Abstract:
Simple, compact, lightweight thermal management system offering reduced inventory of heat transfer fluid. The invention provides heat transfer fluid at a very high flow rate to a heat exchanger. A portion of the heat transfer fluid flow downstream of the heat exchanger is separated and pumped by a fluid-dynamic pump back into the heat exchanger. The fluid dynamic pump is operated by a fresh heat transfer fluid supplied at high-pressure. Because a substantial portion of the flow leaving the heat exchanger is recirculated back to the inlet, the amount of fresh heat transfer fluid consumed is substantially reduced compared to a traditional system. Uses of the invention include cooling of devices at very high heat flux including photovoltaic cells, solar panels, semiconductor laser diodes, semiconductor electronics, and laser gain medium. Other uses of the invention include systems, for refrigeration, air conditioning, and gas liquefaction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. provisional patent application U.S. Ser. No. 60/936,505, filed Jun. 20, 2007; U.S. provisional patent application U.S. Ser. No. 61/011,691, filed Jan. 18, 2008; U.S. provisional patent application U.S. Ser. No. 61/066,249, filed Feb. 19, 2008; and U.S. provisional patent application U.S. Ser. No. 61/130,419, filed May 31, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to systems for thermal management and more specifically to supplying a fluid to a heat exchanger for thermal management. 
       BACKGROUND OF THE INVENTION 
       [0003]    There are many devices which require thermal management. Frequently, thermal management is administered by flowing suitable heat transfer fluid (HTF) through a heat exchanger (HEX) in thermal communication with a device requiring thermal management action, which such as cooling or heating. Depending on the desired effect, the HTF may supply heat to the device or remove heat from it. To obtain high heat transfer effect, HTF may be flowed through the HEX at very high velocity. This may be particularly important in applications where heat is provided from a device to the HEX at very high heat flux, such as may be practiced in solar photovoltaic cells used with concentrator, thermal photovoltaic cells, laser gain medium, semiconductor laser diodes, and semiconductor electronics. To meet such thermal management needs, the HEX may have to be supplied with HTF at very high flow rates. In a traditional thermal management system of prior art, the required high flow rate of HTF through the HEX may be sustained by supplying fresh HTF at the same high flow rate. This necessitates a large thermal management system including large piping, valves, and pumps. As a result, a traditional thermal management system may be large in volume and weight, which makes it less suitable for applications requiring compactness and lightweight. 
         [0004]    One frequent consequence of providing HTF at very high flow rates is that the HTF temperature may not change much more than a few degrees Centigrade after passing though the HEX. This leads to a low utilization of HTF. In addition, a traditional thermal management system of prior art may require a large amount of energy to operate. This situation may be challenging in energy sensitive applications such as when cooling photovoltaic cells used with concentrator, thermal photovoltaic cells, or removing heat from solar panels. 
         [0005]    Furthermore, a traditional thermal management system may require a large amount of HTF inventory. In the event of an accidental HTF release from the system, such a large HTF inventory may pose significant safety, health, and environmental hazards. In addition, a large HTF inventory has a large inertia, which must be overcome during flow start and stop conditions. The above size, weight, energy consumption, HTF inventory, and inertia characteristics of traditional thermal management system may make it less desirable in applications requiring compactness, lightweight, reduced energy consumption, improved safety, and fast startup. 
       SUMMARY OF THE INVENTION 
       [0006]    The subject invention provides a simple, compact, lightweight thermal management system offering reduced HTF inventory and energy consumption. In particular, the subject invention provides HTF at a very high flow rate to a HEX in thermal communication with a device requiring thermal management. A portion of the HTF flow downstream of the HEX outlet is separated and pumped by a fluid-dynamic pump back into the HEX inlet. The fluid dynamic pump is operated by a fresh HTF supplied at high-pressure that may be provided by a pump, a high-pressure tank, or other suitable source. Because a substantial portion of the flow leaving the HEX is recirculated back to the HEX inlet, the amount of fresh HTF consumed is substantially reduced compared to a traditional thermal management system. A portion of the HTF downstream of the HEX that is not recirculated back to the HEX may be fed to the suction port of a pump, or stored in a tank or an accumulator, or it may be released from the thermal system. See, for example, a publication entitled “Improved Cooling for High-Power Laser Diodes,” authored by John Vetrovec in proceedings from Photonics West, San Jose, Calif., Jan. 20-24, 2008, SPIE vol. 6876, and “Lightweight and Compact Thermal Management System for Solid-State High-Energy Laser,” in proceedings from the 21 st  Annual Solid-State and Diode Technology Review, held in Albuquerque, NM, Jun. 3-5, 2008, both of which are hereby expressly incorporated by reference in their entirety. 
