Patent Description:
Exemplary embodiments pertain to the art of vehicle cabin air temperature control and, in particular, to heat rejection based on dynamic control over a range of altitudes.

Air temperature control is an important function in many environments (e.g., homes, businesses, vehicles) and often requires connection to a coolant loop heat sink. In an aircraft or space vehicle, the available means of heat rejection for the coolant loop is affected by different ambient environmental variations and other vehicle constraints (e.g., power consumption, mass, and volume). In a spacecraft, for example, external absolute pressure may change from approximately <NUM> kPa (<NUM> pounds per square inch (psia)) on earth to near vacuum in space. The variations create challenges for controlling a coolant temperature in a heat exchanger that provides the cabin air. <CIT> discloses a heat rejection system of the prior art.

In one exemplary embodiment, a heat rejection system in a vehicle includes a heat exchanger to take in input coolant and to output a warmed coolant, a heat of vaporization device (HVD), and a heat of fusion device (HFD). The heat rejection system also includes a controller to direct the warmed coolant to the HVD or to the HFD based on an input, wherein the input indicates altitude of the vehicle or ambient pressure.

In addition to one or more of the features described herein, the heat rejection system also includes a first valve and a second valve. The controller controls the first valve to direct a flow of the warmed coolant to the HVD or to the second valve and to control the second valve to direct a flow of the warmed coolant or a flow of an output of the HVD to the HFD or to direct the flow of the output of the HVD to the heat exchanger as the input coolant.

In addition to one or more of the features described herein, the warmed coolant is water.

In addition to one or more of the features described herein, the HVD is a water membrane evaporator (WME).

In addition to one or more of the features described herein, the WME includes a hydrophobic membrane through which the water flows and evaporation of the water at a surface of the hydrophobic membrane results in heat rejection.

In addition to one or more of the features described herein, the HFD is a water and ice heat exchanger (WIHX).

In addition to one or more of the features described herein, the water interacts with ice in the WIHX and heat rejection results in melting of the ice.

In addition to one or more of the features described herein, the heat rejection system also includes a filter at an output of the WIHX to prevent ice from exiting the WIHX.

In addition to one or more of the features described herein, the heat rejection system also includes a pump disposed between the heat exchanger and the first valve.

In addition to one or more of the features described herein, the vehicle is a spacecraft.

In another exemplary embodiment, a method of assembling a heat rejection system for a vehicle includes arranging a heat exchanger configured to take in input coolant and to output a warmed coolant. The method also includes assembling a heat of vaporization device (HVD), assembling a heat of fusion device (HFD), and configuring a controller to direct the warmed coolant to the HVD or to the HFD based on an input. The input indicates altitude of the vehicle or ambient pressure.

In addition to one or more of the features described herein, the method also includes arranging a first valve and a second valve. The configuring the controller includes the controller controlling the first valve to direct a flow of the warmed coolant to the HVD or to the second valve and controlling the second valve to direct a flow of the warmed coolant or a flow of an output of the HVD to the HFD or to direct the flow of the output of the HVD to the heat exchanger as the input coolant.

In addition to one or more of the features described herein, the assembling the HVD includes assembling a water membrane evaporator (WME).

In addition to one or more of the features described herein, the assembling the WME includes arranging a hydrophobic membrane through which the water flows and evaporation of the water at a surface of the hydrophobic membrane results in heat rejection.

In addition to one or more of the features described herein, the assembling the HFD includes assembling a water and ice heat exchanger (WIHX).

In addition to one or more of the features described herein, the assembling the WIHX includes filling the WIHX with ice such that water interacts with ice in the WIHX and heat rejection results in melting of the ice.

In addition to one or more of the features described herein, the method also includes arranging a filter at an output of the WIHX to prevent ice from exiting the WIHX.

In addition to one or more of the features described herein, the method also includes disposing a pump between the heat exchanger and the first valve.

Embodiments of the systems and methods detailed herein relate to heat rejection based on dynamic control over a range of altitudes. A cabin air heat exchanger may be used to cool air for reuse in a vehicle cabin. The heat rejection detailed herein is for the coolant supplied to the cabin air heat exchanger. For explanatory purposes, water is assumed as the exemplary coolant for which heat rejection is implemented. However, any coolant material may be used if it is selected with consideration of the pressure differences discussed herein. Heat is rejected via vaporization and/or via fusion based on dynamic control according to the altitude of the vehicle and the associated absolute ambient pressure (i.e., pressure of the external environment).

