Patent Publication Number: US-11639818-B2

Title: Thermal management systems

Description:
CLAIM OF PRIORITY 
     This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 63/214,341, filed on Jun. 24, 2021, and entitled “THERMAL MANAGEMENT SYSTEMS,” the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Refrigeration systems absorb thermal energy from heat sources operating at temperatures below the temperature of the surrounding environment and discharge thermal energy into the surrounding environment. Heat sources operating at temperatures above the surrounding environment can be naturally cooled by the surrounding if there is direct contact between the source and the environment. 
     Conventional refrigeration systems include a compressor, a heat rejection exchanger (i.e., a condenser), a receiver, an expansion device, and a heat absorption exchanger (i.e., an evaporator). Such systems can be used to maintain operating temperature set points for a wide variety of cooled heat sources (loads, processes, equipment, systems) thermally interacting with the evaporator. Closed-circuit refrigeration systems may pump significant amounts of absorbed thermal energy from heat sources into the surrounding environment. 
     In closed-circuit systems, compressors are used to compress vapor from an evaporating pressure the evaporator and to a condensing pressure in the condensers and condense the compressed vapor converting the vapor into a liquid at a temperature higher than the surrounding environment temperature. The combination of condensers and compressors can add a significant amount of weight and can consume relatively large amounts of electrical power. In general, the larger the amount of absorbed thermal energy that the system is designed to handle, the heavier the refrigeration system and the larger the amount of power consumed during operation, even when cooling of a heat source occurs over relatively short time periods. 
     In some cases the surrounding environment temperature can appear below the heat source temperature. The refrigeration system provides a contact via refrigerant. There may be no need to compress vapor from the evaporating to condensing pressure since condensation can happen at a pressure slightly higher or even below the evaporating pressure. 
     SUMMARY 
     In an example implementation, a thermal management system includes a receiver configured to store a refrigerant fluid; a refrigeration system having a refrigerant fluid path that includes the receiver, and at least one evaporator disposed in the refrigerant fluid path. The refrigeration system is configured to receive the refrigerant fluid from the receiver through the refrigerant fluid path. The at least one evaporator is configured to receive the refrigerant fluid and to extract heat from at least one heat load having a specified thermal inertia that is in at least one of thermal conductive or convective contact with the at least one evaporator. 
     An aspect combinable with the example implementation further includes a hot vapor circuit disposed to bypass a portion of the refrigeration system. 
     In another aspect combinable with any of the previous aspects, the refrigerant fluid path further includes a compressor having a compressor inlet and a compressor outlet; a junction having an inlet coupled to the compressor outlet, and having first and second outlets; and a condenser having a condenser inlet coupled to the first outlet of the junction, and having a condenser outlet coupled to an inlet of the receiver, the condenser configured to condense a superheated vapor at the condenser inlet by removing heat from the condensed, superheated vapor, and is bypass-able by operation of the hot vapor circuit. 
     In another aspect combinable with any of the previous aspects, the hot vapor circuit includes a solenoid valve. 
     In another aspect combinable with any of the previous aspects, the hot vapor circuit includes a solenoid valve having an inlet and an outlet; a first junction; and a second junction, with the first junction and the second junction coupling the solenoid valve into the refrigeration system. 
     Another aspect combinable with any of the previous aspects further includes a suction accumulator having a suction accumulator inlet and a vapor-side outlet, the suction accumulator inlet coupled to an outlet of the at least one evaporator and the vapor-side outlet coupled to the compressor inlet. 
     Another aspect combinable with any of the previous aspects further includes a flow control device having an inlet coupled to an outlet of the receiver and having an outlet coupled to transport refrigerant fluid from the receiver outlet to an inlet of the at least one evaporator. 
     In another aspect combinable with any of the previous aspects, the flow control device is an expansion valve that causes an adiabatic flash evaporation of a part of refrigerant fluid received from the receiver. 
     In another aspect combinable with any of the previous aspects, the second junction has an outlet coupled to an inlet of the at least one evaporator, a first inlet coupled to the outlet of the expansion valve and a second inlet coupled to the outlet of the solenoid valve. 
     In another aspect combinable with any of the previous aspects, the second junction has an outlet coupled to the inlet of the expansion valve, a first inlet coupled to the outlet of the receiver and a second inlet coupled to the outlet of the solenoid valve. 
     In another aspect combinable with any of the previous aspects, the hot vapor circuit is configured to operate to supply heat to a heat load thermally coupled to or in proximity to the at least one evaporator. 
     In another aspect combinable with any of the previous aspects, the refrigeration system operates in one of three modes. 
     In another aspect combinable with any of the previous aspects, a first mode is a heating mode, a second mode is a cooling mode, and a third mode that is a combination of heating and cooling. 
     In another aspect combinable with any of the previous aspects, the refrigeration system further operates in a fourth mode that is a standby mode and a fifth mode that is a pump down mode. 
     In another aspect combinable with any of the previous aspects, the at least one evaporator is a first evaporator. 
     Another aspect combinable with any of the previous aspects further includes a suction accumulator having a suction accumulator inlet and a vapor-side outlet, the suction accumulator inlet coupled to an outlet of the first evaporator and the vapor-side outlet coupled to the compressor inlet; a first expansion valve having an inlet and an outlet, with the inlet coupled to the outlet of the solenoid valve; and at least one additional evaporator having an evaporator inlet and an evaporator outlet, with the evaporator inlet coupled to the outlet of the first expansion device and the evaporator outlet coupled to the inlet of the suction accumulator. 
     Another aspect combinable with any of the previous aspects further includes a plurality of expansion valves having inlets coupled to a receiver outlet and having outlets coupled to the inlets of the first evaporator and the at least one additional evaporator, with the plurality of expansion valves causing adiabatic flash evaporation of refrigerant fluid received from the receiver. 
     Another aspect combinable with any of the previous aspects further includes a liquid separator having an inlet, a liquid-side outlet, and a vapor-side outlet. 
     Another aspect combinable with any of the previous aspects further includes an ejector having an ejector inlet, a secondary inlet, and an ejector outlet. 
     Another aspect combinable with any of the previous aspects further includes an expansion valve coupled between an outlet of the receiver and the inlet of the ejector to control a flow of the refrigerant fluid from the receiver to the ejector and to cause an adiabatic flash evaporation of a part of the refrigerant fluid received from the receiver. 
     In another aspect combinable with any of the previous aspects, an inlet of the at least one evaporator is coupled to the liquid-side outlet and an outlet of the at least one evaporator is coupled to the secondary inlet of the ejector. 
     In another aspect combinable with any of the previous aspects, an inlet of the evaporator is coupled to the ejector outlet and an outlet of the at least one evaporator is coupled to the liquid-side outlet of the liquid separator. 
     Another aspect combinable with any of the previous aspects further includes a pump having a pump inlet and a pump outlet. 
     Another aspect combinable with any of the previous aspects further includes an expansion valve coupled between an outlet of the receiver and the inlet of the liquid separator to control a flow of the refrigerant fluid from the receiver to the liquid separator and to cause an adiabatic flash evaporation of a part of the refrigerant fluid received from the receiver. 
     In another aspect combinable with any of the previous aspects, the pump inlet is coupled to the liquid-side outlet and the pump outlet is coupled to an inlet of the at least one evaporator. 
     In another aspect combinable with any of the previous aspects, an inlet of the at least one evaporator is coupled to the pump outlet and an outlet of the at least one evaporator is coupled to the inlet of the liquid separator. 
     In another aspect combinable with any of the previous aspects, the junction is a first junction, the system further including second and third junctions to couple the evaporator inlet to the pump outlet and the evaporator outlet to the inlet of the liquid separator. 
     Another aspect combinable with any of the previous aspects further includes an expansion valve having an inlet coupled to an outlet of the receiver and having an outlet coupled to an inlet of the at least one evaporator to control a flow of the refrigerant fluid from the receiver to the at least one evaporator and to cause an adiabatic flash evaporation of a part of the refrigerant fluid received from the receiver. 
     In another aspect combinable with any of the previous aspects, the hot vapor circuit further includes a solenoid valve having an inlet coupled to the compressor outlet and having an outlet; and a second expansion valve having an inlet coupled to the outlet of the solenoid valve, and having an outlet coupled to the inlet of the at least one evaporator to control a flow of the refrigerant fluid from compressor outlet to the evaporator and to cause an adiabatic flash evaporation of a part of the refrigerant fluid received from the compressor outlet. 
     In another aspect combinable with any of the previous aspects, the pump inlet is coupled to the liquid-side outlet and the pump outlet is coupled to the evaporator inlet. 
     In another aspect combinable with any of the previous aspects, the evaporator inlet is further coupled to the pump outlet and an outlet of the evaporator is coupled to the inlet of the liquid separator. 
     In another aspect combinable with any of the previous aspects, the junction is a first junction, the system further including second, third, and fourth junctions to couple the evaporator inlet to the pump outlet. 
     In another aspect combinable with any of the previous aspects, the expansion valve is configured to control a vapor quality of the refrigerant fluid at an outlet of the at least one evaporator. 
     In another aspect combinable with any of the previous aspects, the vapor quality is in a range of 0.5 up to 1.0. 
     In another aspect combinable with any of the previous aspects, the vapor quality is in a range of 0.6 up to 0.95. 
     In another aspect combinable with any of the previous aspects, the vapor quality is in a range of 0.8 up to 0.85. 
     In another aspect combinable with any of the previous aspects, the refrigerant fluid is ammonia. 
     In another example implementation, a thermal management method includes transporting refrigerant fluid through a refrigeration system having a refrigerant fluid path with a receiver and at least one evaporator that is in at least one of thermal conductive or convective contact with at least one heat load having a specified thermal inertia; and removing heat from the at least one heat load with the refrigerant fluid transported to the at least one evaporator. 
     An aspect combinable with the example implementation further includes transporting at least a portion of the refrigerant fluid through a hot vapor circuit to add heat to the heat load with the evaporator. 
     In another aspect combinable with any of the previous aspects, transporting the portion is a first mode of operation, and the method further includes extracting the heat from the heat load in contact with the at least one evaporator during a second mode of operation. 
     Another aspect combinable with any of the previous aspects further includes controlling the refrigerant fluid received from the receiver to the at least one evaporator, with a flow control device that is disposed the refrigerant fluid path. 
     Another aspect combinable with any of the previous aspects further includes separating a saturated vapor fraction from a liquid fraction of the refrigerant fluid received from the at least one evaporator. 
     Another aspect combinable with any of the previous aspects further includes compressing a saturated vapor received from the liquid separator into a superheated vapor; condensing the superheated vapor into a refrigerant liquid by removing heat from the superheated vapor in the second mode; and delivering the refrigerant liquid to the receiver. 
     Another aspect combinable with any of the previous aspects further includes regulating operation between the first and second modes by controlling operation of a solenoid valve in the hot vapor circuit. 
     In another aspect combinable with any of the previous aspects, the refrigerant is ammonia. 
     One or more of the above aspects or another of the disclosed aspects may include one or more of the following advantages. 
     The aspects enable cooling of high heat loads that are also highly temperature sensitive, while avoiding the size and weight constraints of conventional closed-cycle refrigeration systems. The thermal management systems (TMS) described herein are closed-circuit refrigeration systems that are deliberately undersized for the cooling duty. Instead, the disclosed closed-circuit refrigeration systems are sized according to the thermal inertia of the evaporator, and operates intermittently with sufficient time for cool down, and still extracts excess heat energy from large, high heat flux temperature sensitive components to accurately match temperature set point ranges for the components during the intermittent periods of operation. 
     At the same time, the disclosed thermal management systems require less power than a conventional closed-circuitry system sized for the required amount of refrigeration over the specified period(s) of operation. The conventional refrigeration systems use closed-circuit refrigerant flow paths, the systems and methods disclosed herein use modified closed-circuit refrigerant flow paths to handle the high heat loads, and to maintain a temperature of a load within ranges of the temperature set points for the components. 
     Directed energy systems that are mounted to mobile vehicles, such as trucks or that exist in space may be ideal candidates for cooling by the thermal management system presented, as such systems may include high heat loads, and temperature sensitive components that require precise cooling within a range of a temperature set point during operation over a specified time interval. The thermal management systems disclosed herein, while generally applicable to the cooling of a wide variety of heat loads, are particularly well suited for operation with such directed energy systems. 
     The disclosed TMS avoids the need for a relatively large and heavy refrigeration system, in comparison to the disclosed TMS, with a concomitant need for a large and heavy power system to sustain operation of the refrigeration system). 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1 A  is a schematic diagram of example implementations of a thermal management system that includes a hot vapor circuit in a closed-circuit refrigeration system according to the present disclosure. 
