Manufacture of a heat transfer system

A method of making an evaporator includes orienting a vapor barrier wall, orienting a liquid barrier wall, and positioning a wick between the vapor barrier wall and the liquid barrier wall. The vapor barrier wall is oriented such that a heat-absorbing surface of the vapor barrier wall defines at least a portion of an exterior surface of the evaporator. The exterior surface is configured to receive heat. The liquid barrier wall is oriented adjacent the vapor barrier wall. The liquid barrier wall has a surface configured to confine liquid. A vapor removal channel is defined at an interface between the wick and the vapor barrier wall. A liquid flow channel is defined between the liquid barrier wall and the primary wick.

TECHNICAL FIELD

This description relates to heat transfer systems and methods of manufacturing the heat transfer systems.

BACKGROUND

Heat transfer systems are used to transport heat from one location (the heat source) to another location (the heat sink). Heat transfer systems can be used in terrestrial or extraterrestrial applications. For example, heat transfer systems may be integrated by satellite equipment that operates within zero or low-gravity environments. As another example, heat transfer systems can be used in electronic equipment, which often requires cooling during operation.

Loop Heat Pipes (LHPs) and Capillary Pumped Loops (CPLs) are passive two-phase heat transfer systems. Each includes an evaporator thermally coupled to the heat source, a condenser thermally coupled to the heat sink, fluid that flows between the evaporator and the condenser, and a fluid reservoir for expansion of the fluid. The fluid within the heat transfer system can be referred to as the working fluid. The evaporator includes a primary wick and a core that includes a fluid flow passage. Heat acquired by the evaporator is transported to and discharged by the condenser. These systems utilize capillary pressure developed in a fine-pored wick within the evaporator to promote circulation of working fluid from the evaporator to the condenser and back to the evaporator. The primary distinguishing characteristic between an LHP and a CPL is the location of the loop's reservoir, which is used to store excess fluid displaced from the loop during operation. In general, the reservoir of a CPL is located remotely from the evaporator, while the reservoir of an LHP is co-located with the evaporator.

SUMMARY

In one general aspect, a method of making an evaporator includes orienting a vapor barrier wall, orienting a liquid barrier wall, and positioning a wick between the vapor barrier wall and the liquid barrier wall. The vapor barrier wall is oriented such that a heat-absorbing surface of the vapor barrier wall defines at least a portion of an exterior surface of the evaporator. The exterior surface is configured to receive heat. The liquid barrier wall is oriented adjacent the vapor barrier wall. The liquid barrier wall has a surface configured to confine liquid. At least one of the orienting a vapor barrier wall, orienting a liquid barrier wall, and positioning the wick includes defining a vapor removal channel at an interface between the wick and the vapor barrier wall. At least one of the orienting a vapor barrier wall, orienting a liquid barrier wall, and positioning the wick includes defining a liquid flow channel between the liquid barrier wall and the primary wick.

Implementations may include one or more of the following aspects. For example, the method may also include forming the vapor barrier wall and forming the liquid barrier wall. Forming the vapor barrier wall may include forming the vapor barrier wall into a planar shape and forming the liquid barrier wall may include forming the liquid barrier wall into a planar shape. Forming the vapor barrier wall may include forming the vapor barrier wall into an annular shape and forming the liquid barrier wall may include forming the liquid barrier wall into an annular shape.

Positioning the wick may include heat shrinking the wick on the vapor barrier wall. Positioning the wick may include heat shrinking the liquid barrier wall on the wick.

Positioning may include positioning the wick between the vapor barrier wall and the liquid confining surface of the liquid barrier wall.

The method may also include orienting a subcooler adjacent the liquid barrier wall. Orienting the subcooler may include heat shrinking the subcooler onto the liquid barrier wall.

The method may include electroetching, machining, or photoetching the vapor removal channel into the vapor barrier wall. The method may include embedding the vapor removal channel within the wick.

The method may also include forming the vapor barrier wall by rolling a vapor barrier material into a cylindrical shape and sealing mating edges of the vapor barrier material. The method may include forming the liquid barrier wall by rolling a liquid barrier material into a cylindrical shape and sealing mating edges of the liquid barrier material.

Orienting the liquid barrier wall may include heat shrinking the liquid barrier wall.

The method may include forming the liquid barrier wall, and photoetching the liquid flow channel into the liquid barrier wall.

In another general aspect, a method of making an evaporator includes orienting a liquid barrier wall having an annular shape, orienting a vapor barrier wall having an annular shape coaxially with the liquid barrier wall, and positioning a wick between the liquid barrier wall and the vapor barrier wall, the wick being coaxial with the liquid barrier wall.

Implementations may include one or more of the following aspects. For example, the method may include forming the vapor barrier wall and forming the liquid barrier wall.

Positioning the wick may include heat shrinking the wick on the vapor barrier wall. Positioning the wick may include heat shrinking the liquid barrier wall on the wick. Positioning may include positioning the wick between the vapor barrier wall and a liquid confining surface of the liquid barrier wall.

The method may include orienting a subcooler adjacent the liquid barrier wall. Orienting the subcooler may include heat shrinking the subcooler onto the liquid barrier wall.

The method may include electroetching, machining, or photoetching the vapor removal channel into the vapor barrier wall. The method may include embedding the vapor removal channel within the wick.

The method may include forming the vapor barrier wall by rolling a vapor barrier material into a cylindrical shape and sealing mating edges of the vapor barrier material. The method may further include forming the liquid barrier wall by rolling a liquid barrier material into a cylindrical shape and sealing mating edges of the liquid barrier material.

Orienting the liquid barrier wall may include heat shrinking the liquid barrier wall.

Other features and advantages will be apparent from the description, the drawings, and the claims.

DETAILED DESCRIPTION

As discussed above, in a loop heat pipe (LHP), the reservoir is co-located with the evaporator, thus, the reservoir is thermally and hydraulically connected with the reservoir through a heat-pipe-like conduit. In this way, liquid from the reservoir can be pumped to the evaporator, thus ensuring that the primary wick of the evaporator is sufficiently wetted or “primed” during start-up. Additionally, the design of the LHP also reduces depletion of liquid from the primary wick of the evaporator during steady-state or transient operation of the evaporator within a heat transport system. Moreover, vapor and/or bubbles of non-condensable gas (NCG bubbles) vent from a core of the evaporator through the heat-pipe-like conduit into the reservoir.

Conventional LHPs require that liquid be present in the reservoir prior to start-up, that is, application of power to the evaporator of the LHP. However, if the working fluid in the LHP is in a supercritical state prior to start-up of the LHP, liquid will not be present in the reservoir prior to start-up. A supercritical state is a state in which a temperature of the LHP is above the critical temperature of the working fluid. The critical temperature of a fluid is the highest temperature at which the fluid can exhibit a liquid-vapor equilibrium. For example, the LHP may be in a supercritical state if the working fluid is a cryogenic fluid, that is, a fluid having a boiling point below −150° C., or if the working fluid is a sub-ambient fluid, that is, a fluid having a boiling point below the temperature of the environment in which the LHP is operating.

Conventional LHPs also require that liquid returning to the evaporator be subcooled, that is, cooled to a temperature that is lower than the boiling point of the working fluid. Such a constraint makes it impractical to operate LHPs at a sub-ambient temperature. For example, if the working fluid is a cryogenic fluid, the LHP is likely operating in an environment having a temperature greater than the boiling point of the fluid.

Referring toFIG. 1, a heat transport system100is designed to overcome limitations of conventional LHPs. The heat transport system100includes a heat transfer system105and a priming system110. The priming system110is configured to convert fluid within the heat transfer system105into a liquid, thus priming the heat transfer system105. As used in this description, the term “fluid” is a generic term that refers to a substance that is both a liquid and a vapor in saturated equilibrium.

The heat transfer system105includes a main evaporator115, and a condenser120coupled to the main evaporator115by a liquid line125and a vapor line130. The condenser120is in thermal communication with a heat sink165, and the main evaporator115is in thermal communication with a heat source Qin116. The system105may also include a hot reservoir147coupled to the vapor line130for additional pressure containment, as needed. In particular, the hot reservoir147increases the volume of the system100. If the working fluid is at a temperature above its critical temperature, that is, the highest temperature at which the working fluid can exhibit liquid-vapor equilibrium, its pressure is proportional to the mass in the system100(the charge) and inversely proportional to the volume of the system. Increasing the volume with the hot reservoir147lowers the fill pressure.

The main evaporator115includes a container117that houses a primary wick140within which a core135is defined. The main evaporator115includes a bayonet tube142and a secondary wick145within the core135. The bayonet tube142, the primary wick140, and the secondary wick145define a liquid passage143, a first vapor passage144, and a second vapor passage146. The secondary wick145provides phase control, that is, liquid/vapor separation in the core135, as discussed in U.S. application Ser. No. 09/896,561, filed Jun. 29, 2001, which is incorporated herein by reference in its entirety. As shown, the main evaporator115has three ports, a liquid inlet137into the liquid passage143, a vapor outlet132into the vapor line130from the second vapor passage146, and a fluid outlet139from the liquid passage143(and possibly the first vapor passage144, as discussed below). Further details on the structure of a three-port evaporator are discussed below with respect toFIGS. 5A and 5B.

The priming system110includes a secondary or priming evaporator150coupled to the vapor line130and a reservoir155co-located with the secondary evaporator150. The reservoir155is coupled to the core135of the main evaporator115by a secondary fluid line160and a secondary condenser122. The secondary fluid line160couples to the fluid outlet139of the main evaporator115. The priming system110also includes a controlled heat source Qsp151in thermal communication with the secondary evaporator150.

