Liquid nitrogen cooling system for maintaining continuous infiltration of upper surface of cold cavity and control method

Abstract

The invention provides a liquid nitrogen cooling system for maintaining continuous infiltration of the upper surface of a cold cavity. The liquid nitrogen cooling system comprises a liquid nitrogen Dewar, a gas-liquid separator and a cooling temperature control cavity, wherein the liquid nitrogen Dewar is used for providing low-temperature liquid nitrogen; one end of the gas-liquid separator is connected with the liquid nitrogen Dewar through a liquid-phase pipeline, the bottom of the other end of the gas-liquid separator is connected with the cooling temperature control cavity through a liquid-phase pipeline, and the top of the gas-liquid separator is connected with a gas-phase pipeline for exhausting gas; a temperature sensor and an acoustic emission probe are mounted in the cooling temperature control cavity, the temperature sensor is used for monitoring the wall surface temperature change of the cooling temperature control cavity in real time, and the acoustic emission probe is used for monitoring a high-frequency elastic wave signal in the cooling temperature control cavity; the wetting state of the upper surface of the cooling temperature control cavity can be judged, so that liquid nitrogen on the surface of the cooling temperature control cavity is conveniently controlled, the cooling temperature control cavity is prevented from entering a dry condition, and the liquid nitrogen heat exchange efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cryogenic equipment, in particular to a liquid nitrogen cooling system and control method for maintaining continuous wetting of the upper surface of a cold cavity. BACKGROUND

[0002] In the cooling process of liquid nitrogen, the surface of the cooled cavity or component needs to be continuously wetted by liquid nitrogen. The existing liquid nitrogen cooling method has the problem of dry-out of the surface of the cooling cavity, i.e. the formation of a gas film by evaporation of liquid nitrogen, which leads to a sharp decrease in heat transfer efficiency and temperature loss of control. This phenomenon essentially belongs to the transition from nucleate boiling to film boiling. When the cooling cavity surface loses the liquid helium film, a heat-insulating nitrogen layer is formed, and the boiling rate of liquid nitrogen is significantly reduced.

[0003] In order to ensure stable temperature of the cooling cavity and fully exert the high-efficiency heat transfer performance of liquid nitrogen, it is necessary to avoid dry-out or timely detect and re-wet the dry-out area. Most of the existing technologies only use temperature sensors to detect the temperature of liquid nitrogen, which cannot accurately identify and control the liquid nitrogen coverage of the surface of the cooling cavity. SUMMARY

[0004] To solve the above problems, the present application provides a liquid nitrogen cooling system and control method for maintaining continuous wetting of the upper surface of a cold cavity.

[0005] The present application is realized by the following technical solutions: The present application provides a liquid nitrogen cooling system for maintaining continuous wetting of the upper surface of a cold cavity, which comprises a liquid nitrogen Dewar, a gas-liquid separator and a cooling temperature control cavity, wherein: The liquid nitrogen Dewar is used to provide low-temperature liquid nitrogen; The gas-liquid separator is connected to the liquid nitrogen Dewar through a liquid phase pipeline at one end and connected to the cooling temperature control cavity through a liquid phase pipeline at the bottom at the other end. The top of the gas-liquid separator is connected with a gas phase pipeline for gas exhaust; The cooling temperature control cavity is provided with a temperature sensor and an acoustic emission probe. The temperature sensor is used to monitor the wall temperature change of the cooling temperature control cavity in real time, and the acoustic emission probe is used to monitor the high-frequency elastic wave signal in the cooling temperature control cavity.

[0006] Further, the liquid phase pipeline connecting the liquid nitrogen Dewar and the gas-liquid separator is provided with an inlet valve, the gas phase pipeline is provided with an exhaust valve, and the liquid phase pipeline connecting the gas-liquid separator and the cooling temperature control cavity is provided with a liquid discharge valve.

[0007] Further, the control unit comprises an upper computer, a data acquisition module and an actuator control module, and is connected to the inlet valve, the exhaust valve, the liquid discharge valve, the temperature sensor and the acoustic emission probe.