         FIG.  1 B  is a schematic diagram of an example of a thermal management system (TMS) that includes an open-circuit refrigeration system (OCRS) according to the present disclosure. 
         FIGS.  2 - 6    are schematic diagrams of example implementations of a thermal management system that includes a hot vapor circuit in a closed-circuit refrigeration system according to the present disclosure. 
         FIGS.  7 A- 7 D  are schematic diagrams showing alternative configurations for arrangements of evaporators on the closed-circuit refrigeration system according to the present disclosure. 
         FIG.  8    is a block diagram of a control system or controller for a thermal management system according to the present disclosure. 
         FIG.  9    is a schematic diagram of an example of a thermal management system that includes a power generation apparatus according to the present disclosure. 
         FIG.  10    is a schematic diagram of an example of directed energy system that includes a thermal management system according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Cooling of large heat loads, e.g., high heat loads that are also highly temperature sensitive, can present a number of challenges. On the one hand, such loads generate significant quantities of heat that is extracted during cooling. In conventional closed-cycle refrigeration systems, cooling high heat loads typically involves circulating refrigerant fluid at a relatively high mass flow rate. However, closed-cycle system components that are used for refrigerant fluid circulation—including large compressors to compress vapor at a low pressure to vapor at a high pressure and condensers to remove heat from the compressed vapor at the high pressure and convert to a liquid—are typically heavy and consume significant power. As a result, many closed-cycle systems are not well suited for deployment in mobile platforms—such as on small vehicles or in space—where size and weight constraints may make the use of large compressors and condensers impractical. 
     In some examples, a thermal management system (TMS) cools very high heat loads that operate over very short intervals of time. In some cases, the thermal inertia of the high heat loads is high, the allowed operation temperature range is relatively large, having a low-end of operating temperature limit and a high-end of operating temperature. The interval of time over which the heat load temperature rises from the low end of the operation temperature range to the high end of the operating temperature range, with no external cooling medium other than heat load dissipation into an ambient, is significant, but still less than the required performance period. 
     Some temperature sensitive loads such as electronic components and devices may require temperature regulation within a defined range of operating temperatures. A vapor cycle system (VCS), i.e., a closed-circuit refrigeration system (CCRS), modified as disclosed herein, may be used to maintain temperature within the operation temperature range within the required performance period. 
     Directed energy systems that are mounted to mobile vehicles, such as trucks, or that exist in space may present many of the foregoing operating challenges, as such systems may include high heat flux and temperature sensitive components that require precise cooling during operation for a required performance period. The thermal management systems disclosed herein, while generally applicable to the cooling of a wide variety of heat loads, are particularly well suited for operation with such directed energy systems. 
     In particular, the thermal management systems and methods disclosed herein include a number of features that reduce both overall size and weight relative to conventional closed-circuit refrigeration systems, and still extract excess heat energy from high heat flux temperature sensitive components to accurately match temperature set point ranges for the components. 
     At the same time, the disclosed thermal management systems that use the compressor would in general require less power than conventional closed-circuitry systems for a given amount of refrigeration over a specified period(s) of operation. The condenser rejecting heat would be smaller and lighter. The fans moving air cooling the condenser would be smaller, lighter, and consume less power. Whereas certain conventional refrigeration systems used closed-circuit refrigerant flow paths, the systems and methods disclosed herein use modified closed-circuit refrigerant flow paths to handle a variety of heat loads. 
     In some aspects, “refrigeration” as used in the present disclosure can mean a system (or multiple systems fluidly coupled) that operates to generate a purposeful change of a characteristic of a coolant (e.g., a refrigerant fluid) to effectuate or increase heat transfer between two mediums (one of which can be the coolant). The purposeful change of the characteristic can be, for example, a change in pressure (e.g., depressurization) of a pressurized coolant though an expansion valve. In some embodiments, the change in pressure can include a phase change of the coolant, such as a liquid-to-gas phase change (e.g., endothermic vaporization). In some embodiments, pressurization of the refrigerant can be performed by a powered (e.g., electrically or otherwise) component, such as (but not limited to) a compressor. In some embodiments, pressurization can be performed as part of the refrigeration cycle (e.g., a closed-cycle refrigeration process in which gaseous refrigerant is substantially or completely recycled and compressed into a liquid state) or prior to use (e.g., storing pre-compressed liquid refrigerant for later use in an open-cycle refrigeration process in which a reserve of liquid refrigerant is used but substantially not recycled). In some embodiments, the phase change can be driven by heating a liquid refrigerant with a very low boiling point (e.g., ammonia as used in an absorption-type refrigeration cycle). 
     Referring to  FIG.  1 A , a thermal management system (TMS)  100  includes a closed-circuit refrigeration system (CCRS)  10 . TMS  100  provides closed-circuit refrigeration for one or more heat loads  118 , e.g., high heat loads over short-time intervals. The CCRS  10  includes a receiver  110  that includes an inlet  109  and an outlet  111  and stores a refrigerant fluid  1 . The outlet  111  is coupled to an inlet  113  of an optional solenoid valve  112  that also has an outlet  115 . The outlet  115  of the optional solenoid valve  112  is coupled to an inlet  117  of a flow control device  114  (also referred to as expansion valve  114 ) having an outlet  119 . The solenoid valve  112  can be used when the expansion valve  114  is used but is not able to completely stop refrigerant flow when the TMS  100  is in an OFF state. 
     Receiver  110 , as shown, can include an optional pressure relief valve. To charge receiver  110 , refrigerant fluid  1  is typically introduced into receiver  110  via the inlet  109 , and this can be done, for example, at service locations. In case of emergency, if the fluid pressure within receiver  110  exceeds a pressure limit value, a pressure relief valve opens to allow a portion of the refrigerant fluid to escape through the valve to reduce the fluid pressure within receiver  110 . Receiver  110  is typically implemented as an insulated vessel that stores refrigerant fluid  1  at relatively high pressure. Receiver  110  can also include insulation applied around the receiver to reduce thermal losses. In general, receiver  110  can have a variety of different shapes. In some embodiments, for example, the receiver  110  is cylindrical. Examples of other possible shapes include, but are not limited to, rectangular prismatic, cubic, and conical. In certain embodiments, receiver  110  can be oriented such that outlet  111  is positioned at the bottom of the receiver. In this manner, the liquid portion of the refrigerant fluid  1  within receiver  110  is discharged first through outlet  111 , prior to discharge of refrigerant vapor. In certain embodiments, the refrigerant fluid  1  can be an ammonia-based mixture that includes ammonia and one or more other substances. For example, mixtures can include one or more additives that facilitate ammonia absorption or ammonia burning. 
     The CCRS  10  also includes an evaporator  116  (with detailed configurations shown in  FIGS.  7 A- 7 D ) having an inlet  121  and an outlet  123 . The inlet  121  of the evaporator  116  is coupled to an outlet of a junction  142  and the outlet  123  of the evaporator  116  is coupled to an inlet  125  of a liquid separator  124 . The liquid separator  124  also has a vapor-side outlet  127 . The evaporator  116  is in thermal conductive and/or convective contact or in proximity to a high heat load  118 . 
     Evaporator  116  can be implemented in a variety of ways. In general, evaporator  116  functions as a heat exchanger, providing thermal contact (conductive, convective, or both) between the refrigerant fluid  1  and high heat load  118 . Typically, evaporator  116  includes one or more flow channels extending internally between inlet  121  and outlet  123  of the evaporator  116 , allowing refrigerant fluid  1  to flow through the evaporator  116  and absorb heat from heat load(s)  118 . A variety of different evaporators can be used in TMS  100 . In general, any cold plate may function as the evaporator  116  of the closed-circuit refrigeration systems disclosed herein. Evaporator  116  can accommodate any refrigerant fluid channels (including mini/micro-channel tubes), blocks of printed circuit heat exchanging structures, or more generally, any heat exchanging structures that are used to transport single-phase or two-phase fluids. The evaporator  116  and/or components thereof, such as fluid transport channels, can be attached to the heat load(s)  118  mechanically, or can be welded, brazed, or bonded to the heat load in any manner. In some embodiments, evaporator  116  (or certain components thereof) can be fabricated as part of heat load(s)  118  or otherwise integrated into one or more of the heat load(s)  118 , in which high heat load  118  can have one or more integrated refrigerant fluid channels. The portion of high heat load  118  with the refrigerant fluid channel(s) effectively functions as the evaporator  116  for the CCRS  10 . 
     In this example, and with reference to  FIG.  7 A  as well, the evaporator  116  can act with thermal contact (e.g., conductive and/or convective) to cool a large heat load, such as the heat load  118  that acts or is applied in relatively short time periods. More specifically, heat load  118  can have a relatively high thermal inertia, but the allowed temperature range in which the heat load  118  can operate (e.g., for normal or proper operation) is also large. In some aspects, a time period in which the temperature of heat load  118  rises from a low end of the operation temperature band to its high end with no cooling, is significant, but still less than a required performance period. Generally, the thermal inertia of the heat load  118 , or more specifically, the combination of the evaporator  116  in thermal contact with the heat load  118 , is the rate at which a temperature of this package (evaporator plus heat load) reaches that of its surrounding environment. In other words, the thermal inertia of the package is its capacity to store heat and to delay its transmission. The package that has a high thermal inertia, therefore, will take a longer time to reach the temperature of the surrounding environment, absent additional heating or cooling. 
     The interval of time over which the temperature of heat load  118  rises from the low end of the operation temperature range to the high end of the operating temperature range, with no external cooling medium other than heat load dissipation into an ambient, is significant, but still less than a required performance period. In example aspects according to the present disclosure (which can include open- or closed-circuit refrigeration systems or a combination thereof), the evaporator  116  (and other components of the systems such as compressors, condensers, receivers, valves, or otherwise) can be sized according to the thermal inertia of the package (evaporator  116  and heat load  118 ), and operate intermittently with sufficient time for cool down, and still extracts excess heat energy from the heat load  118  (which can be a high temperature or high heat flux load as well). 
     In this example, liquid separator  124  includes inlet  125 , vapor side outlet  127 , and liquid side outlet  137 , as well as vapor section  144  and liquid section  146 . Other examples of TMS according to the present disclosure may have a suction accumulator  124  (with inlet  125  and vapor side outlet  127  but no liquid side outlet  137 ) in place of a liquid separator. As a liquid separator  124 , this component can be a coalescing liquid separator or a flash drum, for example. Other conventional details such as membranes, coalescing filters, or meshes, etc. are not shown. 
     The CCRS  10  also includes a compressor  104  having an inlet  101  coupled to the vapor-side outlet  127  of the suction accumulator  124 , and also an outlet  103  that is coupled to an inlet  105  of a condenser  106 . The condenser  106  has an outlet  107  that is coupled to the receiver inlet  109 . A fan  108  (or pump  108 ) is positioned to circulate a cooling airflow  126  (or cooling water flow  126 ) across the condenser  106  to condense the refrigerant fluid  1  from the compressor  104 . The aforementioned components are coupled via conduit (not referenced). 
     As used herein the compressor  104  is, in general, a device that increases the pressure of a gas by reducing the gas&#39; volume. Usually, the term compressor refers to devices operating at and above ambient pressure, (some refrigerant compressors may operate inducing refrigerant at pressures below ambient pressure, e.g., desalination vapor compression systems employ compressors with suction and discharge pressures below ambient pressure). 
     In general, the solenoid valves  112 - 128  include a solenoid that uses an electric current to generate a magnetic field to control a mechanism that regulates an opening in a valve to control fluid flow. In some aspects, such valves  112  and  128  (and expansion valve  114  etc.) can act as flow control devices configurable to stop refrigerant flow as an on/off valve. 
     Expansion valve  114  functions as a flow control device and in particular as a refrigerant expansion valve device. In general, expansion valve  114  can be implemented as any one or more of a variety of different mechanical and/or electronic devices. For example, in some embodiments, expansion valve  114  can be implemented as a fixed orifice, a capillary tube, and/or a mechanical or electronic expansion valve. In general, fixed orifices and capillary tubes are passive flow restriction elements which do not actively regulate refrigerant fluid flow. 
     Mechanical expansion valves (usually called thermostatic or thermal expansion valves) are typically flow control devices that enthalpically expand a refrigerant fluid from a first pressure to an evaporating pressure, controlling the superheat at the evaporator exit. Mechanical expansion valves generally include an orifice, a moving seat that changes the cross-sectional area of the orifice and the refrigerant fluid volume and mass flow rates, a diaphragm moving the seat, and a bulb at the evaporator exit. The bulb is charged with a fluid and it hermetically fluidly communicates with a chamber above the diaphragm. The bulb senses the refrigerant fluid temperature at the evaporator exit (or another location) and the pressure of the fluid inside the bulb transfers the pressure in the bulb through the chamber to the diaphragm and moves the diaphragm and the seat to close or to open the orifice. 
     Typical electrically controlled expansion valves include an orifice, a moving seat, a motor or actuator that changes the position of the seat with respect to the orifice, a controller, and pressure and temperature sensors at the evaporator exit. 
