CN118067790A - Dew point monitoring device and method for liquid nitrogen supply system of low-temperature test chamber - Google Patents
Dew point monitoring device and method for liquid nitrogen supply system of low-temperature test chamber Download PDFInfo
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Abstract
The invention relates to the technical field of low-temperature test chamber parameter monitoring, in particular to a dew point monitoring device and method of a liquid nitrogen supply system of a low-temperature test chamber. Dew point monitoring device of cryogenic test chamber liquid nitrogen feed system includes: the system comprises a liquid inlet, at least five fluid inlets, a system pipeline inlet, a back return pipeline inlet after a pump, a supply pipeline inlet, a supply return pipeline tail end and dew point monitoring points arranged at the top of a liquid nitrogen storage tank, wherein the dew point monitoring points are suitable for being communicated with the fluid inlets in a one-to-one correspondence manner; and the fluid inlets of the measuring pipelines are communicated with the measuring pipelines, and the heating part, the pressure reducing part and the dew point monitoring part are sequentially arranged on the measuring pipelines. The fluid is heated and depressurized through the heating element and the depressurization element, so that after liquid nitrogen or nitrogen meets the monitoring requirement of the dew point monitoring element, the liquid nitrogen or nitrogen is introduced into the dew point monitoring element to monitor the dew point. When the monitoring device works, the dew point monitoring point position is directly in butt joint with the fluid inlet for sampling, a plurality of coils are not required to be arranged for preprocessing liquid nitrogen or nitrogen, and the installation work of the device is simplified.
Description
Technical Field
The invention relates to the technical field of low-temperature test chamber parameter monitoring, in particular to a dew point monitoring device and method of a liquid nitrogen supply system of a low-temperature test chamber.
Background
The deep space probe is an unmanned spacecraft developed by human beings and used for detecting remote celestial bodies and spaces, and when the unmanned spacecraft works, the attitude and orbit control engine needs to operate at extremely low ambient temperature to realize the attitude adjustment and orbit adjustment of the deep space probe. In the research and development process of the attitude and orbit control engine, the low-temperature test cabin is an effective device for simulating a deep space low-temperature environment and carrying out various environment simulation tests on the engine.
The lowest temperature of the low-temperature test cabin simulating the deep space environment can reach minus hundred and sixty degrees centigrade, and liquid nitrogen is used as a cooling medium. The water is in the form of ice in liquid nitrogen. If water exists in the supplied medium, small ice crystals can cause the bulkhead of the low-temperature test cabin to condense and freeze, and slightly larger ice particles have the hidden trouble of seriously damaging the cabin body and the test equipment under the action of low-temperature air flow. Therefore, the liquid nitrogen supply system for maintaining the low-temperature environment in the low-temperature test cabin is more critical to ensure that the dew point of a supply medium meets the requirement and the internal environment of the cabin is kept dry besides spraying liquid nitrogen into the cabin according to the pressure and flow requirements.
In order to enable the liquid nitrogen introduced into the cabin body to meet the requirements, the low-temperature test cabin needs to be monitored in real time when in operation. The monitoring medium of the liquid nitrogen supply system of the low-temperature test cabin comprises nitrogen and liquid nitrogen, the pressure range of the medium is 0.5-1.5 MPa, the flow range is 0-23754L/min, the temperature of the medium is as low as-196 ℃, but the dew point sensor for measuring the water content in the gas in the prior art is required to be used at the temperature of-40-70 ℃ and the flow is not more than 5L/min. In order to ensure the effectiveness and correctness of the monitoring, nitrogen and liquid nitrogen are required to be processed into samples with the temperature and flow meeting the monitoring requirements of the dew point sensor. In the prior art, the pipe diameter of the sampling coil pipe is designed according to the flow, the length of the coil pipe is designed according to the temperature, so that a sample is gasified by heat exchange with normal-temperature air in the coil pipe, and in the process, if full gasification cannot be ensured, the measurement time is prolonged, the measurement is wrong, and more serious ice crystals damage the mirror surface of the dew point sensor and damage a monitoring instrument.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is to overcome the defects of long measurement time, large measurement error, high measurement cost and risk of damaging the mirror surface of the dew point sensor in the dew point monitoring of the liquid nitrogen supply system of the deep space low temperature test chamber in the prior art, thereby providing a dew point monitoring device and a dew point monitoring method of the liquid nitrogen supply system of the low temperature test chamber.
