Patent Publication Number: US-2023138902-A1

Title: Device that implements a cryogenic space environment that uses room temperature nitrogen gas and controls temperature

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2021-0147906 filed on Nov. 1, 2021. The entire contents of the above-listed application are hereby incorporated by reference for all purposes. 
     TECHNICAL FIELD 
     The following disclosure relates to a device for implementing a space environment, and more particularly, to a device for implementing a cryogenic space environment capable of controlling a temperature in a vacuum-state container to be maintained in a cryogenic state to implement a space environment. 
     BACKGROUND 
     A device for implementing a space environment is a device for implementing the inside of a vacuum-state container to become a state close to a space environment to perform a test for checking an operation of a test object, such as an artificial satellite, before being launched into an outer space. 
       FIG.  1    is a schematic diagram of a conventional device for implementing a space environment. Referring to  FIG.  1   , a vacuum state of a vacuum container is maintained by a vacuum pump connected to the vacuum container, and a shroud is disposed inside the vacuum container. The shroud has a structure in which liquid nitrogen is supplied thereto through a liquid nitrogen tank connected to the shroud, and the supplied liquid nitrogen is discharged to the outside in a gas phase after exchanging heat with the inside of the vacuum container. 
     In the conventional device for implementing a cryogenic space environment, the space environment is implemented by directly supplying liquid nitrogen to the shroud inside the vacuum container. In order to supply liquid nitrogen, which is cryogenic fluid, a separate fluid storage container (e.g., a liquid nitrogen tank), which is difficult to handle and manage, is required. Furthermore, since a system to which the liquid nitrogen is supplied is exposed to the outside, a temperature can be restrictively maintained only at −196 degrees Celsius, which is a saturation temperature of liquid nitrogen at atmospheric pressure. 
     Therefore, there has been a demand for a technique capable of implementing a cryogenic temperature environment, while controlling the cryogenic temperature environment at a temperature in a predetermined range and replacing a liquid nitrogen tank that is difficult to manage. 
     SUMMARY 
     An embodiment of the present disclosure is directed to providing a device for implementing a cryogenic space environment by controlling a temperature of working fluid that determines a temperature of a shroud. 
     Another embodiment of the present disclosure is directed to providing a device for implementing a cryogenic space environment by supplying room-temperature gas instead of liquid nitrogen that is difficult to manage. 
     Another embodiment of the present disclosure is directed to providing a device for implementing a cryogenic space environment by configuring a closed system for liquefying gas supplied to be injected into a shroud and controlling a saturation temperature of working fluid. 
     In one general aspect, a device for implementing a space environment includes: a vacuum container maintaining a vacuum state through a vacuum pump; a shroud disposed inside the vacuum container to exchange heat between working fluid supplied into the shroud and the inside of the vacuum container; a liquefaction tank connected to both ends of the shroud and including a cryogenic refrigerator liquefying working fluid; a pressure tank connected to an upper end of the liquefaction tank to supply or discharge gas-phase working fluid to or from the liquefaction tank; and a control device controlling a pressure of the pressure tank, by supplying or discharging working fluid to or from the pressure tank, to adjust a saturation temperature of the working fluid. 
     A closed system may be maintained inside the shroud, and radiant heat may be exchanged between the working fluid supplied into the shroud and the inside of the vacuum container. 
     The liquefaction tank may be connected to both ends of the shroud, including: a gas line connected to the upper end of the liquefaction tank to supply vaporized working fluid from the shroud to the liquefaction tank; and a liquid line connected to a lower end of the liquefaction tank to supply liquefied working fluid from the liquefaction tank to the shroud, the liquefaction tank may be disposed above the shroud, and the liquefied working fluid may move in a gravity direction and be injected into the shroud. 
     A plurality of temperature sensors may be disposed along the shroud in the vacuum container, and the plurality of temperature sensors may be disposed to be spaced apart from one another at predetermined intervals from the liquid line to a lower side of the shroud to measure a location-based change in temperature of working fluid. 
     One or more cryogenic refrigerators may be disposed in the liquefaction tank, and the cryogenic refrigerators may be controlled according to an internal temperature of the vacuum container. 
