Passive thermal management systems and related methods

Abstract

Systems, apparatus, articles of manufacture, and methods are disclosed for a thermal management system that includes a first heat exchanger having a first path and a second path for transferring thermal energy between a first fluid and a second fluid; a second heat exchanger comprising a third path and a fourth path for transferring thermal energy between the first fluid and the third fluid; a first thermostatic element for actuating a first thermostatic valve based on a first temperature of the first fluid to control a first flow of the first fluid through the first heat exchanger; and a second thermostatic element for actuating a second thermostatic valve based on a second temperature of the third fluid to control a second flow of the first fluid through the second heat exchanger.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to gas turbine engines, and more particularly to passive thermal management systems for gas turbines and related methods. BACKGROUND

[0002] Conventional commercial aircraft generally include a fuselage, a pair of wings, and a propulsion system that provides thrust. The propulsion system typically includes one or more aircraft engines, such as turbofan jet engines. Conventional aircraft engines are powered by aviation turbine fuel, which is ignited with pressurized air to produce thrust. Fuel temperature plays a critical role in aircraft engine operation. BRIEF DESCRIPTION OF DRAWINGS

[0003] Figure 1 is a schematic illustration of an aircraft in which examples disclosed herein can be implemented.

[0004] Figure 2 is a schematic cross-sectional view of an example engine for an aircraft in which examples disclosed herein can be implemented.

[0005] Figure 3A is a schematic representation of an example passive thermal management system that can be associated with Figure 1 an aircraft of Figure 2 an engine of

[0006] Figure 3B is a schematic representation of a passive thermal management system according to the teachings of the present disclosure when oil and fuel temperatures fall below a low threshold Figure 3A

[0007] Figure 3C is a schematic representation of a passive thermal management system according to the teachings of the present disclosure when oil and fuel temperatures exceed a high threshold Figure 3A

[0008] Figure 4A is a cross-sectional view of an example compound thermostatic valve according to the teachings of the present disclosure that can be associated with the passive thermal management systems disclosed herein in an intermediate position.

[0009] Figure 4B is a cross-sectional view of an example compound thermostatic valve according to the teachings of the present disclosure that can be associated with the passive thermal management systems disclosed herein in a low temperature position.

[0010] Figure 4C is a cross-sectional view of an example compound thermostatic valve according to the teachings of the present disclosure that can be associated with the passive thermal management systems disclosed herein in a high temperature position.

[0011] Figure 5 ​​is a schematic illustration of another alternative example passive thermal management system according to the teachings of this disclosure, which can be associated with an aircraft of Figure 1 and / or an engine of Figure 2 .

[0012] Figure 6 is a schematic illustration of another alternative example passive thermal management system according to the teachings of this disclosure, which can be associated with an aircraft of Figure 1 and / or an engine of Figure 2 .

[0013] Figure 7 is a flowchart representation of an example method for passive thermal control using an example thermal management system according to the teachings of this disclosure. Figures 3A-3C , Figure 5 and / or Figure 6 .

[0014] Generally, the same reference numbers are used throughout the drawings and accompanying written description to refer to the same or like parts. The drawings are not necessarily to scale. DETAILED DESCRIPTION

[0015] “Comprise” and “comprising” (and all forms of these terms, and “include” and “including”) are used herein as open-ended terms. Thus, whenever a claim employs any form of “comprising” or “including,” or “have” or “has” or “contain” or “contains,” or “contain” or “contains,” such terms are used in the sense of open-ended terms that can be read to exclude only those features or steps listed in the specific claim, or in the sense of open-ended terms that can be read to include not only those features or steps listed in the specific claim but also any features or steps that are equivalents of those specifically recited. As used herein, when the phrase “at least” is used as the transition term in, for example, a preamble of a claim, it is open-ended in the sense that additional elements, terms, etc. that are not specified in the preamble can be present in the corresponding claim or claim statement. As used herein, the term “and / or” when used in the form “A, B, and / or C” means A, B, C individually or any combination or subset of these. As used herein in the context of describing structural, componential, item, object, and / or thing related contexts, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. Similarly, as used herein in the context of describing structural, componential, item, object, and / or thing related contexts, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. As used herein in the context of describing performance or execution of processes, instructions, actions, activities, etc., the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. Similarly, as used herein in the context of describing performance or execution of processes, instructions, actions, activities, etc., the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B.

[0016] As used herein, singular references (e.g., “a”, “an”, “first”, “second”, etc.) do not exclude multiple. As used herein, the term “a” or “an” object refers to one or more of the object. The terms “a” (or “an”), “one or more”, and “at least one” are used interchangeably herein. Furthermore, although individually listed, a plurality of means, elements or actions can be implemented by, e.g., a single entity or object. Also, although individual features can be included in different examples or claims, these features can be combinable into other examples or claims and the inclusion of such features in different examples or claims does not imply that a combination of features is not feasible and / or advantageous.

[0017] As used herein, unless otherwise indicated, a connection reference (e.g., attached, coupled, connected, and joined) can include intermediate members and / or relative motion between the elements connected by the connection reference. As such, a connection reference does not necessarily infer that two elements are directly connected and / or have a fixed relationship with each other. As used herein, a statement that any portion is “contacted” with another portion is defined as meaning that there are no intervening portions between the two portions.

[0018] Unless specifically stated otherwise, as used herein the descriptors such as “first,” “second,” “third,” etc. do not assign or otherwise indicate any meaning as to priority, physical order, arrangement within a list, and / or any other ordering, but are merely used as labels and / or arbitrary names to distinguish elements so as to facilitate understanding of the disclosed examples. In some examples, the descriptor “first” can be used to refer to an element in a detailed description, while the same element can be referred to in a claim with a different descriptor (e.g., “second” or “third”). In such instances, it is understood that the descriptors are used only to clearly identify those elements in the context of the discussion (e.g., within a claim) where the elements can otherwise share the same name, for example.

[0019] As used herein, “approximately” and “about” modify the meaning of the term / value to which they refer by identifying the potential existence of variations that occur in real-world applications. For example, “approximately” and “about” can modify a dimension that can not be exact due to manufacturing tolerances and / or other real-world imperfections that would be understood by one of ordinary skill in the art. For example, unless otherwise specified herein, “approximately” and “about” can indicate that a dimension can be within a + / - 10% tolerance range.

[0020] The terms “forward” and “aft” refer to relative positions within a gas turbine engine or vehicle and refer to the normal operating attitude of the gas turbine engine or vehicle. For example, with respect to a gas turbine engine, forward refers to a position closer to the engine inlet and aft refers to a position closer to the engine nozzle or exhaust port.

[0021] The terms “upstream” and “downstream” refer to relative directions with respect to the flow in a path. For example, with respect to fluid flow, “upstream” refers to the direction from which the fluid flows and “downstream” refers to the direction to which the fluid flows.

[0022] One important aspect of aircraft operation is maintaining the temperature of the fuel delivered to the engines. Fuel density, volume, and weight are all affected by the temperature of the fuel. Too low of a fuel temperature can cause problems such as low engine efficiency, waxing, crystallization, and fuel line plugging. Too high of a fuel temperature can cause problems such as cavitation and vapor lock. As oil is delivered through a gas turbine engine, it accumulates heat energy. Conventional oil scavenging systems use oil coolers, such as air-cooled oil coolers (“ACOC”) and fuel-cooled oil coolers (“FCOC”), to reduce the oil temperature before the oil is re-delivered back through the engine.

[0023] In recent years, gas turbine engines have utilized thermal management systems to regulate the temperature of the fuel to maximize efficiency while avoiding the negative effects of over-heating the fuel. Specifically, thermal management systems utilize heat exchangers to regulate the temperature of the fuel.

[0024] Some known thermal management systems utilize multiple heat exchangers to regulate the temperature of the oil and fuel in an aircraft. Such thermal management systems utilize an active control system to control the delivery of oil to the different heat exchangers to optimize the temperature of the fuel. For example, some known thermal management systems utilize a combination of a controller and control valves to distribute the amount of oil delivered to individual heat exchangers. Such systems have various drawbacks. For example, active control systems require the inclusion of a controller, which both adds weight to the aircraft and takes up additional space. Another drawback is that active control systems are susceptible to failure if any component of the system fails, whether that component is the valve itself or the controller. As a result, aircraft utilizing active control systems for thermal management of the fuel require built-in redundancy in the system, or else risk the consequences of a failure. When a failure does occur, it can result in insufficient heating of the fuel and reduced engine efficiency.