In order to solve the technical problems, the invention provides a dew point monitoring device of a low-temperature test chamber liquid nitrogen supply system, wherein the low-temperature test chamber liquid nitrogen supply system comprises a liquid nitrogen storage tank, a system pipeline, a supply pipeline, a test chamber body and a supply return pipeline which are circularly communicated, and an outlet of the supply return pipeline is communicated with an inlet of the liquid nitrogen storage tank;
A low-temperature centrifugal pump is arranged on the system pipeline, and a back-pump return pipeline is arranged on the system pipeline at the downstream of the low-temperature centrifugal pump;
the dew point monitoring device includes:
The system comprises a liquid inlet, at least five fluid inlets, a system pipeline inlet, a back return pipeline inlet after a pump, a supply pipeline inlet, a supply return pipeline tail end and dew point monitoring points arranged at the top of a liquid nitrogen storage tank, wherein the dew point monitoring points are suitable for being communicated with the fluid inlets in a one-to-one correspondence manner;
And the fluid inlets of the measuring pipelines are communicated with the measuring pipelines, and the heating part, the pressure reducing part and the dew point monitoring part are sequentially arranged on the measuring pipelines.
Optionally, a one-way valve is mounted on the measurement conduit downstream of the dew point monitoring element.
Optionally, a filter is installed between the heating member and the pressure reducing member.
The invention provides a dew point monitoring method of a liquid nitrogen supply system of a low-temperature test chamber, and the dew point monitoring device of the liquid nitrogen supply system of the low-temperature test chamber is based on the dew point monitoring method.
Optionally, the method comprises the following steps:
Adopting normal-temperature dry nitrogen to sequentially clean a low-temperature centrifugal pump, a back-pump return pipeline, a supply return pipeline and a supply pipeline, stopping the nitrogen cleaning of the pipeline after the dew point monitoring value of the dew point monitoring point on the previous pipeline is not more than-76.0 ℃ dp and the preset cleaning time is kept, and switching to the next pipeline until the dew point monitoring values of all the dew point monitoring points are more than-76.0 ℃ dp, and completing the nitrogen cleaning work;
optionally, the method comprises:
and pre-cooling the low-temperature centrifugal pump and the back-pumping return pipeline under the action of self gravity of liquid nitrogen in the liquid nitrogen storage tank, starting the low-temperature centrifugal pump to boost the pressure of the liquid nitrogen after the temperature of the back-pumping return pipeline is not more than-190 ℃, controlling the liquid nitrogen to flow by using the low-temperature centrifugal pump to pre-cool the supply return pipeline and the supply pipeline in sequence, and starting the liquid nitrogen pre-cooling of the next pipeline after the temperature of the previous pipeline is not more than-190 ℃ until the temperatures of all pipelines are not more than-190 ℃, thereby completing the liquid nitrogen pre-cooling work.
Optionally, the method comprises:
after the low-temperature centrifugal pump controls the liquid nitrogen to be boosted, the liquid nitrogen is sprayed into the test cabin body through the system pipeline, the supply pipeline and the test cabin body in sequence, and a liquid nitrogen wake flows into the supply return pipeline;
And acquiring dew point monitoring values of dew point monitoring points at the inlet of the supply pipeline and the tail end of the supply return pipeline in real time, if the dew point monitoring values do not meet the supply requirement of the variable working condition, closing a liquid nitrogen jet orifice in the test cabin body, enabling liquid nitrogen to directly flow into the supply return pipeline, controlling the low-temperature centrifugal pump to stop running, and performing fault detection.
Optionally, the method comprises:
When the liquid nitrogen stops spraying, the system enters a safe parking state, the low-temperature centrifugal pump stops running, the spraying valve in the test cabin body is closed, the low-temperature centrifugal pump, the back-flow pipeline of the pump, the supply pipeline and the supply back-flow pipeline are all communicated with a liquid nitrogen storage tank, and the liquid nitrogen is placed in the pipeline in a static manner;
and (3) periodically acquiring the monitoring values of all the dew point monitoring points, and when the change rate of the monitoring value of a certain dew point monitoring point is higher than a safety early warning value, switching the system from being communicated with a liquid nitrogen storage tank to being communicated with a gas-liquid separator for fault detection.
Optionally, the variable operating condition supply requirement includes: the dew point monitoring value is not higher than-76 ℃ dp, and does not rise by more than 5 ℃ dp per minute.
Optionally, the fault detection step includes: and sequentially and isochronously acquiring the dew point monitoring values of the related dew point monitoring points, and judging that the pipeline where the dew point monitoring point is located is faulty if the drop of the dew point monitoring value of a certain dew point monitoring point within the monitoring time is not more than 12 ℃ dp.