     Examples of suitable commercially available expansion valves that can function as expansion valve  114  include, but are not limited to, thermostatic expansion valves available from the Sporlan Division of Parker Hannifin Corporation (Washington, Mo.) and from Danfoss (Syddanmark, Denmark). 
     The control system  999  calculates the superheat for the expanded refrigerant fluid based on pressure and temperature measurements at the evaporator exit. If the superheat is above a set-point value, the seat moves to increase the cross-sectional area and the refrigerant fluid volume and mass flow rates to match the superheat set-point value. If the superheat is below the set-point value the seat moves to decrease the cross-sectional area and the refrigerant fluid flow rates. The control system  999  may be configured to control vapor quality at the evaporator exit as disclosed below. 
     The CCRS  10  can also optionally include a hot vapor circuit  12  including a solenoid valve  128  having an inlet  129  and an outlet  131 , an expansion valve  130  having an inlet  133  and an outlet  135 , a junction  140 , and the junction  142 . The solenoid valve inlet  128  and the expansion valve  130  are coupled to a first outlet of the junction  140  and an inlet of the junction  142 . Junction  140  has an inlet coupled to the compressor outlet  103  and a second outlet coupled to the inlet  105  of the condenser  106 . The junction  142  has a second inlet coupled to the outlet  131  of the solenoid valve  128  (or expansion valve  130  if used) and has the outlet coupled to the inlet  121  of the evaporator  116 . The solenoid valve  128 , expansion valve  130 , and junctions  140 ,  142  couple the hot vapor circuit  12  to the evaporator inlet  121  and outlet  119  of expansion valve  114 . 
     In this example implementation, the TMS  100  can optionally include bypass  138  that fluidly couples the outlet  131  of solenoid valve  128  to the inlet  117  of the expansion valve  114  (and thus the inlet  121  of the evaporator through junction  142  while eliminating optional expansion valve  130 ). As explained in more detail herein, in this optional configuration of the CCRS  10 , hot vapor is diverted to the expansion valve  114  that enthalpically expands the high pressure sub-cooled liquid refrigerant and the hot vapor into liquid-vapor mixture at a low pressure and temperature. 
     As further shown in  FIG.  1 A , TMS  100  can also optionally include an oil circuit that includes conduit  132  fluidly coupled to liquid outlet  137  of the liquid separator  124 . In configurations that do not include the conduit  132  and oil circuit, the liquid separator  124  can be implemented as a suction accumulator  124  with inlet  125  and vapor outlet  127  (but no liquid outlet  137 ). Oil is used for lubrication of the compressor  104  and the oil travels with the refrigerant fluid  1  in the CCRS  10 . The oil is removed from the refrigerant fluid  1  at the liquid-side outlet  137  of the liquid separator  124 , and is recirculated back to the compressor inlet  101 , via a metering orifice  134  and a solenoid valve  136  (both optional as with the oil circuit). The oil also can be removed from the inlet  125  of the suction accumulator  124  or elsewhere within the CCRS  10 . In addition, the CCRS  10  may include an oil separator (OS). The oil separator (OS) is disposed in an oil return path (denoted by dashed line). 
     In an example implementation of the TMS  100  (e.g., that does not include optional bypass  138  or the aforementioned oil circuit), the CCRS  10  can operates in the following modes: Standby (thermolyze the evaporator  116  and heat loads  118  via heating or cooling); Cooling mode (heat load  118  on); Cooling mode (heat load  118  off); and Optional pump-down cycle. 
     In an example Standby operation, the CCRS  10  maintains the heat load  118  at a temperature corresponding to the low end of the allowed operating temperature range. If ambient temperature is higher than the low end of the allowed operating temperature range, the CCRS  10  cools the evaporator  116  and attached heat load(s)  118  bringing its temperature down to the low end of the allowed operating temperature range. When the ambient temperature (e.g., of airflow  126 ) is lower than the low end of the allowed operating temperature range and the hot vapor circuit  12  is available, the hot vapor circuit  12  provides hot vapor that heats the evaporator  116  and attached heat loads  118 , bringing them up to the low end of the allowed operating temperature range. 
     In an example thermolyzing-cooling operation, if ambient temperature is higher than the low end of the allowed operating temperature range for the high heat load  118 , the CCRS  10  operates in a cooling mode. In the cooling mode, the solenoid valve  112  is open and the solenoid valve  128  is closed. When the ambient temperature is higher than the low end of the allowed temperature range for the high heat load  118 , the TMS  100  is configured to have the CCRS  10  provide refrigeration to the high heat load  118 . In this instance, a control system  999  produces signals to cause the solenoid valve  112  to open and solenoid valve  128  to close. 
     Circulating refrigerant enters the compressor  104  as a saturated or superheated vapor and is compressed to a higher pressure at a higher temperature (a superheated vapor). This superheated vapor is at a temperature and pressure at which it can be condensed in the condenser  106  by either cooling water  126  or cooling air  126  flowing across a coil or tubes in the condenser  106 . At the condenser  106 , the circulating refrigerant loses heat and thus removes heat from the system, which removed heat is carried away by either the water or air (whichever may be the case) flowing over the coil or tubes, providing a condensed, sub-cooled liquid refrigerant. 
     The condensed, sub-cooled liquid refrigerant is routed into the receiver  110 , exits the receiver  110 , and enters the solenoid valve  112  and the expansion valve  114 . The condensed, sub-cooled liquid refrigerant is enthalpically expanded in the expansion valve  114  and turns into a two-phase refrigerant mixture of a liquid-vapor at a low pressure and temperature. The temperature of the two-phase refrigerant mixture (evaporating temperature) is lower than the temperature of the high heat load  118 . The two-phase refrigerant mixture is routed through the evaporator  116 . 
     The heat from the high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , partially or completely evaporates the liquid portion of the two-phase refrigerant mixture, according to desired vapor quality, and may superheat the two-phase refrigerant mixture. The refrigerant leaves the evaporator  116  and enters the suction accumulator  124 , as a saturated or superheated vapor. The saturated or superheated vapor exits the suction accumulator  124  and enters the compressor  104  to complete the refrigeration cycle. The evaporator  116  is where the circulating refrigerant absorbs and removes heat from the high heat load  118 , which heat is subsequently rejected in the condenser  106  and transferred to an ambient by water or air used in the condenser  106 . 
     In an example thermolyzing-heating operation, if ambient temperature is lower than the low end of the allowed operating temperature band, the CCRS  10  operates in a heating mode. In the heating mode, the solenoid valve  112  is closed and the solenoid valve  128  is open. When the ambient temperature is lower than the low end of the allowed temperature range for the high heat load  118 , the TMS  100  is configured to have the CCRS  10  provide heat to the high heat load  118 . In this instance, the control system  999  produces signals to cause the solenoid valve  112  to be closed and solenoid valve  128  to be open. 
     Circulating refrigerant enters the compressor  104  as a saturated or superheated vapor and is compressed to a higher pressure at a higher temperature (a superheated vapor). A first portion of the superheated vapor is at a temperature and pressure at which it can be condensed in the condenser  106  by either cooling water  126  or cooling air  126  flowing across a coil or tubes in the condenser  106 . At the condenser  106 , the first portion of the circulating refrigerant loses heat and thus removes heat from the CCRS  10 , which removed heat is carried away by either the water or air (whichever may be the case) flowing over the coil or tubes, providing a condensed liquid refrigerant. The condensed and sub-cooled first portion is now in a liquid refrigerant phase and is routed into the receiver  110 , but does not exit the receiver  110 , while the solenoid valve  112  is closed. 
     However, with the solenoid valve  128  open, a second portion, the superheated vapor, the hot vapor portion is expanded at a constant enthalpy in the expansion valve  130  and enters the evaporator  116  where it heats the high heat load  118 . The gas is cooled in the expansion valve  130  but remains hot. The high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , is heated by the second portion of the superheated vapor. The refrigerant leaves the evaporator  116  and enters the suction accumulator  124 . The superheated (or in ideal case saturated) vapor passes through the suction accumulator  124  and enters the compressor  104 . In this mode, the evaporator  116  is where the circulating refrigerant adds heat to the high heat load  118 . To complete the refrigeration cycle, the refrigerant vapor from the evaporator  116  exits the suction accumulator  124  at the vapor-side outlet  127  entering the compressor  104 . 
     In some cases to avoid entering too hot vapor into the compressor  104 , the solenoid valve  112  may open and the expansion valve  114  will cool the hot vapor to maintain the temperature of superheated vapor within the allowed range. Cold ambient temperature may cause significant reduction of the condensation temperature and discharge pressure. In this case a head pressure control is engaged to prevent discharge pressure reduction below the limit. In the previous inventions we described different methods. 
     In an example cooling mode-heat load ON operation, according to the present disclosure, the evaporator  116  and the high heat load  118  have natural high thermal inertia, which allows under the highest load, the temperature rise from the low end to the high end of the allowed temperature range in a certain, relatively short, period. The CCRS  10  is configured to enable the temperature rise in the given period which is longer than the thermal inertia can provide. To do that the CCRS  10  may be sized for a cooling capacity which is smaller than the power input of the heat load  118  and have a smaller dimensions and weight. 
     After the thermolyzing in cooling mode, in standby mode, the evaporator  116  and the heat load  118  are at the low end of the end of the allowed temperature range. When the heat load  118  is ON, the CCRS  10  is ON. When the evaporator  116  and the heat load  118  hit at the high end of the allowed temperature range, the heat load  118  is switched to an OFF state. 
     In an example cooling mode-heat load OFF operation, the CCRS  10  continues to operate until the evaporator  116  and the heat load  118  hit at the low end of the allowed temperature range. In order to prevent quick reduction of the suction pressure during pump-down cycle, the solenoid valve  128  may be opened to provide hot vapor bypass suction pressure control. 
     In an example pump-down operation, a pump-down cycle may be used to return liquid refrigerant that accumulates in the suction accumulator  124  back to the receiver  110 . In order to prevent quick reduction of the suction pressure during pump-down cycle, the solenoid valve  128  may be opened to provide hot vapor bypass suction pressure control. If the expansion valve  114  is configured to operate at a superheat, then the suction accumulator  124  and the pump-down cycle may not be needed. 
     If bypass  138  is implemented (and expansion valve  130  is eliminated), then an alternative hot vapor circuit can be used. In such a modified configuration, the CCRS  10  can also operate in the following modes: Standby (thermolyze the evaporator  116  and heat loads  118  via heating or cooling); Cooling mode (heat load  118  on); Cooling mode (heat load  118  off); and Optional pump-down cycle. In the Standby operation, the CCRS  10  maintains the high heat load  118  at a temperature corresponding to the low end of the allowed operating temperature range. 
     In a thermolyzing-cooling operation, the CCRS  10  operates as previously described. However, in a thermolyzing-heating operation, the CCRS  10  does not utilize the expansion valve  130 , which has been eliminated. Thus, with the solenoid valve  128  open, a second portion of the hot superheated vapor is diverted to the inlet  117  of the expansion valve  114 . The superheated hot vapor enters the expansion valve  114 . At the outlet  119  of the expansion valve  114 , the expanded refrigerant at the elevated temperature is coupled to the inlet  121  of the evaporator  116 . The high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , is heated by the expanded refrigerant at the elevated temperature, i.e., provided by the second portion of the superheated vapor. The refrigerant leaves the evaporator  116  and enters the suction accumulator  26 . The saturated or superheated vapor exits the suction accumulator  124  and enters the compressor  104 . In this mode, the evaporator  116  is where the circulating refrigerant adds heat to the high heat load  118 . To complete the refrigeration cycle, the refrigerant vapor from the evaporator  116  exits the suction accumulator  124  at the vapor-side outlet  127  and enters the compressor  104 . In the cooling mode (heat load ON or heat load OFF) operation and optional pump down operation, the CCRS  10  with bypass  138  operates as previously described. 
     As shown in  FIG.  1 A , the TMS  100 , as all disclosed embodiments, also includes the control system (or controller)  999  (see  FIG.  8    for an exemplary embodiment) that produces control signals (based on sensed thermodynamic properties) to control operation of one or more of the various devices, e.g., optional solenoid control valve  112 , expansion valve  114 , etc., as needed, as well as to control operation of a motor of the compressor  104 , a fan  108 , or other components in other example implementations of a TMS. Control system  999  may receive signals, process received signals and send signals (as appropriate) from/to the sensors and control devices to operate the TMS  100 . 
     The term “control system,” as used herein, can refer to an overall system that provides control signals and receives feedback data from unit controllers, such as unit controllers (e.g., programmable logic controllers, motor controllers, variable frequency drives, actuators). In some aspects, the control system includes the overall system and the unit controllers. In some aspects, a control system simply refers to as a single unit controller or a network of two or more individual unit controllers that communicate directly with each other (rather than with an overall system. 
     The process streams (e.g., refrigerant flows, ambient airflows, other heat exchange fluid flows) in a TMS according to the present disclosure, as well as process streams within any downstream processes with which the TMS is fluidly coupled, can be flowed using one or more flow control systems (e.g., that include the control system  999 ) implemented throughout the system. A flow control system can include one or more flow pumps, fans, blowers, or solids conveyors to move the process streams, one or more flow pipes through which the process streams are flowed and one or more valves to regulate the flow of streams through the pipes, whether shown in the exemplary figures or not. Each of the configurations described herein can include at least one variable frequency drive (VFD) coupled to a respective pump or fan that is capable of controlling at least one fluid flow rate. In some implementations, liquid flow rates are controlled by at least one flow control valve. 