[0025] Disclosed herein are example passive thermal management systems and related methods. Although the examples disclosed herein are discussed with reference to fuel, oil, and air, any combination of fluids (e.g., water, natural gas (e.g., methane), etc.) can be used in place of fuel, oil, and / or air. The examples disclosed herein utilize multiple heat exchangers arranged in parallel and / or in series for oil cooling. The examples disclosed herein control the amount of oil provided to respective ones of the multiple heat exchangers to regulate the temperature of the fuel in the system. The example passive thermal management systems disclosed herein include thermostatic bypass valves and compound thermostatic valves. Further, the examples disclosed herein passively deliver oil within the oil circuit according to predefined thresholds of fuel temperature and oil temperature to regulate the temperature of the fuel. As a result, the passive thermal management systems disclosed herein are able to thermally regulate aircraft fuel without the need for an active controller to regulate control valves, thereby eliminating the unnecessary weight, use of space, and maintenance required by active control systems.

[0026] Reference is now made to the drawings,Figure 1 is a perspective view of an example vehicle in which examples disclosed herein can be implemented. In particular, for examples of Figure 1 , the vehicle is an aerial vehicle or aircraft 10. The aircraft 10 includes a fuselage 12, a wing 14 attached to the fuselage 12, a tail 16, a thermal management system (“TMS”) 18, and a fuel system 20. The TMS 18 regulates the temperature of oil and aviation fuel. In some examples, the TMS 18 includes at least one heat exchanger, a thermostatic bypass valve, a compound thermostatic valve, an oil supply, an oil return, a fuel supply, and a fuel return. Although in the example of Figure 1 , the TMS 18 is positioned in the aircraft engine, the TMS 18 can be positioned at any other suitable location. The TMS 18 can be implemented by the systems and methods disclosed herein.

[0027] The fuel system 20 includes a fuel tank 22 (e.g., a Jet-A or liquid hydrogen fuel tank, etc.) for containing fuel for the aircraft 10. In the example aircraft 10 shown, Figure 1 at least a portion of the fuel tank 22 is located in the wing 14 of the aircraft 10. However, in some examples, the fuel tank 22 can be located at other suitable locations in the fuselage 12 or the wing 14. The fuel tank 22 can be made of known materials, such as titanium, Inconel (or other suitable superalloy), aluminum, or a composite material. In other examples, the aircraft 10 can include additional and / or alternative fuel tanks 22.

[0028] The aircraft 10 also includes a propulsion system 24 that generates propulsive thrust required to propel the aircraft 10 in flight, during taxi operations, etc. Although the propulsion system 24 is shown in Figure 1 attached to the wing 14, in other examples, it can additionally or alternatively include one or more aspects coupled to other portions of the aircraft 10, such as the tail 16 and / or the fuselage 12.

[0029] In the example of Figure 1 , the propulsion system 24 includes an engine, and more specifically, a pair of engines. More specifically, each engine of the pair of engines is configured as a gas turbine engine 26 (e.g., a turbofan engine, etc.) that is mounted to one of the respective wings 14 of the aircraft 10 in an underwing configuration via a respective pylon 28. Each gas turbine engine 26 is capable of selectively generating propulsive thrust for the aircraft 10. The amount of propulsive thrust can be controlled based at least in part on the volume (e.g., mass flow) of fuel provided to the gas turbine engine 26 via the fuel system 20.

[0030] Figure 2is a schematic cross-sectional view of an example gas turbine engine 26, which can incorporate various examples disclosed herein. The example gas turbine engine 26 can be implemented on an aircraft and thus is referred to as an aircraft engine. In this example, the gas turbine engine 26 is a turbofan engine. However, the principles of the present disclosure are also applicable to other types of engines, such as turboprop engines and engines without a nacelle, such as unducted fan (UDF) engines (sometimes referred to as propfan engines). Moreover, examples disclosed herein can be implemented on other types of engines, such as non-aircraft engines and / or power generators.

[0031] As shown in Figure 2 The gas turbine engine 26 includes an outer bypass duct 102 (which can also be referred to as a nacelle, fan duct, or outer casing), a core turbine engine 104, and a fan section 106. The core turbine engine 104 and the fan section 106 are disposed at least partially within the outer bypass duct 102. The core turbine engine 104 is disposed downstream of the fan section 106 and drives the fan section 106 to produce forward thrust.

[0032] As shown in Figure 2 The gas turbine engine 26 defines a longitudinal or axial centerline axis 108 that extends therethrough for reference. Figure 2 An annotated directional view is also included referencing axial direction A, radial direction R, and circumferential direction C. Generally, as used herein, the axial direction A is a direction that extends generally parallel to the centerline axis 108, the radial direction R is a direction that extends outwardly or inwardly orthogonal from or to the centerline axis 108, and the circumferential direction C is a direction that extends concentrically about the centerline axis 108.

[0033] The core turbine engine 104 includes a substantially tubular outer casing 110 (which can also be referred to as an intermediate casing) that defines an annular inlet 112. The outer casing 110 of the core turbine engine 104 can be formed from a single casing or multiple casings. The outer casing 110 surrounds, in serial flow relationship, a compressor section having a booster or low pressure compressor 114 (“LP compressor 114”) and a high pressure compressor 116 (“HP compressor 116”), a combustion section 118 (which can also be referred to as a combustor 118), a turbine section having a high pressure turbine 120 (“HP turbine 120”) and a low pressure turbine 122 (“LP turbine 122”), and an exhaust section 124.

[0034] The core turbine engine 104 includes a high-pressure shaft 126 (“high-pressure shaft 126”) that is driveably coupled to the HP turbine 120 and the HP compressor 116. The core turbine engine 104 also includes a low-pressure shaft 128 (“LP shaft 128”) that is driveably coupled to the LP turbine 122 and the LP compressor 114. The LP shaft 128 is also coupled to the fan shaft 130.

[0035] Fan section 106 includes a plurality of fan blades 132 coupled to and extending radially outward from fan shaft 130. In some examples, LP shaft 128 may be directly coupled to fan shaft 130 (i.e., direct drive configuration). In alternative configurations, LP shaft 128 may be coupled to fan shaft 130 via reduction gear 134 (i.e., indirect drive or gear drive configuration). While in this example, core turbine engine 104 includes two compressors and two turbines, in other examples, core turbine engine 104 may include only one compressor and one turbine. Furthermore, in other examples, core turbine engine 104 may include more than two compressors and turbines. In such examples, core turbine engine 104 may include more than two drive shafts or spools.

[0036] like Figure 2 As shown, during operation of the gas turbine engine 26, air 136 enters the inlet section 138 of the gas turbine engine 26. The air 136 is accelerated by fan blades 132. A first portion 140 of the air 136 flows into a bypass airflow passage 142, while a second portion 144 of the air 136 flows into the inlet 112 of the core turbine engine 104 (and thus into the LP compressor 114). Downstream of inlet 112, one or more successive stages of the LP compressor stator blades 146 and the LP compressor rotor blades 148 coupled to the LP shaft 128 progressively compress the second portion 144 of the air 136 flowing through the LP compressor 114 and then to the HP compressor 116. Next, one or more successive stages of the HP compressor stator blades 150 and the HP compressor rotor blades 152 coupled to the HP shaft 126 further compress the second portion 144 of the air 136 flowing through the HP compressor 116. This compressed air 154 is supplied to the combustion section 118, where it is mixed with fuel and burned to provide combustion gases 156. Fuel is injected into the combustion section 118 through one or more nozzles 157. The gas turbine engine 26 includes a fuel system for supplying pressurized fuel to the combustion section 118 of the core turbine engine 104 via nozzles 157. An example thermal management system for controlling the temperature of the fuel supplied to the combustion section 118 is disclosed herein.

