperature of approximately 55° C. to 65° C. and a pressure of approximately 12 psia as referenced above. After passing through the orifices 47 and 48, the fluid coolant may still have a temperature of approximately 55° C. to 65° C., but may also have a lower pressure in the range about 2 psia to 3 psia. Due to this reduced pressure, some or all of the fluid coolant will boil or vaporize as it passes through and absorbs heat from the heat exchanger 23 and 24.
After exiting the exits ports 27 of the heat exchanger 23, 24, the subambient coolant vapor travels through the vapor line 61 to the condenser heat exchanger 41 where heat or thermal energy can be transferred from the subambient fluid coolant to the flow 56 of fluid. The flow 56 of fluid in particular embodiments may have a temperature of less than 50° C. In other embodiments, the flow 56 may have a temperature of less than 40° C. As heat is removed from the fluid coolant, any portion of the fluid which is in its vapor phase will condense such that substantially all of the fluid coolant will be in liquid form when it exits the condenser heat exchanger 41. At this point, the fluid coolant may have a temperature of approximately 55° C. to 65° C. and a subambient pressure of approximately 2 psia to 3 psia. The fluid coolant may then flow to pump 46, which in particular embodiments 46 may increase the pressure of the fluid coolant to a value in the range of approximately 12 psia, as mentioned earlier. Prior to the pump 46, there may be a fluid connection to an expansion reservoir 42 which, when used in conjunction with the pressure controller 51, can control the pressure within the cooling loop.
It will be noted that the embodiment of
As alluded to above, teachings of some embodiments of the disclosure recognize a cooling system that compensates for circumstances when the heat sink (e.g., ambient temperature) reaches an undesirable level. The compensation mechanism in certain embodiments described below is sometimes referred to as a “topping cycle.” In
The cooling system 100 of
In general, TECs (also sometimes referred to as a Peltier devices) use electrical energy to transfer thermal energy from one side of the TEC to the other side of the TEC. As an example, in one configuration, a TEC may have a first plate and a second plate with bismuth telluride disposed therebetween. Upon applying a current to the TEC in one direction, the first plate becomes cool while the second plate becomes hot. This is due to the electrical energy causing the thermal energy to be transferred from the first plate to the second plate. Upon applying the current to the same TEC in the opposite direction, the second plate becomes cool while the first plate becomes hot. Thus, TECs can be used to either remove thermal energy from one plate or add thermal energy to same one plate. There are a variety of manufactures of thermoelectric devices, including, but not limited to, Marlow Industries, Inc. of Dallas, Tex. and Melcor of Trenton, N.J.
In the embodiment of
Thus, in one embodiment, the second condenser 170 allows the temperature of the cooling air, TA, to rise to an unacceptable level as compared to the desired cooling fluid temperature, TB. In operation, the condenser heat exchanger 141 may operate when the air temperature, TA, is less than the desired temperature of the cooling fluid, TB. Then, when the air temperature, TA, becomes greater than the fluid operating temperature, TB, the fan for the condenser heat exchanger 141 may be turned off and the second condenser heat exchanger 170 will maintain the desired temperature level of the fluid by absorbing thermal energy therefrom, for example, using a current applied to TEC.
Although a TEC has been described as being used in the second condenser 170, it should be understood that other devices may be utilized to effectuate the desired thermal flow. Examples include, but are not necessarily limited to a vapor cycle with refrigerant that utilize energy to effectuate the desired thermal flow. Any of a variety of energy sources may be utilized for the TEC and other devices, including, but not limited to, batteries, generated energy, solar energy, and/or combinations of the preceding.
The cooling system 200 of
In this embodiment, the second condenser 280 may be a thermoelectric cooler (TEC) designed to transfer thermal energy from one location in the TEC to another location in the TEC using energy such as electrical energy. In the embodiment of the system 200 of
The loop 290 may operate in a similar manner to system 10 of
In particular embodiments, the loop 290 may operate as a two-phase loop. In other embodiments, the loop 290 may be a single phase loop. Additionally, the loop 290 may use similar or different fluids to the system 10 of
In particular embodiments, the use of the system 200 of
In the system 300 of
A coldplate wall 343 of the condenser heat exchanger 341 and a second plate 376 of the second condenser 370 are both in thermal communication with the inner coldplate wall 361. Accordingly, in embodiments in which the inner coldplate wall 361 is aluminum, thermal energy may be transported from either one of the heat exchanger 341 or the second plate 376 for dissipation through the entire inner coldplate wall 361.