         [0007]    If the HTF provided to the driving nozzle of the fluid dynamic pump is substantially in a gas or vapor form, the fluid dynamic pump may be an ejector. If the HTF provided to the driving nozzle of the fluid dynamic pump is substantially is in a liquid form, the fluid dynamic pump may be a jet pump. 
         [0008]    In one preferred embodiment of the subject invention, the thermal management system may use HTF in a substantially liquid form supplied by a supply tank pressurized by pressurant gas at a higher pressure and collected in a receiving tank that may be pressurized by pressurant gas at a lower pressure. HTF temperature may be changed in a suitable secondary heat exchanger prior to supplying it to the fluid dynamic pump. Such a heat exchanger may use a phase change material. 
         [0009]    In another preferred embodiment of the subject invention, the thermal management system may use HTF in a substantially gaseous form supplied by a supply tank at high pressure. HTF temperature may be changed in a suitable secondary heat exchanger, or in a vortex tube, or in a turboexpander prior to supplying it to the fluid dynamic pump. 
         [0010]    In yet another preferred embodiment of the subject invention, the thermal management system may use HTF in a substantially liquid form supplied at high pressure by a pump. HTF temperature may be changed in a suitable secondary heat exchanger prior to supplying it to the fluid dynamic pump. 
         [0011]    In yet further preferred embodiment of the subject invention, the thermal management system evaporate at least a portion of HTF passing though the HEX. Resulting HTF in a substantially vapor form is separated from HTF in a substantially liquid form and released. Separated HTF in a substantially liquid form is then recirculated by the fluid dynamic pump back into the HEX. 
         [0012]    These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
         [0013]    Accordingly, it is an object of the present invention to provide a lightweight and compact thermal management system. 
         [0014]    It is another object of the invention to provide a thermal management system for reduced HTF inventory. 
         [0015]    It is yet another object of the invention to provide a thermal management system conducive to reduced energy consumption. 
         [0016]    It is still another object of the invention to provide a thermal management system conducive to fast startup. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0017]      FIG. 1  is a diagrammatic view of a thermal management system according one embodiment of the present invention. 
           [0018]      FIG. 2  is a diagrammatic view of a thermal management system according alternative embodiment of the present invention suitable for liquid HTF. 
           [0019]      FIG. 3  is a diagrammatic view of a thermal management system according another embodiment of the present invention suitable for gaseous HTF. 
           [0020]      FIG. 4  is a diagrammatic view of a thermal management system according yet another embodiment of the present invention suitable for continuous operation. 
           [0021]      FIG. 5  is a diagrammatic view of a thermal management system according still another embodiment of the present invention suitable for use with evaporative HTF. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Selected embodiments of the present invention will now be explained with reference to drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are merely exemplary in nature and are in no way intended to limit the invention, its application, or uses. 
