Systems and methods for heat balance and transport for aircraft hydraulic systems

A thermal management system includes a first hydraulic system for circulating a first hydraulic fluid at a first temperature and a second hydraulic system for circulating a second hydraulic fluid at a second temperature that is higher than the first temperature. The thermal management system also includes a sealed heat transfer device coupled between the first hydraulic system and the second hydraulic system. The sealed heat transfer device is not in flow communication with either of the first hydraulic system and the second hydraulic system. The sealed heat transfer device is configured to transfer heat from the second hydraulic fluid to the first hydraulic fluid.

BACKGROUND

The present disclosure relates generally to thermal management, and more particularly to systems and methods for use in balancing and transporting heat among hydraulic systems within an aircraft.

In at least some known aircraft, heat from one or more hydraulic systems is dissipated into fuel through a heat exchanger located inside a fuel tank. Other known aircraft have no hydraulic system heat exchangers and address hydraulic fluid heating through restrictions and limitations on operation of such aircraft when an outside ambient temperature is above a predetermined threshold. Additionally, some known aircraft include a thermostat control to selectively cause hydraulic fluid to bypass a heat exchanger, in order to retain heat and to reduce pressure loss in hydraulic lines when the outside ambient temperature is below a predetermined threshold. Additionally, some known aircraft use hydraulic system circulating flow to control the temperature of hydraulic fluid. More specifically, in such aircraft, hydraulic orifice valves are installed in extremities of hydraulic systems to adjust system internal leakage so as to control heat generated through the orifices and total heat loss from hydraulic tubing to the ambient. Additionally, some known aircraft use guided ram air flow to cool the temperature of hydraulic fluid. Accordingly, such systems require substantial modification to structural surfaces of an aircraft. In summary, there exists a need for a cost-effective and efficient system for heating and cooling of hydraulic fluid within an aircraft.

BRIEF DESCRIPTION

In one aspect, a thermal management system is provided. The thermal management system includes a first hydraulic system for circulating a first hydraulic fluid at a first temperature and a second hydraulic system for circulating a second hydraulic fluid at a second temperature that is higher than the first temperature. The thermal management system also includes a sealed heat transfer device coupled between the first hydraulic system and the second hydraulic system. The sealed heat transfer device is not in flow communication with either of the first hydraulic system and the second hydraulic system. The sealed heat transfer device is configured to transfer heat from the second hydraulic fluid to the first hydraulic fluid.

In another aspect, an aircraft is provided. The aircraft includes a first hydraulic system for circulating a first hydraulic fluid at a first temperature and a second hydraulic system for circulating a second hydraulic fluid at a second temperature that is higher than the first temperature. The aircraft also includes a sealed heat transfer device coupled between the first hydraulic system and the second hydraulic system. The sealed heat transfer device is not in flow communication with either of the first hydraulic system and the second hydraulic system. The sealed heat transfer device is configured to transfer heat from the second hydraulic fluid to the first hydraulic fluid.

In another aspect, a method for managing temperatures in a machine is provided. The method includes circulating a first hydraulic fluid at a first temperature through a first hydraulic system coupled to the machine and circulating a second hydraulic fluid at a second temperature that is higher than the first temperature through a second hydraulic system coupled to the machine. The method also includes transferring heat from the second hydraulic fluid to the first hydraulic fluid through a sealed heat transfer device coupled between the first hydraulic system and the second hydraulic system. The sealed heat transfer device is not in flow communication with either of the first hydraulic system and the second hydraulic system.