     Gas-phase working fluid may be supplied from a bombe to the pressure tank to increase an internal pressure of the pressure tank. 
     The pressure tank may be connected to an exhaust line connected to the outside and a supply line connected to the bombe, the pressure of the pressure tank may be input to the control device, and the control device may output whether to open or close an exhaust valve of the exhaust line and a supply valve of the supply line. 
     The bombe may contain nitrogen gas at room temperature. 
     The control device may include a calculation unit calculating the saturation temperature of the working fluid through a pressure sensor connected to the pressure tank. 
     The shroud may maintain a temperature of the working fluid in a range between a triple point temperature and a critical temperature by adjusting a saturation pressure of the fluid in the closed system. 
     In another general aspect, a method for implementing a space environment using the device for implementing a space environment includes: a pressure control step in which the control device controls a pressure of the closed system by supplying or discharging fluid to or from the pressure tank; after the pressure control step, a liquefaction step in which the cryogenic refrigerator liquefies the supplied working fluid; after the liquefaction step, an inflow step in which the liquefied working fluid moves in a gravity direction and flows into the shroud; and after the inflow step, a heat exchange step in which radiant heat is exchanged between the shroud and the inside of the vacuum container. 
     The pressure control step may include: a depressurization step in which the working fluid is discharged to the outside to decrease the pressure in the closed system; and a pressurization step in which working fluid for pressurization is supplied from a bombe containing the working fluid at room temperature to increase the pressure in the closed system. 
     In the liquefaction step, the saturation temperature of the working fluid may be changed according to the pressure adjusted in the pressure control step. 
     The method for implementing a space environment may further include, after the heat exchange step, a regeneration step in which the working fluid subjected to the heat exchange is vaporized, the vaporized working fluid moves to the liquefaction tank, and then the liquefaction step is repeated. 
     According to the present disclosure, a temperature inside the vacuum container can be adjusted by controlling a temperature of working fluid that determines a temperature of the shroud. 
     In addition, by providing the cryogenic refrigerator for liquefying gas, room-temperature gas can be supplied instead of liquid nitrogen that is difficult to manage. 
     In addition, a temperature inside the vacuum container can be formed within a predetermined range by configuring a closed system in the shroud and controlling a pressure in the closed system to control a saturation temperature of working fluid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a configuration diagram illustrating a conventional art. 
         FIG.  2    is a configuration diagram illustrating the present disclosure. 
         FIG.  3   ,  FIG.  4   , and  FIG.  5    are enlarged diagrams illustrating the present disclosure. 
         FIG.  6    is a phase-change graph. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG.  1   , in a conventional device for implementing a space environment, a temperature inside a vacuum-state container  1  is decreased by supplying liquid nitrogen into a shroud  2 . At this time, since the shroud  2  is exposed to atmospheric-pressure outside air through a chamber  4 , the temperature can be maintained only at −196 degrees Celsius, which is a saturation temperature, and thus, it is difficult to control the temperature. 
     In addition, the conventional device for implementing a space environment is disadvantageous in that it is required to continuously supply liquid nitrogen, and it is also required to manage a bombe  3  containing liquid nitrogen and connected to supply the liquid nitrogen. 
     The present disclosure provides a device for implementing a space environment capable of controlling a temperature in a shroud and a vacuum container by controlling a pressure to control a saturation temperature of gas-phase working fluid. 
     In addition, the present disclosure provides a device for implementing a space environment including a cryogenic refrigerator for liquefying room-temperature gas supplied thereto from a bombe, making it possible to reduce time and labor required to manage the bombe. 
     Hereinafter, a device for implementing a cryogenic space environment capable of controlling a temperature using room-temperature nitrogen gas according to the present disclosure having the configuration as described above will be described in detail with reference to the accompanying drawings. 
