Thermodynamic exhaust system and method of controlling the same

Abstract

This invention discloses a thermodynamic exhaust system and its control method. A pressure sensor is installed in the tank, and a throttling solenoid valve is arranged before the throttling valve. A data acquisition unit collects pressure sensor data and transmits it to a computer. The computer controls the on / off state of the circulating pump, throttling valve, throttling solenoid valve, and exhaust port solenoid valve through logic operations. When the tank pressure rises to the upper limit of the control band, the circulating pump and throttling solenoid valve open, the thermodynamic exhaust system operates, and the tank pressure and temperature decrease. When the tank pressure drops to the critical pressure, the throttling solenoid valve closes, while the circulating pump remains open, utilizing liquid subcooling to reduce the tank pressure until it reaches the lower limit of the control band. This control method fully utilizes liquid subcooling, achieving efficient utilization of cooling capacity, reducing exhaust process time, and lowering exhaust losses. Simultaneously, the mixing process mitigates thermal stratification within the tank, significantly improving the efficiency of the thermodynamic exhaust system.

Description

Technical Field

[0001] This invention relates to a thermodynamic exhaust system, and more particularly to a thermodynamic exhaust system and its control method. Background Technology

[0002] Cryogenic propellants possess characteristics such as high fuel performance, non-toxicity, and high specific impulse, effectively meeting the payload and energy density requirements of spacecraft. Cryogenic liquids, represented by liquid hydrogen, liquid oxygen, and liquid methane, remain the preferred propellants for future spacecraft. However, cryogenic conditions impose more stringent requirements on the insulation of on-orbit storage tanks. Even with well-insulated cryogenic storage systems, heat leakage in the space thermal environment must be less than 5 W / m³. 2 This can still cause the local temperature of the cryogenic propellant inside the tank to rise, leading to liquid evaporation or even boiling, which in turn causes the pressure inside the tank to rise, seriously threatening the safety of the spacecraft.

[0003] The Thermodynamic Vent System (TVS) proposed by Rock International Corporation in US Patent Publication No. 5398515 is one of the effective solutions to meet the above requirements. The TVS uses a cryogenic circulating pump to extract a portion of the fluid from the tank and divides it into two streams. One stream passes through a throttling valve to gain cooling capacity and cools the other mainstream fluid before being discharged. The cooled mainstream fluid is then injected into the tank via a spray bar and thoroughly mixes with the fluid inside, thereby achieving cooling and depressurization of the fluid in the tank. However, traditional TVS systems still have the following problems: Initially, the gas and liquid in the tank are saturated. During TVS operation, because most of the cryogenic fluid (cooling capacity) enters the liquid, the liquid becomes somewhat supercooled, and the cooling capacity gained through throttling is not fully utilized, resulting in longer TVS operating time and exhaust losses, thus reducing TVS efficiency. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a thermodynamic exhaust system and its control method, which can make full use of the cooling capacity of the subcooled liquid in the tank, reduce the TVS working time in a targeted and purposeful manner, and thus achieve the purpose of temperature and pressure control with less exhaust loss.

[0005] To achieve the above objectives, the present invention provides a thermodynamic exhaust system comprising a tank for storing propellant, wherein the upper and lower walls of the tank are respectively connected to a propellant exhaust pipe and a circulation pipeline, an exhaust port solenoid valve is provided on the exhaust pipe, and a cryogenic circulation pump for circulating the propellant within the tank is provided on the circulation pipeline.

[0006] A spray bar is installed inside the storage tank, and a shell-and-tube heat exchanger is installed inside the spray bar. One end of the circulation pipeline is connected to the storage tank, and the other end is connected to the shell side of the shell-and-tube heat exchanger inside the storage tank. The exhaust pipe is connected to the tube side of the shell-and-tube heat exchanger inside the storage tank. A nozzle is installed on the outer shell of the spray bar. A throttling pipeline is also installed outside the storage tank, with one end connected to the circulation pipeline and the other end connected to the tube side of the shell-and-tube heat exchanger inside the storage tank. A throttling valve and a throttling solenoid valve are also installed on the throttling pipeline.