DETAILED DESCRIPTION

FIG. 1is a diagram of an aircraft100that includes a first hydraulic system102and a second hydraulic system104. First hydraulic system102and second hydraulic system104are coupled together by a heat exchanger106. First hydraulic system102is pressurized by a pump device204that is driven by an engine108of aircraft100and provides power for certain operating components of aircraft100. For example, first hydraulic system102powers at least one spoiler110, at least one aileron111, at least one elevator112, and/or at least one rudder114in aircraft100. Additionally, second hydraulic system104powers components of aircraft100similar to the first hydraulic system and, in addition, other components that are not powered by first hydraulic system102. For example, second hydraulic system104powers landing gear116and/or brakes118of aircraft100. In some implementations, first hydraulic system102is routed in a way that more heat is dissipated from hydraulic tubing to surrounding ambient and causes hydraulic fluid within first hydraulic system102to be colder than hydraulic fluid in second hydraulic system104. In some implementations, second hydraulic system104uses a pump214that may be different from pump204used in first hydraulic system102and may generate more heat than pump204, resulting in a warmer second hydraulic system104. In some implementations, aircraft100may include additional hydraulic systems that power other components of aircraft100. Additionally, in some implementations, aircraft100is any other machine that includes at least two hydraulic systems coupled by heat exchanger106.

FIG. 2is a block diagram of a first example configuration of first hydraulic system102and second hydraulic system104. Heat exchanger106couples first hydraulic system102with second hydraulic system104such that heat is exchanged from second hydraulic system104to first hydraulic system102. Heat exchanger106includes a first tube120and a second tube122. First tube120is coupled in flow communication with first hydraulic system102and second tube122is coupled in flow communication with second hydraulic system104. First tube120surrounds second tube122, thereby enabling heat to be exchanged between first hydraulic system102and second hydraulic system104without mixing first hydraulic fluid201with second hydraulic fluid211.

In first hydraulic system102, a first hydraulic fluid201flows through a return line200, which may be a trunk return line, through first tube120of heat exchanger106, and then to a reservoir202. A pump204is located downstream of reservoir202and pumps first hydraulic fluid201through a pressure line208. A case drain206is coupled to pump204and to reservoir202and routes any of first hydraulic fluid201that leaks out of pump204back to reservoir202. In second hydraulic system104, a second hydraulic fluid211flows through a return line210to a reservoir212and then to a pump214. Pump214pumps second hydraulic fluid211through a pressure line218. Additionally, a case drain216is coupled to pump214and to reservoir212. Case drain216routes any of second hydraulic fluid211that leaks out of pump214through second tube122of heat exchanger106and back to reservoir212. As a characteristic of a hydraulic pump, for example pump204, case drain fluid carries heat due to pump inefficiency and is, for example, 30 degrees Fahrenheit hotter than the pump inlet fluid from a reservoir, for example reservoir202. Therefore, fluid in case drain206of pump204may be, for example, 30 degrees Fahrenheit hotter than fluid in reservoir202and fluid in case drain216of pump214may be, for example, approximately 30 degrees Fahrenheit hotter than fluid in reservoir212. Additionally, second hydraulic system104may be, for example, 20 degrees Fahrenheit hotter than first hydraulic system102, as described above. As a result, second hydraulic fluid211flowing through second tube122of heat exchanger106may be maintained at a higher temperature (for example, approximately 50 degrees Fahrenheit, assuming no heat is exchanged) than first hydraulic fluid201flowing through first tube120of heat exchanger106.

FIG. 3is a block diagram of a second example configuration of first hydraulic system102and second hydraulic system104of aircraft100. More specifically, heat exchanger106couples first hydraulic system102with second hydraulic system104in a different location than inFIG. 2. In first hydraulic system102, first hydraulic fluid201flowing through pressure line208is received in a first actuator300, which may control, for example, spoiler110(shown inFIG. 1) and a second actuator302, which may control, for example, elevator112(shown inFIG. 1). First hydraulic fluid201then passes through return line200, which may be a branch return line, and through first tube120of heat exchanger106. Second hydraulic system104is configured as described with reference toFIG. 2. The configuration shown inFIG. 3may be used instead of or in addition to the configuration shown inFIG. 2depending on design considerations, for example available space for components and/or how close first hydraulic system102is to second hydraulic system104at various points in aircraft100.

FIG. 4is a graph of temperatures of first hydraulic system102and second hydraulic system104when first hydraulic system102and second hydraulic system104are not coupled together by heat exchanger106. The outside ambient temperature is a first ambient temperature. The temperature of first hydraulic fluid201in case drain206is represented by curve400and the temperature of second hydraulic fluid211in case drain216is represented by curve402. As time progresses, the temperature in case drain216exceeds the temperature in case drain206. After a first time period elapses, the temperature in case drain216is a first number of degrees Fahrenheit higher than the temperature in case drain206.