[0037] Combustion gases 156 flow through the HP turbine 120, in which one or more successive stages of HP turbine stator vanes 158 and HP turbine rotor blades 160 coupled to the HP shaft 126 extract a first portion of kinetic and / or thermal energy. This energy extraction supports operation of the HP compressor 116. The combustion gases 156 then flow through the LP turbine 122, in which one or more successive stages of LP turbine stator vanes 162 and LP turbine rotor blades 164 coupled to the LP shaft 128 extract a second portion of thermal and / or kinetic energy therefrom. This energy extraction causes the LP shaft 128 to rotate, which supports operation of the LP compressor 114 and / or rotation of the fan shaft 130. The combustion gases 156 then exit the core turbine engine 104 through its exhaust section 124. The combustion gases 156 mix with the first portion 140 of air 136 from the bypass airflow passage 142. The combined gases exit an exhaust nozzle 170 (e.g., converging / diverging nozzle) of the bypass airflow passage 142 to produce propulsive thrust.

[0038] The example TMS 18 is positioned within the gas turbine engine 26, in an area indicated by the dashed box 180. The TMS 18 is in contact with the first portion 140 of air 136. In other examples, the TMS 18 can be positioned in other locations (e.g., outside of the gas turbine engine 26, at another location within the gas turbine engine 26, etc.). In some examples, the TMS 18 is located within a core cowl of the gas turbine engine 26. In other examples, the TMS 18 is positioned in a fan cowl of the gas turbine engine 26.

[0039] Figure 3A is a schematic representation of an example passive TMS 300 for regulating a temperature of a fuel. The passive TMS 300 includes an ACOC 302, an FCOC 304, a thermostatic bypass valve 306 (e.g., a first thermostatic valve) and a compound thermostatic valve 308 (e.g., a second thermostatic valve), an oil supply 310, a fuel supply 312, and a fuel management unit (“FMU”) 314.

[0040] The passive TMS 300 includes one or more first conduits 316 (e.g., tubes, pipes, etc.) for fluidically coupling the ACOC 302, the FCOC 304, the thermostatic bypass valve 306, the compound thermostatic valve 308, and the oil supply 310. Thus, the first conduits 316 define an oil flow loop 318, in which a direction of oil flow within the oil flow loop 318 is designated by first arrows. The passive TMS 300 also includes one or more second conduits 320 for fluidically coupling the FCOC 304, the compound thermostatic valve 308, the fuel supply 312, and the FMU 314. Thus, the second conduits 320 define a fuel loop 322, in which a direction of fuel flow within the oil loop is designated by second arrows.

[0041] exist Figure 3A In the example shown, oil enters oil flow loop 318 and is diverted into first branch 324 and second branch 326 of oil flow loop 318. Oil flowing through first branch 324 of oil flow loop 318 enters ACOC 302 through first inlet 328. As oil flows through the first path of ACOC 302 and air flows through the second path of ACOC 302, heat is transferred from the oil to the air. In an example passive TMS utilizing fluids other than air, oil, and fuel, ACOC 302 can be replaced with a different type of heat exchanger. After exiting from first outlet 330 of ACOC 302, oil is diverted into third branch 332 and fourth branch 334 of oil flow loop 318. Oil flowing through the third branch 332 of the oil flow circuit 318 enters the thermostatic bypass valve 306 via the second inlet 336 and exits the thermostatic bypass valve 306 via the second outlet 338. Oil flowing through the fourth branch 334 of the oil flow circuit 318 enters the combined thermostatic valve 308 via the third inlet 340 and exits the combined thermostatic valve 308 via the third outlet 342. Then, the third branch 332 and the fourth branch 334 of the oil flow circuit 318 are reconnected to form the fifth branch 344. Figure 3A In the illustrated example, ACOC 302 and FCOC 304 are arranged in series, with ACOC 302 upstream of FCOC 304. In other examples, FCOC 304 is upstream of ACOC 302. In still other examples, ACOC 302 and FCOC 304 are arranged in parallel. In the example where ACOC 302 and FCOC 304 are arranged in parallel, the arrangement of the oil flow circuit 318 and the fuel circuit 322 can be varied based on the arrangement of ACOC 302 and FCOC 304. In some examples, the passive TMS 300 may include an additional heat exchanger. In this example, the additional heat exchanger may include another type of heat exchanger (e.g., an electric heat exchanger).

[0042] Oil flowing through the second branch 326 of the oil flow loop 318 enters the combined thermostatic valve 308 via the fourth inlet 346 and exits via the fourth outlet 348. Then, the second branch 326 and the fifth branch 344 connect to form the sixth branch 350. Oil flowing through the sixth branch 350 of the oil flow loop 318 enters the FCOC 304 via the fifth inlet 352. As the oil flows through the third path in the FCOC 304 and the fuel flows through the fourth path in the FCOC 304, heat is transferred from the oil to the fuel. After exiting from the fifth outlet 354 of the FCOC 304, the oil returns to the oil supply 310.

[0043] exist Figure 3A In the example shown, fuel enters the fourth path of FCOC 304 through the sixth inlet 356. As described above, when fuel flows through FCOC 304, it receives heat energy from the oil. After exiting from the sixth outlet 358 of FCOC 304, the fuel is supplied to FMU 314. Fuel from FMU 314 enters the second conduit 320 of fuel circuit 322. The fuel passes through the seventh inlet 360 of compound thermostatic valve 308. Figures 4A-4C As shown in the diagram, it enters the composite thermostatic valve 308 and passes through the seventh outlet 362 of the composite thermostatic valve 308. Figures 4A-4C (As shown in the diagram) fuel exits from the combined thermostatic valve 308. Fuel is then supplied to the downstream combustion element (not shown).

[0044] exist Figure 3A In the example shown, the thermostatic bypass valve 306 and the composite thermostatic valve 308 are passive control valves. Figure 3AIn particular embodiments, the thermostatic bypass valve 306 is fluidly coupled to the first conduit 316, the ACOC 302, the FCOC 304, and the oil supply 310. For example, the thermostatic bypass valve 306 can be positioned at the second outlet 338, at the second inlet 336, and / or between the second outlet 338 and the second inlet 336. Accordingly, the thermostatic bypass valve 306 controls the flow of oil through the third branch 332, and thus the flow of oil through the ACOC 302. The thermostatic bypass valve 306 includes a first thermostatic element coupled to a spring, which is coupled to a valve body. In the passive TMS 300, the first thermostatic element is a wax pellet. In other examples, in addition to or instead of a wax pellet, the thermostatic bypass valve 306 uses a shape memory alloy (“SMA”) element (e.g., copper, aluminum, steel, Nitinol, etc.) or other type of thermostatic element. The wax pellet is in contact with the oil at a first temperature sensing point 364 of the oil flow circuit 318. By sensing the oil temperature at the first temperature sensing point 364, the wax pellet can prevent the oil from overheating and overcooling. The temperature of the oil at the first temperature sensing point 364 determines the size of the wax pellet of the thermostatic bypass valve 306. For example, a higher temperature can cause the wax pellet to expand to a larger size, change the position of the valve body, and allow for an increased rate of oil to pass through the third branch 332 of the oil flow circuit 318. Accordingly, the first thermostatic element actuates the thermostatic bypass valve 306 based on the temperature of the oil to control the position of the thermostatic bypass valve 306. The example first temperature sensing point 364 is located downstream of the FCOC 304 and upstream of the oil supply 310. In other examples, the first temperature sensing point 364 can be located in a different portion of the oil flow circuit 318, such as upstream of the FCOC 304.

[0045] In some examples, the type of the first thermostatic element, the size of the first thermostatic element, and / or the geometry of the first thermostatic element can be determined according to a first temperature threshold corresponding to a desired split of oil flow across the ACOC 302 and the FCOC 304. For example, when the temperature of the oil at the first temperature sensing point 364 exceeds a first high temperature threshold, more oil can be needed to be delivered through the ACOC 302 to maximize the available oil cooling and reduce the temperature at the oil supply 310. Likewise, when the temperature of the oil at the first temperature sensing point 364 is below a first low temperature threshold, air cooling of the oil at the ACOC 302 can be desired to be avoided, and fuel cooling at the FCOC 304 is maximized because there is less thermal energy in the oil. Accordingly, the type, size, and geometry of the first thermostatic element can be selected such that more or less oil is allowed to flow through the thermostatic bypass valve 306 based on the first high temperature threshold and the first low temperature threshold.