         [0023]    Referring to  FIG. 1  of the drawings in detail, numeral  10  generally indicates a thermal management system (TMS) generally comprising a fluid-dynamic pump  120 , heat exchanger (HEX)  182 , back-pressure valve  152 , return pipe  136 , and interconnecting pipes  132  and  138 . The HEX  182  may be in good thermal communication with a body  190  that requires thermal management. Alternatively, the HEX may be adapted to exchange heat between two separate HTFs. The HEX  182  may have an inlet port  154  and an outlet port  156 . The fluid dynamic pump  120 , HEX  182 , return pipe  136 , and interconnecting pipes  132  and  138  form a recirculation loop  124 . In general, the fluid-dynamic pump  120  is arranged to feed a suitable HTF to the inlet port  154  of the HEX  182  and to recirculate a portion of HTF flowing from the outlet port  156  back to the inlet port of the HEX. The fluid-dynamic pump  120  may further comprise a driving nozzle  140  and a pump body  134 . The pump body  134  is generally configured as a duct including a suction chamber  128 . The pump body may also include a converging portion, which may be followed by followed by a straight portion, which may be followed by a diverging portion. The suction chamber  128  includes a suction port  162 . The downstream portion of the pump body  134  has a discharge port  164 . The suction port  162  of fluid dynamic pump  120  is fluidly connected to the return pipe  136 . The discharge port  164  of fluid dynamic pump  120  is fluidly connected to the inlet port  154  of heat exchanger  182  by means of the pipe  132 . The back pressure valve  152  is fluidly connected to the outlet port  156  of heat exchanger  182  by means of pipe  138 . The return pipe  136  is also fluidly connected to the outlet port  156  of heat exchanger  182  by means of the pipe  138 . The driving nozzle  140  is of fluid-dynamic pump  120  arranged to discharge high-velocity flow (jet)  142  into the throat of the pump body  134 . This arrangement is common in fluid dynamic pumps. The driving nozzle  140  is fluidly connected by means of a supply line  148  to a source of high-pressure HTF. The back pressure valve  152  is arranged to provide a flow impedance to HTF flowing therethrough. One advantage of the back pressure valve  152  is its adjustability. In variant of the invention not requiring adjustability, alternative flow-impeding device such as an orifice or a venture may be used. 
         [0024]    If the heat transfer fluid is gas, the fluid dynamic pump may be an ejector. Suitable ejectors with a single driving nozzle are Series 20A ejectors made by Penberthy, Prophetstown, Pa. Alternative ejectors may have multiple driving nozzles and/or lobed driving nozzles. If the heat transfer fluid is liquid, the fluid dynamic pump may be a hydraulic ejector also known as a jet pump. Suitable hydraulic ejectors with a single driving nozzle are Series 60A ejectors made by Penberthy, Prophetstown, Pa. Alternative hydraulic ejectors may have multiple driving nozzles and/or lobed driving nozzles. If the heat transfer fluid is liquid, the tank  160  may include a bladder (also known as diaphragm or membrane) which separates the heat transfer fluid from pressurizing gas (pressurant). 
         [0025]    In operation, the fluid dynamic pump  120 , HEX  182 , return pipe  136 , and interconnecting pipes  132  and  138  are substantially filled with suitable HTF. High-pressure HTF is supplied by a stream  175  via the supply line  148  to the driving nozzle  140  where it forms a jet  142  that is directed into the throat portion of the pump body  134 . The jet  142  entrains HTF in the suction chamber  128  and pumps it. Stream  176  containing both the jet flow and the pumped HTF exists the fluid dynamic pump  120  through the discharge port  164  and flows through the pipe  132  into the inlet port  154  of HEX  182 . The HTF exchanges heat inside the HEX  182  and exists the HEX  182  through the outlet port  156  as a stream  176 ′ flowing in the pipe  138 . A portion of the HTF stream  176 ′ is separated and directed as a recirculating stream  172  into the return pipe  136 . The unseparated portion of the stream  176 ′ forms an exit stream  174  that is released the thermal management system  10  through he back pressure valve  152 . The back pressure valve  152  may be adjusted so that a large portion of the stream  176 ′ is directed in the form of the recirculating stream  172  into the return pipe  136 . As a result, a large flow may be maintained through the HEX  182  while the overall consumption of fresh HTF as, for example, measured by the flow in the stream  175  fed to the driving nozzle  140  is substantially smaller. HTF supplied to the nozzle  140  may be provided at a temperature such that the stream  176  (which is a mixture of nozzle flow and the stream  172 ) fed to the HEX  182  is provided at a predetermined temperature value. In particular, if the HTF is gas and a cooling action is desired in the HEX  182 , the gas provided in the line  148  may be chilled in a heat exchanger, a vortex tube, or a turboexpande prior to being fed to nozzle  140 . Temperature of HTD leaving the HEX  182  may be also controlled by appropriately adjusting the backpressure valve  152 . An alternative method for controlling the temperature of HTD leaving the HEX  182  may be achieved by appropriately adjusting the pressure of HTF supplied to the nozzle  140 . 