FIG. 5is a graph of temperatures of first hydraulic system102and second hydraulic system104when first hydraulic system102and second hydraulic system104are coupled together by heat exchanger106. The outside ambient temperature is, again, the first ambient temperature. The temperature of first hydraulic fluid201in case drain206is represented by curve500and the temperature of second hydraulic fluid211in case drain216is represented by curve502. As compared to curves400and402ofFIG. 4, curves500and502indicate that, after the first time period has elapsed, the temperatures in case drains206and216differ by a second number of degrees that is less than the first number of degrees. More specifically, heat exchanger106facilitates cooling second hydraulic fluid211in second hydraulic system104by transferring heat to first hydraulic fluid201in first hydraulic system102.

FIG. 6is another graph of temperatures of first hydraulic system102and second hydraulic system104when first hydraulic system102and second hydraulic system104are not coupled together by heat exchanger106. The outside ambient temperature is a second ambient temperature that is less than the first ambient temperature. The temperature of second hydraulic fluid211in case drain216is represented by curve600and the temperature of first hydraulic fluid201in case drain206is represented by curve602. As time progresses, the temperature in case drain216exceeds the temperature in case drain206. After the first time period has elapse, the temperature in case drain216is a third number of degrees Fahrenheit higher than the temperature in case drain206. The temperature of case drain206is stabilized and the temperature of reservoir202is lower than the temperature of case drain206. The temperature of reservoir202is considered representative of a hydraulic system temperature that may not provide a preferred amount of hydraulic power for takeoff.

FIG. 7is another graph of temperatures of first hydraulic system102and second hydraulic system104when first hydraulic system102and second hydraulic system104are coupled together by heat exchanger106. The outside ambient temperature is, again, the second ambient temperature. The temperature of second hydraulic fluid211in case drain216is represented by curve700and the temperature of first hydraulic fluid201in case drain206is represented by curve702. As compared to curves600and602ofFIG. 6, curves700and702indicate that the temperatures in case drains206and216differ by a fourth number of degrees Fahrenheit after the first time period has elapsed. The fourth number of degrees is less than the third number of degrees discussed with reference toFIG. 6. More specifically, heat exchanger106facilitates heating first hydraulic fluid201in first hydraulic system102with heat transferred from second hydraulic fluid211in second hydraulic system104.

FIG. 8is a flowchart of a method800for managing temperatures in a machine, such as aircraft100(shown inFIG. 1). Method800includes circulating802a first hydraulic fluid, for example first hydraulic fluid201, at a first temperature through a first hydraulic system, for example first hydraulic system102. First hydraulic system102is coupled to a machine, for example aircraft100. Additionally, method800includes circulating804a second hydraulic fluid, for example second hydraulic fluid211, at a second temperature that is different from the first temperature through a second hydraulic system, for example second hydraulic system104. Second hydraulic system104is coupled to the machine, for example aircraft100. Method800additionally includes exchanging806heat between the first hydraulic fluid201and the second hydraulic fluid211with a heat exchanger that couples first hydraulic system102to second hydraulic system104. The heat exchanger may be, for example, heat exchanger106.

In some embodiments, heat exchanger106is a sealed heat transfer device900. The term “sealed” refers to the fact that heat transfer device900contains a working fluid912, but is not coupled in flow communication with first hydraulic system102or second hydraulic system104.FIG. 9is a schematic illustration of an exemplary embodiment of sealed heat transfer device900implemented as a heat pipe902. In the exemplary embodiment, heat pipe902includes a substantially sealed tube904extending longitudinally between a cold interface906and a hot interface908. Cold interface906is configured to be coupled to, and to permit transfer heat to, a relatively colder structure (not shown), and hot interface908is configured to be coupled to, and to permit heat transfer from, a relatively hotter structure (not shown). A wicking structure910extends substantially longitudinally within at least a portion of tube904. In one embodiment, wicking structure910is formed from a plurality of thin metal grooves (not shown) that extend substantially longitudinally along at least a portion of tube904, each groove having an effective width configured to induce liquid to flow therethrough due to capillary action. In alternative embodiments, wicking structure910is any suitable structure configured to induce liquid to flow therethrough due to capillary action.