The secondary evaporator150includes a container152that houses a primary wick190within which a core185is defined. The secondary evaporator150includes a bayonet tube153and a secondary wick180that extend from the core185, through a conduit175, and into the reservoir155. The secondary wick180provides a capillary link between the reservoir155and the secondary evaporator150. The bayonet tube153, the primary wick190, and the secondary wick180define a liquid passage182coupled to the fluid line160, a first vapor passage181coupled to the reservoir155, and a second vapor passage183coupled to the vapor line130. The reservoir155is thermally and hydraulically coupled to the core185of the secondary evaporator150through the liquid passage182, the secondary wick180, and the first vapor passage181. Vapor and/or NCG bubbles from the core185of the secondary evaporator150are swept through the first vapor passage181to the reservoir155and condensable liquid is returned to the secondary evaporator150through the secondary wick180from the reservoir155. The primary wick190hydraulically links liquid within the core185to the heat source Qsp151, permitting liquid at an outer surface of the primary wick190to evaporate and form vapor within the second vapor passage183when heat is applied to the secondary evaporator150.

The reservoir155is cold-biased, and thus, it is cooled by a cooling source that will allow it to operate, if unheated, at a temperature that is lower than the temperature at which the heat transfer system105operates. In one implementation, the reservoir155and the secondary condenser122are in thermal communication with the heat sink165that is thermally coupled to the condenser120. For example, the reservoir155can be mounted to the heat sink165using a shunt170, which may be made of aluminum or any heat conductive material. In this way, the temperature of the reservoir155tracks the temperature of the condenser120.

FIG. 2shows an example of an implementation of the heat transport system100. In this implementation, the condensers120and122are mounted to a cryocooler200, which acts as a refrigerator, transferring heat from the condensers120,122to the heat sink165. Additionally, in the implementation ofFIG. 2, the lines125,130,160are wound to reduce space requirements for the heat transport system100.

Though not shown inFIGS. 1 and 2, elements such as, for example, the reservoir155and the main evaporator115, may be equipped with temperature sensors that can be used for diagnostic or testing purposes.

Referring also toFIG. 3, the system100performs a procedure300for transporting heat from the heat source Qin116and for ensuring that the main evaporator115is wetted with liquid prior to startup. The procedure300is particularly useful when the heat transfer system105is at a supercritical state. Prior to initiation of the procedure300, the system100is filled with a working fluid at a particular pressure, referred to as a “fill pressure.”

Initially, the reservoir155is cold-biased by, for example, mounting the reservoir155to the heat sink165(step305). The reservoir155may be cold-biased to a temperature below the critical temperature of the working fluid, which, as discussed, is the highest temperature at which the working fluid can exhibit liquid-vapor equilibrium. For example, if the fluid is ethane, which has a critical temperature of 33° C., the reservoir155is cooled to below 33° C. As the temperature of the reservoir155drops below the critical temperature of the working fluid, the reservoir155partially fills with a liquid condensate formed by the working fluid. The formation of liquid within the reservoir155wets the secondary wick180and the primary wick190of the secondary evaporator150(step310).

Meanwhile, power is applied to the priming system110by applying heat from the heat source Qsp151to the secondary evaporator150(step315) to enhance or initiate circulation of fluid within the heat transfer system105. Vapor output by the secondary evaporator150is pumped through the vapor line130and through the condenser120(step320) due to capillary pressure at the interface between the primary wick190and the second vapor passage183. As vapor reaches the condenser120, it is converted to liquid (step325). The liquid formed in the condenser120is pumped to the main evaporator115of the heat transfer system105(step330). When the main evaporator115is at a higher temperature than the critical temperature of the fluid, the liquid entering the main evaporator115evaporates and cools the main evaporator115. This process (steps315–330) continues, causing the main evaporator115to reach a set point temperature (step335), at which point the main evaporator is able to retain liquid and be wetted and to operate as a capillary pump. In one implementation, the set point temperature is the temperature to which the reservoir155has been cooled. In another implementation, the set point temperature is a temperature below the critical temperature of the working fluid. In a further implementation, the set point temperature is a temperature above the temperature to which the reservoir155has been cooled.

If the set point temperature has been reached (step335), the system100operates in a main mode (step340) in which heat from the heat source Qin116that is applied to the main evaporator115is transferred by the heat transfer system105. Specifically, in the main mode, the main evaporator115develops capillary pumping to promote circulation of the working fluid through the heat transfer system105. Also, in the main mode, the set point temperature of the reservoir155is reduced. The rate at which the heat transfer system105cools down during the main mode depends on the cold biasing of the reservoir155because the temperature of the main evaporator115closely follows the temperature of the reservoir155. Additionally, though not required, a heater can be used to further control or regulate the temperature of the reservoir155during the main mode. Furthermore, in main mode, the power applied to the secondary evaporator150by the heat source Qsp151is reduced, thus bringing the heat transfer system105down to a normal operating temperature for the fluid. For example, in the main mode, the heat load from the heat source Qsp151to the secondary evaporator150is kept at a value equal to or in excess of heat conditions, as defined below. In one implementation, the heat load from the heat source Qsp is kept to about 5 to 10% of the heat load applied to the main evaporator115from the heat source Qin116.

In this particular implementation, the main mode is triggered by the determination that the set point temperature has been reached (step335). In other implementations, the main mode may begin at other times or due to other triggers. For example, the main mode may begin after the priming system is wet (step310) or after the reservoir has been cold biased (step305).

At any time during operation, the heat transfer system105can experience heat conditions such as those resulting from heat conduction across the primary wick140and parasitic heat applied to the liquid line125. Both conditions cause formation of vapor on the liquid side of the evaporator. Specifically, heat conduction across the primary wick140can cause liquid in the core135to form vapor bubbles, which, if left within the core135, would grow and block off liquid supply to the primary wick140, thus causing the main evaporator115to fail. Parasitic heat input into the liquid line125(referred to as “parasitic heat gains”) can cause liquid within the liquid line125to form vapor.

To reduce the adverse impact of heat conditions discussed above, the priming system110operates at a power level Qsp151greater than or equal to the sum of the head conduction and the parasitic heat gains. As mentioned above, for example, the priming system can operate at 5–10% of the power to the heat transfer system105. In particular, fluid that includes a combination of vapor bubbles and liquid is swept out of the core135for discharge into the secondary fluid line160leading to the secondary condenser122. In particular, vapor that forms within the core135travels around the bayonet tube143directly into the fluid outlet port139. Vapor that forms within the first vapor passage144makes it way into the fluid outlet port139by either traveling through the secondary wick145(if the pore size of the secondary wick145is large enough to accommodate vapor bubbles) or through an opening at an end of the secondary wick145near the outlet port139that provides a clear passage from the first vapor passages144to the outlet port139. The secondary condenser122condenses the bubbles in the fluid and pushes the fluid to the reservoir155for reintroduction into the heat transfer system105.

Similarly, to reduce parasitic heat input to the liquid line125, the secondary fluid line160and the liquid line125can form a coaxial configuration and the secondary fluid line160surrounds and insulates the liquid line125from surrounding heat. This implementation is discussed further below with reference toFIGS. 8A and 8B. As a consequence of this configuration, it is possible for the surrounding heat to cause vapor bubbles to form in the secondary fluid line160, instead of in the liquid line125. As discussed, by virtue of capillary action affected at the secondary wick145, fluid flows from the main evaporator115to the secondary condenser122. This fluid flow, and the relatively low temperature of the secondary condenser122, causes a sweeping of the vapor bubbles within the secondary fluid line160through the condenser122, where they are condensed into liquid and pumped into the reservoir155.

As shown inFIG. 4, data from a test run is shown. In this implementation, prior to startup of the main evaporator115at temperature410, a temperature400of the main evaporator115is significantly higher than a temperature405of the reservoir155, which has been cold-biased to the set point temperature (step305). As the priming system110is wetted (step310), power Qsp450is applied to the secondary evaporator150(step315) at a time452, causing liquid to be pumped to the main evaporator115(step330), the temperature400of the main evaporator115drops until it reaches the temperature405of the reservoir155at time410. Power Qin460is applied to the main evaporator115at a time462, when the system100is operating in LHP mode (step340). As shown, power input Qin460to the main evaporator115is held relatively low while the main evaporator115is cooling down. Also shown are the temperatures470and475, respectively, of the secondary fluid line160and the liquid line125. After time410, temperatures470and475track the temperature400of the main evaporator115. Moreover, a temperature415of the secondary evaporator150follows closely with the temperature405of the reservoir155because of the thermal communication between the secondary evaporator150and the reservoir155.

As mentioned, in one implementation, ethane may be used as the fluid in the heat transfer system105. Although the critical temperature of ethane is 33° C., for the reasons generally described above, the system100can start up from a supercritical state in which the system100is at a temperature of 70° C. As power Qsp is applied to the secondary evaporator150, the temperatures of the condenser120and the reservoir155drop rapidly (between times452and410). A trim heater can be used to control the temperature of the reservoir155and thus the condenser120to −10° C. To startup the main evaporator115from the supercritical temperature of 70° C., a heat load or power input Qsp of 10 W is applied to the secondary evaporator150. Once the main evaporator115is primed, the power input from the heat source Qsp151to the secondary evaporator150and the power applied to and through the trim heater both may be reduced to bring the temperature of the system100down to a nominal operating temperature of about −50° C. For instance, during the main mode, if a power input Qin of 40 W is applied to the main evaporator115, the power input Qsp to the secondary evaporator150can be reduced to approximately 3 W while operating at −45° C. to mitigate the 3 W lost through heat conditions (as discussed above). As another example, the main evaporator115can operate with power input Qin from about 10 W to about 40 W with 5 W applied to the secondary evaporator150and with the temperature405of the reservoir155at approximately −45° C.