The technical scheme of the invention has the following advantages:
1. The invention provides a dew point monitoring device of a liquid nitrogen supply system of a low-temperature test chamber, which comprises: the system comprises a liquid inlet, at least five fluid inlets, a system pipeline inlet, a back return pipeline inlet after a pump, a supply pipeline inlet, a supply return pipeline tail end and dew point monitoring points arranged at the top of a liquid nitrogen storage tank, wherein the dew point monitoring points are suitable for being communicated with the fluid inlets in a one-to-one correspondence manner; and the fluid inlets of the measuring pipelines are communicated with the measuring pipelines, and the heating part, the pressure reducing part and the dew point monitoring part are sequentially arranged on the measuring pipelines.
When the dew point monitoring device of the low-temperature test chamber liquid nitrogen supply system is utilized to monitor the dew point of the low-temperature test chamber liquid nitrogen supply system, the system pipeline inlet, the back-flow pipeline inlet, the supply back-flow pipeline tail end and the dew point monitoring point arranged at the top of the liquid nitrogen storage tank in the low-temperature test chamber liquid nitrogen supply system are communicated with the fluid inlet in a one-to-one correspondence mode, and when the monitoring is carried out, the fluid is heated and depressurized through the heating piece and the depressurization piece, so that the liquid nitrogen or the nitrogen meets the monitoring requirement of the dew point monitoring piece, and then the dew point monitoring piece is introduced to carry out dew point monitoring. The monitoring device can use hose or hard tube during operation, directly dock dew point monitoring point position and fluid inlet and sample, need not to set up many complicated coils and carry out preliminary treatment to liquid nitrogen or nitrogen gas, simplified dew point measuring device's installation work. After the fluid sample is fully heated and gasified by the heating element in the dew point monitoring device, the sampling gas is decompressed and reduced by the decompression element, and then the sampling gas enters the dew point monitoring element for measurement, so that the detection requirements of the dew point monitoring element can be met when the fluid samples with different pressures, flow rates and physical properties enter the dew point monitoring element. The problem of the dew point measuring device complicacy that different monitoring point positions's fluid exists different pressures, different flow rate grades and leads to in the liquid nitrogen feed system has effectively been solved. The dew point monitoring device meets the requirements of the liquid nitrogen supply system on-line measurement in real time in a wide dew point temperature range and high pressure.
2. According to the dew point monitoring device of the liquid nitrogen supply system of the low-temperature test cabin, provided by the invention, the check valve is arranged on the measuring pipeline at the downstream of the dew point monitoring piece, so that the air can be effectively prevented from being sucked backwards to pollute the dew point monitoring device.
3. According to the dew point monitoring device of the liquid nitrogen supply system of the low-temperature test cabin, provided by the invention, the filter is arranged between the heating part and the pressure reducing part and is used for filtering the interference of redundant impurities in the fluid, so that the fluid entering the dew point monitoring part is purer, and the reliability of a monitoring result is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic view of a dew point monitoring device of a cryogenic test chamber liquid nitrogen supply system provided in an embodiment of the invention.
Fig. 2 is a schematic structural view of a dew point monitoring device of a liquid nitrogen supply system of a cryogenic test chamber provided in an embodiment of the invention.
Fig. 3 is a side view of a cryogenic test chamber liquid nitrogen supply system dew point monitoring device provided in an embodiment of the invention.
FIG. 4 is another angled side view of a cryogenic test chamber liquid nitrogen supply system dew point monitoring device provided in an embodiment of the invention.
Fig. 5 is a schematic diagram of a cryogenic test chamber liquid nitrogen supply system provided in an embodiment of the invention.
Reference numerals illustrate: 1. a sampling hand valve; 2. an electromagnetic valve; 3. a heating member; 4. a temperature sensor; 5. a filter; 6. a first pressure sensor; 7. a pressure reducing member; 8. a second pressure sensor; 9. a dew point meter; 10. a one-way valve; 11. a case; 12. a fluid inlet; 13. a fluid outlet; 14. a control unit; 15. a liquid nitrogen storage tank; 16. a low temperature centrifugal pump; 17. a test chamber body; 18. a gas-liquid separator; 19. a manual shut-off valve; 20. a first power valve; 21. a second power valve; 22. a flow rate valve; 23. a first flow valve; 24. a second flow valve; 25. a third flow valve; 26. a fourth flow valve; 27. a fifth flow valve; 28. a sixth flow valve; 29. a seventh flow valve; 30. an eighth flow valve; 31. a ninth flow valve; 32. a tenth flow valve; 33. an eleventh flow valve; 34. a twelfth flow valve; 35. a thirteenth flow valve; 36. a fourteenth flow valve; 37. a fifteenth flow valve; 38. a sixteenth flow valve; 39. a seventeenth flow valve; 40. a first dew point monitoring point location; 41. a second dew point monitoring point location; 42. a third dew point monitoring point; 43. a fourth dew point monitoring point; 44. fifth dew point monitoring point location; 45. a first temperature monitoring point; 46. a second temperature monitoring point; 47. and monitoring the pressure point position.