     In some embodiments, a flow control system can be operated manually. For example, an operator can set a flow rate for each pump or transfer device and set valve open or close positions to regulate the flow of the process streams through the pipes in the flow control system. Once the operator has set the flow rates and the valve open or close positions for all flow control systems distributed across the system, the flow control system can flow the streams under constant flow conditions, for example, constant volumetric rate or other flow conditions. To change the flow conditions, the operator can manually operate the flow control system, for example, by changing the pump flow rate or the valve open or close position. 
     In some embodiments, a flow control system can be operated automatically. For example, the flow control system can be connected to a computer or control system (e.g., control system  999 ) to operate the flow control system. The control system can include a computer-readable medium storing instructions (such as flow control instructions and other instructions) executable by one or more processors to perform operations (such as flow control operations). An operator can set the flow rates and the valve open or close positions for all flow control systems distributed across the facility using the control system. In such embodiments, the operator can manually change the flow conditions by providing inputs through the control system. Also, in such embodiments, the control system can automatically (that is, without manual intervention) control one or more of the flow control systems, for example, using feedback systems connected to the control system. For example, a sensor (such as a pressure sensor, temperature sensor or other sensor) can be connected to a pipe through which a fluid flows. The sensor can monitor and provide a flow condition (such as a pressure, temperature, or other flow condition) of the process stream to the control system. In response to the flow condition exceeding a threshold (such as a threshold pressure value, a threshold temperature value, or other threshold value), the control system can automatically perform operations. For example, if the pressure or temperature in the pipe exceeds the threshold pressure value or the threshold temperature value, respectively, the control system can provide a signal to the pump to decrease a flow rate, a signal to open a valve to relieve the pressure, a signal to shut down process stream flow, or other signals. 
     Referring now to  FIG.  1 B , a thermal management system (TMS)  120  includes an open circuit refrigeration system (OCRS)  5  that utilizes one or more evaporators  116  to cool one or more heat loads  118 . The OCRS  5  includes receiver  110  having receiver inlet  109  and receiver outlet  111  and storing refrigerant fluid  1 , the optional solenoid valve  112  having inlet  113  and outlet  115 , the flow control device  114  (e.g., the expansion valve  114 ), the evaporator  116  having inlet  121  and outlet  123 , and a solenoid valve  16  having an inlet  17  and an outlet  19 . The aforementioned components of OCRS  5  are interconnected by one or more conduit sections to form an open circuit refrigerant fluid path. An optional flow control device  12  having inlet  13  and outlet  15  and optional check valve  14  are positioned along the gas flow path between the optional gas receiver  8  and the receiver  110 . 
     In this example, one or more heat loads  118  can be considered high heat loads (e.g., with a high thermal inertia in combination with the evaporator  116 ) that are in thermal conductive and/or convective contact or in proximity with the evaporator  116 . OCRS  5  optionally includes gas receiver  8  with the outlet  11  fluidly coupled to the inlet  109  of the receiver  110  via conduit, such that a gas flow path extends between the gas receiver  8  and the receiver  110  (that stores the refrigerant fluid  1 ). The optional flow control device  12  having inlet  13  and outlet  15 , as well as the optional check valve  14  are positioned along the gas flow path between the optional gas receiver  8  and the receiver  110 . 
     During operation of OCRS  5 , cooling can be initiated by a variety of different mechanisms. In some embodiments, for example, OCRS  5  includes a temperature sensor attached to heat load  22  (as will be discussed subsequently) or to certain of heat loads  118 . When the temperature of heat load  22  exceeds a certain temperature set point (i.e., threshold value), a control system  999  (described in additional detail below) connected to the temperature sensor can initiate cooling of heat load  22 . Alternatively, in certain embodiments, OCRS  5  operates essentially continuously—provided that the pressure within receiver  110  is sufficient—to cool heat loads  118 . As soon as receiver  110  is charged with refrigerant fluid, refrigerant fluid is ready to be directed into evaporator  116  to cool heat loads  118 . In general, cooling is initiated when a user of the system or the heat load issues a cooling demand. 
     The TMS  120  can also include the control system (or controller)  999  that produces control signals (based on sensed thermodynamic properties) to control operation of one or more of the various devices, e.g., optional solenoid control valve  112 , expansion valve  114 , etc., in other example implementations of a TMS. Control system  999  may receive signals, process received signals and send signals (as appropriate) from/to the sensors and control devices to operate the TMS  120 . 
     Referring to  FIG.  2   , a thermal management system (TMS)  200  includes a closed-circuit refrigeration system (CCRS)  20 . TMS  200  provides closed-circuit refrigeration for one or more heat loads  118 , e.g., high heat loads over short-time intervals, with multiple evaporators  116  in a parallel arrangement. Components shown in the TMS  200  that are also included in TMS  100  generally have the same structure and function as described with reference to  FIG.  1 A . In some aspects, although not shown, the oil circuit from  FIG.  1 A  can be implemented in  FIG.  2    as well (with a liquid separator  124  instead of suction accumulator). 
     As shown in  FIG.  2   , expansion valve  130  is fluidly coupled (at outlet  135 ) to inlets  121  of multiple (three shown, but two or more contemplated by the present disclosure) evaporators  116  (located downstream of the connection of outlet  135 ). As such, the outlet  135  is fluidly coupled to outlets  119  of multiple (three shown, but two or more contemplated by the present disclosure) expansion valves  114  (located upstream of the connection of outlet  135 ). In some aspects, TMS  200  can include a 1:1 ratio of expansion valves  114  to evaporators  116  (e.g., five evaporators  116  will have a corresponding one of five expansion valves  114 ). In some aspects, the CCRS  20  may be configured to have one expansion valve  114  for multiple evaporators  116  (rather than a 1:1 ratio) and use a conventional refrigerant distributor downstream of the single expansion valve  114  to the multiple evaporators  116 . Each of the evaporators  116  may also have an individual suction accumulator  124  (rather than the single, manifolded suction accumulator  124  connected to outlets  123  by junction  148 ). 
     As shown in  FIG.  2   , TMS  200  can also include optional bypass  138 —in such a modified configuration, TMS  200  would not include expansion valve  130 . Thus, in such a modified configuration, the outlet  131  of solenoid valve  128  would be fluidly coupled to inlets  117  of expansion valves  114  through junction  142 . 
     Without optional bypass  138 , the CCRS  20  can also operate in the following modes: Standby (thermolyze the evaporator  116  and heat loads  118  via heating or cooling); Cooling mode (heat load  118  on); Cooling mode (heat load  118  off); and Optional pump-down cycle, similar to that discussed in  FIG.  1 A  (without optional bypass  138 ), except that now three (or more) evaporators  116  are provided, each of which could be independently controlled. 
     With optional bypass  138  (and without expansion valve  130 ), the CCRS  20  can also operate in the following modes: Standby (thermolyze the evaporator  116  and heat loads  118  via heating or cooling); Cooling mode (heat load  118  on); Cooling mode (heat load  118  off); and Optional pump-down cycle. In this optional configuration, operation of CCRS  20  is similar to that discussed in  FIG.  1 A  (with optional bypass  138 ), except that now three (or more) evaporators  116  are provided, each of which could be independently controlled. 
     Referring to  FIG.  3   , a thermal management system (TMS)  300  includes a closed-circuit refrigeration system (CCRS)  30 . TMS  200  provides closed-circuit refrigeration for one or more heat loads  118 , e.g., high heat loads over short-time intervals, with an ejector assist circuit  302 . Thus, in  FIG.  3   , an ejector  304  is used with a liquid separator  124  (in place of a suction accumulator). 
     Components shown in the TMS  300  that are also included in TMS  100  and/or TMS  200  generally have the same structure and function as described with reference to  FIG.  1 A  and/or  FIG.  2   . In some aspects, although not shown, the oil circuit from  FIG.  1 A  can be implemented in  FIG.  3    as well. 
     The ejector assist circuit  302  includes the ejector  304 , one or more evaporators  116 , and the liquid separator  124 . The ejector  304  includes a primary (motive) inlet  301 , a secondary (suction) inlet  303 , and an outlet  305 . The optional solenoid valve  112  feeds refrigerant liquid from the receiver outlet  115  into the inlet  117  of the expansion valve  114 . The outlet  119  of the expansion valve  114  is coupled to three-port junction  142  that has two inlets. One inlet is coupled to the outlet  119  of the expansion valve  114  and the other inlet is coupled to the outlet  131  of the solenoid valve  128 . The outlet of the junction  142  is coupled to the primary inlet  301  of the ejector  304 , feeding the expanded refrigerant into the ejector  304 . The outlet  305  of the ejector  304  is coupled to the inlet  125  of the liquid separator  124 . The liquid separator  124  also includes a vapor-side outlet  127  and a liquid-side outlet  137 . 
     In this example configuration, the evaporator  116  has the outlet  123  fluidly coupled to the secondary inlet  303  (low-pressure inlet) of the ejector  304  and the evaporator  116  has the inlet  121  fluidly coupled to the liquid-side outlet  137  of the liquid separator  124 . In this configuration, the ejector  304  acts as a “pump,” to “pump” a secondary fluid flow, e.g., liquid/vapor from at the outlet of the evaporator  116  using energy of a primary refrigerant flow at the primary inlet  301  of the ejector, e.g., originating from the refrigerant flow from the receiver  110 . 
     In a modified configuration of the ejector assist circuit  302 , the evaporator  116  has the outlet  123  fluidly coupled to the inlet  125  of the liquid separator, and the inlet  121  fluidly coupled to the outlet  305  of the ejector  304 . The liquid outlet  137  of the liquid separator  124  would be fluidly coupled to secondary inlet  303  of the ejector  304 . In this configuration, the ejector  304  still acts as a “pump,” to “pump” a secondary fluid flow, e.g., refrigerant liquid from liquid outlet  137  using energy of a primary refrigerant flow at the primary inlet  301  of the ejector, e.g., originating from the refrigerant flow from the receiver  110 . 
     In a further modified configuration, dual evaporators  116  can be used in the ejector assist circuit  302 . For example, a first evaporator  116  has outlet  123  fluidly coupled to the secondary inlet  303  (low-pressure inlet) of the ejector  304 , and the first evaporator  116  has the inlet  121  fluidly coupled to the liquid-side outlet  137  of the liquid separator  124 . A second evaporator  116  has the outlet  123  fluidly coupled to the inlet  125  of the liquid separator  124 , and the second evaporator  116  has the inlet  121  fluidly coupled to the outlet  305  of the ejector  304 . 
     Ejector  304 , in this example, includes (as noted) a high-pressure motive nozzle or primary inlet  301 , a suction or secondary inlet  303 , a secondary nozzle that feeds a suction chamber, a mixing chamber for the primary flow of refrigerant and secondary flow of refrigerant to mix, and a diffuser. In example aspects, the ejector  304  is passively controlled by built-in flow control. Also, the CCRS  30  may employ the solenoid valve  128  and expansion valve  114  upstream of the primary inlet  301  to the ejector  304 . Liquid refrigerant from the receiver  110  is the primary flow. In the motive nozzle  301 , potential energy of the primary flow is converted into kinetic energy reducing the potential energy (the established static pressure) of the primary flow. The secondary flow from the outlet of the evaporator  116  has a pressure that is higher than the established static pressure in the suction chamber, and thus the secondary flow is entrained through the suction inlet  303  and the secondary nozzle(s) internal to the ejector  304 . The two streams (primary flow and secondary flow) mix together in the mixing chamber. In the diffuser section, the kinetic energy of the mixed streams is converted into potential energy elevating the pressure of the mixed flow liquid/vapor refrigerant that leaves the ejector  304  and is fed to the inlet  125  of the liquid separator  124 . In the context of closed-circuit refrigeration systems, the use of the ejector  304  allows for recirculation of liquid refrigerant captured by the liquid separator  124  to increase the efficiency of the CCRS  30 . That is, by allowing for some recirculation of refrigerant, but without the need for a compressor or a condenser, this recirculation reduces the required amount of refrigerant needed for a given amount of cooling of high heat loads over the given period of operation of the CCRS  30 . 
     The CCRS  30  also includes the hot vapor circuit  12  including the solenoid valve  128  that is coupled between the compressor outlet  103  and condenser inlet  105 , via junction  140 , and between the expansion device outlet  119  and the primary inlet  301  of the ejector  304 , via the junction  142 . The solenoid valve  128  transfers hot vapor to the ejector primary inlet  301 . 
     The CCRS  30  can operate in the following modes: Standby (thermolyze the evaporator  116  and heat loads  118  via heating or cooling); Cooling mode (heat load  118  on); Cooling mode (heat load  118  off); and Optional pump-down cycle. In Standby, the CCRS  30  maintains the heat load  118  at a temperature corresponding to the low end of the allowed operating temperature range. 
     In a thermolyzing-cooling operation, if ambient temperature is higher than the low end of the allowed operating temperature range for the high heat load  118 , the CCRS  300  operates in a cooling mode. In the cooling mode, the solenoid valve  112  is open and the solenoid valve  128  is closed. When the ambient temperature is higher than the low end of the allowed temperature range for the high heat load  118 , the TMS  300  is configured to have the CCRS  30  provide refrigeration to the high heat load  118 . In this instance, the control system  999  produces signals to cause the solenoid valve  112  to open and solenoid valve  128  to close. 
     Circulating refrigerant enters the compressor  104  as a saturated or superheated vapor and is compressed to a higher pressure at a higher temperature (a superheated vapor). This superheated vapor is at a temperature and pressure at which it can be condensed in the condenser  106  by either cooling water  126  or cooling air  126  flowing across a coil or tubes in the condenser  106 . At the condenser  106 , the circulating refrigerant loses heat and thus removes heat from the system, which removed heat is carried away by either the water or air (whichever may be the case) flowing over the coil or tubes, providing a condensed liquid refrigerant. 