         [0026]    Referring now to  FIG. 2 , there is shown a thermal management system  11  in accordance with alternative embodiment of the invention which is particularly suitable for use with liquid HTF. The TMS  11  is generally the same as the TMS  10 , except that it further comprises a supply tank  160  and receiving tank  192 . The supply tank  160  is fluidly connected to the driving nozzle  140  and adapted for supplying high pressure HTF  168  to it. The supply tank  160  may also include a diaphragm  170 . The space  158  above the diaphragm may be provided with gas at high pressure (pressurant) that may be provided by a supply line  116 . A control valve  112  may be provided to control the flow of HTF from the tank  160  to the nozzle  140 . A secondary heat exchanger  180  may be provided to either heat or cool the high pressure HTF prior to delivery to the driving nozzle  140 . The secondary heat exchanger  180  may include a phase change material. The a receiving tank  192  is adapted for collecting HTF in stream  174 , which is the portion of HTF not recirculated back into HEX  182 . The receiving tank  192  may also include a diaphragm  166 . The space  158 ′ above the diaphragm may be provided with gas at pressure (pressurant) that may be provided by a supply line  114 . Pressurant in the space  158 ′ of the receiving tank  192  should be at a substantially lower pressure than gas in the space  158  of the supply tank  160 . In some variants of this embodiment, the backpressure valve  152  may be omitted and the back pressure in HTF stream  174  maintained by the pressure of gas in space  158  of the receiving tank  192 . 
         [0027]    In operation, pressure of pressurant in the supply tank is set substantially higher than the pressure of pressurant in the receiving tank, and the control valve  112  is set open. Fresh HTF flows from the supply tank  160  to the driving nozzle  140  and “expended” HTF flows in stream  174  to the receiving tank. When the supply tank  160  becomes empty, means may be provided to transfer the HTF from the receiving tank  192  into the tank  160 . Such means may include a pump and appropriate plumbing. 
         [0028]    Referring now to  FIG. 3 , there is shown a thermal management system  12  in accordance with another embodiment of the invention which is particularly suitable for use with gaseous HTF. The TMS  12  is generally the same as the TMS  11 , except that the supply tank  160 ′ may not include a diaphragm and the receiving tank may be omitted. In addition, the driving nozzle  140 ′ is preferably a supersonic nozzle. A secondary heat exchanger  180  may be provided to either heat or cool the high pressure HTF prior to delivery to the driving nozzle  140 . Alternatively, a cooling or heating action may be provided by flowing HTF through a vortex tube prior to feeding it to the nozzle  140 ′. As a yet another alternative, a cooling action may be provided by flowing HTF through a turboexpander prior to feeding it to the nozzle  140 ′. 
         [0029]      FIG. 4  shows a thermal management system  13  in accordance with yet another embodiment of the invention which is particularly suitable for continuous operation using liquid HTF. The TMS  13  is generally the same as the TMS  10 , except that it further comprises a pump which receives the HTF stream  174  after it has passed through the backpressure valve  152 , and feed HTF at high pressure to the secondary heat exchanger  180 , and therethrough to the driving nozzle  140  of the fluid dynamic pump  120 . If the HEX  180  is arranged to deposit heat into HTF flowing therethrough, then the secondary heat exchanger  180  may be arranged to remove heat from HTF flowing therethrough. Conversely, if the HEX  180  is arranged to remove heat from HTF flowing therethrough, then the secondary heat exchanger  180  may be arranged to deposit heat to HTF flowing therethrough. 
         [0030]      FIG. 5  shows a thermal management system  14  in accordance with still another embodiment of the invention which is particularly suitable for operation using evaporative HTF. The TMS  14  is generally the same as the TMS  10 , except that it further includes a gas-liquid separator  199 . The gas-liquid separator  199  has an inlet port, a gas outlet port, and a liquid outlet port. The suction port  162  of the fluid dynamic pump  120  is fluidly connected via the return pipe  136  to the liquid output port of the gas-liquid separator  199 . The outlet port  156  of the HEX  182  is fluidly connected via the pipe  138  to the inlet port of the gas-liquid separator  199 . The gas outlet port of the gas-liquid separator  199  is fluidly connected to the backpressure valve  152  via the line  189 . 