     [1] Overall Configuration and Operating Principle of Present Disclosure 
     First,  FIG.  2    is a configuration diagram illustrating the present disclosure. Referring to  FIG.  2   , the device for implementing a space environment includes: a vacuum container  100  maintaining a vacuum state through a vacuum pump  110 ; a shroud  200  disposed inside the vacuum container  100  to exchange heat between working fluid supplied into the shroud  200  and the inside of the vacuum container  100 ; a liquefaction tank  300  connected to both ends of the shroud  200  and including a cryogenic refrigerator  310  liquefying working fluid; a pressure tank  400  connected to an upper end of the liquefaction tank  300  and stably maintaining a pressure therein before supplying or discharging gas-phase working fluid; and a control device  500  controlling the pressure of the pressure tank  400 , by supplying and discharging working fluid, to adjust a saturation temperature of the working fluid. 
     The vacuum container  100  is connected to the vacuum pump  110  disposed outside the vacuum container  100  to maintain the inside of the vacuum container  100  in a vacuum state and to implement the inside of the vacuum container  100  to have a pressure similar to that in the space environment. The inside of the vacuum container  100  is implemented to have a temperature similar to that in the space environment by exchanging radiant heat with the shroud  200  disposed inside the vacuum container  100 . 
     The shroud  200  disposed in the vacuum container  100  is formed in the form of a tube to which working fluid for exchanging heat with the inside of the vacuum container  100  is supplied. Liquid-phase working fluid is supplied to the shroud  200  through one end thereof, and gas-phase working fluid is discharged from the shroud  200  after heat exchange through the other end thereof. Both ends of the shroud  200  according to the present disclosure are connected to one tank, and the supplying and the discharging of the working fluid are performed simultaneously. 
     The liquefaction tank  300  is connected to both ends of the shroud  200 . A liquid line through which liquid-phase working fluid is supplied is connected to a lower end or a lower surface of the liquefaction tank  300 , and a gas line through which gas-phase working fluid is discharged is connected to an upper end or an upper surface of the liquefaction tank  300 . The cryogenic refrigerator  310  liquefying gas-phase working fluid is contained inside the liquefaction tank  300  to liquefy gas-phase working fluid in the liquefaction tank and collect liquid-phase working fluid at the lower end of the liquefaction tank. The collected liquid-phase working fluid is supplied into the shroud  200  through the liquid line. 
     The shroud  200 , the liquefaction tank  300 , and the pressure tank  400  are connected to one another, and a closed system is maintained therebetween. The pressure tank  400  is a tank for controlling a pressure of the closed system by supplying and discharging gas-phase working fluid. The pressure tank  400  is connected to the liquefaction tank  300  through a connection line, and is connected to the upper end or the upper surface of the liquefaction tank  300  to prevent the liquefied working fluid from moving. 
     In this case, it is a feature of the present disclosure to adjust a temperature of working fluid supplied into the shroud  200  by controlling a pressure of the closed system to change a saturation temperature of the working fluid to a required temperature. 
     This results in the ability to implement a space environment even at a temperature higher or lower than −196° C., without having to maintain the vacuum container  100  at a constant temperature (−196° C.). 
       FIGS.  3  to  5    are enlarged views illustrating the present disclosure.  FIG.  3    is an enlarged view illustrating the shroud and the liquid tank. Referring to  FIG.  3   , the liquefaction tank  300  is connected to both ends of the shroud  200 , including a gas line  210  connected to the upper end of the liquefaction tank  300  to supply vaporized working fluid from the shroud  200  to the liquefaction tank  300  and a liquid line  220  connected to the lower end of the liquefaction tank  300  to supply liquefied working fluid from the liquefaction tank  300  to the shroud  200 . 
     The liquefaction tank  300  is disposed above the shroud  200  so that the liquefied working fluid moves in a gravity direction to be injected through the liquid line  220  connected to the lower surface or the lower end of the liquefaction tank  300 . This may reduce the number of components because a pump or the like for supplying working fluid into the shroud  200  is not necessary, thereby simplifying the configuration. Accordingly, it is possible to reduce costs and decrease generation of heat. 
     A plurality of temperature sensors  230  are disposed inside the vacuum container  100 , some of the temperature sensors  230  are disposed along an outer surface of the shroud  200 . The temperature sensors  230  are disposed to be spaced apart from one another at predetermined intervals from the liquid line  220  to a lower side of the shroud  200  to measure a location-based change in temperature of working fluid. The positions of the temperature sensors  230  are not limited thereto, and the temperature sensors  230  may be disposed to be spaced apart from the shroud  200  by a predetermined distance, and may be disposed from the lower side of the shroud  200  to the gas line  210 . 