As detailed, at lower altitudes (e.g., on the earth's surface with an absolute ambient pressure around <NUM> psia), heat may be rejected from the coolant only via fusion. At very high altitudes (e.g., in space with a near <NUM> psia), heat may sufficiently also be rejected via vaporization. At altitudes between earth and space, heat rejection via vaporization may not cool the coolant sufficiently such that both vaporization and fusion are implemented. By using fusion, vaporization, or a combination of the two based on altitude (and corresponding external pressure), the coolant (e.g., water) that is lost to the vaporization may be replenished with melted ice resulting from the fusion. Overall, the heat rejection process according to one or more embodiments benefits from requiring less replenishment (and, thus, transport) of coolant.

In the exemplary case of the coolant being water, heat rejection via vaporization (i.e., with a heat of vaporization device (HVD)) may be accomplished via a water membrane evaporator (WME) and heat rejection via fusion (i.e., with a heat of fusion device (HFD)) may be accomplished via a water/ice heat exchanger (WIHX). Unlike prior WIHX devices, the coolant (e.g., water) is not routed through the ice while being kept separated from the ice via piping. Instead, according to one or more embodiments, the water used as the coolant interacts with the ice such that any water that results from the ice melting is added to the coolant loop. In this way, replenishment of water lost in the WME as vapor via vaporization may be needed less frequently, thereby reducing the amount and weight of water or ice that must be carried in the vehicle. The WIHX may also act as an accumulator for the coolant system. Thus, as previously noted, using both the WME and the WIHX reduces the need for replenishment of the coolant, which must be transported in the vehicle.

<FIG> is a block diagram of a heat rejection system <NUM> in a vehicle <NUM> according to one or more embodiments. As previously noted, the heat rejection system <NUM> may be used with a cabin air heat exchanger <NUM>, as shown. Generally, warm cabin air <NUM> and input coolant <NUM> interact in the cabin air heat exchanger <NUM>. The result is cool cabin air <NUM> that is provided to the vehicle cabin <NUM> and warmed coolant <NUM> that must be cooled in a coolant loop <NUM>. Heat rejection is implemented in the coolant loop <NUM> by the heat rejection system <NUM> to cool down the warmed coolant <NUM> and produce input coolant <NUM>. As previously noted, the specific heat rejection that is implemented may be altitude specific and may be controlled by the controller <NUM>. As also noted, as altitude increases, ambient pressure (pressure of the external environment <NUM>) decreases.

The warmed coolant <NUM> is provided to a pump <NUM> that keeps the coolant moving through the coolant loop <NUM>. The controller <NUM> controls two controlled valves <NUM> and <NUM> to determine whether the WME <NUM> and the WIHX <NUM> participate in the heat rejection. The controller <NUM> controls the two controlled valves <NUM>, <NUM> based on altitude and a corresponding ambient pressure (i.e., pressure of the external environment <NUM>). This control is summarized in Table <NUM>, which indicates the input to the WME <NUM> and to the WIHX <NUM> at different altitudes / pressure differences.

A scenario involving a relatively low altitude (i.e., a relatively high ambient pressure and a relatively low corresponding pressure difference) is discussed first. This scenario may occur on the earth's surface, for example, where the absolute ambient pressure is about <NUM> psia. In this case, as Table <NUM> indicates, none of the warmed coolant <NUM> may be input to the WME <NUM>. Instead, the controller <NUM> may control the controlled valve <NUM> to direct the warmed coolant <NUM> to the controlled valve <NUM>, which is controlled to direct the warmed coolant <NUM> to the WIHX <NUM>.

The warmed coolant <NUM>, assumed to be water for explanatory purposes, mixes with the ice <NUM> in the WIHX <NUM>. Based on the temperature of the warmed coolant <NUM>, some of the ice <NUM> may melt. The water <NUM> in the WIHX <NUM> is cooler than the warmed coolant <NUM> based on the heat rejection via fusion with the ice <NUM>. This cooler water <NUM> is output by the WIHX <NUM> as the WIHX output <NUM>. In this scenario, there is no WME output <NUM> (i.e., the WME <NUM> is bypassed). Thus, the WIHX output <NUM> is the input coolant <NUM> to the cabin air heat exchanger <NUM>.

A scenario involving a relatively high altitude (i.e., a relatively low ambient pressure and a relatively high corresponding pressure difference) is addressed next. This scenario may occur in space, for example, where the absolute ambient pressure is about <NUM> psia. In this case, as Table <NUM> indicates, the warmed coolant <NUM> is input to the WME <NUM> and nothing is input to the WIHX <NUM> (i.e., the WIHX <NUM> is bypassed). That is, the controller <NUM> controls the controlled valve <NUM> to direct the warmed coolant <NUM> to the WME <NUM> and controls the controlled valve <NUM> to direct the WME output <NUM> to the cabin air heat exchanger <NUM> as the input coolant <NUM>.