         [0031]    In operation, suitable HTF in a substantially liquid form is supplied under high pressure via the supply line  148  to the motive nozzle  140  of the fluid dynamic pump  120  where it forms a jet  142  which is directed into the throat portion of the pump body  1834 . The jet  142  entrains HTF in the suction chamber  128  and pumps it. HTF stream  176  containing both the jet flow and the pumped HTF from the pipe  136  exists the fluid dynamic pump  120  through the discharge port  164  and flows through the pipe  132  into the inlet port  154  of the HEX  182 . The HTF receives heat from the HEX  182 , which may cause a portion of the HTF to evaporate. The HTF exists the HEX  182  as a stream  176 ″ (which may be a mixture of liquid and vapor, e.g., in the form of bubbles) through the outlet port  156  and flows through the pipe  138  into the inlet port of the gas-liquid separator  199 . The gas-liquid separator  199  separates the incoming HTF mixture of liquid and vapor into a portion of that is substantially in a liquid state and a portion that is substantially in a vapor (gaseous) state. The portion of HTF in a substantially liquid state is fed as a stream  172  through the liquid output port of the gas-liquid separator  199  into the return pipe  136 , and therethrough into the suction chamber  128  of the fluid dynamic pump  120 , where it may be pumped by the jet  142 . The portion of HTF in a substantially vapor (gaseous) state is fed as a stream  174  through the gas output port of the gas-liquid separator  199  into the pipe  189 . The pipe  189  carries the stream  174  through the backpressure valve  128  that may release it from the thermal management system  14 . In some variants of the invention, the backpressure valve releases the stream  174  into the atmosphere. In some other variants of the invention, the backpressure valve releases the stream  174  into a compressor. Such a compressor may be a part of a vapor-compression refrigeration system that may liquefy the HTF vapor, chill it, and feed it as a stream  175  into the driving nozzle  140 . 
         [0032]    The backpressure valve  152  may be adjusted so that a desired pressure can be attained in the recirculation loop  124 ′. The pressure in the recirculation loop  124 ′ influences the amount of flow in the stream  172 . Preferably, the backpressure valve  152  is adjusted so that the stream  172  contains the HTF mostly in a liquid form. In some variants of the invention, the backpressure valve  152  may be replaced by a suitable flow-impeding element such as an orifice or a venturi. In some other variants of the invention, the backpressure valve  152  may be an expansion valve. In yet other alternative versions of the invention, a flow impeding device (such as valve, orifice, venture, or like) may be installed in the pipe  138 . Such a flow impeding device may suppress (at least in-part) evaporation (boiling) of the heat transfer fluid in the HEX  182 , which may be desirable in some applications of the invention. Evaporation may then occur downstream of the flow impeding device. By appropriately setting the backpressure valve  152 , a large mass flow may be maintained through the HEX  182  while the overall consumption of the HTF as, for example, measured by the HTF mass flow through the driving nozzle  140  may be substantially smaller. The selection of HTF for practicing with the thermal management system  14  may include water, alcohol, refrigerants (e.g., Freons and ammonia), and cryogenic liquids (e.g., liquid nitrogen, liquid helium, liquid carbon dioxide, liquid natural gas, and liquid propane). 
         [0033]    Uses of the subject invention include cooling of devices requiring heat transfer at very high heat flux including photovoltaic cells used with a concentrator, thermal photovoltaic cells, semiconductor laser diodes, semiconductor electronics, and laser gain medium. Other uses of the invention include removing heat from solar panels. Further uses of the invention include systems for refrigeration, air conditioning, and gas liquefaction. 
         [0034]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” and “includes” and/or “including” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0035]    HTF suitable for use with the subject invention include 1) liquids such as water, aqueous solution of alcohol, antifreeze, and oil, 2) gases including air, helium, natural gas, and nitrogen, and 3) vapors such water steam, Freon, and ammonia. 
         [0036]    The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies. 
         [0037]    Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention. In addition, the term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function. 
         [0038]    While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the present invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the present invention as defined by the appended claims and their equivalents. Thus, the scope of the present invention is not limited to the disclosed embodiments.