[0008] Further, the outer wall of the cooling temperature control cavity is provided with a heat preservation layer, and the liquid nitrogen Dewar is provided with a mass flow meter connected to the liquid phase pipeline of the gas-liquid separator.

[0009] Further, the control method for maintaining the liquid nitrogen cooling of the upper surface of the cold cavity includes: S1. Filling liquid in the cooling cavity and forming a stable liquid nitrogen liquid film; S2. Monitoring the temperature of the formed liquid nitrogen liquid film and entering the constant temperature maintenance stage; S3. Real-time monitoring of the constant temperature liquid nitrogen liquid film and determining whether the liquid nitrogen liquid film enters the loss of wetness determination stage; S4. When entering the loss of wetness stage, adjusting the liquid nitrogen inflow and entering the re-wetting stage; S5. Entering the periodic cycle stage.

[0010] Further, the constant temperature maintenance in the S2 step includes: The inflow valve is closed or maintained at a very small opening, the exhaust valve is kept open to exhaust evaporated nitrogen gas, a small amount of liquid nitrogen is continuously introduced, the control unit collects real-time data of the acoustic emission probe and the temperature sensor, monitors the wetness condition of the upper surface of the inner wall of the cooling cavity, and keeps the wall temperature slightly higher than 77K.

[0011] Further, the determination of the liquid nitrogen liquid film entering the loss of wetness determination stage in the S3 step includes: The acoustic emission probe and temperature sensor data are continuously monitored, when the acoustic emission signal intensity or acoustic emission event frequency decreases below threshold A, and the temperature sensor reading rises above threshold B, and lasts for several seconds, it is determined that the liquid nitrogen liquid film is in the loss of wetness state.

[0012] Further, the adjustment of the liquid nitrogen inflow and the entering of the re-wetting stage in the S4 step includes: The inflow valve is opened, the acoustic emission probe and temperature sensor data are continuously monitored, when the acoustic emission signal intensity is higher than threshold C, and the cooling cavity inner wall temperature decreases below threshold D, it is determined that the cooling cavity inner wall is covered by the liquid nitrogen liquid film, the inflow valve is adjusted, and when the added liquid nitrogen reaches a predetermined value E, the inflow valve is closed or intermittently opened.

[0013] Further, the entering of the periodic cycle stage in the S5 step includes: The cooling cavity inner wall is always in a stable state, when the loss of wetness phenomenon occurs again, the liquid nitrogen inflow is immediately adjusted to enter the re-wetting state, and continuous monitoring is maintained to keep the cooling cavity inner wall in a stable state.

[0014] Further, the filling of liquid in the cooling cavity and the forming of a stable liquid nitrogen liquid film in the S1 step include: Open the exhaust valve to release gas, then open the liquid inlet valve, so that liquid nitrogen passes through the gas-liquid separator into the cooling temperature control cavity, after pre-cooling and temperature control of the cavity, the low-temperature liquid nitrogen gradually flows into the cavity wall of the contact cooling temperature control cavity, and forms a stable liquid film, when the temperature of the cavity wall approaches 77K and the signal received by the acoustic emission probe tends to be stable, it indicates that the upper surface of the cavity is completely covered by liquid nitrogen and enters a stable boiling state.

[0015] Advantages of the present application: (1) The liquid nitrogen cooling system for maintaining the upper surface of the cold cavity continuously wetted uses temperature sensors and acoustic emission probes to determine the wetting state of the upper surface of the cooling temperature control cavity, so as to control the liquid nitrogen on the surface of the cooling temperature control cavity and prevent the cooling temperature control cavity from drying out, thereby improving the heat exchange efficiency of liquid nitrogen.