A working fluid912disposed within tube904transfers heat from hot interface908to cold interface906. More specifically, working fluid912is disposed within tube904in an amount such that working fluid912exists partially in a liquid phase and partially in a vapor phase within tube904throughout an operating temperature range of heat pipe902. In the exemplary embodiment, tube904is at least partially evacuated before or during the insertion of working fluid912into tube904. In alternative embodiments, a non-condensable gas such as argon is added to tube902in addition to working fluid912.

Working fluid912near hot interface908absorbs heat from hot interface908and evaporates into a vapor914, which expands and travels toward cold interface906. In turn, working fluid912near cold interface906loses heat to cold interface906and condenses into a liquid916, which is absorbed into wicking structure910. Capillary action within wicking structure910transfers liquid916toward hot interface908to complete a self-contained heat transfer flow circuit within heat pipe902. Wicking structure910enables heat pipe902to operate regardless of a relative elevation of cold interface906and hot interface908.

Working fluid912, and a compatible material for tube904, may be chosen based on a desired operating temperature range of heat pipe902. In one embodiment, heat pipe902operates within a temperature range of about 40 degrees Fahrenheit to about 450 degrees Fahrenheit, working fluid912is water, and tube904is formed from at least one of copper and nickel. In another embodiment, heat pipe902operates within a temperature range of about −50 degrees Fahrenheit to about 250 degrees Fahrenheit, working fluid912is methanol, and tube904is formed from at least one of copper, nickel, and stainless steel. In alternative embodiments, other suitable combinations of working fluid912and a material for tube904are used based on a desired operating temperature range of heat pipe902. As used herein, the operating temperature range is defined as the temperature range that working fluid912within sealed heat transfer device900experiences over the full range of operation of the platform, such as aircraft100, on which it is installed. In any given operational condition, working fluid912will reach an equilibrium operational temperature that is between the temperature to which cold interface906is exposed and the temperature to which hot interface908is exposed, typically with only minor internal temperature variations within working fluid912.

FIG. 10is a schematic illustration of an alternative embodiment of sealed heat transfer device900implemented as a thermosyphon1002. Similarly to heat pipe902, thermosyphon1002includes a sealed tube1004extending between a cold interface1006and a hot interface1008. Cold interface1006is configured to be coupled to, and to permit transfer heat to, a relatively colder structure (not shown), and hot interface1008is configured to be coupled to, and to permit heat transfer from, a relatively hotter structure (not shown).

A working fluid1012disposed within tube1004transfers heat from hot interface1008to cold interface1006. More specifically, working fluid1012is disposed within tube1004in an amount such that working fluid1012exists partially in a liquid phase and partially in a vapor phase within tube1004throughout an operating temperature range of thermosyphon1002. In the exemplary embodiment, tube1004is at least partially evacuated before or during the insertion of working fluid1012into tube1004. In alternative embodiments, a non-condensable gas such as argon is added to tube1002in addition to working fluid1012.

Working fluid1012near hot interface1008absorbs heat from hot interface1008and evaporates into a vapor1014, which expands and travels upward toward cold interface1006. In turn, working fluid1012near cold interface1006loses heat to cold interface1006and condenses into a liquid1016. However, unlike heat pipe902, thermosyphon1002need not include a wicking structure. Instead, the force of gravity causes liquid1016to travel downward toward hot interface1008, while vapor1014heated by hot interface1008rises toward cold interface1006due to natural buoyancy to complete a self-contained heat transfer flow circuit within thermosyphon1002. An elevation1020of cold interface1006relative to hot interface1008enables thermosyphon1002to operate regardless of the presence of a wicking structure.

In certain embodiments, working fluid1012and compatible materials for tube1004for a desired operating temperature range of thermosyphon1002are substantially the same as those described above for heat pipe902. In alternative embodiments, other suitable combinations of working fluid1012and a material for tube1004are used.