[0007] The tank is also equipped with a pressure sensor, and the circulation pipeline and the throttling pipeline are respectively equipped with flow sensors;

[0008] The pressure sensor, the flow sensor on the circulation pipeline and the throttling pipeline are respectively connected to the data acquisition instrument and transmit the acquired data to the computer.

[0009] The storage tank has elliptical end caps at both ends and a cylindrical structure in the middle. The storage tank is covered with multiple layers of variable density insulation material.

[0010] The flow sensor on the circulation pipeline is positioned before the circulation pump, and the flow sensor and throttling solenoid valve on the throttling pipeline are positioned before the throttling valve.

[0011] The exhaust port solenoid valve and the throttling solenoid valve are cryogenic solenoid valves.

[0012] A control method based on the above-mentioned thermodynamic exhaust system includes the following steps:

[0013] Step 1: The computer collects data from the pressure sensor using a data acquisition device and then compares it with the upper limit P of the pressure control band. max Controlled pressure band lower limit P min and critical pressure P cr Perform logical judgments;

[0014] Step 2: When the tank pressure is greater than or equal to the upper limit P of the pressure control band. max At that time, the computer issues a command to open the cryogenic circulating pump, the throttling solenoid valve, the throttling valve, and the exhaust port solenoid valve 7;

[0015] Step 3: The cryogenic propellant enters the circulation pipeline under the action of the cryogenic circulation pump and is divided into two fluids. The first fluid flows through the throttle valve and then exchanges heat with the second fluid in the shell-and-tube heat exchanger inside the injection rod. After the heat exchange, the first fluid is discharged through the exhaust pipe, and the second fluid is injected into the storage tank from the nozzle.

[0016] Step 4: When the tank pressure drops to the critical pressure P cr At that time, the computer issues a command to close the throttle solenoid valve, the throttle valve and the exhaust port solenoid valve, keep the cryogenic circulation pump on, and the cryogenic propellant is extracted and directly injected into the storage tank.

[0017] Step 5: When the tank pressure drops to the lower limit P of the pressure control zone... min After completing one pressure boosting / depressurization cycle, the computer issues a command to shut down the cryogenic circulation pump and begin the next pressure boosting / depressurization cycle.

[0018] The critical pressure P cr The pressure value is equal to the area of ​​the effective pressure drop rate during the mixing phase, and the critical pressure P is... cr The pressure value is negatively correlated with the filling rate and positively correlated with the external heat leakage density.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The thermodynamic exhaust system of this invention replaces the final stage of the original full exhaust process with a mixing process, making full use of the liquid subcooling formed during the exhaust process to reduce losses caused by exhaust. Simultaneously, the turbulence effect of the mixing process alleviates thermal stratification within the tank, extending the pressurization time for the next cycle. This control method provides a new approach to the space orbital thermal management of cryogenic propellants, is technically easy to implement, significantly improves the temperature and pressure control efficiency of the TVS, and reduces energy consumption. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the thermodynamic exhaust system of the present invention;

[0022] Figure 2 This is a flowchart of the thermodynamic exhaust system control method of the present invention;

[0023] Figure 3 For specific working conditions (70% filling rate, 0.2W / m) 2 The curve of the rate of the step-down transformer in exhaust mixing mode under heat leakage density as a function of time.

[0024] Among them: 1-storage tank, 2-low temperature circulating pump, 3-throttle valve, 4-jet rod, 5-shell heat exchanger, 6-exhaust pipe, 7-exhaust port solenoid valve, 8-throttle solenoid valve, 9-flow sensor, 10-pressure sensor, 11-data acquisition instrument, 12-computer, 13-nozzle. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but this is not intended to limit the present invention.

[0026] like Figure 1 As shown, the thermodynamic exhaust system of the present invention includes a storage tank 1, a cryogenic circulating pump 2, a throttling valve 3, an injection rod 4, a shell-and-tube heat exchanger 5, an exhaust pipe 6, an exhaust port solenoid valve 7, a throttling solenoid valve 8, a flow sensor 9, a pressure sensor 10, a data acquisition instrument 11, a computer 12, and a nozzle 13.