Detailed Description
The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
In addition, the technical features of the different embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
Fig. 1 to 4 show a dew point monitoring device of a liquid nitrogen supply system of a low-temperature test chamber according to the present embodiment. The cryogenic test chamber liquid nitrogen supply system comprises a liquid nitrogen storage tank 15, a system pipeline, a supply pipeline, a test chamber body 17 and a supply return pipeline which are in circulating communication as shown in fig. 5.
An injection pipeline and an injection return pipeline are arranged in the test cabin body 17, one end of the injection pipeline is communicated with the supply pipeline, the other end of the injection pipeline is provided with an injection port, and the injection port is arranged towards the inside of the test cabin body 17. The injection return pipeline is communicated with the injection pipeline as a branch, the injection return pipeline is communicated with the supply return pipeline, and a regulating pipeline is communicated between the inlet end of the supply pipeline and the supply return pipeline. The outlet of the feed return line is provided with two branches, one of which communicates with the inlet of the liquid nitrogen tank 15 and the other with the gas-liquid separator 18. The system pipeline is provided with a low-temperature centrifugal pump 16, and the system pipeline downstream of the low-temperature centrifugal pump 16 is provided with a post-pump return pipeline which is also communicated with a gas-liquid separator 18. The liquid nitrogen or nitrogen gas introduced into the gas-liquid separator 18 is discharged to the atmosphere through the gas-liquid separator 18. A manual shutoff valve 19 is attached to the outlet of the liquid nitrogen tank 15. A first flow valve 23 is arranged at the inlet of the system pipeline, a second flow valve 24 is arranged at the inlet end of the back-flow pipeline after the pump, a back-flow branch is communicated between the back-flow pipeline after the pump and the liquid nitrogen storage tank 15, a third flow valve 25 is arranged on the back-flow branch, a fourth flow valve 26 is arranged at the tail end of the back-flow pipeline after the pump, a fifth flow valve 27 is arranged at the tail end of the system pipeline, and a sixth flow valve 28 is arranged at the inlet of the supply pipeline. A seventh flow valve 29, an eighth flow valve 30, a ninth flow valve 31, and a tenth flow valve 32 are respectively installed upstream of the injection ports of the four injection lines, an eleventh flow valve 33, a twelfth flow valve 34, a thirteenth flow valve 35, and a fourteenth flow valve 36 are respectively installed on the four injection return lines, and a fifteenth flow valve 37 and a flow rate valve 22 are installed on the regulation line. A sixteenth flow valve 38 is provided in the two branches at the end of the supply return line, and a seventeenth flow valve 39 is provided in the branch connected to the gas-liquid separator 18. A first power valve 20 and a second power valve 21 are respectively installed at the inlet and outlet ends of the system pipeline for introducing gaseous nitrogen into the liquid nitrogen supply system in the nitrogen purging stage.
The system pipeline inlet is provided with first dew point monitoring point position 40, and the back return line inlet is provided with second dew point monitoring point position 41 behind the pump, and the supply line inlet is provided with third dew point monitoring point position 42, and supply return line end is provided with fourth dew point monitoring point position 43, and liquid nitrogen storage tank 15 top is provided with fifth dew point monitoring point position 44. The third dew point monitoring point position 42 is further provided with a pressure monitoring point position 47, the second dew point monitoring point position 41 is provided with a first temperature monitoring point position 45, and the fourth dew point monitoring point position 43 is further provided with a second temperature monitoring point position 46.
The dew point monitoring device comprises a housing 11, a measuring line and a control unit 14. Five low-temperature fluid inlet ports are designed on the side wall of the box body 11 and serve as fluid inlets 12, a gas discharge port is designed on the opposite side and serves as a fluid outlet 13, and an operation platform is integrated on the top of the box body 11; the measuring pipeline is arranged in the box 11, the input end of the measuring pipeline is connected with the five sampling hand valves 1 positioned on the operating platform, and the output end of the measuring pipeline is fixed with the gas discharge interface. The control unit 14 is installed inside the box 11, and is provided with an independent dew point monitoring controller, and is used for receiving an instruction issued by the main controller of the liquid nitrogen supply system, executing a corresponding control program, sending a fault signal to the main controller, and executing a linkage action with unqualified dew point. Five paths of low-temperature fluid liquid inlet ports in the box body 11 are installed in parallel and are designed into threads or clamping sleeve forms, one end of each port is quickly connected with a low-temperature pipeline monitoring point in a butt joint mode, and the other end of each port is connected with the sampling hand valve 1 of the operating platform. The measuring pipeline is provided with an electromagnetic valve 2, a heating element 3, a temperature sensor 4, a filter 5, a first pressure sensor 6, a pressure reducing element 7, a second pressure sensor 8, a dew point meter 9 serving as a dew point monitoring element and a one-way valve 10 in sequence.