     By observing an internal temperature of the vacuum container and a change in temperature of the injected working fluid, the temperature of the supplied working fluid can be controlled to implement a required temperature environment within a short period time. 
       FIG.  4    is an enlarged view illustrating the liquefaction tank and the pressure tank. Referring to  FIG.  4   , the liquefaction tank  300  is connected to the liquid line  220  and the gas line  210  of the shroud  200 , and the connection line  320  is connected to the upper end of the liquefaction tank  300  to be connected to the pressure tank  400 . The pressure tank  400  is connected to a gas exhaust line  511  for discharging gas-phase working fluid to the outside and a gas supply line  521  for supplying gas-phase working fluid. Each of the gas exhaust line  511  and the gas supply line  521  is blocked from the outside by a valve to form a closed system inside. 
     The cryogenic refrigerator  310  is disposed at the upper end of the liquefaction tank  300  to liquefy gas-phase working fluid supplied through the gas line  210  and the connection line  320  connected to the upper end of the liquefaction tank  300 . One or more cryogenic refrigerators  310  are disposed in the liquefaction tank  300 , and the number of cryogenic refrigerators  310  to be operated and an operation time thereof are controlled according to the internal temperature of the vacuum container  100 . When a difference between a required temperature and a current internal temperature of the vacuum container  100  is large, the number of operated cryogenic refrigerators  310  increases. When a difference between a required temperature and a current internal temperature of the vacuum container  100  is not large or when the current internal temperature of the vacuum container  100  remains equal to the required temperature, the number of operated cryogenic refrigerators  310  decreases to reduce power consumption. 
     The pressure tank  400  is included in the closed system to serve to control an internal pressure. The pressure tank  400  controls the internal pressure by supplying and discharging gas-phase working fluid, and includes a pressure sensor  410  and a pressure gauge  420  for measuring a pressure, and a safety valve  430  provided for emergency. 
     The present disclosure uses a saturation curve of working fluid, based on the principle that the working fluid is liquefied at a relatively high temperature when gas is supplied to the pressure tank  400 , that is, the closed system, to increase the pressure, and the working fluid is liquefied at a relatively low temperature when the gas in the closed system is discharged to decrease the pressure. 
     When the required temperature is lower than the current temperature, gas is discharged through the gas exhaust line  511  connected to the pressure tank  400 . In this case, when a pressure lower than atmospheric pressure is required, a vacuum pump may be arranged. When the required temperature is higher than the current temperature, gas is supplied through the gas supply line  521  connected to the pressure tank  400  to increase the pressure in the closed system. 
       FIG.  5    is an enlarged view illustrating the pressure tank  400  and the control device  500 . Referring to  FIG.  5   , the pressure tank  400  is connected to the gas exhaust line  511  connected to the outside and the gas supply line  521  connected to a bombe  600 . A pressure is input to the control device  500  through the pressure sensor  410  of the pressure tank  400 , and the control device  500  outputs whether to open or close an exhaust valve  510  of the gas exhaust line  511  and a supply valve  520  of the gas supply line  521 . 
     A temperature required for the vacuum container  100 , that is, a required space environment condition, is input to the control device  500 , and the control device  500  controls the components of the present disclosure to implement a space environment. In order to match a saturation temperature of working fluid with the required space environment condition, a pressure of the pressure tank  400  is input to the control device  500  through the pressure sensor  410 , and the control device  500  controls the pressure by opening or closing the exhaust valve  510  and the supply valve  520 . 
     In this case, the feature of the present disclosure is not limited to the saturation temperature of the working fluid being matched with the required temperature, and the saturation temperature may be set to a temperature higher or lower than the required temperature to quickly reach the required temperature. 
     The control device  500  includes a calculation unit calculating a saturation temperature of working fluid through the pressure sensor  410  connected to the pressure tank  400 . The control device  500  includes phase-change data about working fluid, controls the valves  510  and  520  based on the phase-change data, and forms a pressure of the closed system corresponding to the saturation temperature of the working fluid. The phase-change data will be described with reference to  FIG.  6    below. 