[0046] In Figure 3AIn particular embodiments, the first fluid path of the compound thermostat valve 308 is fluidly coupled to the first conduit 316, the ACOC 302, the FCOC 304, and the oil supply 310, and the second fluid path of the compound thermostat valve 308 is fluidly coupled to the first conduit 316, the FCOC 304, and the oil supply 310. For example, the first fluid path of the compound thermostat valve 308 is fluidly coupled between a third inlet 340 and a third outlet 342, and the second fluid path of the compound thermostat valve 308 is fluidly coupled between a fourth inlet 346 and a fourth outlet 348. Thus, the compound thermostat valve 308 controls the flow of oil through the second branch 326 and the fourth branch 334. In other examples, the compound thermostat valve 308 is split into two separate valves. The third fluid path of the compound thermostat valve 308 is fluidly coupled to the second conduit 320, the FCOC 304, the fuel supply 312, and the FMU 314. For example, the third fluid path of the compound thermostat valve 308 is fluidly coupled between a seventh inlet 360 (shown in FIG. 13) and a seventh outlet 362 (shown in FIG. 13). Thus, the compound thermostat valve 308 controls the flow of fuel through the third branch 328 and the fourth branch 334. Figures 4A-4C Figures 4A-4C ​The third fluid path of the compound thermostatic valve 308 includes a second thermostatic element coupled to a spring coupled to the valve body. In the passive TMS 300, the second thermostatic element is a wax pellet. In other examples, in addition to or instead of a wax pellet, the compound thermostatic valve 308 utilizes a shape memory alloy (“SMA”) element or another type of thermostatic element that changes size and / or shape as a function of temperature. The wax pellet is in contact with the fuel at a second temperature sensing point 366 of the fuel circuit 322. By sensing the fuel temperature at the second temperature sensing point 366, the wax pellet prevents fuel from overheating and overcooling while providing fuel cooling superior to air cooling. The temperature of the fuel at the second temperature sensing point 366 determines the size of the wax pellet of the compound thermostatic valve 308. For example, a higher temperature can cause the wax pellet to expand to a larger size, changing the position of the valve body of the compound thermostatic valve 308 and allowing for increased oil rate to pass through the fourth branch 334 and decreased oil amount to pass through the second branch 326. Thus, the second thermostatic element actuates the compound thermostatic valve 308 based on the temperature of the fuel to control the position of the compound thermostatic valve 308. The example second temperature sensing point 366 is located downstream of the FCOC 304 and downstream of the FMU 314. In other examples, the second temperature sensing point 366 can be located in a different portion of the fuel circuit 322, such as upstream of the FMU 314. Advantageously, the combination of the thermostatic bypass valve 306 that senses the temperature of the oil and the compound thermostatic valve 308 that senses the temperature of the fuel allows for maximum heat transfer between the oil and the fuel while also protecting the oil and the fuel from extreme temperatures. In some examples, the type of the second thermostatic element, the size of the second thermostatic element, and / or the geometry of the second thermostatic element can be determined according to a second temperature threshold that corresponds to a desired fuel temperature. For example, when the temperature of the fuel at the second temperature sensing point 366 exceeds a second high temperature threshold, even if the oil temperature at the first temperature sensing point 364 does not increase air cooling, it can be necessary to increase the oil flow through the ACOC 302 to reduce the thermal load on the FCOC 304 and allow the temperature of the fuel to decrease. Likewise, when the temperature of the fuel at the second temperature sensing point 366 is below a second low temperature threshold, less oil flow through the ACOC 302 can be desired, maximizing heat transfer at the FCOC 304, which will result in an increase in the temperature of the fuel to the desired range. Thus, the type, size, and geometry of the second thermostatic element can be selected such that more or less oil flow through the compound thermostatic valve 308 is allowed based on the second high temperature threshold and the second low temperature threshold.

[0047] The precise values of the first and second temperature thresholds are specific to a particular passive TMS. For example, in a passive TMS for regulating the temperature of fuel in an aircraft, contributing factors include the type of fuel used, the maximum temperature of the fuel before coking and / or other negative effects occur, the freezing point of the fuel, the efficiency of the engine at different fuel temperatures, the type of oil used, the maximum temperature of the oil, the minimum temperature of the oil, fuel system and oil system component temperature capabilities, acceleration or delay response to transients, etc. For example, the first threshold can correspond to a typical range of oil temperature that falls within 150°F and 300°F.

[0048] In Figure 3A In the illustrated example of FIG. 3, the thermostatic bypass valve 306 and the compound thermostatic valve 308 are located downstream of the ACOC 302 and upstream of the FCOC 304. In other examples of the passive TMS 300, at least one of the thermostatic bypass valve 306 and the compound thermostatic valve 308 can be located upstream of the ACOC 302 or downstream of the FCOC 304.

[0049] Figure 3A The flow of oil within the passive TMS 300 is illustrated when the temperature of the oil at the first temperature sensing point 364 is between the first low temperature threshold and the first high temperature threshold and the temperature of the fuel at the second temperature sensing point 366 is between the second low temperature threshold and the second high temperature threshold. Accordingly, the thermostatic bypass valve 306 is in an intermediate position as indicated by the first metering window 368, and the compound thermostatic valve 308 is in an intermediate position as indicated by the second metering window 370 and the third metering window 372. The unshaded portion of the first metering window 368 corresponds to a portion of the thermostatic bypass valve 306 through which oil from the third branch 332 can flow. The unshaded portion of the second metering window 370 corresponds to a portion of the compound thermostatic valve 308 through which oil from the fourth branch 334 can flow. The unshaded portion of the third metering window 372 corresponds to a portion of the compound thermostatic valve 308 through which oil from the second branch 326 can flow.

[0050] Figure 3B The flow of oil within the passive TMS 300 is illustrated when the temperature of the oil at the first temperature sensing point 364 is below (e.g., less than) the first low temperature threshold and the temperature of the fuel at the second temperature sensing point 366 is below the second low temperature threshold. Figure 3Athe passive TMS 300. As shown, the thermostatic bypass valve 306 is closed due to the lower temperature of the oil at the first temperature sensing point 264. The closing of the thermostatic bypass valve 306 reduces the flow of oil through the third branch 332. In some examples, the thermostatic bypass valve 306 is not fully closed to prevent the third branch 332 from becoming clogged with oil buildup due to prolonged low temperature conditions. For example, the thermostatic bypass valve 306 can be in a near-closed position when the temperature of the oil at the first temperature sensing point 364 falls below a first low temperature threshold. As used herein, a “near-closed position” means the valve and / or flow path is less than 10% open.

[0051] In response to the temperature of the fuel at the second temperature sensing point 366 decreasing, the compound thermostatic valve 308 adjusts to close a first flow path fluidly coupled to the fourth branch 334 as shown by the second metering window 370 and open a second flow path fluidly coupled to the second branch 326 as shown by the third metering window 372. The closing of the first flow path and the opening of the second flow path results in a decrease in the flow of oil through the fourth branch 334 and an increase in the flow of oil through the second branch 326. In some examples, the first flow path is not fully closed to prevent the fourth branch 334 from becoming clogged with oil buildup due to prolonged low temperature conditions. For example, the first flow path can be in a near-closed position when the temperature of the fuel at the second temperature sensing point 366 falls below a second low temperature threshold.

[0052] The combination of closing the thermostatic bypass valve 306, closing the first flow path of the compound thermostatic valve 308, and opening the second flow path of the compound thermostatic valve 308 results in a decrease in the flow of oil delivered through the first branch 324 and thus the ACOC 302, and an increase in the flow of oil delivered through the second branch 326, thereby increasing the amount of oil delivered to the FCOC 304 without first passing through the ACOC 302. The increase in the amount of oil delivered to the FCOC without first passing through the ACOC 302 increases the amount of heat exchange between the oil and the fuel.

[0053] Figure 3C is shown when the temperature of the oil at the first temperature sensing point 364 is above a first high temperature threshold (e.g., higher than the first high temperature threshold) and the temperature of the fuel at the second temperature sensing point 366 is above a second high temperature threshold, Figure 3APassive TMS 300. As shown, the thermostatic bypass valve 306 is open due to the higher temperature of the oil at the first temperature sensing point 364. The opening of the thermostatic bypass valve 306 increases the flow of oil through the third branch 332. In some examples, the second high temperature threshold corresponds to the highest temperature of the fuel (e.g., 200 degrees Fahrenheit, 300 degrees Fahrenheit, etc.). In these examples, the second high temperature threshold advantageously enables the compound thermostatic valve 308 to passively prevent the fuel from overheating without the need for a controller circuit.