     The condensed and sub-cooled liquid refrigerant is routed into the receiver  110 , exits the receiver  110 , and enters via the solenoid valve  112 . The primary inlet  301  of the ejector  304  is entrained with the refrigerant received at the secondary inlet  303  of the ejector  304  from the outlet of the evaporator  116  (with the evaporator  116  positioned as shown in  FIG.  3   ). The heat from the high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , partially or completely evaporates the liquid portion of the two-phase liquid and vapor refrigerant mixture, and may superheat the two-phase liquid and vapor refrigerant mixture. The refrigerant leaves the evaporator  116  and enters the secondary inlet  303  of the ejector  304 . The saturated or superheated vapor exits at the vapor-side outlet  127  of the liquid separator  124  and enters the compressor  104  completing the cycle. The expansion valve  114  may be controlled (e.g., by control system  999 ) to control pressure differential across the ejector. 
     In the case of the evaporator  116  placed in the modified configuration (as previously described), the liquid-vapor refrigerant mixture is routed through the evaporator  116  from the outlet  305  of the ejector  304 , where heat is transferred from the high heat load  118  to partially or completely evaporate the liquid portion of the two-phase refrigerant mixture, and may superheat the mixture. The refrigerant leaves the evaporator  116  and enters the liquid separator  124 . The saturated or superheated vapor exits at the vapor-side outlet  127  of the liquid separator  124  and enters the compressor  104  completing the cycle. Liquid refrigerant leaves the outlet  137  of the liquid separator  124  and enters secondary inlet  303  of the ejector  304 . 
     Regardless of the placement of the evaporator  116 , the temperature of the two-phase liquid and vapor refrigerant mixture (evaporating temperature) is lower than the temperature of the high heat load  118 . The liquid-vapor refrigerant mixture is routed through the evaporator  116 . 
     In a thermolyzing-heating operation, if ambient temperature is lower than the low end of the allowed operating temperature band, the CCRS  30  operates in a heating mode. In the heating mode, the solenoid valve  112  is closed and the solenoid valve  128  is open. When the ambient temperature is lower than the low end of the allowed temperature range for the high heat load  118 , the TMS  300  is configured to have the CCRS  30  provide heat to the high heat load  118 . In this instance, the control system  999  produces signals to cause the solenoid valve  112  to be closed and solenoid valve  128  to be open. 
     Circulating refrigerant enters the compressor  104  as a saturated or superheated vapor and is compressed to a higher pressure at a higher temperature (a superheated vapor). A first portion of the superheated vapor is at a temperature and pressure at which it can be condensed in the condenser  106  by either cooling water  126  or cooling air  126  flowing across a coil or tubes in the condenser  106 . The condensed and sub-cooled first portion is now in a liquid refrigerant phase and is routed into the receiver  110 , but does not exit the receiver  110 , while the solenoid valve  112  is closed. 
     However, with the solenoid valve  128  open, a second portion of the hot superheated vapor is diverted to the primary inlet  301  of the ejector  304  The hot superheated vapor at the primary inlet  301  entrains liquid at the secondary inlet  303  from the evaporator  116  outlet (if the evaporator  116  is positioned as shown in  FIG.  3   ). The hot superheated vapor heats the evaporator  116  and heat load  118 , and evaporates liquid formed and accumulated in the liquid separator  124  at low ambient temperature. At the condenser  106 , the first portion of the circulating refrigerant loses heat and thus removes heat from the CCRS  30 , which removed heat is carried away by either the water  126  or air  126  (whichever may be the case) flowing over the coil or tubes, providing a condensed liquid refrigerant. The high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , is heated by the second portion of the superheated vapor. In this mode, the evaporator  116  is where the circulating refrigerant adds heat to the high heat load  118 . To complete the refrigeration cycle, the refrigerant vapor from the ejector  304  exits the liquid separator  124  at the vapor-side outlet  127  and enters the compressor  104 . 
     For cooling modes (heat load  118  ON or heat load  118  OFF), the CCRS  30  can be configured to engage both liquid and hot vapor streams to modulate needed cooling or heating effect by placing both solenoid valves  112 ,  128  open or both solenoid valves  112 ,  128  closed. Also, the CCRS  30  can be configured to adjust a speed of compressor  104  (as a variable speed compressor) to modulate needed cooling or heating capacity. When the heat load is ON, the solenoid valve  112  is open and the solenoid valve  128  is closed. The CCRS  30  is configured to generate cooling capacity which is less than the generated heat load. As a result, the heat load temperature rises until it reaches the high end of the allowed operating temperature range during the period of the heat load performance. When the heat load is OFF, the solenoid valve  112  is closed and the solenoid valve  128  is opened, and the CCRS  30  continues to operate until the temperature reaches the low end of the allowed operating temperature range. 
     In an optional pump down operation, a pump-down cycle may be used to return liquid refrigerant that accumulates in the liquid separator  124  back to the receiver  110 . In order to prevent quick reduction of the suction pressure during pump-down cycle, the solenoid valve  128  may be opened. If the expansion valve  114  is configured to operate at a superheat, then the liquid separator  124  and the pump-down cycle may not be needed. If the compressor capacity exceeds the hot vapor capacity demand, the suction pressure and/or discharge pressure may hit the limit: suction pressure reduce below the low-pressure limit and discharge pressure exceeds the high-pressure limit. One way to prevent that is to reduce the speed of the compressor. Another way to do that is to flow some amount of liquid refrigerant via the expansion valve  114  (as controlled, e.g., by the control system  999 ). This increases the overall mass flow rate circulating flow rate, decrease the temperature of refrigerant entering the evaporator  116 , but keep the same hot vapor capacity. 
     Referring now to  FIG.  4   , this figures shows TMS  400  with CCRS  40 , which is an alternative ejector assist-based system to the TMS  300  shown in  FIG.  3   . Common components between TMS  300  and TMS  400  have been numbered accordingly, with components unique to TMS  400  being labeled. TMS  400  includes a gas mixer and multiple control valves (1-to-n) fed at inlets by a liquid manifold downstream of receiver  110  with outlets of the control valves connected to one or more liquid outlets of the gas mixer. TMS  400  includes multiple ejectors  304  (1-to-n), multiple evaporators  116  (e.g., cold plates) (1-to-n), and multiple liquid separators  124  (1-to-n). The gas mixer mixes the hot vapor with the liquid, and the liquid cools the gas at a high pressure. As a result, the overall mass flow rate in TMS  400  is increased, the hot vapor temperature is decreased, and the overall hot vapor capacity remains the same (compared to TMS  300 ). 
     Referring to  FIG.  5   , a thermal management system (TMS)  500  includes a closed-circuit refrigeration system (CCRS)  50 . TMS  500  provides closed-circuit refrigeration for one or more heat loads  118 , e.g., high heat loads over short-time intervals, with a pump assist circuit  502 . Thus, in  FIG.  5   , a pump  504  is used with a liquid separator  124  (in place of a suction accumulator). 
     Components shown in the TMS  500  that are also included in TMS  100 -TMS  300  generally have the same structure and function as described with reference to  FIGS.  1 A,  2 , and  3   . In some aspects, although not shown, the oil circuit from  FIG.  1 A  can be implemented in  FIG.  5    as well. 
     As shown in  FIG.  5   , the pump assist circuit  502  includes a pump  504  with an inlet  501  and an outlet  503 . The optional solenoid valve  112  feeds refrigerant liquid from the receiver  110  into expansion valve  114 . Refrigerant at the outlet  119  of the expansion valve  114  is fed to one of two inlets of a three-port junction  510 , with the second of the two inlets coupled to the outlet  123  of the evaporator  116 . The junction  510  also includes an outlet that feeds refrigerant from the receiver  110  and the evaporator  116  to the inlet  125  of the liquid separator  124 . The pump inlet  501  receives refrigerant liquid from the liquid-side outlet  137  of the liquid separator  124 . 
     The pump outlet  503  outputs the refrigerant into an inlet  6505  of an optional solenoid valve  514 . An outlet  507  of the solenoid valve  514  feeds the refrigerant into one of the inlets of the junction  142 , with the second inlet of the junction  142  receiving refrigerant from outlet  135  of expansion valve  130 . The expansion valve  130  includes inlet  133  that is coupled to the outlet  131  of solenoid valve  128 . The vapor-side outlet  127  of the liquid separator  124  feeds refrigerant vapor into the inlet  101  of the compressor  104 . The outlet  103  of the compressor  104  feeds junction  140 , with the outlets of the junction  140  coupled to the inlet  105  of the condenser  106  and inlet  129  of the solenoid valve  128 . The evaporator  116  is coupled, via the junction  142 , to the pump outlet  503  and the outlet of the expansion valve  130  by junction  142 . In this configuration, the pump  504  pumps liquid refrigerant from the liquid-side outlet  137  of the liquid separator  124  to the junction  142  and towards the inlet  121  of the evaporator  116 . 
     In some aspects, pump  504  is located distal from the liquid-side outlet  137 . This configuration potentially presents the possibility of cavitation. To minimize the possibility of cavitation. other configurations can also be used. For example, the pump  504  can be located distal from the liquid-side outlet  137 , but the height at which the inlet  125  is located is relatively high in the liquid separator  124 . This would result in an increase in liquid pressure at the liquid-side outlet  137  of the liquid separator  124  and concomitant therewith an increase in liquid pressure at the inlet  501  of the pump  504 . Increasing the pressure at the inlet  501  to the pump  504  should minimize possibility of cavitation. As another example, the pump  504  can be located proximate to or indeed inside of the liquid-side outlet  137 . In addition, the height at which the inlet  125  is located can be relatively high as well. This would result in an additional increase in liquid pressure at the inlet  501  of the pump  504  further minimizing the possibility of cavitation. Another alternative strategy that can be used for any pump configuration involves the use of a sensor that produces a signal that is a measure of the height of a column of liquid in the liquid separator  124 . The signal is sent to the control system  999  that will be used to start the pump  504 , once a sufficient height of liquid is contained by the liquid separator  124 . Another alternative strategy that can be used for any of the pump configurations involves the use of a heat exchanger in liquid separator  124 . The heat exchanger is an evaporator, which brings in thermal contact two refrigerant streams. In the above systems, a first of the streams is the liquid stream leaving the liquid separator  124 . A second stream is the liquid refrigerant expanded to a pressure lower than the evaporator pressure in the evaporator  116  and evaporating the related evaporating temperature lower than the liquid temperature at the liquid separator exit. Thus, the liquid from the liquid separator  124  exit is subcooled rejecting thermal energy to the second side of the heat exchanger. The second side absorbs the rejected thermal energy due to evaporating and superheating of the second refrigerant stream. 
     The CCRS  50  can operate in the following modes: Standby (thermolyze the evaporator  116  and heat loads  118  via heating or cooling); Cooling mode (heat load  118  on); Cooling mode (heat load  118  off); and Optional pump-down cycle. In Standby, the CCRS  50  maintains the heat load  118  at a temperature corresponding to the low end of the allowed operating temperature range. 
     In a thermolyzing-cooling operation, if ambient temperature is higher than the low end of the allowed operating temperature range for the high heat load  118 , the CCRS  50  operates in a cooling mode. In the cooling mode, the solenoid valve  112  is open and the solenoid valve  128  is closed. When the ambient temperature is higher than the low end of the allowed temperature range for the high heat load  118 , the TMS  500  is configured to have the CCRS  50  provide refrigeration to the high heat load  118 . In this instance, the control system  999  produces signals to cause the solenoid valve  112  to open and solenoid valve  128  to close. 
     Circulating refrigerant enters the compressor  104  as a saturated or superheated vapor and is compressed to a higher pressure at a higher temperature (a superheated vapor). This superheated vapor is at a temperature and pressure at which it can be condensed in the condenser  106  by either cooling water  126  or cooling air  126  flowing across a coil or tubes in the condenser  106 . At the condenser  106 , the circulating refrigerant loses heat and thus removes heat from the CCRS  50 , which removed heat is carried away by either the water  126  or air  126  (whichever may be the case) flowing over the coil or tubes, providing a condensed, sub-cooled liquid refrigerant. 
     The condensed, sub-cooled liquid refrigerant is routed into the receiver  110 , exits the receiver  110 , and enters the solenoid valve  112  and the expansion valve  114 . The refrigerant is enthalpically expanded in the expansion valve  114 . The expanded refrigerant exits the expansion valve  114 , enters junction  510 , and is mixed in the junction  510  with a liquid/vapor refrigerant mixture that exits the evaporator  116 . The high pressure sub-cooled liquid refrigerant turns into liquid-vapor mixture at a low pressure and temperature and exits the junction  510 . The temperature of the liquid-vapor mixture (evaporating temperature) is lower than the temperature of the high heat load  118 . The liquid-vapor mixture is routed through the evaporator  116 . The heat from the high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , partially or completely evaporates the liquid portion of the two-phase liquid-vapor mixture, and may superheat the liquid-vapor mixture. The refrigerant leaves the evaporator  116  and enters junction  510  through conduit  508 . 
     Saturated or superheated vapor exits the liquid separator  124  at the vapor-side outlet  127  enters the compressor  104  through conduit  512 . The evaporator  116  is where the circulating refrigerant absorbs and removes heat from the high heat load  118 , which heat is subsequently rejected in the condenser  106  and transferred to an ambient by water or air used in the condenser  106 . To complete the refrigeration cycle, the refrigerant vapor from the evaporator  116  exits the liquid separator  124  at the vapor-side outlet  127  and enters the compressor  104 . 
     In a thermolyzing-heating operation, if ambient temperature is lower than the low end of the allowed operating temperature band, the CCRS  50  operates in a heating mode. In the heating mode, the solenoid valve  112  is closed and the solenoid valve  128  is open. When the ambient temperature is lower than the low end of the allowed temperature range for the high heat load  118 , the TMS  500  is configured to have the CCRS  50  provide heat to the high heat load  118 . In this instance, the control system  999  produces signals to cause the solenoid valve  112  to be closed and solenoid valve  128  to be open. 