Referring toFIGS. 5A and 5B, in one implementation, the main evaporator115is designed as a three-port evaporator500(which is the design shown inFIG. 1). Generally, in the three-port evaporator500, liquid flows into a liquid inlet505into a core510, defined by a primary wick540, and fluid from the core510flows from a fluid outlet512to a cold-biased reservoir (such as reservoir155). The fluid and the core510are housed within a container515made of, for example, aluminum. In particular, fluid flowing from the liquid inlet505into the core510flows through a bayonet tube520, into a liquid passage521that flows through and around the bayonet tube520. Fluid can flow through a secondary wick525(such as secondary wick145of evaporator115) made of a wick material530and an annular artery535. The wick material530separates the annular artery535from a first vapor passage560. As power from the heat source Qin116is applied to the evaporator500, liquid from the core510enters a primary wick540and evaporates, forming vapor that is free to flow along a second vapor passage565that includes one or more vapor grooves545and out a vapor outlet550into the vapor line130. Vapor bubbles that form within first vapor passage560of the core510are swept out of the core510through the first vapor passage560and into the fluid outlet512. As discussed above, vapor bubbles within the first vapor passage560may pass through the secondary wick525if the pore size of the secondary wick525is large enough to accommodate the vapor bubbles. Alternatively, or additionally, vapor bubbles within the first vapor passage560may pass through an opening of the secondary wick525formed at any suitable location along the secondary wick525to enter the liquid passage521or the fluid outlet512.

Referring toFIG. 6, in another implementation, the main evaporator115is designed as a four-port evaporator600, which is a design described in U.S. application Ser. No. 09/896,561, filed Jun. 29, 2001. Briefly, and with emphasis on aspects that differ from the three-port evaporator configuration, liquid flows into the evaporator600through a fluid inlet605, through a bayonet610, and into a core615. The liquid within the core615enters a primary wick620and evaporates, forming vapor that is free to flow along vapor grooves625and out a vapor outlet630into the vapor line130. A secondary wick633within the core615separates liquid within the core from vapor or bubbles in the core (that are produced when liquid in the core615heats). The liquid carrying bubbles formed within a first fluid passage635inside the secondary wick633flows out of a fluid outlet640and the vapor or bubbles formed within a vapor passage642positioned between the secondary wick633and the primary wick620flow out of a vapor outlet645.

Referring also toFIG. 7, a heat transport system700is shown in which the main evaporator is a four-port evaporator600. The system700includes one or more heat transfer systems705and a priming system710configured to convert fluid within the heat transfer systems705into a liquid to prime the heat transfer systems705. The four-port evaporators600are coupled to one or more condensers715by a vapor line720and a fluid line725. The priming system710includes a cold-biased reservoir730hydraulically and thermally connected to a priming evaporator735.

Design considerations of the heat transport system100include startup of the main evaporator115from a supercritical state, management of parasitic heat leaks, heat conduction across the primary wick140, cold biasing of the cold reservoir155, and pressure containment at ambient temperatures that are greater than the critical temperature of the working fluid within the heat transfer system105. To accommodate these design considerations, the body or container (such as container515) of the evaporator115or150can be made of extruded6063aluminum and the primary wicks140and/or190can be made of a fine-pored wick. In one implementation, the outer diameter of the evaporator115or150is approximately 0.625 inches and the length of the container is approximately 6 inches. The reservoir155may be cold-biased to an end panel of the radiator165using the aluminum shunt170. Furthermore, a heater (such as a kapton heater) can be attached at a side of the reservoir155.

In one implementation, the vapor line130is made with smooth walled stainless steel tubing having an outer diameter (OD) of 3/16″ and the liquid line125and the secondary fluid line160are made of smooth walled stainless steel tubing having an OD of ⅛″. The lines125,130,160may be bent in a serpentine route and plated with gold to minimize parasitic heat gains. Additionally, the lines125,130,160may be enclosed in a stainless steel box with heaters to simulate a particular environment during testing. The stainless steel box can be insulated with multi-layer insulation (MLI) to minimize heat leaks through panels of the heat sink165.

In one implementation, the condenser122and the secondary fluid line160are made of tubing having an OD of 0.25 inches. The tubing is bonded to the panels of the heat sink165using, for example, epoxy. Each panel of the heat sink165is an 8×19 inch direct condensation, aluminum radiator that uses a 1/16-inch thick face sheet. Kapton heaters can be attached to the panels of the heat sink165, near the condenser120to prevent inadvertent freezing of the working fluid. During operation, temperature sensors such as thermocouples can be used to monitor temperatures throughout the system100.

The heat transport system100may be implemented in any circumstances where the critical temperature of the working fluid of the heat transfer system105is below the ambient temperature at which the system100is operating. The heat transport system100can be used to cool down components that require cryogenic cooling.

Referring toFIGS. 8A–8D, the heat transport system100may be implemented in a miniaturized cryogenic system800. In the miniaturized system800, the lines125,130,160are made of flexible material to permit coil configurations805, which save space. The miniaturized system800can operate at −238° C. using neon fluid. Power input Qin116is approximately 0.3 to 2.5 W. The miniaturized system800thermally couples a cryogenic component (or heat source that requires cryogenic cooling)816to a cryogenic cooling source such as a cryocooler810coupled to cool the condensers120,122.

The miniaturized system800reduces mass, increases flexibility, and provides thermal switching capability when compared with traditional thermally-switchable, vibration-isolated systems. Traditional thermally-switchable, vibration-isolated systems require two flexible conductive links (FCLs), a cryogenic thermal switch (CTSW), and a conduction bar (CB) that form a loop to transfer heat from the cryogenic component to the cryogenic cooling source. In the miniaturized system800, thermal performance is enhanced because the number of mechanical interfaces is reduced. Heat conditions at mechanical interfaces account for a large percentage of heat gains within traditional thermally-switchable, vibration-isolated systems. The CB and two FCLs are replaced with the low-mass, flexible, thin-walled tubing used for the coil configurations805of the miniaturized system800.

Moreover, the miniaturized system800can function of a wide range of heat transport distances, which permits a configuration in which the cooling source (such as the cryocooler810) is located remotely from the cryogenic component816. The coil configurations805have a low mass and low surface area, thus reducing parasitic heat gains through the lines125and160. The configuration of the cooling source810within miniaturized system800facilitates integration and packaging of the system800and reduces vibrations on the cooling source810, which becomes particularly important in infrared sensor applications. In one implementation, the miniaturized system800was tested using neon, operating at 25–40K.

Referring toFIGS. 9A–9C, the heat transport system100may be implemented in an adjustable mounted or Gimbaled system1005in which the main evaporator115and a portion of the lines125,160, and130are mounted to rotate about an elevation axis1020within a range of ±45° and a portion of the lines125,160, and130are mounted to rotate about an azimuth axis1025within a range of ±220°. The lines125,160,130are formed from thin-walled tubing and are coiled around each axis of rotation. The system1005thermally couples a cryogenic component (or heat source that requires cryogenic cooling)1016such as a sensor of a cryogenic telescope to a cryogenic cooling source such as a cryocooler1010coupled to cool the condensers120,122. The cooling source1010is located at a stationary spacecraft1060, thus reducing mass at the cryogenic telescope. Motor torque for controlling rotation of the lines125,160,130, power requirements of the system1005, control requirements for the spacecraft1060, and pointing accuracy for the sensor1016are improved. The cryocooler1010and the radiator or heat sink165can be moved from the sensor1016, reducing vibration within the sensor1016. In one implementation, the system1005was tested to operate within the range of 70–115K when the working fluid is nitrogen.

The heat transfer system105may be used in medical applications, or in applications where equipment must be cooled to below-ambient temperatures. As another example, the heat transfer system105may be used to cool an infrared (IR) sensor, which operates at cryogenic temperatures to reduce ambient noise. The heat transfer system105may be used to cool a vending machine, which often houses items that preferably are chilled to sub-ambient temperatures. The heat transfer system105may be used to cool components such as a display or a hard drive of a computer, such as a laptop computer, handheld computer, or a desktop computer. The heat transfer system105can be used to cool one or more components in a transportation device such as an automobile or an airplane.

Other implementations are within the scope of the following claims. For example, the condenser120and heat sink165can be designed as an integral system, such as, for example, a radiator. Similarly, the secondary condenser122and heat sink165can be formed from a radiator. The heat sink165can be a passive heat sink (such as a radiator) or a cryocooler that actively cools the condensers120,122.

In another implementation, the temperature of the reservoir155is controlled using a heater. In a further implementation, the reservoir155is heated using parasitic heat.

In another implementation, a coaxial ring of insulation is formed and placed between the liquid line125and the secondary fluid line160, which surrounds the insulation ring.

Evaporator Design

Evaporators are integral components in two-phase heat transfer systems. For example, as shown above inFIGS. 5A and 5B, the evaporator500includes an evaporator body or container515that is in contact with the primary wick540that surrounds the core510. The core510defines a flow passage for the working fluid. The primary wick540is surrounded at its periphery by a plurality of peripheral flow channels or vapor grooves545. The channels545collect vapor at the interface between the wick540and the evaporator body515. The channels545are in contact with the vapor outlet550that feeds into the vapor line that feeds into the condenser to enable evacuation of the vapor formed within the evaporator115.

The evaporator500and the other evaporators discussed above often have a cylindrical geometry, that is, the core of the evaporator forms a cylindrical passage through which the working fluid passes. The cylindrical geometry of the evaporator is useful for cooling applications in which the heat acquisition surface is cylindrically hollow. Many cooling applications require that heat be transferred away from a heat source having a flat surface. In these sort of applications, the evaporator can be modified to include a flat conductive saddle to match the footprint of the heat source having the flat surface. Such a design is shown, for example, in U.S. Pat. No. 6,382,309.

The cylindrical geometry of the evaporator facilitates compliance with thermodynamic constraints of LHP operation (that is, the minimization of heat leaks into the reservoir). The constraints of LHP operation stem from the amount of subcooling an LHP needs to produce for normal equilibrium operation. Additionally, the cylindrical geometry of the evaporator is relatively easy to fabricate, handle, machine, and process.