[0054] In response to the temperature of the fuel at the second temperature sensing point 366 increasing, the compound thermostatic valve 308 adjusts to open the first flow path as shown by the second metering window 370 and to close the second flow path as shown by the third metering window 372. This adjustment of the compound thermostatic valve 308 results in an increase in the flow of oil through the fourth branch 334 and a decrease in the flow of oil through the second branch 326. In some examples, the second flow path is not fully closed to prevent the second branch 326 from becoming clogged with oil buildup due to prolonged low temperature conditions. For example, the second flow path can be in a near closed position when the temperature of the fuel at the second temperature sensing point 366 exceeds the second high temperature threshold.

[0055] The combination of opening the thermostatic bypass valve 306, opening the first flow path of the compound thermostatic valve 308, and closing the second flow path of the compound thermostatic valve 308 results in an increase in the flow of oil being delivered through the first branch 324 and thus through the ACOC 302 and a decrease in the flow of oil being delivered through the second branch 326, thereby decreasing the amount of oil delivered to the FCOC 304 without first passing through the ACOC 302. The decrease in the amount of oil delivered to the FCOC 304 without first passing through the ACOC 302 reduces the amount of heat transferred to the fuel, resulting in a decrease in the temperature of the fuel.

[0056] Figure 4A is a cross-sectional view of an example compound thermostatic valve 308. The example compound thermostatic valve 308 includes a thermostatic element 402, a first spring 404, a valve body 406, a second spring 408, and a housing 410. The thermostatic element 402 is a wax pellet. In other examples, the compound thermostatic valve 308 utilizes an SMA element or another type of thermostatic element in addition to or instead of a wax pellet. The example valve body 406 includes a stem 412 and a plurality of spools 414. In other examples, the valve body 406 includes a different number of spools 414 or a different type of spool 414. The housing 410 is a cylindrical tube that is coupled to the valve body 406. In other examples, the housing 410 is a different shape or includes a different number of spools 414. Figures 4A-4CIn the illustrated example, the valve body 406 includes a first spool 414A, a second spool 414B, and a third spool 414C. In other examples, the valve body 406 can include fewer (e.g., two) or more (e.g., four, five, etc.) spools 414. The housing 410 includes a third inlet 340 and a third outlet 342 to provide a first oil circuit 450 through the composite thermostat 308, a fourth inlet 346 and a fourth outlet 348 to provide a second oil circuit 460 through the composite thermostat 308, and a seventh inlet 360 and a seventh outlet 362 to provide a fuel path through the composite thermostat 308. In other examples, the housing 410 can include fewer or more inlets and / or outlets. In other examples, the housing 410 provides fewer or more different flow paths for oil through the composite thermostat 308.

[0057] Fuel enters the composite thermostat 308 at the seventh inlet 360 and contacts the thermostatic element 402. The thermostatic element 402 reacts to temperature changes by expanding or contracting in response to an increase or decrease in temperature. The thermostatic element 402 is coupled to the first spring 404 and the second spring 408. As the dimensions of the thermostatic element 402 change, the first spring 404 and the second spring 408 compress or decompress. Thus, the thermostatic element 402 actuates the composite thermostat 308 based on the temperature of the fuel. Figure 4A The composite thermostat 308 is shown when the temperature of the fuel in contact with the thermostatic element 402 is at a first temperature between the low fuel temperature threshold and the high fuel temperature threshold. When the fuel is at the first temperature, the thermostatic element 402 has a first height 420. The thermostatic element 402 pushes against the first spring 404, the valve body 406, and the second spring 408. When the thermostatic element 402 has the first height 420, the first spring has a first length 422, and the second spring has a second length 424. Thus, the valve body 406 is placed in an intermediate position by the thermostatic element 402 and the first spring 404 and the second spring 408. More specifically, the valve body 406 is positioned such that the first spool 414A covers about half of the third inlet 340, and the third spool 414C covers about half of the fourth inlet 346. This position of the valve body 406 is shown in the middle by the second metering window 370 and the third metering window 372. The amount that the valve body 406 covers the third inlet 340 and the fourth inlet 346 is determined by the height of the thermostatic element 402 at a given temperature. In the intermediate position, the valve body 406 and the composite thermostat 308 generally allow oil to flow through the first oil circuit 450 and the second oil circuit 460 at an intermediate flow rate. Figure 4A

[0058] Figure 4B ​The compound thermostat valve 308 is shown when the temperature of the fuel in contact with the thermostat element 402 is at a third temperature that is higher than the high fuel temperature threshold. In response to the higher temperature, the thermostat element 402 expands to a third height 432 that is higher than the first height 420. As a result, the first spring 404 compresses to a fifth length 434, and the second spring 408 compresses to a sixth length 436. Accordingly, the valve body 406 is placed in a high temperature position by the thermostat element 402 and the first spring 404 and the second spring 408. More specifically, the valve body 406 is positioned such that the third inlet 340 is substantially unobstructed by the first spool 414A, and the third spool 414C covers almost the entire fourth inlet 346. This position of the valve body 406 is shown in FIG. 3B by the second metering window 370 and the third metering window 372. In the high temperature position, the valve body 406 and the compound thermostat valve 308 generally allow oil to flow through the first oil passage 450 at a higher flow rate than oil flowing through the second oil passage 460. The higher oil flow rate through the first oil passage 450 than through the second oil passage 460 results in more thermal energy from the oil being transferred to the air via the ACOC 302, thereby lowering the temperature of the fuel. Figure 4B

[0059] Figure 4C The compound thermostat valve 308 is shown when the temperature of the fuel in contact with the thermostat element 402 is at a third temperature that is higher than the high fuel temperature threshold. In response to the higher temperature, the thermostat element 402 expands to a third height 432 that is higher than the first height 420. As a result, the first spring 404 compresses to a fifth length 434, and the second spring 408 compresses to a sixth length 436. Accordingly, the valve body 406 is placed in a high temperature position by the thermostat element 402 and the first spring 404 and the second spring 408. More specifically, the valve body 406 is positioned such that the third inlet 340 is substantially unobstructed by the first spool 414A, and the third spool 414C covers almost the entire fourth inlet 346. This position of the valve body 406 is shown in FIG. 3B by the second metering window 370 and the third metering window 372. In the high temperature position, the valve body 406 and the compound thermostat valve 308 generally allow oil to flow through the first oil passage 450 at a higher flow rate than oil flowing through the second oil passage 460. The higher oil flow rate through the first oil passage 450 than through the second oil passage 460 results in more thermal energy from the oil being transferred to the air via the ACOC 302, thereby lowering the temperature of the fuel. Figure 4C

[0060] ​​In some examples, the compound thermostatic valve 308 is designed such that neither the first oil line 450 nor the second oil line 460 can be fully closed. For example, the compound thermostatic valve 308 can be designed such that the thermostatic element 402 can be adjusted between a minimum height at extremely cold temperatures and a maximum height at extremely high temperatures. In these examples, the valve body 406 is configured to leave at least a portion of the third inlet 340 and the fourth inlet 346 unobstructed when the thermostatic element is at the minimum height and the maximum height.

[0061] Figure 5 is another alternative example passive thermal management system 500. The passive TMS 500 includes an ACOC 502, an FCOC 504, a thermostatic bypass valve 506, and a compound thermostatic valve 508, an oil supply 510, a fuel supply 512, and a fuel management unit (“FMU”) 514. In the passive TMS 500, the ACOC 502 and the FCOC 504 are arranged in parallel. By arranging the ACOC 502 and the FCOC 504 in parallel, hot oil can be delivered directly to the ACOC 502 and the FCOC 504 without first passing through the other of the ACOC 502 and the FCOC 504. By delivering hot oil directly to each of the ACOC 502 and the FCOC 504, the passive TMS 500 is able to maximize the temperature difference between the oil and the cooling fluid, thereby enabling a higher heat transfer rate.