FIG. 11is a block diagram of a third example configuration of first hydraulic system102and second hydraulic system104in which sealed heat transfer device900, implemented as heat pipe902, is coupled to first hydraulic system102and second hydraulic system104. More specifically, cold interface906is coupled to reservoir202of first hydraulic system102, and hot interface908is coupled to case drain216of second hydraulic system104. In the exemplary embodiment, hot interface908is configured to encapsulate a portion of case drain216to facilitate increasing a heat transfer from case drain216to hot interface908. Similarly, cold interface906is configured to contact an extended portion of a surface of reservoir202to facilitate increasing a heat transfer from cold interface906to reservoir202.

With reference also toFIG. 9, a heat transport capability of heat pipe902depends upon the materials used for tube904and working fluid912, the operational temperature of working fluid912, and an outer diameter918of tube904. In the exemplary embodiment ofFIG. 11, heat pipe902includes tube904formed of copper with outer diameter918equal to approximately 0.5 inches and a working fluid912of water. As described above, second hydraulic system104generally may be, for example, 20 degrees Fahrenheit hotter than first hydraulic system102, and fluid in case drain216may be, for example, approximately 30 degrees Fahrenheit hotter than fluid in reservoir212. As a result, in the absence of heat exchange, second hydraulic fluid211flowing through case drain216may be, for example, approximately 50 degrees Fahrenheit higher than first hydraulic fluid201flowing through reservoir202. At an operational temperature of 150 degrees Fahrenheit, heat pipe902has a heat transport capability of approximately 600 watts. The heat transport provided by heat pipe902from case drain216to reservoir202increases the temperature of first hydraulic fluid201and decreases the temperature of second hydraulic fluid211, to result in a reduced temperature difference of, for example, 10 degrees Fahrenheit between first hydraulic fluid201and second hydraulic fluid211. In an alternative embodiment, heat pipe902includes copper and water and has outer diameter 0.875 inches. In this alternative embodiment, heat pipe902has a heat transport capability of approximately 1,700 watts at an operational temperature of 150 degrees Fahrenheit, and the temperature difference between first hydraulic fluid201and second hydraulic fluid211may be reduced to, for example, 5 degrees Fahrenheit.

FIG. 12is a block diagram of a fourth example configuration of first hydraulic system102and second hydraulic system104in which sealed heat transfer device900, implemented as heat pipe902, is coupled to first hydraulic system102and second hydraulic system104. More specifically, cold interface906is coupled to return line200of first hydraulic system102, and hot interface908is coupled to return line210of second hydraulic system104. In the exemplary embodiment, hot interface908is configured to encapsulate a portion of return line210to facilitate increasing a heat transfer from return line210to hot interface908. Similarly, cold interface906is configured to encapsulate a portion of return line200to facilitate increasing a heat transfer from cold interface906to return line200. As described above, in the absence of heat exchange, second hydraulic fluid211flowing through return line210may be, for example, approximately 20 degrees Fahrenheit hotter than first hydraulic fluid201flowing through return line200. Despite the relatively low temperature difference between cold interface906and hot interface908, however, the relatively high heat transport capability of heat pipe902at such relatively low temperature differences facilitates effective heat transfer through heat pipe902.

In certain embodiments, a larger heat transport capability is required to facilitate reducing a temperature of second hydraulic system104or increasing a temperature of first hydraulic system102. In some embodiments, outer diameter918of tube904is increased further. Alternatively, a plurality (not shown) of heat pipes902may be installed between first hydraulic system102and second hydraulic system104. For example, but not by way of limitation, a first heat pipe902may be installed between reservoir202of first hydraulic system102and case drain216of second hydraulic system104(as shown inFIG. 11), a second heat pipe902may be installed between return line200of first hydraulic system102and return line210of second hydraulic system104(as shown inFIG. 12), and/or a third heat pipe902(not shown) may be installed between return line200of first hydraulic system102and case drain216of second hydraulic system104.

FIG. 13is a schematic illustration andFIG. 14is a block diagram of a fifth example configuration of first hydraulic system102and second hydraulic system104in which sealed heat transfer device900, implemented as thermosyphon1002, is coupled to first hydraulic system102and second hydraulic system104. More specifically, cold interface1006is coupled to return line200of first hydraulic system102, and hot interface1008is coupled to return line210of second hydraulic system104. As described above, for thermosyphon1002to function properly, cold interface1006must have an elevation1020that is higher than hot interface1008, as shown inFIG. 13. Thus, thermosyphon1002is suited for locations on aircraft100where a portion of return line200is at an elevation1020relative to a portion of return line210when aircraft100is in an operating orientation.