[0027] Among them, area I is the internal area of ​​the tank, area II is the external circulation pipeline area of ​​the tank, and area III is the signal processing area.

[0028] The storage tank 1 is a cylindrical structure with elliptical end caps at both ends and a cylindrical body in the middle. The storage tank 1 is a cryogenic storage tank, and its outer side is lined with multiple layers of variable density insulation material. The storage tank 1 is used to store propellant. The upper and lower walls of the storage tank 1 are respectively connected to the propellant exhaust pipe 6 and the circulation pipeline. The exhaust pipe 6 is equipped with an exhaust port solenoid valve 7, which controls the exhaust pipeline according to computer instructions and is used to control the opening and closing of the exhaust pipe. The circulation pipeline is equipped with a cryogenic circulation pump 2, which is located outside the storage tank and is used to realize the circulation of propellant in the storage tank.

[0029] The throttle valve 3 is installed outside the storage tank 1, with one end connected to the low-temperature circulating pump 3 and the other end connected to the injection rod 4. Its function is to obtain cold energy through the Joule-Thomson effect.

[0030] The spray rod 4 is located inside the storage tank 1. One end of the spray rod 4 is connected to the circulation pipeline, and the other end is connected to the exhaust pipe 6. It is used for cooling the mainstream fluid and spraying the fluid after the temperature drop. The spray rod 4 has a shell-and-tube heat exchanger 5 embedded in it, and multiple nozzles 13 are arranged outside it. The throttled fluid and the mainstream fluid exchange heat in the shell-and-tube heat exchanger 5. After the mainstream fluid is cooled, it is sprayed into the storage tank 1 from the nozzles 13. After the throttled fluid is heated, it is discharged from the exhaust pipe 6.

[0031] The sensors include a pressure sensor 10 for tank pressure, a flow sensor 9 for total propellant circulation flow and throttling flow; the pressure sensor 10 is installed inside the tank 1 to monitor the internal pressure of the tank 1; the flow sensor 9 is arranged before the circulation pump 2 and before the throttling valve 3 to collect the total propellant flow in the circulation pipeline and the flow through the throttling valve 3, respectively.

[0032] The data acquisition unit 11 is connected to the sensors. The data acquisition unit 11 collects data from the pressure sensor 10 and the flow sensor 9 and transmits it to the computer 12. The computer 12 receives the data from the data acquisition unit 11, performs logical operations, makes logical judgments, and sends signals to the cryogenic circulating pump 2, the throttle valve 3, the throttle solenoid valve 8, and the exhaust port solenoid valve 7 to control their on / off states and complete the thermodynamic exhaust system response.

[0033] As a further limitation of the present invention, the spray rod 4 includes a shell-and-tube heat exchanger 5 and a plurality of nozzles 13. The main fluid flows through the tube side and the throttling fluid flows through the shell side of the shell-and-tube heat exchanger 5. The main fluid and the throttling fluid flow in the same direction within the shell-and-tube heat exchanger. After the main fluid exchanges heat, its temperature decreases and then flows in the opposite direction to reach different nozzles, from which it is sprayed into the storage tank.

[0034] As a further limitation of the present invention, a throttling solenoid valve 8 is installed in front of the throttling valve 3. The throttling solenoid valve is controlled by the computer 12 to realize the conversion of the exhaust process into the mixing process.

[0035] See Figure 2 The working principle of this invention is as follows:

[0036] Initially, the cryogenic propellant in tank 1 consists of two phases, gas and liquid, and is in a saturated state.

[0037] During the pressurization process, due to the heating of the outer wall of tank 1 by space radiation, the pressure and temperature of the cryogenic propellant inside tank 1 slowly increase until the tank pressure rises to the upper limit P of the pressure control zone. max .