[0062] The passive TMS 500 includes one or more first conduits 516 (e.g., tubes, pipes, etc.) to fluidly couple the ACOC 502, the FCOC 504, the thermostatic bypass valve 506, the compound thermostatic valve 508, and the oil supply 510. Accordingly, the first conduits 516 define an oil flow loop 518, where the direction of oil flow within the oil flow loop 518 is designated by the arrows. The passive TMS 500 also includes one or more second conduits 520 to fluidly couple the FCOC 504, the compound thermostatic valve 508, the fuel supply 512, and the FMU 514. Accordingly, the second conduits 520 define a fuel flow loop 522, where the direction of fuel flow is designated by the arrows.

[0063] In Figure 5In the illustrated example, oil enters the oil flow circuit 518 and is split into a first branch 524 of the oil flow circuit 518 and a second branch 526 of the oil flow circuit 518. Oil flowing through the first branch 524 of the oil flow circuit 518 enters the ACOC 502 through a first inlet 528 of the ACOC 502. In examples of passive TMS that utilize fluids other than air, oil, and fuel, the ACOC 502 can instead be a different type of heat exchanger. After flowing out of a first outlet 530 of the ACOC 502, the oil is split into a third branch 532 of the oil flow circuit 518 and a fourth branch 534 of the oil flow circuit 518. Oil flowing through the third branch 532 of the oil flow circuit 518 enters the thermostatic bypass valve 506 through a second inlet 536 of the thermostatic bypass valve 506 and exits the thermostatic bypass valve 506 through a second outlet 538 of the thermostatic bypass valve 506. Oil flowing through the fourth branch 534 of the oil flow circuit 518 enters the compound thermostatic valve 508 through a third inlet 540 of the compound thermostatic valve 508 and exits the compound thermostatic valve 508 through a third outlet 542 of the compound thermostatic valve 508. The third branch 532 and the fourth branch 534 of the oil flow circuit 518 then recombine to form a fifth branch 544.

[0064] Oil flowing through the second branch 526 of the oil flow circuit 518 enters the FCOC 504 through a fourth inlet 546 of the FCOC 504 and exits the FCOC 504 through a fourth outlet 548 of the FCOC 504. The oil enters the compound thermostatic valve 508 through a fifth inlet 550 of the compound thermostatic valve 508 and exits the compound thermostatic valve 508 through a fifth outlet 552 of the compound thermostatic valve 508. The second branch 526 and the fourth branch 534 combine into the fifth branch 544. Oil flowing through the fifth branch 544 returns to the oil supply 510.

[0065] In Figure 5 In the illustrated example, fuel enters the FCOC 504 through a sixth inlet 554 of the FCOC 504. As described above, the fuel receives thermal energy from the oil as the fuel flows through the FCOC 504. After flowing out of a sixth outlet 556 of the FCOC 504, the fuel is delivered to the FMU 514. The fuel enters the second conduit 520 of the fuel circuit 522 from the FMU 514. The fuel enters the compound thermostatic valve 508 through a seventh inlet 558 (not shown) of the compound thermostatic valve 508 and exits the compound thermostatic valve 508 through a seventh outlet 560 (not shown) of the compound thermostatic valve 508. The fuel is then provided to a downstream combustion element (not shown).

[0066] In Figure 5In this circuit, a thermostatic bypass valve 506 is fluidly connected to a first conduit 516, ACOC 502, FCOC 504, and oil supply 510. For example, the thermostatic bypass valve 506 may be positioned at a second outlet 538, a second inlet 536, and / or between the second outlet 538 and the second inlet 536. Therefore, the thermostatic bypass valve 506 controls the flow rate of oil through the third branch 532, and thus controls the flow rate of oil through ACOC 502. The thermostatic bypass valve 506 contacts the oil at a first temperature sensing point 562 in the oil flow circuit 518. The temperature of the oil at the first temperature sensing point 562 determines the position of the valve body of the thermostatic bypass valve 506. For example, a higher temperature may cause the valve body to change position, thereby allowing an increased rate of oil flowing through the third branch 532 of the oil flow circuit 518. Example: The first temperature sensing point 562 is located downstream of FCOC 504 and upstream of oil supply 510. In other examples, the first temperature sensing point 562 may be located in a different part of the oil flow loop 518, such as upstream of FCOC 504.

[0067] exist Figure 5 In this configuration, the first fluid path of the composite thermostatic valve 508 is fluidly connected to the first conduit 516, ACOC 502, and oil supply 510, and the second fluid path of the composite thermostatic valve 508 is fluidly connected to the first conduit 516, FCOC 504, and oil supply 510. For example, the first fluid path of the composite thermostatic valve 508 is fluidly connected between the third inlet 540 and the third outlet 542, and the second fluid path of the composite thermostatic valve 508 is fluidly connected between the fifth inlet 550 and the fifth outlet 552. Therefore, the composite thermostatic valve 508 controls the flow rate of oil flowing through the second branch 526 and the fourth branch 534. The third fluid path of the composite thermostatic valve 508 is fluidly connected to the second conduit 520, FCOC 504, fuel supply 512, and FMU 514. For example, the third fluid path of the composite thermostatic valve 508 is fluidly connected to the seventh inlet 558. Figure 5 (not shown in the image) and the seventh exit 560 ( Figure 5 (Not shown in the image). The compound thermostatic valve 508 contacts the fuel at a second temperature sensing point 564 in the fuel circuit 522. The temperature of the fuel at the second temperature sensing point 564 determines the position of the valve body of the compound thermostatic valve 508. For example, a higher temperature may cause the valve body to change position, thereby allowing an increased rate of oil flowing through the fourth branch 534 and a reduced amount of oil flowing through the second branch 526. Example: The second temperature sensing point 564 is located downstream of FCOC 504 and downstream of FMU 514. In other examples, the second temperature sensing point 564 may be located in different parts of the fuel circuit 522, such as upstream of FMU 514.

[0068] exist Figure 5In the illustrated example, the thermostatic bypass valve 506 and the compound thermostatic valve 508 are positioned downstream of the ACOC 502 and the FCOC 504. In other examples of the passive TMS 500, at least one of the thermostatic bypass valve 506 and the compound thermostatic valve 508 can be positioned upstream of the ACOC 502 and the FCOC 504.

[0069] Figure 5 The flow of oil in the passive TMS 500 is illustrated when the oil temperature at the first temperature sensing point 562 is between the first low temperature threshold and the first high temperature threshold and the temperature of the fuel at the second temperature sensing point 564 is between the second low temperature threshold and the second high temperature threshold. Accordingly, the thermostatic bypass valve 506 is in an intermediate position as indicated by the first metering window 568 and the compound thermostatic valve 508 is in an intermediate position as indicated by the second metering window 570 and the third metering window 572.

[0070] Figure 6 is a schematic representation of another alternative example passive thermal management system 600. The passive TMS 600 includes an ACOC 602, a FCOC 604, a thermostatic bypass valve 606, a compound thermostatic valve 608, an oil supply 610, a fuel supply 612, and a fuel system 614. In the passive TMS 600, the ACOC 602 and the FCOC 604 are in parallel, and the thermostatic bypass valve 606 is positioned in the fuel circuit, while the compound thermostatic valve is positioned in the oil circuit. By positioning the heat exchangers 602, 604 and the valves 606, 608 in this manner, the passive TMS 600 does not require a complex conduit arrangement while achieving a wider range of heat energy transfer between the oil and the fuel. For example, the amount of heat energy transfer is highest when the fuel is being delivered through the FCOC 604 at a high rate and the oil is being delivered through the FCOC 604 at a certain rate. On the other hand, the least amount of heat transfer occurs between the oil and the fuel when the fuel is being delivered primarily through the thermostatic bypass valve 606 and the oil is being delivered primarily through the ACOC 602.

[0071] The passive TMS 600 includes one or more first conduits 616 (e.g., tubes, pipes, etc.) to fluidly couple the ACOC 602, the FCOC 604, the compound thermostatic valve 608, and the oil supply 610. Accordingly, the first conduits 616 define an oil flow circuit 618, where the direction of the oil flow within the oil flow circuit 618 is designated by the arrows. The passive TMS 600 also includes one or more second conduits 620 to fluidly couple the FCOC 604, the thermostatic bypass valve 606, the fuel supply 612, and the fuel system 614. Accordingly, the second conduits 620 define a fuel flow circuit 622, where the direction of the fuel flow is designated by the arrows.