In the WME <NUM>, the warmed coolant <NUM>, which is assumed to be water for explanatory purposes, flows through a membrane <NUM>. The membrane <NUM> is a hydrophobic membrane that passively controls the water liquid/vapor interface. At the membrane <NUM>, water flowing through evaporates and passes out of the membrane <NUM> as gas <NUM> (i.e., water vapor in the case of the warmed coolant <NUM> being water). The gas <NUM> is vented to the external environment <NUM> via a vacuum vent line <NUM>, as shown. This heat rejection via evaporation during flow through the membrane <NUM> results in the WME output <NUM> being cooler than the warmed coolant <NUM> that enters the WME <NUM>.

A scenario involving an altitude and corresponding ambient pressure in between the relatively low and relatively high altitudes/ambient pressures may occur during aircraft or spacecraft flight. For example, at an altitude of <NUM>,<NUM> (<NUM>,<NUM> feet (ft)), the ambient pressure may be sufficiently high to obtain a WME output <NUM> of <NUM> (<NUM> degrees Fahrenheit), the desired temperature for the input coolant <NUM>. However, at an altitude of <NUM>,<NUM> (<NUM>,<NUM> ft), the ambient pressure may be such that the WME <NUM> provides a WME output <NUM> with a temperature of <NUM> (<NUM> degrees Fahrenheit). In this case, as indicated in Table <NUM>, the WME output <NUM> may additionally be directed to the WIHX <NUM> based on the controller <NUM> controlling the controlled valve <NUM>. The WME output <NUM> may be further cooled by the WIHX <NUM> such that the WIHX output <NUM> is provided as the input coolant <NUM> at the desired temperature of <NUM> (<NUM> degrees Fahrenheit).

The controller <NUM> may include one or more memory devices and processors to perform the control of the controlled valves <NUM>, <NUM>. The heat rejection from the warmed coolant <NUM> is based on dynamic control of the controlled valves <NUM>, <NUM> by the controller <NUM>. This dynamic control accounts for the fact that the WME <NUM>, WIHX <NUM>, or both are needed according to ambient pressure and the difference between the pressure of the warmed coolant <NUM> and the absolute ambient pressure. Because the ambient pressure and pressure difference varies with altitude, the control of the controlled valves <NUM>, <NUM> may be based on altitude. The control may also be predetermined and static, following set points obtained analytically or experimentally.

The controller <NUM> may obtain an input of the current altitude and may use the altitude as the basis for control of the controlled valves <NUM>, <NUM>. Alternately or additionally, the controller <NUM> may obtain an input of the absolute ambient pressure and may map the pressure value to a control scheme for the controlled valves <NUM>, <NUM>. Alternately or additionally, the controller <NUM> may obtain an input of the temperature of the warmed coolant <NUM> at the input to the controlled valve <NUM> and the temperature of the WME output <NUM> at the input to the controlled valve <NUM> to determine where to direct flow through each of the controlled valves <NUM>, <NUM>. According to alternate embodiments, the controller <NUM> may implement machine learning to obtain input (e.g., altitude, absolute ambient pressure) and determine corresponding control of the controlled valves <NUM>, <NUM>.

<FIG> is a block diagram of a heat rejection system <NUM> according to one or more embodiments. As <FIG> shows, most of the components of the coolant loop <NUM> are the same as those discussed with reference to <FIG>. These components are not discussed again. Additional components include an optional gas trap <NUM> is shown at the inlet of the pump <NUM>. The gas trap <NUM> may be used to prevent cavitation. In addition, the WIHX <NUM> is shown with an optional filter <NUM> that prevents ice from entering the coolant loop <NUM>.

<FIG> is a process flow of a method <NUM> of performing heat rejection according to one or more embodiments. The processes may be performed by the controller <NUM>. At block <NUM>, obtaining input refers to obtaining altitude, ambient pressure, and/or temperature of the warmed coolant <NUM> and WME output <NUM>, as previously noted. At block <NUM>, determining whether the WME <NUM>, WIHX <NUM>, or both are needed may be based on a mapping (e.g., altitude or pressure difference is mapped to actions as indicated in Table <NUM>, for example) or may be based on machine learning. At block <NUM>, controlling the controlled valves <NUM>, <NUM> is based on the determination (e.g., mapping, machine learning) at block <NUM>.

Claim 1:
A heat rejection system (<NUM>) for a vehicle, the heat rejection system comprising:
a heat exchanger (<NUM>) configured to take in input coolant (<NUM>) and to output a warmed coolant (<NUM>);
a heat of vaporization device, HVD;
a heat of fusion device, HFD;
a controller (<NUM>) configured to direct the warmed coolant to the HVD or to the HFD based on an input, characterised in that the input indicates altitude of the vehicle or ambient pressure.