[0038] When the tank pressure reaches P max Afterwards, the circulation pump 2, throttle valve 3, throttle solenoid valve 8, and exhaust port solenoid valve 7 are opened, and the TVS exhaust process begins. Cryogenic propellant flows out of tank 1, passes through cryogenic circulation pump 2, and then splits into two streams. A small stream flows through throttle valve 3. According to the Joule-Thomson effect, high-pressure fluids, under adiabatic conditions and without external work, rapidly expand to low pressure, causing temperature changes. For cryogenic liquid propellant, its temperature decreases as it flows through throttle valve 3. The cooled fluid exchanges heat with the other mainstream fluid in the shell-and-tube heat exchanger 5. The throttled fluid's temperature increases after heat exchange and is discharged through exhaust pipe 6. The mainstream fluid's temperature decreases after heat exchange and is injected into tank 1 through the open nozzle 13, thus achieving temperature and pressure control of the tank.

[0039] During the depressurization process, computer 12 collects real-time data from the pressure sensor inside tank 1. When the pressure in tank 1 drops to the critical pressure P... cr At this time, the throttle valve 3, the throttle solenoid valve 8, and the exhaust port solenoid valve 7 are closed, and only the circulation pump 2 is kept on. The circulation pump 2 is used to achieve the mixing and stirring of the fluid in the storage tank, further reducing the pressure in the storage tank 1 and alleviating the thermal stratification phenomenon.

[0040] When the pressure inside tank 1 drops to the lower limit P of the pressure control zone... min Afterwards, the circulation pump 2 is turned off, one pressure boosting cycle is completed, the fluid in the storage tank 1 is basically saturated, and the next pressure boosting cycle begins.

[0041] Critical pressure P cr The calculation is based on the liquid volume content (filling ratio) in the tank and external radiative heat loss, and is obtained from numerical simulation results. For example... Figure 2 As shown, with a filling rate of 70% and a flow rate of 0.2 W / m 2Taking heat leakage density as an example, the pressure control range is 100kPa-150kPa. When the mixing time is too long, the pressure in tank 1 will rise. Therefore, the mixing process is divided into effective mixing and ineffective mixing according to the sign of the pressure drop rate. The area enclosed by the effective mixing and the time axis (shaded area) is the maximum pressure drop capacity ΔP of the mixing process. Critical pressure P cr Equal to the lower limit P of the voltage control band min The sum of the maximum pressure reduction capacity ΔP during the mixing process. Using the venting mode before the critical pressure and the mixing mode after the critical pressure is reached not only ensures that the tank pressure drops to the lower limit of the control pressure, but also helps to shorten the venting time and reduce venting losses.

[0042] exist Figure 3 The operating conditions shown (70% filling rate and 0.2 W / m) 2 Under the condition of heat leakage density, the lower limit P of the pressure control band. min =100kPa, the maximum pressure reduction capacity (shaded area) of the mixing process ΔP = 0.88kPa, then P cr Equal to 100.88 kPa, this control method reduces exhaust loss by 0.17 kg compared to the full exhaust mode.

[0043] Within the same pressure control range, the critical pressure P cr It shows a negative correlation with the filling rate and a positive correlation with the external heat leakage density.

[0044]

[0045] Traditional TVS injection modules use a full exhaust mode, and when the temperature inside the tank reaches the upper limit of the pressure control P... max At this time, the cryogenic circulating pump 2, throttle valve 3, and exhaust port solenoid valve 7 are all opened until the tank pressure drops to P. min Afterwards, the circulation pump 2, throttle valve 3, and exhaust port solenoid valve 7 are all closed.

[0046] By comparison, it can be found that the present invention makes full use of the liquid supercooling formed in the early exhaust process and completes the turbidity of the liquid in the tank 1 through the mixing process. Compared with the traditional TVS, it can reduce the propellant discharge loss during the exhaust process, while alleviating the thermal stratification of the liquid in the tank 1, extending the spacecraft's on-orbit operation time, and is easy to implement technically, which greatly improves the temperature and pressure control efficiency of the TVS.