[0072] In Figure 6In the illustrated example, oil enters the oil flow loop 618 and is split into a first branch 624 of the oil flow loop 618 and a second branch 626 of the oil flow loop 618. Oil flowing through the first branch 624 of the oil flow loop 618 enters the ACOC 602 through a first inlet 628 of the ACOC 602. In examples of passive TMS that utilize fluids other than air, oil, and fuel, the ACOC 602 can instead be a different type of heat exchanger. After exiting a first outlet 630 of the ACOC 602, the oil enters the compound thermostatic valve 608 through a second inlet 632 of the compound thermostatic valve 608 and exits the compound thermostatic valve 608 through a second outlet 634 of the thermostatic bypass valve 606. Oil flowing through the second branch 626 of the oil flow loop 618 enters the FCOC 604 through a third inlet 636 of the FCOC 604 and exits the FCOC 604 through a third outlet 638 of the FCOC 604. The oil enters the compound thermostatic valve 608 through a fourth inlet 640 of the compound thermostatic valve 608 and exits the compound thermostatic valve 608 through a fourth outlet 642 of the compound thermostatic valve 608. The second branch 626 then merges with the first branch 624, and the oil flow loop 618 returns to the oil supply 610.

[0073] In Figure 6 In the illustrated example, fuel from the fuel supply 612 enters the second conduit 620 of the fuel flow loop 622. The fuel is split into a third branch 644 of the fuel flow loop 622 and a fourth branch 646 of the fuel flow loop 622. Fuel flowing through the third branch 644 enters the thermostatic bypass valve 606 through a fifth inlet 648 of the thermostatic bypass valve 606 and exits the thermostatic bypass valve 606 through a fifth outlet 650. Fuel flowing through the fourth branch 646 enters the FCOC 604 through a sixth inlet 652 of the FCOC 604 and exits the FCOC 604 through a sixth outlet 654. The third branch 644 and the fourth branch 646 merge, and the fuel continues into the fuel system 614.

[0074] In Figure 6In particular embodiments, the thermostatic bypass valve 606 is fluidly coupled to the second conduit 620, the FCOC 604, the fuel supply 612, and the fuel system 614. For example, the thermostatic bypass valve 606 can be positioned at the fifth outlet 650, at the fifth inlet 648, and / or between the fifth outlet 650 and the fifth inlet 648. Accordingly, the thermostatic bypass valve 606 controls the flow of fuel through the third branch 644, and thus the flow of fuel through the fourth branch 646 and the FCOC 604. The thermostatic bypass valve 606 is in contact with fuel at a first temperature sensing point 656 of the fuel circuit 622. The temperature of the fuel at the first temperature sensing point 656 determines the position of the valve body of the thermostatic bypass valve 606. For example, a higher temperature can cause the valve body to change position and allow an increased rate of fuel through the third branch 644 of the fuel circuit 622. The example first temperature sensing point 656 is located proximate to the fuel supply 612. In other examples, the first temperature sensing point 656 can be located in a different portion of the fuel circuit 622.

[0075] In particular embodiments, Figure 6 In particular embodiments, the first fluid path of the compound thermostatic valve 608 is fluidly coupled to the first conduit 616, the ACOC 602, the oil supply 610, and the second fluid path of the compound thermostatic valve 608 is fluidly coupled to the first conduit 616, the ACOC 602, the FCOC 604, and the oil supply 610. For example, the first fluid path of the compound thermostatic valve 608 is fluidly coupled between the second inlet 632 and the second outlet 634, and the second fluid path of the compound thermostatic valve 608 is fluidly coupled between the fourth inlet 640 and the fourth outlet 642. Accordingly, the compound thermostatic valve 608 controls the flow of oil through the first branch 624 and the second branch 626. The third fluid path of the compound thermostatic valve 608 is fluidly coupled to the first conduit 616, the ACOC 602, the FCOC 604, and the oil supply 610. The compound thermostatic valve 608 is in contact with oil at a second temperature sensing point 658 of the oil flow circuit 618. The temperature of the oil at the second temperature sensing point 658 determines the position of the valve body of the compound thermostatic valve 608. For example, a higher temperature can cause the valve body to change position, allowing an increased rate of oil through the first branch 624 of the oil flow circuit 618. The example second temperature sensing point 658 is located downstream of the ACOC 602 and the FCOC 604. In other examples, the second temperature sensing point 658 can be located in a different portion of the oil flow circuit 618, for example, upstream of the ACOC 602 and the FCOC 604.

[0076] Figure 6Oil flow in passive TMS 600 is shown when the temperature of the fuel at first temperature sensing point 656 is between the first low temperature threshold and the first high temperature threshold and the temperature of the oil at second temperature sensing point 658 is between the second low temperature threshold and the second high temperature threshold. Accordingly, thermostatic bypass valve 606 is in an intermediate position as shown by first metering window 660 and compound thermostatic valve 608 is in an intermediate position as shown by second metering window 662 and third metering window 664.

[0077] In some examples, Figures 3A-6 Passive TMS 300, 500, 600 of the kind

[0078] In some examples, Figures 3A-6 Passive TMS 300, 500, 600 of the kind

[0079] In some examples, Figures 3A-6 Passive TMS 300, 500, 600 of the kind

[0080] Figure 7 is a flowchart representing an example process 700 of passive thermal control with example thermal management system 300, 500, 600. Figure 7 Example process 700 of the kind begins at block 702, where passive TMS 300, 500, 600 delivers a first amount of a first fluid through a first heat exchanger at a first time. The first amount of the first fluid delivered through the heat exchanger is passively controlled by at least one thermostatic valve. For example, the first amount of the first fluid can be controlled by compound thermostatic valve 308, 508, 608 based on a temperature of a second fluid at the first time and / or thermostatic bypass valve 306, 506, 606 based on a temperature of the first fluid at the first time. In some examples, the first heat exchanger is ACOC 302, 502, 602.

[0081] At block 704, a second amount of the first fluid is delivered through a second heat exchanger. The second amount of the first fluid is passively controlled by at least one thermostatic valve. For example, the second amount of the first fluid can be controlled by compound thermostatic valve 308, 508, 608 based on a temperature of the second fluid at the first time. In some examples, the second heat exchanger is FCOC 304, 504, 604.

[0082] At block 706, the passive TMS 300, 500, 600, at a second time later than the first time, delivers a third amount of the first fluid through the first heat exchanger. In some examples, the third amount of the first fluid is different than the first amount of the first fluid. For example, if the temperature of the first fluid in contact with the thermostatic element of the thermostatic valve at the second time is a different temperature than at the first time, the size of the thermostatic element changes, causing the position of the valve to change. When the valve changes position, the amount of fluid allowed to pass through the valve, and thus the heat exchanger fluidly connected to the valve, increases or decreases.

[0083] At block 708, at a second time later than the first time, a fourth amount of the first fluid is delivered through the second heat exchanger. In some examples, the fourth amount of the first fluid is different than the second amount of the first fluid. For example, if the temperature of the second fluid at the second time is different than the temperature of the second fluid at the first time, the position of the valve will change, causing the second amount of fluid to increase or decrease. The process 700 then terminates.

[0084] From the foregoing, it will be appreciated that example systems, apparatus, articles of manufacture, and methods have been disclosed that passively control the temperature of a target fluid using multiple heat exchangers and multiple thermostatic valves. Accordingly, the examples disclosed herein eliminate problems that can otherwise arise from the need for an active control system, such as additional cost and space and weight requirements associated with an active control system. Moreover, the examples disclosed herein improve ACOC efficiency by increasing the temperature difference between air and oil at the ACOC. Furthermore, the examples disclosed herein improve the efficiency of a fuel-powered engine by maintaining the fuel at an optimal temperature.

[0085] Example passive thermal management systems and related methods are disclosed. Further aspects are provided by the subject matter of the following clauses:

[0086] A thermal management system comprising a first heat exchanger comprising a first path for a first fluid and a second path for a second fluid, the first heat exchanger for transferring thermal energy between the first fluid and the second fluid; a second heat exchanger comprising a third path for the first fluid and a fourth path for a third fluid, the second heat exchanger for transferring thermal energy between the first fluid and the third fluid, the second heat exchanger being in circuit with the first heat exchanger; a first thermostatic valve comprising a first thermostatic element that actuates the first thermostatic valve to control a first flow rate of the first fluid through the first heat exchanger based on a first temperature of the first fluid; and a second thermostatic valve comprising a second thermostatic element that actuates the second thermostatic valve to control a second flow rate of the first fluid through the second heat exchanger based on a second temperature of the third fluid.