However, as will be described hereinafter, an evaporator can be designed with a planar form to more naturally attach to a flat heat source.

Planar Design

Referring toFIG. 10, an evaporator1000for a heat transfer system includes a vapor barrier wall1005, a liquid barrier wall1010, a primary wick1015between the vapor barrier wall and the inner side of the liquid barrier wall1010, vapor removal channels1020, and liquid flow channels1025.

The vapor barrier wall1005is in intimate contact with the primary wick1015. The liquid barrier wall1010contains working fluid on an inner side of the liquid barrier wall1010such that the working fluid flows only along the inner side of the liquid barrier wall1010. The liquid barrier wall1010closes the evaporator's envelope and helps to organize and distribute the working fluid through the liquid flow channels1025. The vapor removal channels1020are located at an interface between a vaporization surface1017of the primary wick1015and the vapor barrier wall1005. The liquid flow channels1025are located between the liquid barrier wall1010and the primary wick1015.

The vapor barrier wall1005acts as a heat acquisition surface for a heat source. The vapor barrier wall1005is made from a heat-conductive material, such as, for example, sheet metal. Material chosen for the vapor barrier wall1005typically is able to withstand internal pressure of the working fluid.

The vapor removal channels1020are designed to balance the hydraulic resistance of the channels1020with the heat conduction through the vapor barrier wall1005into the primary wick1015. The channels1020can be electro-etched, machined, or formed in a surface with any other convenient method.

The vapor removal channels1020are shown as grooves in the inner side of the vapor barrier wall1005. However, the vapor removal channels can be designed and located in several different ways, depending on the design approach chosen. For example, according to other implementations, the vapor removal channels1020are grooved into the outer surface of the primary wick1015or embedded into the primary wick1015such that they are under the surface of the primary wick. The design of the vapor removal channels1020is selected to increase the ease and convenience of manufacturing and to closely approximate one or more of the following guidelines.

First, the hydraulic diameter of the vapor removal channels1020should be sufficient to handle a vapor flow generated on the vaporization surface1017of the primary wick1015without a significant pressure drop. Second, the surface of contact between the vapor barrier wall1005and the primary wick1015should be maximized to provide efficient heat transfer from the heat source to vaporization surface of the primary wick1015. Third, a thickness1030of the vapor barrier wall1005, which is in contact with the primary wick1015, should be minimized. As the thickness1030increases, vaporization at the surface of the primary wick1015is reduced and transport of vapor through the vapor removal channels1020is reduced.

The evaporator1000can be assembled from separate parts. Alternatively, the evaporator1000can be made as a single part by in-situ sintering of the primary wick1015between two walls having special mandrels to form channels on both sides of the wick.

The primary wick1015provides the vaporization surface1017and pumps or feeds the working fluid from the liquid flow channels1025to the vaporization surface of the primary wick1015.

The size and design of the primary wick1015involves several considerations. The thermal conductivity of the primary wick1015should be low enough to reduce heat leak from the vaporization surface1017, through the primary wick1015, and to the liquid flow channels1025. Heat leakage can also be affected by the linear dimensions of the primary wick1015. For this reason, the linear dimensions of the primary wick1015should be properly optimized to reduce heat leakage. For example, an increase in a thickness1019of the primary wick1015can reduce heat leakage. However, increased thickness1019can increase hydraulic resistance of the primary wick1015to the flow of the working fluid. In working LHP designs, hydraulic resistance of the working fluid due to the primary wick1015can be significant and a proper balancing of these factors is important.

The force that drives or pumps the working fluid of a heat transfer system is a temperature or pressure difference between the vapor and liquid sides of the primary wick. The pressure difference is supported by the primary wick and it is maintained by proper management of the incoming working fluid thermal balance.

The liquid returning to the evaporator from the condenser passes through a liquid return line and is slightly subcooled. The degree of subcooling offsets the heat leak through the primary wick and the heat leak from the ambient into the reservoir within the liquid return line. The subcooling of the liquid maintains a thermal balance of the reservoir. However, there exist other useful methods to maintain thermal balance of the reservoir.

One method is an organized heat exchange between reservoir and the environment. For evaporators having a planar design, such as those often used for terrestrial applications, the heat transfer system includes heat exchange fins on the reservoir and/or on the liquid barrier wall1010of the evaporator1000. The forces of natural convection on these fins provide subcooling and reduce stress on the condenser and the reservoir of the heat transfer system.

The temperature of the reservoir or the temperature difference between the reservoir and the vaporization surface1017of the primary wick1015supports the circulation of the working fluid through the heat transfer system. Some heat transfer systems may require an additional amount of subcooling. The required amount may be greater than what the condenser can produce, even if the condenser is completely blocked.

In designing the evaporator1000, three variables need to be managed. First, the organization and design of the liquid flow channels1025needs to be determined. Second, the venting of the vapor from the liquid flow channels1025needs to be accounted for. Third, the evaporator1000should be designed to ensure that liquid fills the liquid flow channels1025. These three variables are interrelated and thus should be considered and optimized together to form an effective heat transfer system.

As mentioned, it is important to obtain a proper balance between the heat leak into the liquid side of the evaporator and the pumping capabilities of the primary wick. This balancing process cannot be done independently from the optimization of the condenser, which provides subcooling, because the greater heat leak allowed in the design of the evaporator, the more subcooling needs to be produced in the condenser. The longer the condenser, the greater are the hydraulic losses in a fluid lines, which may require different wick material with better pumping capabilities.

In operation, as power from a heat source is applied to the evaporator1000, liquid from the liquid flow channels1025enters the primary wick1015and evaporates, forming vapor that is free to flow along the vapor removal channels1020. Liquid flow into the evaporator1000is provided by the liquid flow channels1025. The liquid flow channels1025supply the primary wick1015with the enough liquid to replace liquid that is vaporized on the vapor side of the primary wick1015and to replace liquid that is vaporized on the liquid side of the primary wick1015.

The evaporator1000may include a secondary wick1040, which provides phase management on a liquid side of the evaporator1000and supports feeding of the primary wick1015in critical modes of operation (as discussed above). The secondary wick1040is formed between the liquid flow channels1025and the primary wick1015. The secondary wick can be a mesh screen (as shown in theFIG. 10), or an advanced and complicated artery, or a slab wick structure. Additionally, the evaporator1000may include a vapor vent channel1045at an interface between the primary wick1015and the secondary wick1040.

Heat conduction through the primary wick1015may initiate vaporization of the working fluid in a wrong place—on a liquid side of the evaporator1000near or within the liquid flow channels1025. The vapor vent channel1045delivers the unwanted vapor away from the wick into the two-phase reservoir.

The fine pore structure of the primary wick1015can create a significant flow resistance for the liquid. Therefore, it is important to optimize the number, the geometry, and the design of the liquid flow channels1025. The goal of this optimization is to support a uniform, or close to uniform, feeding flow to the vaporization surface1017. Moreover, as the thickness1019of the primary wick1015is reduced, the liquid flow channels1025can be space farther apart.

The evaporator1000may require significant vapor pressure to operate with a particular working fluid within the evaporator1000. Use of a working fluid with a high vapor pressure can cause several problems with pressure containment of the evaporator envelope. Traditional solutions to the pressure containment problem, such as thickening the walls of the evaporator, are not always effective. For example, in planar evaporators having a significant flat area, the walls become so thick that the temperature difference is increased and the evaporator heat conductance is degraded. Additionally, even microscopic deflection of the walls due to the pressure containment results in a loss of contact between the walls and the primary wick. Such a loss of contact impacts heat transfer through the evaporator. And, microscopic deflection of the walls creates difficulties with the interfaces between the evaporator and the heat source and any external cooling equipment.

Annular Design

Referring toFIGS. 10–13, an annular evaporator1100is formed by effectively rolling the planar evaporator1000such that the primary wick1015loops back into itself and forms an annular shape. The evaporator1100can be used in applications in which the heat sources have a cylindrical exterior profile, or in applications where the heat source can be shaped as a cylinder. The annular shape combines the strength of a cylinder for pressure containment and the curved interface surface for best possible contact with the cylindrically-shaped heat sources.

The evaporator1100includes a vapor barrier wall1105, a liquid barrier wall1110, a primary wick1115positioned between the vapor barrier wall1105and the inner side of the liquid barrier wall1110, vapor removal channels1120, and liquid flow channels1125. The liquid barrier wall1110is coaxial with the primary wick1115and the vapor barrier wall1105.

The vapor barrier wall1105intimately contacts the primary wick1115. The liquid barrier wall1110contains working fluid on an inner side of the liquid barrier wall1110such that the working fluid flows only along the inner side of the liquid barrier wall1110. The liquid barrier wall1110closes the evaporator's envelope and helps to organize and distribute the working fluid through the liquid flow channels1125.

The vapor removal channels1120are located at an interface between a vaporization surface1117of the primary wick1115and the vapor barrier wall1105. The liquid flow channels1125are located between the liquid barrier wall1110and the primary wick1115. The vapor barrier wall1105acts a heat acquisition surface and the vapor generated on this surface is removed by the vapor removal channels1120.

The primary wick1115fills the volume between the vapor barrier wall1105and the liquid barrier wall1110of the evaporator1100to provide reliable reverse menisci vaporization.

The evaporator1100can also be equipped with heat exchange fins1150that contact the liquid barrier wall1110to cold bias the liquid barrier wall1110. The liquid flow channels1125receive liquid from a liquid inlet1155and the vapor removal channels1120extend to and provide vapor to a vapor outlet1160.

The evaporator1100can be used in a heat transfer system that includes an annular reservoir1165adjacent the primary wick1115. The reservoir1165may be cold biased with the heat exchange fins1150, which extend across the reservoir1165. The cold biasing of the reservoir1165permits utilization of the entire condenser area without the need to generate subcooling at the condenser. The excessive cooling provided by cold biasing the reservoir1165and the evaporator1100compensates the parasitic heat leaks through the primary wick1115into the liquid side of the evaporator1100.