In the exemplary embodiment, hot interface1008is configured to encapsulate a portion of return line210to facilitate increasing a heat transfer from return line210to hot interface1008. Similarly, cold interface1006is configured to encapsulate a portion of return line200to facilitate increasing a heat transfer from cold interface1006to return line200. A heat transport capability of thermosyphon1002depends upon the materials used for tube1004and working fluid1012, a temperature difference between cold interface1006and hot interface1008, and an outer diameter1018of tube1004(as shown inFIG. 10) approximately in the same manner as described for heat pipe902. In the exemplary embodiment ofFIG. 13, thermosyphon1002includes tube1004formed of copper with outer diameter1018equal to approximately 0.5 inches and a working fluid1012of water. As described above, in the absence of heat exchange, second hydraulic fluid211flowing through return line210may be, for example, approximately 20 degrees Fahrenheit hotter than first hydraulic fluid201flowing through return line200. At an operational temperature of 150 degrees Fahrenheit, thermosyphon1002has a heat transport capability of approximately 500 watts. In an alternative embodiment, thermosyphon1002includes copper and water and has outer diameter 0.875 inches. In this alternative embodiment, thermosyphon1002has a heat transport capability of approximately 1,800 watts at a 150 degree Fahrenheit operational temperature. Thus, as with heat pipe902, the temperature difference between first hydraulic fluid201and second hydraulic fluid211may be reduced to, for example, 5 degrees Fahrenheit.

In certain embodiments, a larger heat transport capability is required to facilitate reducing a temperature of second hydraulic system104or increasing a temperature of first hydraulic system102. In some embodiments, outer diameter1018of tube1004is increased to meet these requirements. Additionally or alternatively, a plurality (not shown) of thermosyphons1002may be installed between first hydraulic system102and second hydraulic system104, as described previously with regard to a plurality of heat pipes902. Alternatively, in a sixth example configuration of first hydraulic system102and second hydraulic system104illustrated schematically inFIG. 15, tube1004includes a vapor conduit1022and a liquid conduit1024coupled to cold interface1006and hot interface1008to form a loop. With reference also toFIG. 10, working fluid1012near hot interface1008absorbs heat, evaporates into vapor1014, and rises through vapor conduit1022toward cold interface1006. Working fluid1012near cold interface1006releases heat, condenses into liquid1016, and flows down liquid conduit1024toward hot interface1008. The use of vapor conduit1022and liquid conduit1024facilitates increasing a heat transfer efficiency of thermosyphon1002by reducing entrainment friction that arises when vapor1014and liquid1016travel past each other in opposite directions in tube1004.

In some embodiments, a risk of system or component malfunction presents a risk that heat transfer between first hydraulic system102and second hydraulic system104eventually may lead to overheating of first hydraulic system102.FIG. 16is a schematic illustration of a seventh example configuration of first hydraulic system102and second hydraulic system104, in which sealed heat transfer device900is implemented as a thermostat-regulated thermosyphon system1600that facilitates preventing a potential overheat condition. In the exemplary embodiment, thermosyphon system1600includes a thermostat1602, a first tube1604, a second tube1614, and a third tube1624. More specifically, first tube1604extends between hot interface1008and thermostat1602, second tube1614extends between thermostat1602and cold interface1006, and third tube1624extends between thermostat1602and a surface interface1606. Thermostat1602is configured to selectively switch first tube1604between flow communication with second tube1614and flow communication with third tube1624.