In this embodiment, the second condenser 370 is a TEC, which includes a first plate 374 and the second plate 376 which are separated by a structure 374 that may include bismuth telluride. The second condenser 370 may be a single TEC or have a series of TECs located therein. As discussed above, the application of current to the structure 374 (which includes the contents of the structure 374) in one direction may force thermal energy from the first plate 372 towards the second plate 376. Conversely, application of current to the structure 372 in the opposite direction may force thermal energy from the second plate 376 to the first plate 374, for example, for a heating operation that will be described in further details below. Although a TEC has been described as being used in the second condenser 370 in this embodiment, other devices may be used in the second condenser 370, including, but not limited to standard refrigeration cycles.
The system 300 includes two valves 322, 324, which may facilitate an apportioned distribution to the condenser heat exchanger 341 and the second condenser 370. For example, in operation, if the temperature of the air, TA, is suitable for operation of the system 300, the valve 322 may be substantially open and the valve 324 may be substantially closed. As the temperature, TA, approaches an undesirable level, the valve 322 may begin to close and the valve 324 may begin to open. Additionally, current may begin to be applied to the structure 374 to transfer thermal energy from the first plate 372 to the second plate 376. As the air temperature meets or exceeds the undesirable level, the valve 322 may become substantially closed and the valve 324 may begin to become substantially open. Additionally, even more current be applied to the structure 374 to transfer thermal energy from the first plate 372 to the second plate 376. In particular embodiments, the amount of current applied to the structure 374 may be adjusted or modulated, according to a desired need, for example, based not only on the temperature, TB, of the fluid in the fluid line 361, but also on the temperature, TA, of the heat sink, ambient air.
Although not expressly shown, a variety of monitoring systems may be utilized in conjunction with logic that is used to determine the degree of opening of the valves and the amount of current applied to the structure 374. The following illustrates a non-limiting example: valve 322 may be open when the temperature of the air is less than 50° C. and valve 324 may be slightly open when temperature of the air is greater than 40° C. As the temperature traverses this range, valve 322 may begin to close while valve 324 begins to open and the TECs begins to receive a higher current.
Although a general configuration has been illustrated above, it should be understood that a variety of configurations may be utilized in an interoperation between a condenser heat exchanger and a secondary condenser. Additionally, as indicated above, in particular embodiments the secondary condenser may be a standard refrigeration cycle.
As alluded to above, in particular embodiments, current may be applied to the structure 374 in the opposite direction to transfer thermal energy from the second plate 376 towards the first plate 372. In such an embodiment, the TEC would effectively be heating the fluid. Such an operation may be used in embodiments where the ambient temperature, TA, becomes critically low, for example, freezing or close to freezing.
Using the TEC in the second condenser 370 may allow the system 300 to operate in not only extremely cold environments, but also in extremely hot environments. In either of these environments, the TEC allows for compensation for these environmental conditions. For example, when the ambient air becomes too hot, the TEC removes thermal energy from the system to compensate for the undesirable heat sink (the ambient air). Conversely, when the ambient air becomes too cold, the TEC injects thermal energy into the system to compensate for the undesirable cold (freezing up of the fluid in the system).
Using the TEC may also allow reduced amounts of antifreeze being mixed with water in the fluid. In general, a fluid coolant containing only water has a higher heat transfer coefficient than a fluid coolant containing both water and antifreeze. Antifreeze is generally added to lower the freezing point of the coolant. Thus, in particular embodiments, the TEC may allow the a mixture with less antifreeze or water, alone, to remain above the higher freezing temperature by injecting thermal energy into the fluid at a location at the opposite end of the loop of the heat source.
Additionally, Because the TEC in particular embodiments may be utilized to inject thermal energy into the fluid, the TEC in some embodiments may be utilized to facilitate a separation of water from antifreeze in embodiments in which the fluid comprises a mixture of antifreeze and water. In such embodiments, the TEC may be used to vaporize water while leaving the antifreeze behind. Descriptions of such systems in which the dual-use TECs may be incorporated are described with reference to 11/689,947, the entirety of which is hereby incorporated by reference.
With reference to fluids, in addition to the fluids described herein, fluids such as R-134a could be used in both parts of the system (general loop and loop 290 of