     In addition, the control device  500  may be connected to one or more cryogenic refrigerators  310  to control the number of cryogenic refrigerators  310  that need to be operated and an operation time thereof in consideration of the required temperature and a time required to reach the set temperature. 
     In addition, the control device  500  is connected to the plurality of temperature sensors  230  disposed along the shroud  200  to control a pressure with temperature-change data according to the movement of the working fluid input thereto from the temperature sensors  230 . 
     That is, when a temperature required for the vacuum container  100  is input, the calculation unit of the control device  500  may derive an estimated time by obtaining current information through the temperature sensors  230  and the pressure sensor  410  and controlling the plurality of valves and the number of cryogenic refrigerators  310  to be operated. 
     Recalling the problem of the conventional art, if a cryogenic bombe  600  containing liquefied fluid is connected, it is difficult to handle and manage the cryogenic bombe  600 . In the present disclosure, however, the bombe  600  contains gas-phase working fluid at room temperature, and the bombe  600  is connected to the pressure tank  400  to supply the working fluid to the pressure tank  400 . The working fluid is supplied to the shroud  200  after being liquefied in the cryogenic refrigerator  310  provided inside the liquefaction tank  300 . 
       FIG.  6    is a general phase-change graph. Referring to  FIG.  6   , the range in which working fluid is liquefied to be supplied into the shroud refers to a range between a triple point temperature and a critical point temperature of the working fluid. A space environment is implemented by providing a pressure in a range between a triple point pressure and a critical point pressure according to the temperatures for the respective points. For example, in a case where nitrogen is selected and supplied as working fluid, a triple point temperature of nitrogen is −210° C., and a triple point pressure of nitrogen is 12.53 kPa. In addition, a critical point temperature of nitrogen is −146.96° C., and a critical point pressure of nitrogen is 3.3978 MPa. The control device forms a pressure of 12.53 kPa to 3.3978 MPa by controlling the exhaust valve and the supply valve, and forms a temperature of −210° C. to −146.96° C. in the vacuum container through the liquefied working fluid. 
     [2] Method for Implementing Space Environment According to Present Disclosure 
     A method for implementing a space environment using the device for implementing a cryogenic space environment according to the present disclosure having the above-described features will be described with reference to  FIG.  2   . 
     The method for implementing a space environment using the device for implementing a space environment includes: a pressure control step in which the control device  500  controls a pressure of the closed system by supplying or discharging fluid to or from the pressure tank  400 ; after the pressure control step, a liquefaction step in which the cryogenic refrigerator  310  liquefies the supplied working fluid; after the liquefaction step, an inflow step in which the liquefied working fluid moves in a gravity direction and flows into the shroud  200 ; and after the inflow step, a heat exchange step in which radiant heat is exchanged between the shroud  200  and the inside of the vacuum container  100 . 
     The pressure control step is a step in which a pressure of the closed system is input to the control device  500 , and the control device  500  controls the exhaust valve and the supply valve to be opened or closed. The control device  500  adjusts an internal pressure to a required pressure by supplying or exhausting gas-phase working fluid through the exhaust valve and the supply valve. 
     In addition, the pressure control step includes: a depressurization step in which the working fluid is discharging to the outside to decrease the pressure in the closed system; and a pressurization step in which working fluid for pressurization is supplied from the bombe  600  containing the working fluid at room temperature to increase the pressure in the closed system. In the depressurization step, gas-phase working fluid is discharged to the outside through the exhaust valve, and if necessary, the pressure in the closed system is decreased by using a pump. In the pressurization step, if necessary, a pressurizing device is provided or a plurality of bombes  600  are connected for pressurization. 
     The liquefaction step is a step in which the gas-phase working fluid is liquefied under the pressure adjusted in the pressure control step. The gas-phase working fluid supplied to the closed system is liquefied by one or more cryogenic refrigerators  310  provided in the liquefaction tank  300 . At this time, a temperature of the liquefied working fluid is equal to a saturation temperature, and the liquefied working fluid is formed as working fluid having a temperature corresponding to the pre-adjusted pressure. The pressure decreased by liquefaction or increased by vaporization is continuously adjusted in the control device  500 . 