[0016] (2) The liquid nitrogen control method for maintaining the upper surface of the cold cavity continuously wetted divides the cooling process into multiple states such as liquid film establishment, constant temperature detection, dry detection, and re-wetting liquid supplement, and designs corresponding control strategies and actions for each state, so as to realize stable liquid film of liquid nitrogen. BRIEF DESCRIPTION OF DRAWINGS

[0017] Fig. 1 The structure diagram of the liquid nitrogen system for maintaining the upper surface of the cold cavity continuously wetted; Fig. 2 The flow chart of the liquid nitrogen control method for maintaining the upper surface of the cold cavity continuously wetted; Fig. 3 The control system state diagram of the liquid nitrogen cooling system for maintaining the upper surface of the cold cavity continuously wetted; In the figure: liquid nitrogen Dewar 1, gas-liquid separator 2, control unit 3, cooling temperature control cavity 4, temperature sensor 5, acoustic emission probe 6, liquid phase pipeline 7, liquid inlet valve 8, liquid outlet valve 9, gas phase pipeline 10, exhaust valve 11; The purpose, functional characteristics and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0018] In order to more clearly and completely illustrate the technical solutions of the present application, the present application will be further described below with reference to the accompanying drawings.

[0019] Please refer to Figs. 1-3 The present application proposes a liquid nitrogen cooling system for maintaining the upper surface of the cold cavity continuously wetted, which comprises a liquid nitrogen Dewar 1, a gas-liquid separator 2 and a cooling temperature control cavity 4, wherein: The liquid nitrogen Dewar 1 is used to provide low-temperature liquid nitrogen; The gas-liquid separator 2 is connected to the liquid nitrogen Dewar 1 through a liquid phase pipeline 7 at one end and connected to the cooling temperature control cavity 4 through a liquid phase pipeline 7 at the bottom at the other end, and the top of the gas-liquid separator 2 is connected to a gas phase pipeline 10 for discharging gas; The cooling temperature control cavity 4 is provided with a temperature sensor 5 and an acoustic emission probe 6, the temperature sensor 5 is used to monitor the wall temperature change of the cooling temperature control cavity 4 in real time, and the acoustic emission probe 6 is used to monitor the high-frequency elastic wave signal in the cooling temperature control cavity 4.

[0020] In the specific embodiment, the liquid nitrogen Dewar 1 is used to provide low-temperature liquid nitrogen, after the liquid nitrogen enters the gas-liquid separator 2, the evaporated nitrogen gas rises and gathers at the top, and the liquid nitrogen settles and accumulates at the bottom, the bottom of the gas-liquid separator 2 is connected to the cooling temperature control cavity 4 through a liquid phase pipeline 7, the cooling temperature control cavity 4 refers to the target component that needs to be cooled, such as a container, a pipeline or a device cavity, the inner surface of which requires to be always wetted by liquid nitrogen, the cavity is provided with a liquid inlet and a liquid outlet for introducing liquid nitrogen and discharging excess liquid nitrogen or gas respectively; the temperature sensor 5 is attached to the upper surface of the cooling temperature control cavity 4 to monitor the wall temperature change of the cooling temperature control cavity 4 in real time, and the acoustic emission probe 6 is installed on the outer wall of the cooling temperature control cavity 4 near the upper surface area to monitor the high-frequency elastic wave signal generated when the liquid nitrogen boils, the acoustic emission signal can reflect the boiling intensity of the liquid nitrogen in the cavity, when the liquid nitrogen is fully wetted and in the nucleate boiling state, continuous and obvious acoustic emission activity will be generated, when the liquid nitrogen is insufficient or the cooling temperature control cavity 4 is dry, the boiling weakens or even appears in the film boiling state, and the intensity and frequency of the acoustic emission signal obviously decrease, by using this feature, the wetting state of the upper surface of the cooling temperature control cavity 4 can be determined to control the liquid nitrogen on the surface of the cooling temperature control cavity 4, so as to prevent the cooling temperature control cavity 4 from entering the dry state and improve the heat exchange efficiency of the liquid nitrogen.

[0021] Further, the liquid phase pipeline 7 connecting the liquid nitrogen Dewar 1 and the gas-liquid separator 2 is provided with a liquid inlet valve 8, the gas phase pipeline 10 is provided with an exhaust valve 11, and the liquid phase pipeline 7 from the gas-liquid separator 2 to the cooling temperature control cavity 4 is provided with a liquid outlet valve 9.