In another implementation, the evaporator design can be inverted and vaporization features can be placed on an outer perimeter and the liquid return features can be placed on the inner perimeter.

The annular shape of the evaporator1100may provide one or more of the following or additional advantages. First, problems with pressure containment may be reduced or eliminated in the annular evaporator1100. Second, the primary wick1115may not need to be sintered inside, thus providing more space for a more sophisticated design of the vapor and liquid sides of the primary wick1115.

Referring also toFIGS. 14A–H, an annular evaporator1400is shown having a liquid inlet1455and a vapor outlet1460. The annular evaporator1400includes a vapor barrier wall1700(FIGS. 14G,14H, and17A–D), a liquid barrier wall1500(FIGS. 14G,14H, and17A–17D), a primary wick1600(FIGS. 14G,14H, and16A–D) positioned between the vapor barrier wall1700and the inner side of the liquid barrier wall1500, vapor removal channels1465(FIGS. 14H,15A,15B), and liquid flow channels1505(FIG. 14H). The annular evaporator1400also includes a ring1800(FIGS.14G and18A–D) that ensures spacing between the vapor barrier wall1700and the liquid barrier wall1500and a ring1900(FIGS. 14G,14H, and19A–D) at a base of the evaporator1400that provides support for the liquid barrier wall1500and the primary wick1600. The vapor barrier wall1700, the liquid barrier wall1500, the ring1800, the ring1900, and the wick1600are preferably formed of stainless steel.

The upper portion of the evaporator1400(that is, above the wick1600) includes an expansion volume1470(FIG. 14H). The liquid flow channels1505, which are formed in the liquid barrier wall1500, are fed by the liquid inlet1455. The wick1600separates the liquid flow channels1505from the vapor removal channels1465that lead to the vapor outlet1460through a vapor annulus1475(FIG. 14H) formed in the ring1900. The vapor channels1465may be photo-etched into the surface of the vapor barrier wall1700, as discussed below in greater detail.

The evaporators disclosed herein can operate in any combination of materials, dimensions and arrangements, so long as they embody the features as described above. There are no restrictions other than criteria mentioned here; the evaporator can be made of any shape size and material. The only design constraints are that the applicable materials be compatible with each other and that the working fluid be selected in consideration of structural constraints, corrosion, generation of noncondensable gases, and lifetime issues.

Many terrestrial applications can incorporate an LHP with an annular evaporator1100. The orientation of the annular evaporator in a gravity field is predetermined by the nature of application and the shape of the hot surface.

Cyclical Heat Exchange System

Cyclical heat exchange systems may be configured with one or more heat transfer systems to control a temperature at a region of the heat exchange system. The cyclical heat exchange system may be any system that operates using a thermodynamic cycle, such as, for example, a cyclical heat exchange system, a Stirling heat exchange system (also known as a Stirling engine), or an air conditioning system.

Referring toFIG. 20, a Stirling heat exchange system2000utilizes a known type of environmentally friendly and efficient refrigeration cycle. The Stirling system2000functions by directing a working fluid (for example, helium) through four repetitive operations; that is, a heat addition operation at constant temperature, a constant volume heat rejection operation, a constant temperature heat rejection operation and a heat addition operation at constant volume.

The Stirling system2000is designed as a Free Piston Stirling Cooler (FPSC), such as Global Cooling's model M100B (Available from Global Cooling Manufacturing, 94 N. Columbus Rd., Athens, Ohio). The FPSC2000includes a linear motor portion2005housing a linear motor (not shown) that receives an AC power input2010. The FPSC2000includes a heat acceptor2015, a regenerator2020, and a heat rejecter2025. The FPSC2000includes a balance mass2030coupled to the body of the linear motor within the linear motor portion2005to absorb vibrations during operation of the FPSC. The FPSC2000also includes a charge port2035. The FPSC2000includes internal components, such as those shown in the FPSC2100ofFIG. 21.

The FPSC2100includes a linear motor2105housed within the linear motor portion2110. The linear motor portion2110houses a piston2115that is coupled to flat springs2120at one end and a displacer2125at another end. The displacer2125couples to an expansion space2130and a compression space2135that form, respectively, cold and hot sides. The heat acceptor2015is mounted to the cold side2130and the heat rejector is mounted to the hot side2135. The FPSC2100also includes a balance mass2140coupled to the linear motor portion2110to absorb vibrations during operation of the FPSC2100.

Referring also toFIG. 22, in one implementation, a FPSC2200includes heat rejector2205made of a copper sleeve and a heat acceptor2210may of a copper sleeve. The heat rejector2205has an outer diameter (OD) of approximately 100 mm and a width of approximately 53 mm to provide a 166 cm2heat rejection surface capable of providing a flux of 6 W/cm2when operating in a temperature range of 20–70° C. The heat acceptor2210has an OD of approximately 100 mm and a width of approximately 37 mm to provide a 115 cm2heat accepting surface capable of providing a flux of 5.2 W/cm2in a temperature range of −30–5° C.

Briefly, in operation an FPSC is filled with a coolant (such as, for example, Helium gas) that is shuttled back and forth by combined movements of the piston and the displacer. In an ideal system, thermal energy is rejected to the environment through the heat rejector while the coolant is compressed by the piston and thermal energy is extracted from the environment through the heat acceptor while the coolant expands.

Referring toFIG. 23, a thermodynamic system2300includes a cyclical heat exchange system such as a cyclical heat exchange system2305(for example, the systems2000,2100,2200) and a heat transfer system2310thermally coupled to a portion2315of the cyclical heat exchange system2305. The cyclical heat exchange system2305is cylindrical and the heat transfer system2310is shaped to surround the portion2315of the cyclical heat exchange system2305to reject heat from the portion2315. In this implementation, the portion2315is the hot side (that is, the heat rejector) of the cyclical heat exchange system2305. The thermodynamic system2300also includes a fan2320positioned at the hot side of the cyclical heat exchange system2305to force air over a condenser of the heat transfer system2310and thus to provide additional convection cooling.

A cold side2335(that is, the heat acceptor) of the cyclical heat exchange system2305is thermally coupled to a CO2refluxer2340of a thermosiphon2345. The thermosiphon2345includes a cold-side heat exchanger2350that is configured to cool air within the thermodynamic system2300that is forced across the heat exchanger2350by a fan2355. A thermosiphon is a closed system of tubes that are connected to a cooling engine (in this case, the heat exchanger2350) that permits natural circulation and cooling of the liquid within the refluxer.

Referring toFIG. 24, in another implementation, a thermodynamic system2400includes a cyclical heat exchange system such as a cyclical heat exchange system2405(for example, the systems2000,2100,2200) and a heat transfer system2410thermally coupled to a hot side2415of the cyclical heat exchange system2405. The thermodynamic system2400includes a heat transfer system2420thermally coupled to a cold side2425of the cyclical heat exchange system2405. The thermodynamic system2400also includes fans2430,2435. The fan2430is positioned at the hot side2415to force air through a condenser of the heat transfer system2410. The fan2435is positioned at the cold side2425to force air through a condenser of the heat transfer system2420.

Referring toFIG. 25, in one implementation, a thermodynamic system2500includes a heat transfer system2505coupled to a cyclical heat exchange system such as a cyclical heat exchange system2510. The heat transfer system2505is used to cool a hot side2515of the cyclical heat exchange system2510. The heat transfer system2505includes an annular evaporator2520that includes an expansion volume (or reservoir)2525, a liquid return line2530providing fluid communication between liquid outlets2535of a condenser2540and the liquid inlet of the evaporator2520. The heat transfer system2505also includes a vapor line2545providing fluid communication between the vapor outlet of the evaporator2520and vapor inlets2550of the condenser2540.

The condenser2540is constructed from smooth wall tubing and is equipped with heat exchange fins2555or fin stock to intensify heat exchange on the outside of the tubing.

The evaporator2520includes a primary wick2560sandwiched between a vapor barrier wall2565and a liquid barrier wall2570and separating the liquid and the vapor. The liquid barrier wall2570is cold biased by heat exchange fins2575formed along the outer surface of the wall2565. The heat exchange fins2575provide subcooling for the reservoir2525and the entire liquid side of the evaporator2520. The heat exchange fins2575of the evaporator2520may be designed separately from the heat exchange fins2555of the condenser2540.

The liquid return line2530extends into the reservoir2525located above the primary wick2560, and vapor bubbles, if any, from the liquid return line2530and the vapor removal channels at the interface of the primary wick2560and the vapor barrier wall2565are vented into the reservoir2525. Typical working fluids for the heat transfer system2505include (but are not limited to) methanol, butane, CO2, propylene, and ammonia.

The evaporator2520is attached to the hot side2515of the cyclical heat exchange system2510. In one implementation, this attachment is integral in that the evaporator2520is an integral part of the cyclical heat exchange system2510. In another implementation, attachment can be non-integral in that the evaporator2520can be clamped to an outer surface of the hot side2510. The heat transfer system2505is cooled by a forced convection sink, which can be provided by a simple fan2580. Alternatively, the heat transfer system2505is cooled by a natural or draft convection.

Initially, the liquid phase of the working fluid is collected in a lower part of the evaporator2520, the liquid return line2530, and the condenser2540. The primary wick2560is wet because of the capillary forces. As soon as heat is applied (for example, the cyclical heat exchange system2510is turned on), the primary wick2560begins to generate vapor, which travels through the vapor removal channels (similar to vapor removal channels1120of evaporator1100) of the evaporator2520, through the vapor outlet of the evaporator2520, and into the vapor line2545.