In certain embodiments, hot interface1008is coupled to second hydraulic system104, cold interface1006is coupled to first hydraulic system102, and surface interface1606is coupled to a structural surface1626of aircraft100. For example, in the exemplary embodiment illustrated inFIG. 15, hot interface1008is coupled to return line210of second hydraulic system104, cold interface1006is coupled to return line200of first hydraulic system102, and surface interface1606is coupled to a surface1626of a skin of aircraft100. In a particular embodiment, hot interface1008is configured to encapsulate a portion of return line210to facilitate increasing a heat transfer from return line210to hot interface1008, cold interface1006is configured to encapsulate a portion of return line200to facilitate increasing a heat transfer from cold interface1006to return line200, and surface interface1606is configured to contact an extended portion of surface1626to facilitate increasing a heat transfer from surface interface1606to surface1626. In alternative embodiments, hot interface1008is coupled to a different location within second hydraulic system104and/or cold interface1006is coupled to a different location within first hydraulic system102.

In a first operational condition, thermostat1602couples first tube1604in flow communication with second tube1614, such that first tube1604and second tube1614cooperate to form a sealed heat transfer device900. More specifically, and with reference also toFIG. 10, in the first operational condition, working fluid1012near hot interface1008absorbs heat from hot interface1008and evaporates into vapor1014, which expands and travels upward through thermostat1602toward cold interface1006. In turn, working fluid1012near cold interface1006loses heat to cold interface1006and condenses into liquid1016, which travels downward through thermostat1602toward hot interface1008. As previously described, elevation1020of cold interface1006relative to hot interface1008enables first tube1604and second tube1614to transfer heat despite the absence of a wicking structure. Thus, in the first operational condition, thermostat system1600substantially forms thermosyphon1002between return line210and return line200.

In a second operational condition, thermostat1602couples first tube1604in flow communication with third tube1624. A location of surface1626is chosen such that surface1626is at an elevation1620relative to hot interface1008, and such that a temperature of surface1626is lower than a temperature of second hydraulic system104when thermosyphon system1600is in operation. As a result, in the second operational condition, first tube1604and third tube1624cooperate to form a sealed heat transfer device900. More specifically, and with reference also toFIG. 10, in the second operational condition, working fluid1012near hot interface1008absorbs heat from hot interface1008and evaporates into vapor1014, which expands and travels upward through thermostat1602toward surface interface1606. In turn, working fluid1012near surface interface1606loses heat to surface interface1606and condenses into liquid1016, which travels downward through thermostat1602toward hot interface1008. Elevation1620of surface interface1606relative to hot interface1008enables first tube1604and third tube1624to transfer heat despite the absence of a wicking structure. Thus, in the second operational condition, thermostat system1600substantially forms thermosyphon1002between return line210and surface1626.

FIG. 17is a schematic illustration of an exemplary embodiment of a thermostat1602for use with thermostat-regulated thermosyphon system1600shown inFIG. 16. In the exemplary embodiment, thermostat1602includes an actuator1630configured to move a valve1632between a first position1640and a second position1642within a housing1634. When valve1632is in first position1640, first tube1604is coupled in flow communication with second tube1614, while third tube1624is substantially blocked from flow communication with first tube1604and second tube1614. In some embodiments, positioning valve1632in first position1640implements the first operational condition described above. When valve1632is in second position1642, first tube1604is coupled in flow communication with third tube1624, while second tube1614is substantially blocked from flow communication with first tube1604and third tube1624. In some embodiments, positioning valve1632in second position1642implements the second operational condition described above.

In certain embodiments, valve1632is positioned in first position1640at a commencement of an operation of aircraft100, and if a temperature associated with first hydraulic system102exceeds a predetermined threshold value, actuator1630moves valve1632to second position1642. For example, in the exemplary embodiment, actuator1630actuates valve1632in response to input from a temperature sensor1636(shown inFIG. 15) configured to measure a temperature of hydraulic fluid201flowing in return line200of first hydraulic system102. If the temperature measured by sensor1636exceeds the predetermined threshold value, actuator1630moves valve1632to second position1642. In certain embodiments, by switching the heat transfer sink of thermosyphon system1600from cold interface1006, which transfers heat to first hydraulic system102, to surface interface1606, which transfers heat to surface1626, thermostat1602facilitates preventing a potential overheat condition of first hydraulic system102.