[0022] In the specific embodiment, the liquid inlet valve 8 is used to control the flow of liquid nitrogen introduced from the liquid nitrogen Dewar 1, the liquid outlet valve 9 is used to control the flow of liquid nitrogen introduced into the cooling temperature control cavity 4, and the exhaust valve 11 is used to discharge nitrogen gas, since the liquid nitrogen will evaporate into nitrogen gas, the gas can be discharged to the outside in time through the exhaust valve 11 to prevent the gas pressure from being too high.

[0023] Further, the control unit 3 is also included, which comprises a host computer, a data acquisition module and an actuator control module, and the control unit 3 is connected to the liquid inlet valve 8, the exhaust valve 11, the liquid outlet valve, the temperature sensor 5 and the acoustic emission probe 6.

[0024] In the specific embodiment, the control unit 3 is connected with the temperature sensor 5, the acoustic emission probe 6, the mass flow meter, etc., collects multiple signals, and outputs instructions through a control algorithm to drive the liquid inlet valve 8, the exhaust valve 11, and the liquid outlet valve 9 to execute the instructions, automatically adjusts the opening degree and opening and closing state of each valve according to the real-time condition in the cooling temperature control cavity 4, and dynamically maintains the liquid nitrogen film layer on the upper surface of the cooling temperature control cavity 4.

[0025] Further, the outer wall of the cooling temperature control cavity 4 is provided with a heat preservation layer, and the liquid nitrogen Dewar 1 is provided with a mass flow meter on the liquid phase pipeline 7 connected with the gas-liquid separator 2.

[0026] In the specific embodiment, the heat preservation layer is used to reduce heat leakage and liquid nitrogen consumption, and the mass flow meter is used to measure the liquid nitrogen flow entering the system, so as to subsequently estimate the liquid supplement, liquid nitrogen consumption statistics, and provide auxiliary criteria for the system.

[0027] Further, the control method for maintaining the liquid nitrogen cooling of the upper surface of the cooling cavity includes: S1. Filling liquid in the cooling cavity and forming a stable liquid nitrogen liquid film; S2. Monitoring the temperature of the formed liquid nitrogen liquid film, and entering a constant temperature maintenance stage; S3. Real-time monitoring of the constant temperature liquid nitrogen liquid film, and determining whether the liquid nitrogen liquid film enters a loss of wetness determination stage; S4. When entering the loss of wetness stage, adjusting the liquid nitrogen inlet, and entering a re-wetting stage; S5. Entering a periodic cycle stage.

[0028] In the specific embodiment, after the experiment or operation is completed, an end liquid discharge stage is entered, the control unit 3 closes the liquid inlet valve 8, opens the exhaust valve 11 to release pressure to normal pressure, and then opens the liquid outlet valve 9 to discharge the residual liquid nitrogen in the cooling temperature control cavity 4 and the gas-liquid separator 2 to a recovery container or a safe area. During the liquid discharge process, whether the liquid is discharged is determined by the activity of the acoustic emission probe 6.

[0029] Further, the constant temperature maintenance in S2 includes: The liquid inlet valve 8 is closed or maintained at a very small opening, the exhaust valve 11 is kept open to discharge evaporated nitrogen gas, a small amount of liquid nitrogen is continuously introduced, the control unit 3 collects data of the acoustic emission probe 6 and the temperature sensor 5 in real time, monitors the wetness condition of the upper surface of the inner wall of the cooling cavity, and keeps the wall surface temperature slightly higher than 77K.

[0030] In the specific embodiment, the liquid nitrogen in the cooling cavity is in a saturated boiling state and gradually vaporizes and is consumed. If not continuously replenished, the liquid level will gradually decrease. In this stage, the opening of the liquid inlet valve 8 is adjusted, and the data of the acoustic emission probe 6 and the temperature sensor 5 are monitored at the same time. When the liquid nitrogen is fully covered, the upper surface of the cavity is in a nucleate boiling state, the boiling is violent and stable, the acoustic emission signal remains stable, and the temperature is stable at a low temperature close to the boiling point of liquid nitrogen. In this stage, the stability of the system in the natural boiling process is observed.