Claims

1. A control method for a thermodynamic exhaust system, characterized in that, It includes a storage tank (1) for storing propellant. The upper and lower walls of the storage tank (1) are respectively connected to a propellant exhaust pipe (6) and a circulation pipeline. An exhaust port solenoid valve (7) is installed on the exhaust pipe (6), and a cryogenic circulation pump (2) is installed on the circulation pipeline to realize the circulation of propellant in the storage tank (1). A spray rod (4) is installed inside the storage tank (1). A shell-and-tube heat exchanger (5) is installed inside the spray rod (4). One end of the circulation pipeline is connected to the storage tank (1) and the other end is connected to the shell side of the shell-and-tube heat exchanger inside the storage tank (1). The exhaust pipe (6) is connected to the tube side of the shell-and-tube heat exchanger inside the storage tank. A nozzle (13) is installed on the outer shell of the spray rod (4). A throttling pipeline with one end connected to the circulation pipeline and the other end connected to the tube side of the shell-and-tube heat exchanger inside the storage tank (1) is also installed outside the storage tank (1). A throttling valve (3) and a throttling solenoid valve (8) are also installed on the throttling pipeline. A pressure sensor (10) is also installed on the storage tank (1), and flow sensors (9) are installed on the circulation pipeline and the throttling pipeline respectively. The pressure sensor (10), the flow sensor (9) on the circulation pipeline and the throttling pipeline are respectively connected to the data acquisition instrument (11) and transmit the acquired data to the computer (12). Step 1: The computer (12) collects the data from the pressure sensor (10) through the data acquisition instrument (11) and then compares it with the upper limit P of the pressure control band. max Controlled pressure band lower limit P min and critical pressure P cr Perform logical judgments; Step 2: When the pressure in tank (1) is greater than or equal to the upper limit P of the pressure control band. max At that time, the computer issues a command to open the cryogenic circulating pump (2), the throttling solenoid valve (8), the throttling valve (3), and the exhaust port solenoid valve (7); Step 3: The cryogenic propellant enters the circulation pipeline under the action of the cryogenic circulation pump (2) and is divided into two streams of fluid. The first stream of fluid flows through the throttle valve (3) and exchanges heat with the second stream of fluid in the shell-and-tube heat exchanger (5) inside the jet rod (4). After the heat exchange, the first stream of fluid is discharged through the exhaust pipe (6), and the second stream of fluid is injected into the storage tank (1) from the nozzle (13). Step 4: When the pressure in tank (1) drops to the critical pressure P cr At that time, the computer issues an instruction to close the throttle solenoid valve (8), the throttle valve (3) and the exhaust port solenoid valve (7), while the cryogenic circulation pump remains on, and the cryogenic propellant is extracted and directly injected into the storage tank (1). Step 5: When the pressure in tank (1) drops to the lower limit P of the pressure control zone. min After completing one cycle of pressure increase and decrease, the computer issues a command to shut down the cryogenic circulating pump (2) and begin the next cycle of pressure increase and decrease.

2. The control method for the thermodynamic exhaust system according to claim 1, characterized in that, The storage tank (1) has elliptical end caps at both ends and a cylindrical structure in the middle. The storage tank (1) is covered with multiple layers of variable density insulation material.

3. The control method for the thermodynamic exhaust system according to claim 1, characterized in that, The flow sensor (9) on the circulation pipeline is arranged before the circulation pump (2), and the flow sensor (9) and the throttling solenoid valve (8) on the throttling pipeline are arranged before the throttling valve (3).

4. The control method for the thermodynamic exhaust system according to claim 1, characterized in that, The exhaust port solenoid valve (7) and the throttling solenoid valve (8) are low-temperature solenoid valves.

5. The control method for the thermodynamic exhaust system as described in claim 1, characterized in that, The critical pressure P cr The pressure value is equal to the area of ​​the effective pressure drop rate during the mixing phase, and the critical pressure P is... cr The pressure value is negatively correlated with the filling rate and positively correlated with the external heat leakage density.

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