     Circulating refrigerant enters the compressor  104 , as a saturated or superheated vapor, and is compressed to a higher pressure at a higher temperature (a superheated vapor). A first portion of the superheated vapor is at a temperature and pressure at which it can be condensed in the condenser  106  by either cooling water  126  or cooling air  126  flowing across a coil or tubes in the condenser  106 . At the condenser  106 , the first portion of the circulating refrigerant loses heat and thus removes heat from the CCRS  50 , which removed heat is carried away by either the water  126  or air  126  (whichever may be the case) flowing over the coil or tubes, providing a condensed liquid refrigerant. The condensed and sub-cooled first portion is now in a liquid refrigerant phase and is routed into the receiver  110 , but does not exit the receiver  110 , while the solenoid valve  112  is closed. 
     However, with the solenoid valve  128  open, a second portion of the superheated vapor is diverted through the expansion valve  130  back to the evaporator  116 , where it heats the high heat load  118 . The high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , is heated by the second portion of the superheated vapor. The refrigerant leaves the evaporator  116  and enters the inlet  125  of the liquid separator  124 . The liquid-side outlet  137  delivers liquid refrigerant to the pump  504 . The pump  504 , is in an off state and does not pump the liquid refrigerant into solenoid valve  514 . The solenoid valve  514  is optional, provided that the pump  504  can block liquid when not in use. The saturated or superheated vapor exits the liquid separator  124  and enters the compressor  104  through conduit  512 . In this mode, the evaporator  116  is where the circulating refrigerant adds heat to the high heat load  118 . To complete the refrigeration cycle, the refrigerant vapor from the evaporator  116  exits the liquid separator  124  at the vapor-side outlet  127  and enters the compressor  104 . 
     The CCRS  50  can be configured to engage both liquid and hot vapor streams to modulate needed cooling or heating effect by placing both solenoid valves  112 ,  128  open or both solenoid valves  112 ,  128  closed. Also, the CCRS  50  can be configured to adjust a speed of the compressor  104  (if variable speed) to modulate needed cooling or heating capacity. 
     When the heat load  118  is ON, the solenoid valve  112  is open and the solenoid valve  128  is closed. The CCRS  50  is configured to generate cooling capacity which is less than the generated heat load  118 . As a result, the heat load temperature rises until it reaches the high end of the allowed operating temperature range during the period of the heat load performance. 
     When the heat load  118  is OFF, the solenoid valve  112  is off and the solenoid valve  128  is opened, and the CCRS  50  continues to operate until the temperature reaches the low end of the allowed operating temperature band. 
     In an optional pump down operation, a pump-down cycle may be used to return liquid refrigerant that accumulates in the liquid separator  124  back to the receiver  110 . In order to prevent quick reduction of the suction pressure during pump-down cycle, the solenoid valve  128  may be opened. If the expansion valve  114  is configured to operate at a superheat, then the liquid separator  124  and the pump-down cycle may not be needed. 
     Referring to  FIG.  6   , a thermal management system (TMS)  600  includes a closed-circuit refrigeration system (CCRS)  60 . TMS  600  provides closed-circuit refrigeration for one or more heat loads  118 , e.g., high heat loads over short-time intervals, with a pump assist circuit  502  as well. Thus, in  FIG.  6   , a pump  504  is used with a liquid separator  124  (in place of a suction accumulator). 
     Components shown in the TMS  600  that are also included in TMS  100 -TMS  300  and TMS  500  generally have the same structure and function as described with reference to  FIGS.  1 A,  2 ,  3 , and  5   . In some aspects, although not shown, the oil circuit from  FIG.  1 A  can be implemented in  FIG.  6    as well. 
     As shown in  FIG.  6   , the pump assist circuit  502  includes pump  504  with inlet  501  and outlet  503 , as well optional check valve  606  and junctions  604  and  610 . The optional solenoid valve  112  feeds refrigerant liquid from the receiver  110  into the expansion valve  114 . Refrigerant at the outlet  119  of the expansion valve  114  is fed to one of two inlets of the three-port junction  610 . The junction  610  also includes an outlet that feeds refrigerant from the receiver  110  and the evaporator  116  toward the inlet  125  of the liquid separator  124 . 
     The second of the two inlets of the three-port junction  610  is coupled to the outlet  503  of the pump  504 , via a first inlet of three-port junction  604  and optional check valve  606 . The three-port junction  604  has a second inlet that is coupled to an outlet of another three-port junction  602  through conduit  608 . The check valve  606  is arranged such that refrigerant passes from the pump outlet  503  through the check valve  606 , but any refrigerant from the hot vapor circuit  12 , via the junction  602 , is inhibited from passing to the pump outlet  503 . The junction  142  also includes an outlet that feeds the refrigerant from the receiver  110  and the refrigerant from the pump outlet  503  into the inlet  121  of the evaporator  116 . The outlet  123  of the evaporator  116  feeds refrigerant into the inlet  125  of the liquid separator  124 . 
     The pump outlet  503  outputs the refrigerant into an inlet of the check valve  606 . An outlet of the check valve  606  feeds the refrigerant into one of the inlets of the junction  604  with the second inlet of the junction  142  receiving refrigerant from expansion valve  130  of hot vapor circuit  12 . The expansion valve  130  includes inlet  133  that is coupled to the solenoid valve  128  at outlet  131 . The vapor-side outlet  127  of the liquid separator  124  feeds refrigerant vapor into the inlet  101  of the compressor  104 . In this configuration, the pump  504  also pumps liquid refrigerant from the liquid-side outlet  137  of the liquid separator  124  towards the evaporator  116 . 
     The CCRS  60  can operate in the following modes: Standby (thermolyze the evaporator  116  and heat loads  118  via heating or cooling); Cooling mode (heat load  118  on); Cooling mode (heat load  118  off); and Optional pump-down cycle. In Standby, the CCRS  60  maintains the heat load  118  at a temperature corresponding to the low end of the allowed operating temperature range. 
     In a thermolyzing-cooling operation, if ambient temperature is higher than the low end of the allowed operating temperature range for the high heat load  118 , the CCRS  60  operates in a cooling mode. In the cooling mode, the solenoid valve  112  is open and the solenoid valve  128  is closed. When the ambient temperature is higher than the low end of the allowed temperature range for the high heat load  118 , the TMS  600  is configured to have the CCRS  60  provide refrigeration to the high heat load  118 . In this instance, the control system  999  produces signals to cause the solenoid valve  112  to open and solenoid valve  128  to close. 
     Circulating refrigerant enters the compressor  104  as a saturated or superheated vapor and is compressed to a higher pressure at a higher temperature (a superheated vapor). The condensed, sub-cooled liquid refrigerant is routed into the receiver  110 , exits the receiver  110 , and enters the solenoid valve  112  and the expansion valve  114 . The refrigerant is enthalpically expanded in the expansion valve  114 . The expanded refrigerant exits the expansion valve  114 , enters junction  610 , and is mixed in the junction  610  with liquid refrigerant from the outlet  503  of the pump  504 , via the check valve  606 . The liquid and vapor refrigerant mixture from an outlet of the junction  610  is fed to the inlet  121  of the evaporator  116 . The temperature of the liquid and vapor refrigerant mixture (evaporating temperature) is lower than the temperature of the high heat load  118 . The liquid and vapor refrigerant mixture is routed through the evaporator  116 . The heat from the high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , partially or completely evaporates the liquid portion of the liquid and vapor refrigerant mixture, and may superheat the liquid and vapor refrigerant mixture. The liquid and vapor refrigerant mixture (now mostly vapor) leaves the evaporator  116  and enters the liquid separator  124 . 
     Saturated or superheated vapor exits the liquid separator  124  at the vapor-side outlet  127  and enters the compressor  104 . The evaporator  116  is where the circulating refrigerant absorbs and removes heat from the high heat load  118 , which heat is subsequently rejected in the condenser  106  and transferred to an ambient by water  126  or air  126  used in the condenser  106 . To complete the refrigeration cycle, the refrigerant vapor from the evaporator  116  exits the liquid separator  124  at the vapor-side outlet  127  and enters the compressor  104 . 
     In a thermolyzing-heating operation, if ambient temperature is lower than the low end of the allowed operating temperature band, the CCRS  60  operates in a heating mode. In the heating mode, the solenoid valve  112  is closed and the solenoid valve  128  is open. When the ambient temperature is lower than the low end of the allowed temperature range for the high heat load  118 , the TMS  600  is configured to have the CCRS  60  provide heat to the high heat load  118 . In this instance, the control system  999  produces signals to cause the solenoid valve  112  to be closed and solenoid valve  128  to be open. 
     Circulating refrigerant enters the compressor  104  as a saturated or superheated vapor and is compressed to a higher pressure at a higher temperature (a superheated vapor). A first portion of the superheated vapor is at a temperature and pressure at which it can be condensed in the condenser  106  by either cooling water  126  or cooling air  126  flowing across a coil or tubes in the condenser  106 . At the condenser  106 , the first portion of the circulating refrigerant loses heat and thus removes heat from the CCRS  60 , which removed heat is carried away by either the water  126  or air  126  (whichever may be the case) flowing over the coil or tubes, providing a condensed liquid refrigerant. The condensed and sub-cooled first portion is now in a liquid refrigerant phase and is routed into the receiver  110 , but does not exit the receiver  110 , while the solenoid valve  112  is closed. 
     However, with the solenoid valve  128  open, a second portion of the superheated vapor is diverted back to the evaporator  116  where it heats the high heat load  118 . Meanwhile, the high heat load  118 , in thermal conductive and/or convective contact with or proximate to the evaporator  116 , is heated by the second portion of the superheated vapor. The refrigerant leaves the evaporator  116  and enters the inlet  125  of the liquid separator  124 . The liquid-side outlet  137  delivers liquid refrigerant to the pump  504 . The pump  504 , is in an off state and does not pump the liquid refrigerant into check valve  606 . The saturated or superheated vapor exits the liquid separator  124  at the vapor-side outlet  127 , and enters the compressor  104 . In this mode, the evaporator  116  is where the circulating refrigerant adds heat to the high heat load  118 . To complete the refrigeration cycle, the refrigerant vapor from the evaporator  116  exits the liquid separator  124  at the vapor-side outlet  127  and enters the compressor  104 . 
     The CCRS  60  can be configured to engage both liquid and hot vapor streams to modulate needed cooling or heating effect by placing both solenoid valves  112 ,  128  open or both solenoid valves  112 ,  128  closed. Also, the CCRS  60  can be configured to adjust a speed of compressor  104  (if variable speed) to modulate needed cooling or heating capacity. 
     When the heat load  118  is ON, the solenoid valve  112  is open and the solenoid valve  128  is closed. The CCRS  60  is configured to generate cooling capacity which is less than the generated heat load  118 . As a result, the heat load temperature rises until it reaches the high end of the allowed operating temperature range during the period of the heat load performance. 
     When the heat load  118  is OFF, the solenoid valve  112  is closed and the solenoid valve  128  is opened, the CCRS  60  continues to operate until the temperature reaches the low end of the allowed operating temperature band. 
     In an example pump down operation, a pump-down cycle may be used to return liquid refrigerant that accumulates in the liquid separator  124  back to the receiver  110 . In order to prevent quick reduction of the suction pressure during pump-down cycle, the solenoid valve  128  may be opened. If the expansion valve  114  is configured to operate at a superheat, then the liquid separator  124  and the pump-down cycle may not be needed. 
     Referring now to  FIGS.  7 A- 7 D  additional evaporator arrangements that are alternative configurations of the evaporator  116  and heat load(s)  118  are shown. In the configuration of  FIG.  7 A , multiple high heat loads  118  are coupled to (or are in proximately to) a single, i.e., the same, evaporator  116 . In the configuration of  FIG.  7 B , each of a pair of evaporators  116  is coupled to the high heat load  118  or to each high heat load  118  if there are multiple. In the configurations of  FIGS.  7 C and  7 D , the high heat load  118  is thermally coupled (or proximate) to corresponding both of the pair of evaporators  116  or each of a pair of high heat loads  118  is thermally coupled to a respective evaporator  116 . In the configurations of  FIGS.  7 C and  7 D , a T-valve  702  (passive or active), as shown, splits refrigerant flow from the receiver  110 , into two paths that feed two evaporators  116  and heat load  118 . The liquid separator  124  could also be used in either of the configurations of  FIGS.  7 C and  7 D . As also shown in  FIG.  7 D  expansion valves are coupled at inlet sides of the evaporators  116 . At least one expansion valve would be configured to control a vapor quality at the evaporator  116  exit to allow discharging liquid into the suction accumulator, while the other would controls a superheat. Other configurations are possible. In the configuration of  FIG.  7 C , the outlets  123  of the evaporators  116  are coupled to a second T-valve  702  (active or passive) that has an output that feeds the inlet  125  of the suction accumulator  124 . On the other hand, in the configuration of  FIG.  7 D , the outlets  123  of the evaporators  116  are coupled differently. The outlet  123  of one evaporator  116  with high heat load  118  feeds an inlet of the T-valve  702 , whereas the outlet  123  of another evaporator  116  with another high heat load  118  feeds inlet  125  of the suction accumulator  124 . This arrangement in effect, removes the liquid separator  124  from one of the paths of the evaporators  116 . In some configurations, the T valves  702  can be switched (meaning that they can be controlled (automatically or manually) to shut off either or both inlets) or passive meaning that they do not shut off either inlet and thus can be T junctions. 
     Regarding refrigerant vapor quality and with respect to any of the example implementations of a TMS according to the present disclosure, the vapor quality of the refrigerant fluid  1  after passing through evaporator  116  can be controlled either directly or indirectly with respect to a vapor quality set point by the control system  999 . The evaporator  116  may be configured to maintain exit vapor quality substantially below the critical vapor quality defined as “1.” 
     Vapor quality is the ratio of mass of vapor to mass of liquid+vapor and is generally kept in a range of approximately 0.5 to almost 1.0; more specifically 0.6 to 0.95; more specifically 0.75 to 0.9 more specifically 0.8 to 0.9 or more specifically about 0.8 to 0.85. “Vapor quality” is thus defined as mass of vapor/total mass (vapor+liquid). In this sense, vapor quality cannot exceed “1” or be equal to a value less than “0.” In practice vapor quality may be expressed as “equilibrium thermodynamic quality” that is calculated as follows:
 