[0031] Further, the determination of the liquid film of liquid nitrogen entering the dry-out determination stage in S3 step includes: The data of the acoustic emission probe 6 and the temperature sensor 5 are continuously monitored. When the acoustic emission signal intensity or the acoustic emission event frequency is reduced to below the threshold value A, and the temperature sensor 5 reading rises above the threshold value B, and lasts for several seconds, it is determined that the liquid film of liquid nitrogen is in a dry-out state.

[0032] In the specific embodiment, after the liquid nitrogen is reduced, the liquid nitrogen will continue to vaporize and be consumed over time. In the case of not replenishing the liquid for a long time, the cooling temperature control cavity 4 will appear local dryness phenomenon (i.e. dry-out). The acoustic emission probe 6 and the temperature sensor 5 can be used to determine the precursor of dry-out. From the boiling heat transfer theory, when the local heat flux density of the heating surface exceeds the critical value (critical heat flux density CHF), the efficient nucleate boiling will occur "boiling crisis", and quickly transfer into film boiling, and the wall surface forms a heat insulation vapor film, resulting in a sharp rise in temperature. Based on this mechanism, the acoustic emission (AE) signal intensity or time frequency is reduced to below the threshold value A, and the temperature sensor 5 reading rises above the threshold value B, and both last for several seconds, then it is determined that the liquid film of liquid nitrogen will appear dry-out. The acoustic emission (AE) event can be set according to the actual situation, for example, the case of multiple intensity reductions of acoustic emission signal.

[0033] In one embodiment, the acoustic emission probe 6 is extremely sensitive to bubble activity. In nucleate boiling, bubbles are frequently generated, enlarged and detached, which will produce a large number of acoustic emission events. After entering the film boiling, the bubble activity is greatly reduced, and the acoustic emission event frequency and amplitude will decrease accordingly. Therefore, when the acoustic emission signal intensity or the acoustic emission event frequency is reduced to below the threshold value A, and the temperature sensor 5 reading rises above the threshold value B, it is determined to be dry-out, avoiding the misjudgment of a single signal.

[0034] Further, the adjustment of the liquid nitrogen inlet liquid and the entering of the re-wetting stage in S4 step includes: The liquid inlet valve 8 is opened, and the data of the acoustic emission probe 6 and the temperature sensor 5 are continuously monitored. When the acoustic emission signal intensity is higher than the threshold value C, and the temperature of the inner wall of the cooling cavity is reduced to below the threshold value D, it is determined that the inner wall of the cooling cavity is covered by the liquid film of liquid nitrogen. The liquid inlet valve 8 is adjusted, and when the replenished liquid nitrogen reaches the predetermined value E, the liquid inlet valve 8 is closed or intermittently opened.

[0035] In the specific embodiment, when the loss of wetting signs appears, the control unit 3 quickly replenishes the liquid, and makes the surface re-wet; at this time, the liquid inlet valve 8 is adjusted to a larger opening, liquid nitrogen is quickly injected into the gas-liquid separator 2, and flows into the cooling temperature control cavity 4, at the same time, the exhaust valve 11 is adjusted to timely exhaust, and the nitrogen gas accumulated in the gas-liquid separator 2 can quickly push the liquid nitrogen into the cooling temperature control cavity 4, so that the dry area is covered faster, and the liquid nitrogen delivery speed can be improved by using this method. With the liquid nitrogen contacting the upper surface of the cooling temperature control cavity 4, a violent nucleate boiling phenomenon reappears, the acoustic emission signal is greatly enhanced, and the cavity wall temperature rapidly decreases to close to the liquid nitrogen temperature. When the acoustic emission signal intensity is higher than the threshold value C, and the cooling cavity inner wall temperature decreases to below the threshold value D, it is determined that the cooling cavity inner wall is covered by the liquid film of liquid nitrogen, and the dry area is eliminated. In order to avoid excessive liquid replenishment leading to liquid nitrogen overflow or temperature fluctuation, it is necessary to finely control the liquid replenishment amount, or indirectly inject a small amount of liquid for multiple times. In the liquid replenishment process, the exhaust valve 11 is kept at a small opening to exhaust the vaporized nitrogen gas.