[0087] The thermal management system of any of the preceding clauses, wherein the first heat exchanger and the second heat exchanger are arranged in parallel.

[0088] The thermal management system of any of the preceding clauses, wherein the first heat exchanger and the second heat exchanger are arranged in series.

[0089] The thermal management system of any of the preceding clauses, wherein the first heat exchanger is an air-cooled oil cooler, the second heat exchanger is a fuel-cooled oil cooler, the first fluid is oil, the second fluid is air, and the third fluid is fuel.

[0090] The thermal management system of any of the preceding clauses, wherein at least one of a size or a shape of the first thermostatic element changes in response to the first temperature of the first fluid at a first temperature sensing point, the first temperature sensing point being downstream of the second heat exchanger.

[0091] The thermal management system of any of the preceding clauses, wherein the first thermostatic element actuates the first thermostatic valve to a position near closed in response to the first temperature falling below a first low temperature threshold, and the first thermostatic element actuates the first thermostatic valve to an open position in response to the first temperature exceeding a first high temperature threshold.

[0092] The thermal management system of any of the preceding clauses, wherein at least one of a size or a shape of the second thermostatic element changes in response to the second temperature of the third fluid at a second temperature sensing point, the second temperature sensing point being downstream of a fuel management unit.

[0093] The thermal management system of any of the preceding clauses, wherein the second thermostatic valve comprises a first flow path and a second flow path, the second thermostatic element actuates the second thermostatic valve to nearly close the first flow path and open the second flow path in response to the second temperature falling below a second low temperature threshold, and the second thermostatic element actuates the second thermostatic valve to open the first flow path and nearly close the second flow path in response to the second temperature exceeding a second high temperature threshold.

[0094] The thermal management system of any of the preceding clauses, wherein the first and second thermostatic elements are wax pellets.

[0095] A thermal management system comprising an air-cooled oil cooler (ACOC); a fuel-cooled oil cooler (FCOC), wherein the FCOC is in circuit with the ACOC; a first thermostatic valve fluidically coupled to the ACOC to control a first oil flow through the ACOC based on a first temperature of oil; and a second thermostatic valve fluidically coupled to the FCOC to control a second oil flow through the FCOC based on a second temperature of fuel.

[0096] The thermal management system of any of the preceding clauses, wherein the ACOC and the FCOC are arranged in parallel.

[0097] The thermal management system of any of the preceding clauses, wherein the ACOC and the FCOC are arranged in series.

[0098] The thermal management system of any of the preceding clauses, wherein the second thermostatic valve is a compound thermostatic valve, a first oil way of the compound thermostatic valve is fluidically coupled to the ACOC, and a second oil way of the compound thermostatic valve is fluidically coupled to the FCOC.

[0099] The thermal management system of any of the preceding clauses, wherein the second thermostatic valve comprises a thermostatic element, at least one spring, and a valve body.

[0100] The thermal management system of any of the preceding clauses, wherein the first thermostatic valve is actuated by a first thermostatic element in contact with the oil, and the second thermostatic valve is actuated by a second thermostatic element in contact with the fuel.

[0101] The thermal management system of any of the preceding clauses, wherein the second thermostatic element is in contact with the fuel upstream of a fuel management unit.

[0102] The thermal management system of any of the preceding clauses, wherein, in response to the first temperature falling below a first low temperature threshold and the second temperature falling below a second low temperature threshold, the first and second thermostatic valves decrease the first oil flow through the ACOC and increase the second oil flow through the FCOC.

[0103] The thermal management system of any of the preceding clauses, wherein, in response to the first temperature exceeding a first high temperature threshold and the second temperature exceeding a second high temperature threshold, the first and second thermostatic valves increase the first oil flow through the ACOC and decrease the second oil flow through the FCOC.

[0104] A gas turbine engine comprising a compressor section, a combustion section, a turbine section, one or more components operably coupled with at least one of the compressor section, the combustion section, or the turbine section, and a thermal management system according to any of the preceding clauses.

[0105] A method comprising routing a first amount of a first fluid through a first heat exchanger; and routing a second amount of the first fluid through a second heat exchanger, the first and second amounts based on a first thermostatic valve actuated by a first thermostatic element and a second thermostatic valve actuated by a second thermostatic element.

[0106] The method of any of the preceding clauses, wherein at least one of a first size or a first shape of the first thermostatic element changes based on a first temperature of the first fluid, and at least one of a second size or a second shape of the second thermostatic element changes based on a second temperature of the second fluid.

[0107] The above examples of passive TMSs can be used in aircraft engines. While each of the above-disclosed examples of passive TMSs has certain features, it should be understood that particular features of one example passive TMS are not necessarily used only in conjunction with that passive TMS. Rather, any of the features described above and / or depicted in the drawings can be combined with any passive TMS, in addition to or in lieu of any other features of that passive TMS. That is, the features of one passive TMS are not mutually exclusive of the features of another passive TMS. Rather, the scope of the present disclosure includes any combination of any features.

[0108] The following claims are hereby incorporated into this detailed description by reference. While certain example systems, devices, articles, and methods have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all systems, devices, articles, and methods falling within the scope of the claims.

Claims

1. A thermal management system, characterized in that, include: A first heat exchanger includes a first path for a first fluid and a second path for a second fluid, the first heat exchanger being used to transfer heat energy between the first fluid and the second fluid; The second heat exchanger includes a third path for the first fluid and a fourth path for the third fluid, the second heat exchanger is used to transfer heat energy between the first fluid and the third fluid, and the second heat exchanger forms a loop with the first heat exchanger. A first thermostatic valve, the first thermostatic valve including a first thermostatic element, the first thermostatic element actuating the first thermostatic valve to control the first flow rate of the first fluid through the first heat exchanger based on a first temperature of the first fluid; and The second thermostatic valve includes a second thermostatic element that actuates the second thermostatic valve to control the second flow rate of the first fluid through the second heat exchanger based on the second temperature of the third fluid.

2. The thermal management system according to claim 1, characterized in that, in, The first heat exchanger and the second heat exchanger are arranged in parallel.

3. The thermal management system according to claim 1, characterized in that, in, The first heat exchanger and the second heat exchanger are arranged in series.

4. The thermal management system according to claim 1, characterized in that, in, The first heat exchanger is an air-cooled oil cooler, the second heat exchanger is a fuel-cooled oil cooler, the first fluid is oil, the second fluid is air, and the third fluid is fuel.

5. The thermal management system according to claim 1, characterized in that, in, At least one of the dimensions or shape of the first thermostatic element changes in response to the first temperature of the first fluid at a first temperature sensing point located downstream of the second heat exchanger.

6. The thermal management system according to claim 1, characterized in that, in, The first thermostatic element actuates the first thermostatic valve to a near-closed position in response to the first temperature dropping below a first low temperature threshold, and the first thermostatic element actuates the first thermostatic valve to an open position in response to the first temperature exceeding a first high temperature threshold.

7. The thermal management system according to claim 1, characterized in that, in, At least one of the dimensions or shape of the second thermostatic element changes in response to the second temperature at the second temperature sensing point, which is located downstream of the fuel management unit.

8. The thermal management system according to claim 1, characterized in that, in, The second thermostatic valve includes a first flow path and a second flow path. The second thermostatic element actuates the second thermostatic valve to almost close the first flow path and open the second flow path in response to the second temperature dropping below a second low temperature threshold. The second thermostatic element also actuates the second thermostatic valve to open the first flow path and almost close the second flow path in response to the second temperature exceeding a second high temperature threshold.

9. The thermal management system according to claim 1, characterized in that, in, The first and second thermostatic elements are wax pellets.

10. A thermal management system, characterized in that, include: Air-cooled oil cooler (ACOC); A fuel-cooled oil cooler (FCOC) is connected in a loop with the ACOC; A first thermostatic valve is fluidly connected to the ACOC to control the first oil flow rate through the ACOC based on a first oil temperature. and A second thermostatic valve is fluidly connected to the FCOC to control the second oil flow rate through the FCOC based on a second temperature of the fuel.

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