 X =( h−h ′)/( h″−h ′),
 
where h is specific enthalpy, specific entropy or specific volume, h‘ is of saturated liquid and “ is of saturated vapor. In this case X can be mathematically below 0 or above 1, unless the calculation process is forced to operate differently. Either approach is acceptable.
 
     During operation of a TMS, cooling can be initiated by a variety of different mechanisms. In some embodiments, for example, a TMS includes temperature sensors attached to loads  118  (as will be discussed subsequently). When the temperature of loads  118  exceeds a certain temperature set point (i.e., threshold value), the control system  999  connected to the temperature sensor can initiate cooling of loads  118 . Alternatively, in certain embodiments, a TMS operates essentially continuously—provided that the refrigerant fluid pressure within receiver  110  is sufficient—to cool low high heat load  118  and a temperature sensor attached to high heat load  118  will cause the control system  999  to switch the operating mode of a CCRS when the temperature of high heat load  118  exceeds a certain temperature set point (i.e., threshold value). As soon as receiver  110  is charged with refrigerant fluid, refrigerant fluid is ready to be directed into evaporator  116  to cool high heat load  118 . In general, cooling is initiated when a user of the system or the heat load issues a cooling demand. 
     Upon initiation of a cooling operation, refrigerant fluid from receiver  110  is discharged from an outlet, through an optional solenoid valve, if present, and is transported through conduit to expansion valve  114 , which directly or indirectly controls vapor quality (or superheat) at the evaporator outlet. In the following discussion, expansion valve  114  is implemented as an electronic expansion valve device. However, it should be understood that more generally, expansion valve  114  can be implemented as any component or device that performs the functional steps described below and provides for vapor quality control (or superheat) at the evaporator outlet. 
     Once inside the expansion valve  114 , the refrigerant fluid undergoes constant enthalpy expansion from an initial pressure p r  (i.e., the receiver pressure) to an evaporation pressure p e  at the outlet of the expansion valve  114 . In general, the evaporation pressure p e  depends on a variety of factors, e.g., the desired temperature set point value (i.e., the target temperature) at which high heat load  118  is/are to be maintained and the heat input generated by the respective heat loads. Set points will be discussed below. 
     The initial pressure in the receiver  110  tends to be in equilibrium with the surrounding temperature and is different for different refrigerants. (Operational conditions of the compressor  104  and condenser  106  may be configured to maintain a higher condensing pressure.) The pressure in the evaporator  116  depends on the evaporating temperature, which is lower than the heat load temperature and is defined during design of a TMS. A TMS is operational as long as the receiver-to-evaporator pressure difference is sufficient to drive adequate refrigerant fluid flow through the expansion valve  114 . After undergoing constant enthalpy expansion in the expansion valve  114 , the liquid refrigerant fluid is converted to a mixture of liquid and vapor phases at the temperature of the fluid and evaporation pressure p e . The two-phase refrigerant fluid mixture is transported via conduit to evaporator  116 . 
     When the two-phase mixture of refrigerant fluid is directed into evaporator  116 , the liquid phase absorbs heat from load  118 , driving a phase transition of the liquid refrigerant fluid into the vapor phase. Because this phase transition occurs at (nominally) constant temperature, the temperature of the refrigerant fluid mixture within evaporator  116  remains unchanged, provided at least some liquid refrigerant fluid remains in evaporator  116  to absorb heat. 
     Further, the constant temperature of the refrigerant fluid mixture within evaporator  116  can be controlled by adjusting the pressure p e  of the refrigerant fluid, since adjustment of p e  changes the boiling temperature of the refrigerant fluid. Thus, by regulating the refrigerant fluid pressure p e  upstream from evaporator  116 , the temperature of the refrigerant fluid within evaporator  116  (and, nominally, the temperature of high heat load  118 ) can be controlled to match a specific temperature set-point value for high heat load  118 , ensuring that high heat load  118  is maintained at, or very near, a target temperature. 
     The pressure drop across the evaporator  116  causes drop of the temperature of the refrigerant mixture (which is the evaporating temperature), but still the evaporator  116  can be configured to maintain the heat load temperature within the set tolerances. 
     In some embodiments, for example, the evaporation pressure of the refrigerant fluid can be adjusted by pressure of the back-pressure regulator  36  to ensure that the temperature of heat loads  25  is maintained to within ±5 degrees C. (e.g., to within ±4 degrees C., to within ±3 degrees C., to within ±2 degrees C., to within ±1 degree C.) of the temperature set point value for load  49 . 
     As discussed above, within evaporator  116 , a portion of the liquid refrigerant in the two-phase refrigerant fluid mixture is converted to refrigerant vapor by undergoing a phase change. As a result, the refrigerant fluid mixture that emerges from evaporator  116  has a higher vapor quality (i.e., the fraction of the vapor phase that exists in refrigerant fluid mixture) than the refrigerant fluid mixture that enters evaporator  116 . 
     As the refrigerant fluid mixture emerges from evaporator  116 , a portion of the refrigerant fluid can optionally be used to cool one or more additional heat loads. Typically, for example, the refrigerant fluid that emerges from evaporator  116  is nearly in the vapor phase. The refrigerant fluid vapor (or, more precisely, high vapor quality fluid vapor) can be directed into a heat exchanger coupled to another heat load, and can absorb heat from the additional heat load during propagation through the heat exchanger. 
     A variety of different refrigerant fluids can be used in a TMS. Depending on the application, emissions regulations and operating environments may limit the types of refrigerant fluids that can be used. More generally, any fluid can be used as a refrigerant in the closed-circuit refrigeration systems disclosed herein, provided that the fluid is suitable for cooling heat loads  25  (e.g., the fluid boils at an appropriate temperature) and, in embodiments where the refrigerant fluid is exhausted directly to the environment, regulations and other safety and operating considerations do not inhibit such discharge. For example, in certain embodiments, the refrigerant fluid can be ammonia having very large latent heat; after passing through the cooling circuit, the ammonia refrigerant vapor in the closed-circuit operation can be disposed of by incineration, by chemical treatment (i.e., neutralization), and/or by direct venting to the atmosphere. In certain embodiments, the refrigerant fluid can be an ammonia-based mixture that includes ammonia and one or more other substances. For example, mixtures can include one or more additives that facilitate ammonia absorption or ammonia burning. 
     Ammonia under standard conditions of pressure and temperature is in a liquid or two-phase state. Thus, the receiver  110  typically will store ammonia at a saturated pressure corresponding to the surrounding temperature. The pressure in the receiver  110  storing ammonia will change during operation. The use of the expansion valve  114  can stabilize pressure in the receiver  110  during operation, by adjusting the expansion valve  114  (e.g., automatically or by control system  999 ) based on a measurement of the evaporation pressure (p e ) of the refrigerant fluid and/or a measurement of the evaporation temperature of the refrigerant fluid. 
       FIG.  8    shows the control system  999  that includes a processor  802 , memory  804 , storage  806 , and I/O interfaces  808 , all of which are connected/coupled together via a bus  810 . Any two of the optional devices, as pressure sensors, upstream and downstream from a control device, can be configured to measure information about a pressure differential p r -p e  across the respective control device and to transmit electronic signals corresponding to the measured pressure from which a pressure difference information can be generated by the control system  999 . Other sensors such as flow sensors and temperature sensors can be used as well. In certain embodiments, sensors can be replaced by a single pressure differential sensor, a first end of which is connected adjacent to an inlet and a second end of which is connected adjacent to an outlet of a device to which differential pressure is to be measured, such as the evaporator. The pressure differential sensor measures and transmits information about the refrigerant fluid pressure drop across the device, e.g., the evaporator  116 . 
     Control system  999  can adjust expansion valve  114  based on measurements of one or more of the following system parameter values: the pressure drop (p r −p e ) across expansion valve  114 , the pressure drop across evaporator  116 , the refrigerant fluid pressure in receiver  110  (p r ), the vapor quality of the refrigerant fluid emerging from evaporator  116  (or at another location in the system), the superheat value of the refrigerant fluid in the system, the evaporation pressure (p e ) of the refrigerant fluid, and the evaporation temperature of the refrigerant fluid. 
     To adjust expansion valve  114  based on a particular value of a measured system parameter value, control system  999  compares the measured value to a range of set point values (or threshold values) for the system parameter, as will be discussed below. 
     Since liquid refrigerant temperature is sensitive to ambient temperature, the density of liquid refrigerant changes even though the pressure in the receiver  110  remains the same. Also, the liquid refrigerant temperature impacts the vapor quality at the evaporator inlet. Therefore, the refrigerant mass and volume flow rates change and the expansion valve  114  can be used to adjust for the changes. 
     Various combinations of the sensors can be used to measure thermodynamic properties of a TMS that are used to adjust expansion valves and/or pumps discussed above and which signals are processed by the control system  999 . Connections (wired or wireless) are provided between each of the sensors and control system  999 . In many embodiments, system includes only certain combinations of the sensors (e.g., one, two, three, or four of the sensors) to provide suitable control signals for the control devices. 
     Temperature sensors can be positioned adjacent to an inlet or an outlet of e.g., the evaporator  116  or between the inlet and the outlet. Such a temperature sensor measures temperature information for the refrigerant fluid within evaporator  116  (which represents the evaporating temperature) and transmits an electronic signal corresponding to the measured information. A temperature sensor can be attached to high heat load  118 , which measures temperature information for the load and transmits an electronic signal corresponding to the measured information. An optional temperature sensor can be adjacent to the outlet of evaporator  116  that measures and transmits information about the temperature of the refrigerant fluid as it emerges from evaporator  116 . 
     In certain embodiments, the systems disclosed herein are configured to determine superheat information for the refrigerant fluid based on temperature and pressure information for the refrigerant fluid measured by any of the sensors disclosed herein. The superheat of the refrigerant vapor refers to the difference between the temperature of the refrigerant fluid vapor at a measurement point in a TMS and the saturated vapor temperature of the refrigerant fluid defined by the refrigerant pressure at the measurement point in the thermal management a TMS. 
     To determine the superheat associated with the refrigerant fluid, the system control system  999  (as described) receives information about the refrigerant fluid vapor pressure after emerging from a heat exchanger downstream from evaporator  116 , and uses calibration information, a lookup table, a mathematical relationship, or other information to determine the saturated vapor temperature for the refrigerant fluid from the pressure information. The control system  999  also receives information about the actual temperature of the refrigerant fluid, and then calculates the superheat associated with the refrigerant fluid as the difference between the actual temperature of the refrigerant fluid and the saturated vapor temperature for the refrigerant fluid. 
     The foregoing temperature sensors can be implemented in a variety of ways in a TMS. As one example, thermocouples and thermistors can function as temperature sensors in a TMS. Examples of suitable commercially available temperature sensors for use in a TMS include, but are not limited to, the  88000  series thermocouple surface probes (available from OMEGA Engineering Inc., Norwalk, Conn.). 
     A TMS can include a vapor quality sensor that measures vapor quality of the refrigerant fluid emerging from evaporator  116 . Typically, such a sensor is implemented as a capacitive sensor that measures a difference in capacitance between the liquid and vapor phases of the refrigerant fluid. The capacitance information can be used to directly determine the vapor quality of the refrigerant fluid (e.g., by control system  999 ). Alternatively, sensor can determine the vapor quality directly based on the differential capacitance measurements and transmit an electronic signal that includes information about the refrigerant fluid vapor quality. Examples of commercially available vapor quality sensors that can be used in a TMS include, but are not limited to, HBX sensors (available from HB Products, Hasselager, Denmark). 
     It should generally be understood that the systems disclosed herein can include a variety of combinations of the various sensors described above, and control system  999  can receive measurement information periodically or aperiodically from any of the various sensors. Moreover, it should be understood any of the sensors described can operate autonomously, measuring information and transmitting the information to control system  999  (or directly to the first and/or second control device) or, alternatively, any of the sensors described above can measure information when activated by control system  999  via a suitable control signal, and measure and transmit information to control system  999  in response to the activating control signal. 
     To adjust a control device on a particular value of a measured system parameter value, control system  999  compares the measured value to a set point value (or threshold value) for the system parameter. Certain set point values represent a maximum allowable value of a system parameter, and if the measured value is equal to the set point value (or differs from the set point value by 10% or less (e.g., 5% or less, 3% or less, 1% or less) of the set point value), control system  999  adjusts a respective control device to modify the operating state of a TMS. Certain set point values represent a minimum allowable value of a system parameter, and if the measured value is equal to the set point value (or differs from the set point value by 10% or less (e.g., 5% or less, 3% or less, 1% or less) of the set point value), control system  999  adjusts the respective control device to modify the operating state of a TMS, and increase the system parameter value. The control system  999  executes algorithms that use the measured sensor value(s) to provide signals that cause the various control devices to adjust refrigerant flow rates, etc. 
     Some set point values represent “target” values of system parameters. For such system parameters, if the measured parameter value differs from the set point value by 1% or more (e.g., 3% or more, 5% or more, 10% or more, 20% or more), control system  999  adjusts the respective control device to adjust the operating state of the system, so that the system parameter value more closely matches the set point value. 
     Optional pressure sensors are configured to measure information about the pressure differential p r −p e  across a control device and to transmit an electronic signal corresponding to the measured pressure difference information. Two sensors can effectively measure p r , p e . In certain embodiments two sensors can be replaced by a single pressure differential sensor. Where a pressure differential sensor is used, a first end of the sensor is connected upstream of a first expansion device (i.e., expansion valve  114 ) and a second end of the sensor is connected downstream from the first expansion device. 
     System also includes optional pressure sensors positioned at the inlet and outlet, respectively, of evaporator  116 . A sensor measures and transmits information about the refrigerant fluid pressure upstream from evaporator  116 , and a sensor measure and transmit information about the refrigerant fluid pressure downstream from evaporator  116 . This information can be used (e.g., by a system controller) to calculate the refrigerant fluid pressure drop across evaporator  116 . As above, in certain embodiments, sensors can be replaced by a single pressure differential sensor to measure and transmit the refrigerant fluid pressure drop across evaporator  116 . 
     To measure the evaporating pressure (p e ) a sensor can be optionally positioned between the inlet and outlet of evaporator  116 , i.e., internal to evaporator  116 . In such a configuration, the sensor can provide a direct a direct measurement of the evaporating pressure. 
     To measure refrigerant fluid pressure at other locations within system, sensor can also optionally be positioned, for example, in-line along a conduit. Pressure sensors at each of these locations can be used to provide information about the refrigerant fluid pressure downstream from evaporator  116 , or the pressure drop across evaporator  116 . 
     It should be appreciated that, in the foregoing discussion, any one or various combinations of two sensors discussed in connection with system can correspond to the first measurement device connected to expansion valve  114 , and any one or various combination of two sensors can correspond to the second measurement device. In general, as discussed previously, the first measurement device provides information corresponding to a first thermodynamic quantity to the first control device, and the second measurement device provides information corresponding to a second thermodynamic quantity to the second control device, where the first and second thermodynamic quantities are different, and therefore allow the first and second control device to independently control two different system properties (e.g., the vapor quality of the refrigerant fluid and the heat load temperature, respectively). 
     In some embodiments, one or more of the sensors shown in system are connected directly to expansion valve  114 . The first and second control device can be configured to adaptively respond directly to the transmitted signals from the sensors, thereby providing for automatic adjustment of the system&#39;s operating parameters. In certain embodiments, the first and/or second control device can include processing hardware and/or software components that receive transmitted signals from the sensors, optionally perform computational operations, and activate elements of the first and/or second control device to adjust the control device in response to the sensor signals. 
     In addition, control system  999  is optionally connected to expansion valve  114 . In embodiments where expansion valve  114  is implemented as a device controllable via an electrical control signal, control system  999  is configured to transmit suitable control signals to the first and/or second control device to adjust the configuration of these components. In particular, control system  999  is configured to adjust expansion valve  114  to control the vapor quality of the refrigerant fluid in a TMS. 
     During operation of a TMS, control system  999  typically receives measurement signals from one or more sensors. The measurements can be received periodically (e.g., at consistent, recurring intervals) or irregularly, depending upon the nature of the measurements and the manner in which the measurement information is used by control system  999 . In some embodiments, certain measurements are performed by control system  999  after particular conditions—such as a measured parameter value exceeding or falling below an associated set point value—are reached. 
     By way of example, Table 1 summarizes various examples of combinations of types of information (e.g., system properties and thermodynamic quantities) that can be measured by the sensors of system and transmitted to control system  999 , to allow control system  999  to generate and transmit suitable control signals to expansion valve  114  and/or other control devices. The types of information shown in Table 1 can generally be measured using any suitable device (including combination of one or more of the sensors discussed herein) to provide measurement information to control system  999 . 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Measurement Information Used 
               
               
                   
                 to Adjust First Control Device 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Evap 
                   
                   
                   
                   
                   
                   
               
               
                   
                 Press 
                 Press 
                 Rec 
                   
                   
                 Evap 
                 Evap 
                 HL 
               
               
                   
                 Drop 
                 Drop 
                 Pres 
                 VQ 
                 SH 
                 VQ 
                 P/T 
                 Temp 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Measure- 
                 Press 
                   
                   
                   
                   
                   
                   
                 x 
                 x 
               
               
                 ment 
                 Drop 
               
               
                 Infor- 
                 Evap 
                   
                   
                   
                   
                   
                   
                 x 
                 x 
               
               
                 mation 
                 Press 
               
               
                 Used to 
                 Drop 
               
               
                 Adjust 
                 Rec 
                   
                   
                   
                   
                   
                   
                 x 
                 x 
               
               
                 Control 
                 Press 
               
               
                 Device 
                 VQ 
                   
                   
                   
                   
                   
                   
                 x 
                 x 
               
               
                   
                 SH 
                   
                   
                   
                   
                   
                   
                 x 
                 x 
               
               
                   
                 Evap 
                   
                   
                   
                   
                   
                   
                 x 
                 x 
               
               
                   
                 VQ 
               
               
                   
                 Evap 
                 x 
                 x 
                 x 
                 x 
                 x 
                 x 
                   
                 x 
               
               
                   
                 P/T 
               
               
                   
                 HL 
                 x 
                 x 
                 x 
                 x 
                 x 
                 x 
                 x 
               
               
                   
                 Temp 
               
               
                   
               
               
                 Press Drop = refrigerant fluid pressure drop across control device (expansion valve 114) 
               
               
                 Evap Press Drop = refrigerant fluid pressure drop across evaporator 
               
               
                 Rec Press = refrigerant fluid pressure in receiver 
               
               
                 VQ = vapor quality of refrigerant fluid 
               
               
                 SH = superheat of refrigerant fluid 
               
               
                 Evap VQ = vapor quality of refrigerant fluid at evaporator outlet 
               
               
                 Evap P/T = evaporation pressure or temperature 
               
               
                 HL Temp = heat load temperature 
               
            
           
         
       