[0036] Further, the entering into the periodic cycle stage in the S5 step includes: Monitoring the cooling cavity inner wall to be always in a stable state, when the loss of wetting phenomenon appears again, immediately adjusting the liquid nitrogen inlet to enter the wetting state, and continuously monitoring to maintain the cooling cavity inner wall to be always in a stable state.

[0037] In the specific embodiment, after the re-wetting is completed, the liquid inlet valve 8 is closed, and the constant temperature stage is entered, and the next stable cycle is entered. Once the dry trend is detected again, the liquid is replenished to re-wet, and then continuous monitoring is maintained, so that the liquid film of liquid nitrogen is always in a stable state, that is, the cavity wall temperature is stably near the liquid nitrogen temperature most of the time, and only a small amplitude is increased before the liquid is replenished. The acoustic emission signal is maintained at an active level most of the time, and only decreases before the loss of wetting. The cooling temperature control cavity 4 is continuously immersed in liquid nitrogen.

[0038] Further, the liquid is filled in the cooling cavity and a stable liquid film of liquid nitrogen is formed in the S1 step, including: The exhaust valve 11 is opened to release the gas, then the liquid inlet valve 8 is opened, so that the liquid nitrogen enters the cooling temperature control cavity 4 through the gas-liquid separator 2. After the cavity is pre-cooled and cooled, the low-temperature liquid nitrogen gradually flows into the cavity wall contacting the cooling temperature control cavity 4, and a stable liquid film is formed. When the cavity wall temperature is close to 77K and the signal received by the acoustic emission probe 6 tends to be stable, it indicates that the upper surface of the cavity is completely covered by liquid nitrogen and enters a stable boiling state.

[0039] In the specific embodiment, the low-temperature liquid nitrogen contact cooling temperature control cavity 4 instantaneously generates intense boiling, the acoustic emission sensor detects a large number of high-amplitude acoustic emission pulses, and the reading of the temperature sensor 5 rapidly decreases. At this time, a stable liquid nitrogen film is formed on the upper surface of the cooling temperature control cavity 4, and the heat exchange is rapidly changed from the initial convection to the efficient nucleate boiling. When the cavity wall temperature approaches the boiling point of liquid nitrogen (about 77K) and the acoustic emission signal tends to be a stable pulse mode, it indicates that a stable liquid nitrogen film is established.

[0040] Of course, the present application can have other various embodiments, and based on the embodiments, other embodiments obtained by those skilled in the art without any creative labor are within the scope of protection of the present application.

Claims

1. A liquid nitrogen cooling system for maintaining continuous wetting of the upper surface of a cold cavity, characterized in that, Includes a liquid nitrogen Dewar, a gas-liquid separator, and a cooling temperature control chamber, wherein: The liquid nitrogen Dewar is used to provide cryogenic liquid nitrogen; One end of the gas-liquid separator is connected to the liquid nitrogen Dewar via a liquid phase pipe, and the bottom of the other end is connected to the cooling temperature control chamber via a liquid phase pipe. The top of the gas-liquid separator is connected to a gas phase pipe for exhausting gas. A temperature sensor and an acoustic emission probe are installed inside the cooling temperature control cavity. The temperature sensor is used to monitor the wall temperature change of the cooling temperature control cavity in real time, and the acoustic emission probe is used to monitor the high-frequency elastic wave signal inside the cooling temperature control cavity.

2. The liquid nitrogen cooling structure for maintaining continuous wetting of the upper surface of the cold cavity according to claim 1, characterized in that, An inlet valve is provided on the liquid phase pipeline connecting the liquid nitrogen Dewar to the gas-liquid separator, an exhaust valve is provided on the gas phase pipeline, and a drain valve is provided on the liquid phase pipeline from the gas-liquid separator to the cooling temperature control chamber.

3. The liquid nitrogen cooling structure and control method for maintaining continuous wetting of the upper surface of the cold cavity according to claim 2, characterized in that, It also includes a control unit, which includes a host computer, a data acquisition module and an actuator control module. The control unit is connected to the inlet valve, the exhaust valve, the drain valve, the temperature sensor and the acoustic emission probe.