In the embodiment illustrated inFIGS. 16 and 17, sensor1636may communicate with actuator1630using a wired, wireless, or any other suitable connection (not shown). Moreover, in alternative embodiments, temperature sensor1636measures a temperature at a different location, such as at another location within first hydraulic system102or an ambient temperature that can be correlated with an approximate temperature of first hydraulic system102. In still other embodiments, actuator1630actuates valve1632in response to an average of a plurality of temperatures measured at a plurality of corresponding locations, and the predetermined threshold temperature is a predetermined threshold average temperature.

In certain embodiments, sealed heat transfer devices900, such as heat pipe902, thermosyphon1002, and thermosyphon system1600, provides an advantage over heat exchangers106having first tube120coupled in flow communication with first hydraulic system102and second tube122coupled in flow communication with second hydraulic system104. In particular, safety regulations may require that, in certain embodiments, all components in flow communication with first hydraulic system102are located at least a required distance, such as for example three feet, from all components in flow communication with second hydraulic system104to mitigate a risk of single-event damage to both first hydraulic system102and second hydraulic system104. Because sealed heat transfer devices900are not in flow communication with either first hydraulic system102or second hydraulic system104, it is not necessary to locate any component of first hydraulic system102within the minimum separation distance of any component of second hydraulic system104to achieve efficient heat transfer through sealed heat transfer devices900.

In certain embodiments, with reference toFIGS. 11 and 12, a length of heat pipe902is in the range of about three feet to about ten feet. In alternative embodiments, heat pipe902has a length of more than ten feet or less than three feet. Moreover, in certain embodiments, with reference toFIGS. 13 and 14, a length of thermosyphon1002is in the range of about three feet to about ten feet. In alternative embodiments, thermosyphon1002has a length of more than ten feet or less than three feet. Similarly, in certain embodiments, with reference toFIG. 16, a combined length of first tube1604and second tube1614is in the range of about three feet to about ten feet. In alternative embodiments, first tube1604and second tube1614have a combined length of more than ten feet or less than three feet. Thus, sealed heat transfer devices900facilitate heat transfer between first hydraulic system102and second hydraulic system104while maintaining a desired minimum separation distance between components in flow communication with first hydraulic system102and components in flow communication with second hydraulic system104.

FIG. 18is a flowchart of another exemplary method1800for managing temperatures in a machine, such as aircraft100(shown inFIG. 1). Exemplary method1800includes circulating1802a first hydraulic fluid, for example first hydraulic fluid201, at a first temperature through a first hydraulic system, for example first hydraulic system102. First hydraulic system102is coupled to a machine, for example aircraft100. Additionally, method1800includes circulating1804a second hydraulic fluid, for example second hydraulic fluid211, at a second temperature that is higher than the first temperature through a second hydraulic system, for example second hydraulic system104. Second hydraulic system104is coupled to the machine, for example aircraft100. Method1800additionally includes transferring1806heat from the second hydraulic fluid211to the first hydraulic fluid201through a sealed heat transfer device coupled between first hydraulic system102and second hydraulic system104. The sealed heat transfer device may be, for example, sealed heat transfer device900, such as heat pipe902, thermosyphon1002, or thermosyphon system1600. The sealed heat transfer device is not in flow communication with either of first hydraulic system102and second hydraulic system104.

As compared to known methods and systems for heating or cooling hydraulic fluid within an aircraft, the methods and systems described herein facilitate both heating and cooling hydraulic fluid with the same setup, and in a more efficient and cost-effective way by coupling hydraulic systems of different temperatures together with a heat exchanger or a sealed heat transfer device, such as a heat pipe or thermosyphon. Moreover, the methods and systems described herein facilitate preventing a potential overheat condition of hydraulic systems by providing a thermostat-regulated heat transfer system. In addition, the methods and systems described herein facilitate both heating and cooling of hydraulic fluid within different hydraulic systems while maintaining a desired minimum separation distance between components in flow communication with the first system and components in flow communication with the second system.

The description of the different advantageous implementations has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the implementations in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous implementations may provide different advantages as compared to other advantageous implementations. The implementation or implementations selected are chosen and described in order to best explain the principles of the implementations, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various implementations with various modifications as are suited to the particular use contemplated. This written description uses examples to disclose various implementations, which include the best mode, to enable any person skilled in the art to practice those implementations, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.