The vapor then enters the condenser2540at an upper part of the condenser2540. The condenser2540condenses the vapor into liquid and the liquid is collected at a lower part of the condenser2540. The liquid is pushed into the reservoir2525because of the pressure difference between the reservoir2525and the lower part of the condenser2540. Liquid from the reservoir2525enters liquid flow channels of the evaporator2520. The liquid flow channels of the evaporator2520are configured like the channels1125of the evaporator1100and are properly sized and located to provide adequate liquid replacement for the liquid that vaporized. Capillary pressure created by the primary wick2560is sufficient to withstand the overall LHP pressure drop and to prevent vapor bubbles from traveling through the primary wick2560toward the liquid flow channels.

The liquid flow channels of the evaporator2520can be replaced by a simple annulus, if the cold biasing discussed above is sufficient to compensate the increased heat leak across the primary wick2560, which is caused by the increase in surface area of the heat exchange surface of annulus versus the surface area of the liquid flow channels.

Referring toFIGS. 26–28, a heat transfer system2600includes an evaporator2605coupled to a cyclical heat exchange system2610and an expansion volume2615coupled to the evaporator2605. The vapor channels of the evaporator2605feed to a vapor line2620that feed a series of channels2625of a condenser2630. The condensed liquid from the condenser2630is collected in a liquid return channel2635. The heat transfer system2600also includes fin stock2640thermally coupled to the condenser2630.

The evaporator2605includes a vapor barrier wall2700, a liquid barrier wall2705, a primary wick2710positioned between the vapor barrier wall2700and the inner side of the liquid barrier wall2705, vapor removal channels2715, and liquid flow channels2720. The liquid barrier wall2705is coaxial with the primary wick2710and the vapor barrier wall2700. The liquid flow channels2720are fed by a liquid return channel2725and the vapor removal channels2715feed into a vapor outlet2730.

The vapor barrier wall2700intimately contacts the primary wick2710. The liquid barrier wall2705contains working fluid on an inner side of the liquid barrier wall2705such that the working fluid flows only along the inner side of the liquid barrier wall2705. The liquid barrier wall2705closes the evaporator's envelope and helps to organize and distribute the working fluid through the liquid flow channels2720.

In one implementation, the evaporator2605is approximately 2″ tall and the expansion volume2615is approximately 1″ in height. The evaporator2605and the expansion volume2615are wrapped around a portion of the cyclical heat exchange system2610having a 4″ outer diameter. The vapor line2620has a radius of ⅛″. The cyclical heat exchange system2610includes approximately 58 condenser channels2625, with each condenser channel2625having a length of 2″ and a radius of 0.012,″ the channels2625being spread out such that the width of the condenser2630is approximate 40″. The liquid return channel2725has a radius of 1/16″. The heat exchanger2800(which includes the condenser2630and the fin stock2640is approximately 40″ long and is wrapped into an inner and outer loop (seeFIGS. 30,33, and34) to produce a cylindrical heat exchanger having an outer diameter of approximately 8″. The evaporator2605have a cross-sectional width2750of approximately ⅛,″ as defined by the vapor barrier wall2700and the liquid barrier wall2705. The vapor removal channels2715have widths of approximately 0.020″ and depths of approximately 0.020″ and are separated from each other by approximately 0.020″ to produce 25 channels per inch.

As mentioned above, the heat transfer system (such as system2310) is thermally coupled to the portion (such as portion2315) of the cyclical heat exchange system. The thermal coupling between the heat transfer system and the portion can be by any suitable method. In one implementation, if the evaporator of the heat transfer system is thermally coupled to the hot side of the cyclical heat exchange system, the evaporator may surround and contact the hot side and the thermal coupling may be enabled by a thermal grease compound applied between the hot side and the evaporator. In another implementation, if the evaporator of the heat transfer system is thermally coupled to the hot side of the cyclical heat exchange system, the evaporator may be constructed integrally with the hot side of the cyclical heat exchange system by forming vapor channels directly into the hot side of the cyclical heat exchange system.

Referring toFIGS. 30–32, a heat transfer system3000is packaged around a cyclical heat exchange system3005. The heat transfer system3000includes a condenser3010surrounding an evaporator3015. Working fluid that has been vaporized exits the evaporator3015through a vapor outlet3020connected to the condenser3010. The condenser3010loops around and doubles back inside itself at junction3025.

The cyclical heat exchange system3005is surrounded about its heat rejection surface3100by the evaporator3015. The evaporator3015is in intimate contact with the heat rejection surface3100. The refrigeration assembly (which is the combination of the cyclical heat exchange system3005and the heat transfer system3000) is mounted in a tube3205, with a fan3210mounted at the end of the tube3205to force air through fins3030of the condenser3010to exhaust channels3035.

The evaporator3015has a wick3215in which working fluid absorbs heat from the heat rejection surface3100and changes phase from liquid to vapor. The heat transfer system3000includes a reservoir3220at the top of the evaporator3015that provides an expansion volume. For simplicity of illustration, the evaporator3015has been illustrated in this view as a simple hatched block that shows no internal detail. Such internal details are discussed elsewhere in this description.

The vaporized working fluid exits the evaporator3015through the vapor outlet3020and enters a vapor line3040of the condenser3010. The working fluid flows downward from the vapor line3040, through channels3045of the condenser3010, to the liquid return line3050. As the working fluid flows through the channels3045of the condenser3010it loses heat, through the fins3030to the air passing between the fins, to change phase from vapor to liquid. Air that has passed through the fins3030of the condenser3010flows away through the exhaust channel3035. Liquefied working fluid (and possibly some uncondensed vapor) flows from the liquid return line3050back into the evaporator3015through the liquid return port3055.

Referring toFIGS. 33 and 34, a heat transport system3300surrounds a portion of a cyclical heat exchange system3302, that is surrounded, in turn, by exhaust channels3305. The heat transport system3300includes an evaporator3310having an upper portion that surrounds the cyclical heat exchange system3302. A vapor port3315connects the evaporator3310to a vapor line3312of a condenser3320. The vapor line3312includes an outer region that circles around the evaporator3310and then doubles back on itself at junction3325to form an inner region that circles back around the evaporator3310in the opposite direction. The heat transport system3300also includes cooling fins3330on the condenser3320.

The heat transport system3300also includes a liquid return port3400that provides a path for condensed working fluid from the liquid line3405of the condenser3320to return to the evaporator3310.

As mentioned above, the interface between the evaporator3310and the heat rejection surface of the cyclical heat exchange system3302may be implemented according one of several alternate implementations.

Referring toFIG. 35, in one implementation, an evaporator3500slips over a heat rejection surface3502of a cyclical heat exchange system3505. The evaporator3500includes a vapor barrier wall3510, a liquid barrier wall3515, and a wick3520sandwiched between the walls3510and3515. The wick3520is equipped with vapor channels3525and liquid flow channels3530are formed at the liquid barrier wall3515in simplified form for clarity.

The evaporator3500is slipped over the cyclical heat exchange system3050and may be held in place with the use of a clamp3600(shown inFIG. 36). To aid heat transfer, thermally conductive grease3535is disposed between the cyclical heat exchange system3050and vapor barrier wall3510of the evaporator3500. In an alternate implementation, the vapor channels3525are formed in the vapor barrier wall3510instead of in the wick3520.

Referring toFIG. 37, in another implementation, an evaporator3700is fit over a heat rejection surface3702of a cyclical heat exchange system3705with an interference fit. The evaporator3700includes a vapor barrier wall3710, a liquid barrier wall3715, and a wick3720sandwiched between the walls3710and3715. The evaporator3700is sized to have an interference fit with the heat rejection surface3702of the cyclical heat exchange system3705.

The evaporator3700is heated so that its inner diameter expands to permit it to slip over the unheated heat rejection surface3702. As the evaporator3700cools, it contracts to fix onto the cyclical heat exchange system3705in an interference fit relationship. Because of the tightness of the fit, no thermally conductive grease is needed to enhance heat transfer. The wick3720is equipped with vapor channels3725. In an alternate implementation, the vapor channels are formed in the vapor barrier wall3710instead of in the wick3720. Liquid flow channels3730are formed at the liquid barrier wall3715in a simplified form for clarity.

Referring toFIG. 38, in another implementation, an evaporator3800is fit over a heat rejection surface3802of a cyclical heat exchange system3805and features previously designed within the evaporator3800are now integrally formed within the heat rejection surface3802. In particular, the evaporator3800and the heat rejection surface3802are constructed together as an integrated assembly. The heat rejection surface3802is modified to have vapor channels3825; in this way, the heat rejection surface3802acts as a vapor barrier wall for the evaporator3800.

The evaporator3800includes a wick3820and a liquid barrier wall3815formed about the modified heat rejection surface3802, the wick3820and the liquid barrier wall3815being integrally bonded to the heat rejection surface3802to form a sealed evaporator3800. Liquid flow channels3830are portrayed in a simplified form for clarity. In this way, a hybrid cyclical heat exchange system with an integrated evaporator is formed. This integral construction provides enhanced thermal performance in comparison to the clamp-on construction and the interference fit construction because thermal resistance is reduced between the cyclical heat exchange system and the wick of the evaporator.

Referring toFIG. 29, graphs2900and2905show the relationship between a maximum temperature of the surface of the portion of the cyclical heat exchange system that is to be cooled by the heat transfer system and a surface area of the interface between the heat transfer system and the portion of the cyclical heat exchange system to be cooled. The maximum temperature indicates the maximum amount of heat rejection. In graph2900, the interface between the portion and the heat transfer system is accomplished with a thermal grease compound. In graph2905, the heat transfer system is made integral with the portion.

As shown, at an air flow of 300 CFM, if the interface is a thermal grease interface, then the maximum amount of heat rejection would fall within a maximum heat rejection surface temperature2907(for example, 70° C.) with a heat exchange surface area2910(for example, 100 ft2). When the evaporator is constructed integrally with the portion by forming vapor channels directly in the heat rejection surface, that heat rejection surface would operate below the maximum heat rejection surface temperature of the thermal grease interface with significantly smaller heat exchange surface areas.