4. The liquid nitrogen cooling structure and control method for maintaining continuous wetting of the upper surface of the cold cavity according to claim 1, characterized in that, The outer wall of the cooling temperature control cavity is provided with a heat insulation layer, and a mass flow meter is provided on the liquid phase pipeline connecting the liquid nitrogen Dewar to the gas-liquid separator.

5. A method for controlling liquid nitrogen cooling to maintain continuous wetting of the upper surface of a cold cavity, applied as described in any one of claims 1 to 4, characterized in that, include: S1. The cooling chamber is filled with liquid, forming a stable liquid nitrogen film; S2. Monitor the temperature of the formed liquid nitrogen film and enter the isothermal maintenance stage; S3. Real-time monitoring of the constant-temperature liquid nitrogen film and determination of whether the liquid nitrogen film has entered the de-lubrication determination stage; S4. When entering the dewetting stage, adjust the liquid nitrogen inlet and enter the rewetting stage; S5. Entering the cycle phase.

6. The liquid nitrogen cooling structure and control method for maintaining continuous wetting of the upper surface of the cold cavity according to claim 5, characterized in that, The isotemperature maintenance in step S2 includes: The inlet valve is closed or kept at a very small opening, the exhaust valve is kept open to discharge evaporated nitrogen, a small amount of liquid nitrogen is continuously introduced, the control unit collects data from the acoustic emission probe and temperature sensor in real time, monitors the wetting status of the upper surface of the inner wall of the cooling chamber, and keeps the wall temperature slightly above 77K.

7. The liquid nitrogen cooling structure and control method for maintaining continuous wetting of the upper surface of the cold cavity according to claim 5, characterized in that, The determination of whether the liquid nitrogen film has entered the de-lubrication determination stage in step S3 includes: Continuously monitor the acoustic emission probe and temperature sensor data. When the acoustic emission signal intensity or acoustic emission event frequency drops below threshold A, and the temperature sensor reading rises above threshold B for several seconds, the liquid nitrogen film is determined to be in a de-lubricated state.

8. The liquid nitrogen cooling structure and control method for maintaining continuous wetting of the upper surface of the cold cavity according to claim 5, characterized in that, The S4 step, which involves adjusting the liquid nitrogen inlet and entering the rewetting stage, includes: Open the liquid inlet valve and continuously monitor the data from the acoustic emission probe and temperature sensor. When the acoustic emission signal intensity is higher than the threshold C and the temperature of the inner wall of the cooling chamber drops below the threshold D, it is determined that the inner wall of the cooling chamber is covered by a liquid nitrogen film. Adjust the liquid inlet valve and close or intermittently open the liquid inlet valve when the liquid nitrogen replenishment reaches the predetermined value E.

9. The liquid nitrogen cooling structure and control method for maintaining continuous wetting of the upper surface of the cold cavity according to claim 5, characterized in that, The S5 step, which involves entering the cycle phase, includes: The cooling chamber inner wall is monitored to ensure it remains stable. If dehydration occurs again, liquid nitrogen is immediately introduced to restore lubrication, and continuous monitoring is maintained to ensure the cooling chamber inner wall remains stable.

10. The liquid nitrogen cooling structure and control method for maintaining continuous wetting of the upper surface of the cold cavity according to claim 5, characterized in that, The step S1, which involves filling the cooling chamber with liquid and forming a stable liquid nitrogen film, includes: Open the exhaust valve to release the gas, then open the liquid inlet valve to allow liquid nitrogen to enter the cooling temperature control chamber through the gas-liquid separator. After the chamber is pre-cooled, the low-temperature liquid nitrogen gradually flows into the cavity wall of the cooling temperature control chamber and forms a stable liquid film. When the cavity wall temperature approaches 77K and the signal received by the acoustic emission probe tends to be stable, it indicates that the upper surface of the cavity is completely covered by liquid nitrogen and has entered a stable boiling state.

Images