     
     For example, in some embodiments, expansion valve  114  is adjusted (e.g., automatically or by control system  999 ) based on a measurement of the evaporation pressure (p e ) of the refrigerant fluid and/or a measurement of the evaporation temperature of the refrigerant fluid. In certain embodiments, expansion valve  114  is adjusted (e.g., automatically or by control system  999 ) based on a measurement of the temperature of heat load  118 . 
     To adjust any of the control devices, compressor (if variable), or pump based on a particular value of a measured system parameter value, control system  999  compares the measured value to a set point value (or threshold value) for the system parameter. Certain set point values represent a maximum allowable value of a system parameter, and if the measured value is equal to the set point value (or differs from the set point value by 10% or less (e.g., 5% or less, 3% or less, 1% or less) of the set point value), control system  999  adjusts, e.g., the expansion valve  114 , etc. to adjust the operating state of the system, and reduce the system parameter value. 
     Certain set point values represent a minimum allowable value of a system parameter, and if the measured value is equal to the set point value (or differs from the set point value by 10% or less (e.g., 5% or less, 3% or less, 1% or less) of the set point value), control system  999  adjusts, e.g., the expansion valve  114 , etc. to adjust the operating state of the system, and increase the system parameter value. 
     Some set point values represent “target” values of system parameters. For such system parameters, if the measured parameter value differs from the set point value by 1% or more (e.g., 3% or more, 5% or more, 10% or more, 20% or more), control system  999  adjusts, e.g., the expansion valve  114 , etc. to adjust the operating state of the system, so that the system parameter value more closely matches the set point value. 
     Measured parameter values are assessed in relative terms based on set point values (i.e., as a percentage of set point values). Alternatively, in some embodiments, measured parameter values can be accessed in absolute terms. For example, if a measured system parameter value differs from a set point value by more than a certain amount (e.g., by 1 degree C. or more, 2 degrees C. or more, 3 degrees C. or more, 4 degrees C. or more, 5 degrees C. or more), then control system  999  adjusts expansion valve  114 , etc. to adjust the operating state of the system, so that the measured system parameter value more closely matches the set point value. 
     In the foregoing examples, measured parameter values are assessed in relative terms based on set point values (i.e., as a percentage of set point values). Alternatively, in some embodiments, measured parameter values can be in absolute terms. For example, if a measured system parameter value differs from a set point value by more than a certain amount (e.g., by 1 degree C. or more, 2 degrees C. or more, 3 degrees C. or more, 4 degrees C. or more, 5 degrees C. or more), then control system  999  adjusts expansion valve  114 , etc. to adjust the operating state of the system, so that the measured system parameter value more closely matches the set point value. 
     In certain embodiments, refrigerant fluid emerging from evaporator  116  can be used to cool one or more additional heat loads. In addition, systems can include a second heat load connected to a heat exchanger. A variety of mechanical connections can be used to attach second heat load to heat exchanger, including (but not limited to) brazing, clamping, welding, and any of the other connection types discussed herein. 
     Heat exchanger includes one or more flow channels through which high vapor quality refrigerant fluid flows after leaving evaporator  116 . During operation, as the refrigerant fluid vapor phases through the flow channels, it absorbs heat energy from high heat load  118 , cooling the high heat load  118 . 
     In general, the systems disclosed herein can include more than one (e.g., two or more, three or more, four or more, five or more, or even more) heat loads in addition to heat loads depicted. Each of the additional heat loads can have an associated heat exchanger; in some embodiments, multiple additional heat loads are connected to a single heat exchanger, and in certain embodiments, each additional heat load has its own heat exchanger. Moreover, each of the additional heat loads can be cooled by the superheated refrigerant fluid vapor after a heat exchanger attached to the second load or cooled by the high vapor quality fluid stream that emerges from evaporator  116 . 
     Although evaporator  116  and heat exchanger are implemented as separate components, in certain embodiments, these components can be integrated to form a single heat exchanger, with heat load and second heat load both connected to the single heat exchanger. The refrigerant fluid vapor that is discharged from the evaporator portion of the single heat exchanger is used to cool second heat load, which is connected to a second portion of the single heat exchanger. 
     The vapor quality of the refrigerant fluid after passing through evaporator  116  can be controlled either directly or indirectly with respect to a vapor quality set point by control system  999 . In some embodiments, the system includes a vapor quality sensor that provides a direct measurement of vapor quality, which is transmitted to control system  999 . Control system  999  adjusts control device depending on configuration to control the vapor quality relative to the vapor quality set point value. 
     In certain embodiments, the system includes a sensor that measures superheat and indirectly, vapor quality. For example, a combination of temperature and pressure sensors measure the refrigerant fluid superheat downstream from a second heat load, and transmit the measurements to control system  999 . Control system  999  adjusts control device according to the configuration based on the measured superheat relative to a superheat set point value. By doing so, control system  999  indirectly adjusts the vapor quality of the refrigerant fluid emerging from evaporator  116 . 
     Further, eliminating (or nearly eliminating) the refrigerant vapor from the refrigerant fluid stream entering evaporator  116  can help to reduce the cross-section of the evaporator and improve film boiling in the refrigerant channels. In film boiling, the liquid phase (in the form of a film) is physically separated from the walls of the refrigerant channels by a layer of refrigerant vapor, leading to poor thermal contact and heat transfer between the refrigerant liquid and the refrigerant channels. Reducing film boiling improves the efficiency of heat transfer and the cooling performance of evaporator  116 . 
     In addition, by eliminating (or nearly eliminating) the refrigerant vapor from the refrigerant fluid stream entering evaporator  116 , distribution of the liquid refrigerant within the channels of evaporator  116  can be made easier. In certain embodiments, vapor present in the refrigerant channels of evaporator  116  can oppose the flow of liquid refrigerant into the channels. Diverting the vapor phase of the refrigerant fluid before the fluid enters evaporator  116  can help to reduce this difficulty. 
     In addition to phase separator, or as an alternative to phase separator, in some embodiments the systems disclosed herein can include a phase separator downstream from evaporator  116 . Such a configuration can be used when the refrigerant fluid emerging from evaporator is not entirely in the vapor phase, and still includes liquid refrigerant fluid. 
     The foregoing examples of thermal management systems illustrate a number of features that can be included in any of the systems within the scope of this disclosure. In addition, a variety of other features can be present in such systems. 
     In certain embodiments, refrigerant fluid that is discharged from evaporator  116  and passes through conduit can be directly discharged as exhaust from conduit without further treatment. Direct discharge provides a convenient and straightforward method for handling spent refrigerant, and has the added advantage that over time, the overall weight of the system is reduced due to the loss of refrigerant fluid. For systems that are mounted to small vehicles or are otherwise mobile, this reduction in weight can be important. 
     In some embodiments, however, refrigerant fluid vapor can be further processed before it is discharged. Further processing may be desirable depending upon the nature of the refrigerant fluid that is used, as direct discharge of unprocessed refrigerant fluid vapor may be hazardous to humans and/or may be deleterious to mechanical and/or electronic devices in the vicinity of a TMS. For example, the unprocessed refrigerant fluid vapor may be flammable or toxic, or may corrode metallic device components. In situations such as these, additional processing of the refrigerant fluid vapor may be desirable. 
     In general, a refrigerant processing apparatus can be implemented in various ways. In some embodiments, a refrigerant processing apparatus is a chemical scrubber or water-based scrubber. Within the apparatus, the refrigerant fluid is exposed to one or more chemical agents that treat the refrigerant fluid vapor to reduce its deleterious properties. For example, where the refrigerant fluid vapor is basic (e.g., ammonia) or acidic, the refrigerant fluid vapor can be exposed to one or more chemical agents that neutralize the vapor and yield a less basic or acidic product that can be collected for disposal or discharged from the apparatus. 
     As another example, where the refrigerant fluid vapor is highly chemically reactive, the refrigerant fluid vapor can be exposed to one or more chemical agents that oxidize, reduce, or otherwise react with the refrigerant fluid vapor to yield a less reactive product that can be collected for disposal or discharged from the apparatus. 
     In certain embodiments, a refrigerant processing apparatus can be implemented as an adsorptive sink for the refrigerant fluid. The apparatus can include, for example, an adsorbent material bed that binds particles of the refrigerant fluid vapor, trapping the refrigerant fluid within apparatus and preventing discharge. The adsorptive process can sequester the refrigerant fluid particles within the adsorbent material bed, which can then be removed from apparatus and sent for disposal. 
     In some embodiments, where the refrigerant fluid is flammable, a refrigerant processing apparatus can be implemented as an incinerator. Incoming refrigerant fluid vapor can be mixed with oxygen or another oxidizing agent and ignited to combust the refrigerant fluid. The combustion products can be discharged from the incinerator or collected (e.g., via an adsorbent material bed) for later disposal. 
     As an alternative, the refrigerant processing apparatus can also be implemented as a combustor of an engine or another mechanical power-generating device. Refrigerant fluid vapor from conduit can be mixed with oxygen, for example, and combusted in a piston-based engine or turbine to perform mechanical work, such as providing drive power for a vehicle or driving a generator to produce electricity. In certain embodiments, the generated electricity can be used to provide electrical operating power for one or more devices, including high heat load  118 . For example, high heat load  118  can include one or more electronic devices that are powered, at least in part, by electrical energy generated from combustion of refrigerant fluid vapor in the refrigerant processing apparatus. 
     The thermal management systems disclosed herein can optionally include a phase separator upstream from the refrigerant processing apparatus. 
     Particularly during start-up of the systems disclosed herein, liquid refrigerant may be present in conduits because the systems generally begin operation before high heat load  118  is activated. Accordingly, phase separator functions in a manner similar to phase separators to separate liquid refrigerant fluid from refrigerant vapor. The separated liquid refrigerant fluid can be re-directed to another portion of the system, or retained within phase separator until it is converted to refrigerant vapor. By using a phase separator, liquid refrigerant fluid can be prevented from entering the refrigerant processing apparatus. 
     In some embodiments, the refrigeration systems disclosed herein can be combined with power systems to form integrated power and thermal systems, in which certain components of the integrated systems are responsible for providing refrigeration functions and certain components of the integrated systems are responsible for generating operating power. 
       FIG.  9    shows an integrated power and a TMS that includes many features similar to those discussed above (e.g., see  FIG.  1 A ). In addition, a TMS includes an engine  900  with an inlet that receives the stream of waste refrigerant fluid. Engine  900  can combust the waste refrigerant fluid directly, or alternatively can mix the waste refrigerant fluid with one or more additives (such as oxidizers) before combustion. Where ammonia is used as the refrigerant fluid in a TMS, suitable engine configurations for both direct ammonia combustion as fuel, and combustion of ammonia mixed with other additives, can be implemented. In general, combustion of ammonia improves the efficiency of power generation by the engine. 
     The energy released from combustion of the refrigerant fluid can be used by engine  900  to generate electrical power, e.g., by using the energy to drive a generator. The electrical power can be delivered via electrical connection to high heat load  118  to provide operating power for the high heat load  118 . For example, in certain embodiments, high heat load  118  includes one or more electrical circuits and/or electronic devices, and engine  900  provides operating power to the circuits/devices via combustion of refrigerant fluid. Byproducts  902  of the combustion process can be discharged from engine  900  via exhaust conduit, as shown in  FIG.  9   . 
     Various types of engines and power-generating devices can be implemented as engine  900  in a TMS. In some embodiments, for example, engine  900  is a conventional four-cycle piston-based engine, and the waste refrigerant fluid is introduced into a combustor of the engine. In certain embodiments, engine  900  is a gas turbine engine, and the waste refrigerant fluid is introduced via the engine inlet to the afterburner of the gas turbine engine. As discussed above, in some embodiments, a TMS can include phase separator (not shown) positioned upstream from engine  900 . Phase separator functions to prevent liquid refrigerant fluid from entering engine  900 , which may reduce the efficiency of electrical power generation by engine  900 . 
     In certain embodiments, the thermal management systems disclosed herein operate differently at, and immediately following, system start-up, compared to the manner in which the systems operate after an extended running period. Upon start-up, the compressor  104  and a device (usually a fan) moving a cooling fluid (usually ambient air) through the condenser  106  are powered. The compressor  104  discharges compressed refrigerant into the condenser  106 . The refrigerant is condensed and subcooled in the condenser  106 . Liquid refrigerant fluid enters receiver  110  at a pressure and temperature generated by operation of the compressor  104  and condenser  106 . 
     The thermal management systems and methods disclosed herein can be implemented as part of (or in conjunction with) directed energy systems such as high energy laser systems. Due to their nature, directed energy systems typically present a number of cooling challenges, including certain heat loads for which temperatures are maintained during operation within a relatively narrow range. 
       FIG.  10    shows one example of a directed energy system, specifically, a high energy laser system  1000 . System  1000  includes a bank of one or more laser diodes  1002  and an amplifier  1004  connected to a power source  1006 . During operation, laser diodes  1002  generate an output radiation beam  1008  that is amplified by amplifier  1004 , and directed as output beam  1010  onto a target. Generation of high energy output beams can result in the production of significant quantities of heat. Certain laser diodes, however, are relatively temperature sensitive, and the operating temperature of such diodes is regulated within a relatively narrow range of temperatures to ensure efficient operation and avoid thermal damage. Amplifiers are also temperature-sensitively, although typically less sensitive than diodes. 
     To regulate the temperatures of various components of directed energy systems such as diodes  1002  and amplifier  1004 , such systems can include components and features of the thermal management systems disclosed herein. In  FIG.  10   , evaporator  116  ( FIGS.  1 A , etc.) is coupled to diodes  1002 , while a heat exchanger  1012  (which can be evaporator  116 ) is coupled to amplifier  1004 . The other components of the thermal management systems disclosed herein are not shown for clarity. However, it should be understood that any of the features and components discussed above can optionally be included in directed energy systems. Diodes  1002 , due to their temperature-sensitive nature, effectively function as high heat load  118  in system  1000  and/or diodes and amplifier  1004  functions as high heat load  118 . 
     System  1000  is one example of a directed energy system that can include various features and components of the thermal management systems and methods described herein. However, it should be appreciated that the thermal management systems and methods are general in nature, and can be applied to cool a variety of different heat loads under a wide range of operating conditions. 
     Control system  999  can generally be implemented as any one of a variety of different electrical or electronic computing or processing devices, and can perform any combination of the various steps discussed above to control various components of the disclosed thermal management systems. 
     Control system  999  can generally, and optionally, include any one or more of a processor (or multiple processors), a memory, a storage device, and input/output device. Some or all of these components can be interconnected using a system bus. The processor is capable of processing instructions for execution. In some embodiments, the processor is a single-threaded processor. In certain embodiments, the processor is a multi-threaded processor. Typically, the processor is capable of processing instructions stored in the memory or on the storage device to display graphical information for a user interface on the input/output device, and to execute the various monitoring and control functions discussed above. Suitable processors for the systems disclosed herein include both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer or computing device. 
     The memory stores information within the system, and can be a computer-readable medium, such as a volatile or non-volatile memory. The storage device can be capable of providing mass storage for the control system  999 . In general, the storage device can include any non-transitory tangible media configured to store computer readable instructions. For example, the storage device can include a computer-readable medium and associated components, including: magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory including by way of example, semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Processors and memory units of the systems disclosed herein can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     The input/output device provides input/output operations for control system  999 , and can include a keyboard and/or pointing device. In some embodiments, the input/output device includes a display unit for displaying graphical user interfaces and system related information. 
     The features described herein, including components for performing various measurement, monitoring, control, and communication functions, can be implemented in digital electronic circuitry, or in computer hardware, firmware, or in combinations of them. Methods steps can be implemented in a computer program product tangibly embodied in an information carrier, e.g., in a machine-readable storage device, for execution by a programmable processor (e.g., of control system  999 ), and features can be performed by a programmable processor executing such a program of instructions to perform any of the steps and functions described above. Computer programs suitable for execution by one or more system processors include a set of instructions that can be used directly or indirectly, to cause a processor or other computing device executing the instructions to perform certain activities, including the various steps discussed above. 
     Computer programs suitable for use with the systems and methods disclosed herein can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as stand-alone programs or as modules, components, subroutines, or other units suitable for use in a computing environment. 
     In addition to one or more processors and/or computing components implemented as part of control system  999 , the systems disclosed herein can include additional processors and/or computing components within any of the control device (e.g., expansion valve  114 ) and any of the sensors discussed above. Processors and/or computing components of the control devices and sensors, and software programs and instructions that are executed by such processors and/or computing components, can generally have any of the features discussed above in connection with control system  999 . 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.