Referring toFIG. 39, a condenser3900is formed with fins3905, which provide thermal communication between the air or the environment and a vapor line3910of the condenser3900. The vapor line3910couples to a vapor outlet3915that connects the evaporator3920positioned within the condenser3900.

Referring toFIGS. 40–43, in one implementation, the condenser3900is laminated and is formed with flow channels that extend through a flat plate4000of the condenser3900between a vapor head3925and a liquid head3930. Copper is a suitable material for use in making a laminated condenser. The laminated structure condenser3900includes a base4200having fluid flow channels4205(shown in phantom) formed therein and a top layer4210is bonded to the base4200to cover and seal the fluid flow channels4205. The fluid flow channels4205are designed as trenches formed in the base4200and sealed beneath the top layer4210. The trenches for the fluid flow channels4205may be formed by chemical etching, electrochemical etching, mechanical machining, or electrical discharge machining processes.

Referring toFIGS. 44 and 45, in another implementation, the condenser3900is extruded and small flow channels4400extend through a flat plate4405of the condenser3900. Aluminum is a suitable material for use in such an extruded condenser. The extruded micro channel flat plate4405extends between a vapor header4410and a liquid header4415. Moreover, corrugated fin stock4420is bonded (for example, brazed or epoxied) to both sides of the flat plate4405.

Referring toFIG. 46, a cross-sectional view of one side of a heat transfer system4600that is coupled to a cyclical heat exchange system4605. This view shows relative dimensions that provide for particularly compact packaging of the heat transfer system. In this view, fins4610are portrayed as being 90 degrees out of phase for ease of illustration. To cool the heat rejection surface4615of the cyclical heat exchange system4605having a 4 inch diameter, the evaporator4620has a thickness of 0.25 inch and the radial thickness of the condenser is 1.75 inches. This provides on overall dimension for the packaging (the combination of the heat transfer system4600and the cyclical heat exchange system4605of 8 inches.

As discussed, the evaporator used in the heat transfer system is equipped with a wick. Because a wick is employed within the evaporator of the heat transfer system, the condenser may be positioned at any location relative to the evaporator and relative to gravity. For example, the condenser may be positioned above the evaporator (relative to a gravitational pull), below the evaporator (relative to a gravitational pull), or adjacent the evaporator, thus experiencing the same gravitational pull as the evaporator.

Notably, the terms Stirling engine, Stirling heat exchange system, and Free Piston Stirling Cooler have been referenced in several implementations above. However, the features and principals described with respect to those implementations also may be applied to other engines capable of conversions between mechanical energy and thermal energy.

Moreover, the features and principals described above may be applied to any heat engine, which is a thermodynamic system that can undergo a cycle, that is, a sequence of transformations that ultimately return it to its original state. If every transformation in the cycle is reversible, the cycle is reversible and the heat transfers occur in the opposite direction and the amount of work done switches sign. The simplest reversible cycle is a Carnot cycle, which exchanges heat with two heat reservoirs.

Manufacture

Referring toFIG. 47, a thermodynamic system4700includes a heat source such as, for example, a cyclical heat exchange system4705, and a heat transfer system4710thermally coupled to a portion4715of the cyclical heat exchange system4705. The heat transfer system4710is designed with an annular evaporator4713such as, for example, the annular evaporator1100ofFIG. 11. The evaporator4713is shaped to surround the portion4715of the cyclical heat exchange system4705to reject heat from the portion4715. The thermodynamic system4700also includes a fan4720positioned to force air over a condenser4712of the heat transfer system4710along a path5100(FIG. 51) and thus to provide additional convection cooling.

Referring also toFIGS. 48–51, the heat transfer system4710includes a liquid line4800that pumps liquid from the condenser4712into the evaporator4713and a vapor line4805that feeds vapor into the condenser4712. A discussion of the operation of a heat transfer system is provided above and is not repeated here. The heat transfer system4710may also include a reservoir4810coupled to the vapor line4805through a port4812for additional pressure containment, as needed. In particular, the reservoir4810increases the volume of the heat transfer system4710, as also discussed above.

As shown, the cyclical heat exchange system4705is cylindrical. The cyclical heat exchange system4705includes a cold side4735, that is, the heat acceptor, and a hot side, that is, the heat rejector or portion4715, which is surrounded by the evaporator4713.

Referring also toFIG. 52, the cold side4735of the cyclical heat exchange system4705may be thermally coupled to a refluxer4740of a thermosiphon4745. The thermosiphon4745includes a cold-side heat exchanger4750that is configured to cool air within the thermodynamic system4700that is forced across the heat exchanger4750by a thermosiphon fan (not shown inFIGS. 50 and 52, but mounted adjacent the heat exchanger4750). The thermosiphon fan blows the air into the thermosiphon along path5000and blows the air out of the thermosiphon along path5005(FIG. 50). The thermosiphon includes a vapor line5200from the refluxer4740to the heat exchanger4750and a liquid line5205from the heat exchanger4750to the refluxer4740. Vapor that is heated at the cold side4735flows through the heat exchanger from the line5200, where it is condensed and cooled by the thermosiphon fan and the condensed liquid is returned through the line5205to the refluxer4740.

Referring toFIG. 48and also toFIGS. 53A–E, the evaporator4713includes a wick subassembly5300surrounded by an outer subassembly. The outer subassembly includes an outer ring or liquid barrier wall5305and a subcooler5310. The subcooler5310is an array of fins that help dissipate heat from the liquid barrier wall5305. The wick subassembly5300includes an inner ring or vapor barrier wall5315such as, for example, the vapor barrier wall1700ofFIGS. 14A–H,15A,15B, and17A–D. The wick subassembly5300also includes a wick5320such as, for example, the wick1600ofFIGS. 14G,14H, and16A–D. The vapor barrier wall5315includes vapor removal channels5325such as, for example, the channels1465ofFIGS. 14A–H,15A,15B, and17A–D. The vapor barrier wall5315is surrounded by the wick5320.

As discussed above with respect to the evaporator1400, in one implementation, the wick5320and the vapor barrier wall5315are made of stainless steel. The wick5320has, prior to manufacture, a pore radius of about 9.8 microns, an outer diameter of about 4.141 inches, an inner diameter of about 3.985 inches, and a length of about 1.75 inches. The vapor barrier wall5315has, for example, 186 vapor removal channels5325, with each channel5325formed as a semicircle having about a 0.025 inch radius (FIG. 53B). The vapor barrier wall5315has a thickness of about 0.035 inches.

The liquid barrier wall5305includes one or more liquid flow channels5330such as, for example, the liquid flow channels1505of the wall1500ofFIGS. 14A–H. The liquid flow channels5330are formed along an inner surface of the wall5305. The liquid barrier wall5305can also include cooling grooves5335formed along an outer surface of the wall5305to provide additional convection cooling for the liquid. The liquid barrier wall5305also includes a liquid port5340for receiving liquid from the liquid line4800.

The liquid barrier wall5305can be made of stainless steel and can have seven liquid flow channels5330, with each channel5330having a radius of about 0.030 inches. The liquid barrier wall5305can have, prior to manufacture, an outer diameter of about 4.24 inches, an inner diameter of about 4.13 inches, and a length of about 1.69 inches.

The subcooler5310includes an array of fins5345that surround an inner body5350. The fins5345and the inner body5350include openings5355for the vapor line4805and an opening5360for the reservoir port4812. The subcooler5310can be made from copper or any other suitable heat transferring metal. The subcooler5310can be designed with, for example, 119 fins. The inner body5350can have an outer diameter of, for example, 4.25 inches and have a length of 1.57 inches.

The evaporator4713also includes a reservoir plate5365(FIG. 53E) that is sealed to an edge of the liquid barrier wall5305, as shown in more detail below. The reservoir plate5365is in fluid communication with the reservoir4810and the vapor line4805.

Referring toFIG. 54, a procedure5400is performed for manufacturing the thermodynamic system4700ofFIG. 47. Initially, the wick subassembly5300(that is, the vapor barrier wall5315and the wick5320) is prepared (step5405). Next, the liquid barrier wall5305is prepared (step5410). The outer subassembly (that is, the liquid barrier wall5305and the subcooler5310) is then prepared (step5415) and the prepared outer subassembly is joined with the wick subassembly to form the evaporator body (step5420). Next, the evaporator body is finalized to form the evaporator4713(step5425) and the evaporator4713is coupled to the heat source (for example, the cyclical heat exchange system) (step5430).

Referring toFIG. 55, a procedure5405is performed for preparing the wick subassembly5300. Initially, the wick subassembly5300is assembled (step5500). Assembly of the wick subassembly5300includes forming the vapor removal channels5325the material that will form the vapor barrier wall5315(FIGS. 15A and 15Bshow the material used for forming the vapor barrier wall5315). For example, the vapor removal channels5325can be photoetched into the material. The photoetched material is rolled into a cylindrical form and then welded at its edges to form the vapor barrier wall5315. The wick5320is formed from a wick material that is cut to a suitable length, rolled, and formed around the vapor barrier wall5315. The wick5320is mechanically squeezed onto the vapor barrier wall5315to improve the fit between the wick5320and the vapor barrier wall5315and to reduce the space between the wick5320and the wall5315, thus improving thermal transfer between the wick5320and the vapor barrier wall5315. Next, the wick is welded at its seams to form a complete cylindrical form.

In another implementation, the wick5320also may be sintered onto the vapor barrier wall5315by heating the wick5320and the wall5315at a temperature that is below the melting point of the materials used in the wick5320and the wall5315. During this heating, pressure may be applied to the wick5320and to the wall5315to help form the sintered bond. Sintering can be used to further improve the thermal transfer between the wick5320and the vapor barrier wall5315.