     The inflow step is a step in which the liquefied working fluid is transferred in the gravity direction and supplied into the shroud  200 . The liquefaction tank  300  is disposed above the shroud  200 , and the liquid line through which the liquefied working fluid is supplied is disposed at the lower surface or the lower end of the liquefaction tank  300 , such that the liquefied working fluid is supplied into the shroud  200  without applying additional force. 
     The heat exchange step is a step in which the working fluid supplied into the shroud  200  exchanges heat with the inside of the vacuum container  100 . At this time, the exchange of the heat is exchange of radiant heat, and a space environment having a required temperature is created through the heat exchange. 
     After the heat exchange step, the method for implementing a space environment further includes a recycling step in which the working fluid subjected to the heat exchange is vaporized, the vaporized working fluid moves to the liquefaction tank  300 , and then the liquefaction step is repeated. The liquefied working fluid supplied into the shroud  200  is vaporized through the heat exchange and transferred to the liquefaction tank  300  through the gas line. The transferred gas-phase working fluid is liquefied by the cryogenic refrigerator  310 , and the liquefied working fluid is supplied to the shroud  200 . The closed system has a circulation structure in the following order: the liquefaction tank, the liquid line, the shroud, the gas line, and the liquefaction tank, which may reduce an amount of working fluid to be consumed. The gas line is connected to the upper end or the upper surface of the liquefaction tank  300  to prevent the liquefied working fluid from moving. 
     The method for implementing a space environment according to the present disclosure includes: before the pressure control step, a condition input step in which a required temperature condition is input to the control device  500 ; and after the condition input step, a calculation step in which how much the pressure is to be adjusted is calculated to implement the required temperature according to the input required temperature condition. 
     In the condition input step, a pressure and a temperature in the vacuum container  100  are input. The required pressure is implemented through the vacuum pump  110  connected to the vacuum container  100 , and the required temperature is implemented through heat exchange with the shroud  200  disposed inside the vacuum container  100 . 
     In order to implement the required temperature, the calculation step includes a calculation unit having phase-change data about the supplied working fluid. The calculation unit calculates whether to open or close the plurality of valves and the number of cryogenic refrigerators  310  to be operated, and drives each component through the control device  500 . 
     In addition, the calculating unit may estimate a time required to reach the required pressure and temperature through the temperature sensors  230  and the pressure sensor  410  and based on the specifications of each component. 
     The present disclosure may be modified in various ways and may have various embodiments. Although specific embodiments have been illustrated in the drawings and described in detail above, it should be understood that the present disclosure is not limited to the specific embodiments, but covers all modifications, equivalents or substitutes that fall within the spirit and scope of the present disclosure. 
     Also, it should be understood that when one component is referred to as being “coupled” or “connected” to another component, the one component may be coupled or connected to the another component either in a direct manner or through an intervening component. 
     Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meanings as commonly understood by those having ordinary skill in the art to which the present disclosure pertains. 
     Terms such as those defined in generally used dictionaries should be interpreted to have meanings consistent with the contextual meanings in the relevant art, and are not to be interpreted to have ideal or excessively formal meanings unless clearly defined in the present application. 
     The present disclosure is not limited to the above-described embodiments, and may be applied in a wide range. Also, various modification may be made without departing from the gist of the present disclosure described herein. 
     DETAILED DESCRIPTION OF MAIN ELEMENTS 
     
         
           100 : Vacuum container 
           110 : Vacuum pump 
           200 : Shroud 
           210 : Gas line 
           220 : Liquid line 
           230 : Temperature sensor 
           300 : Liquefaction tank 
           310 : Cryogenic refrigerator 
           320 : Connection line 
           400 : Pressure tank 
           410 : Pressure sensor 
           420 : Pressure gauge 
           430 : Safety valve 
           500 : Control device 
           510 : Exhaust valve 
           511 : Gas exhaust line 
           520 : Supply valve 
           521 : Gas supply line 
           600 : Bombe