After the wick subassembly5300is assembled (step5500), the wick subassembly is heat shrunk to ensure that it is as round as needed to properly join with the outer subassembly at step5420. Initially during the heat shrink process, the wick subassembly5300is heated (step5505). In one implementation, the subassembly5300is placed in a furnace5600(shown inFIGS. 56Aand B) that heats the subassembly to 460° C.±15° C. Next, as also shown inFIG. 56A, a temperature control block5605is cooled to a temperature at which its outer diameter is smaller than the inner diameter of the heated subassembly5300(step5510). The temperature control block5605can be cooled using liquid nitrogen. Referring also toFIGS. 56Cand D, the cooled temperature control block5605is inserted into the heated wick subassembly5300(step5515). Next, as shown inFIG. 56E, upon insertion of the control block5605(step5515), the heat is removed from the wick subassembly5300and the cooling is removed from the temperature control block5605, thus permitting the temperature of the wick subassembly5300to stabilize (step5520). After the temperature of the wick subassembly5300has stabilized (step5520), the wick subassembly5300is inspected to ensure that the outer diameter of the wick subassembly5300is as round as needed (step5525).

Referring toFIG. 57, a procedure5410is performed for preparing the liquid barrier wall5305. Initially, the liquid barrier wall5305is formed (step5700) by rolling the material and then welding the material at the seam to form a nearly cylindrical shape (FIG. 53C). Then, the welded material is photoetched on its inner surface to form the liquid flow channels5330and is photoetched on its outer surface to form the cooling grooves5335(FIG. 53C).

The formed liquid barrier wall5305is heat shrunk to ensure that it is as round as needed to properly prepare the outer subassembly at step5415. Initially during the heat shrink process, the liquid barrier wall5305is heated (step5705). In one implementation, the liquid barrier wall5305is placed in a furnace5800(shown inFIGS. 58Aand B) that heats the wall5305to 460° C.±15° C. Next, as also shown inFIG. 58A, a temperature control block5805is cooled to a temperature at which its outer diameter is smaller than the inner diameter of the vapor barrier wall5305(step5710). The temperature control block5805can be cooled using liquid nitrogen. Referring also toFIGS. 58Cand D, the cooled temperature control block5605is inserted into the heated liquid barrier wall5305(step5715). Next, as shown inFIG. 58E, upon insertion of the control block5805, the heat is removed from the liquid barrier wall5305and the cooling is removed from the temperature control block5805, thus permitting the temperature of the liquid barrier wall5305to stabilize (step5720). After the temperature of the liquid barrier wall5305has stabilized, the liquid barrier wall5305is inspected to ensure that the outer diameter of the wall5305is as round as needed (step5725).

Referring toFIG. 59, a procedure5415is performed for preparing the outer subassembly, that is, the liquid barrier wall5305and the subcooler5310. Initially, the subcooler5310is heated (step5900). In one implementation, the subcooler5310is placed in a furnace6000(shown inFIGS. 60Aand B) that heats the subcooler5310to 235° C.±15° C. Next, as also shown inFIGS. 60Aand B, the temperature control block5805, and liquid barrier wall5305, which is thermally coupled to the block5805, are cooled to a temperature at which the outer diameter of the wall5305is smaller than the inner diameter of the subcooler5310(step5905). For example, the liquid barrier wall5305can be cooled to below about −120° C. The temperature control block5805can be cooled using liquid nitrogen. Referring also toFIG. 60C, the cooled temperature control block5805and liquid barrier wall5305are inserted into the heated subcooler5310to form the outer subassembly6001(step5910). Next, as shown inFIG. 60D, upon insertion of the control block5805(step5910), the heat is removed from the subcooler5310and the cooling is removed from the temperature control block5805, thus permitting the temperature of the outer subassembly6001to stabilize (step5915). After the temperature of the outer subassembly6001has stabilized (step5915), the temperature control block5805is removed from the liquid barrier wall5305(step5920), as shown inFIG. 60E.

Next, referring also toFIGS. 60Fand G, various parts are assembled to the outer subassembly6001(step5925). First, as shown inFIG. 60F, a reservoir plate6005is attached to the liquid barrier wall5305and is adjacent the subcooler5310. The plate6005can be attached by welding the plate6005onto the wall5305to form a weld seam6010. Second, as shown inFIG. 60G, the liquid line4800is sealed to the liquid barrier wall5305by, for example, welding. After assembly is complete, the outer subassembly and all of the welded joints are inspected to ensure that the seams are sealed and that the inner diameter of the wall5305is as round as needed to interfit with the wick subassembly later in the process (step5930).

Referring toFIG. 61, a procedure5420is performed for joining the outer subassembly6001with the wick subassembly to form the evaporator body. In general, during this process, the outer subassembly6001is heat shrunk onto the wick subassembly5300to ensure that the pieces are properly joined. Initially, the outer subassembly6001is heated (step6100). In one implementation, the outer subassembly6001is placed in a furnace6200(shown inFIG. 62A) that heats the outer subassembly6001to 350° C.±10° C. Next, as also shown inFIG. 62B, the temperature control block5605is cooled to a temperature at which the outer diameter of the wick subassembly5300is smaller than the inner diameter of the heated outer subassembly6001(step6105). The temperature control block5605can be cooled using liquid nitrogen. Referring also toFIGS. 62Cand D, the cooled temperature control block5605and wick subassembly5300is inserted into the heated outer subassembly6001to form the evaporator body6101(step6110). Next, as shown inFIG. 62D, upon insertion of the control block5605and the wick subassembly5300, the heat is removed from the outer subassembly6001and the cooling is removed from the temperature control block5605, thus permitting the temperature of the evaporator body6101to stabilize (step6115). Referring also toFIG. 62E, after the temperature of the evaporator body6101has stabilized, the evaporator body6101may be inspected to ensure that the heat shrink process was successful.

Referring toFIG. 63, a procedure5425is performed for finalizing the evaporator body6101to form the evaporator4713. With reference toFIGS. 49 and 64, various parts are now assembled to the evaporator body6101(step6300). For example, a volume plate6400is tacked to the liquid barrier wall5305and the wick5320and tubes are welded to the reservoir plate6005and the volume plate6400. The reservoir4810is welded to the reservoir plate6005and a vapor barrier plate6405is welded to the reservoir plate6005and to the wick subassembly5300. Caps6410and6415are placed over the volume plate6400and the vapor barrier plate6405, respectively. Next, the evaporator body6101is inspected and tested (step6305) and then additional parts are attached to the evaporator body6101(step6310). For example, the vapor line4805is welded to the cap6410and the cap6410is machined as needed due to possible warpage during welding. The cap6410is welded to the volume plate6400and to the vapor barrier wall5315and the cap6415is welded to the reservoir plate6005and to the vapor barrier wall5315. Next, the evaporator body6101is inspected for leaks (step6315).

Referring toFIG. 65, a procedure5430is performed for coupling the evaporator4713to the heat source or cyclical heat exchange system4705. Initially, an outer diameter of the heat source is machined, as needed (step6500) to ensure that the evaporator4713will fit over the heat source. Next, referring also toFIGS. 66Aand B, the evaporator4713is prepared (step6505) by welding the vapor and liquid lines to the evaporator body and then aligning the evaporator4713with the system4705using a suitable alignment system.

Then, the evaporator4713is heat shrunk onto the system4705to ensure that the pieces are properly joined. Initially, the evaporator4713is heated (step6510). In one implementation, the evaporator4713is placed in a furnace6600(shown inFIGS. 66Aand B) that heats the evaporator4713to about 375° C. Next, the system4705and in particular, the hot end4715, is cooled to a temperature at which the outer diameter of the hot end4715is smaller than the inner diameter of the heated evaporator4713(step6515). The system4705can be cooled using liquid nitrogen. The cooled system4705is inserted into the heated evaporator4713(step6520). Upon insertion of the cooled system4705, the heat is removed from the evaporator4713and the cooling is removed from the system4705, thus permitting the temperature of the evaporator4713and the system4705to stabilize (step6525).

Referring also toFIG. 47, after the temperature has stabilized (step6525), evaporator4713and system4705are removed from the alignment and furnace setup and the heat transfer system4710is assembled (step6530). For example, the liquid line4800and the vapor line4805are connected to the condenser4712. The heat transfer system4710and the cyclical heat exchange system4705are then installed in the housing5090, as shown inFIGS. 50 and 52(step6535).

Other implementations are within the scope of the following claims. For example, the wick subassembly5300may be assembled at step5500by heat shrinking the wick5320onto the vapor barrier wall5315. In this implementation, the wick5320is formed from a wick material that is cut to a suitable length, rolled into a cylindrical form and then welded at its mating edges to form a cylinder. The cylindrical wick5320is then heated and placed over the vapor barrier wall5315. After the cylindrical wick5320cools, a thermal interface is formed between the wick5320and the vapor barrier wall5315. At this point, sintering can then be used to further improve the thermal transfer between the wick5320and the vapor barrier wall5315.

The parts of the wick subassembly and the outer subassembly can be made of other materials, as long as thermal contact can be achieved with these other materials. For example, the subcooler5310can be made of stainless steel or the liquid barrier wall5305and the vapor barrier wall5315can be made of copper.

The heat may be removed from the wick subassembly5300and the cooling may be removed from the control block5605prior to insertion of the control block5605. Likewise, the heat may be removed from the liquid barrier wall5305and the cooling may be removed from the control block5805prior to insertion of the control block5805into the liquid barrier wall5305. Similarly, the heat may be removed from the outer subassembly6001and the cooling may be removed from the temperature control block5605prior to insertion of the control block5605and the wick subassembly5300into the outer subassembly6001. Lastly, the heat may be removed from the evaporator4713and the cooling may be removed from the system4705prior to inserting the system4705into the heated evaporator4713.