One end of the electromagnetic valve is fixed with the sampling hand valve, so that the other end of the electromagnetic valve is connected with the parallel main pipeline, and the electromagnetic valve is an ultralow-temperature electromagnetic valve with the working temperature of-196 ℃ to +90 ℃ and is used for controlling all dew point monitoring points. After the heating element is installed on the electromagnetic valve, the heating power covers the whole supply pressure and flow range of the supply system. The maximum power is determined based on the principle of conservation of energy, the flow of the device is approximately calculated by using a liquid orifice plate formula, under the conditions of constant pressure of a power unit KJ/s, liquid nitrogen is converted into isothermal nitrogen required power w 1, the nitrogen is increased from 83.617K to 290K required power w 2, the liquid nitrogen is fully gasified into 290K nitrogen required power w, and thenWherein P 1 is the conveying pressure of a low-temperature system, and the unit is MPa; ρ i is the saturation density of liquid nitrogen at P 1 in kg/m 3.
After the temperature sensor 4 is installed on the heating element 3, the control unit 14 collects temperature and performs closed-loop control on the output power of the heating device. The filter 5 is in a thread form, one end of the filter is connected with the outlet of the heating element 3, and the other end of the filter is connected with the inlet of the pressure reducing element 7, and is used for filtering the redundant substances in the gas gasified by the sampling liquid, so that the damage to the dew point meter 9 under the action of high-pressure air flow is avoided; signals of the first pressure sensor 6 and the second pressure sensor 8 are collected by a control unit 14 and are respectively arranged at the front and the rear of the pressure reducing device for stabilizing the gas pressure output at 0.2MPa. Wherein, the first pressure sensor 6 and the temperature sensor 4 jointly judge the gasification degree of the low-temperature liquid, and the second pressure sensor 8 is used for closed-loop control of pressure. The dew point meter 9 has an inlet connected with the pressure reducing member 7, an outlet connected with the check valve 10, and a control unit 14 for collecting dew point signals. After the check valve 10 is installed on the dew point meter 9, the outlet is connected with a gas discharge interface, and the air is directly discharged to the atmosphere, so that the air is prevented from being sucked back into the device to pollute the system.
The control unit 14 collects signals of the temperature sensor 4, the first pressure sensor 6 and the second pressure sensor 8, respectively makes differences with a temperature set value of 15 ℃ and a pressure set value of 0.2MPa, and controls the heating element 3 and the pressure reducing element 7 in a closed loop manner, and can receive running instructions and polling time issued by a liquid nitrogen supply master controller. All connecting pipe fittings and the inner cavity of the heating piece 3 in the dew point monitoring device are polished in 316 stainless steel, so as to avoid monitoring result distortion caused by water adsorption of the inner wall material of the pipeline.
The embodiment also provides a dew point monitoring method of the liquid nitrogen supply system of the low-temperature test chamber, and the monitoring method relates to five stages of system preparation, nitrogen cleaning, liquid nitrogen precooling, variable working condition supply and safe parking. Dew point monitoring device of low-temperature test chamber liquid nitrogen supply system is provided based on this embodiment.
The system preparation stage at least comprises one-to-one connection of dew point monitoring points and a fluid inlet 12, power-on self-detection of a liquid nitrogen master controller in a liquid nitrogen supply system, power-on self-detection of a controller in a dew point monitoring device, writing in closed-loop temperature, closed-loop pressure and polling time, and opening a sampling hand valve 1 in the dew point monitoring device.
In the nitrogen cleaning stage, nitrogen gas which is dried at normal temperature and is 0.6MPa is adopted to sequentially clean the low-temperature centrifugal pump 16, the back-flow pipeline, the supply pipeline and the injection pipeline, and cleaning tail gas is discharged into the atmosphere through the gas-liquid separator 18. In the nitrogen purging process, after the dew point monitoring value of the dew point monitoring point position on the previous pipeline meets the requirement, stopping the nitrogen purging of the pipeline, and switching to the next pipeline until the dew point of all the loops meets the qualified requirement of nitrogen purging, thereby completing the nitrogen purging work of the supply system. The dew point qualification standard under the nitrogen cleaning flow is that the dew point value in all the cleaned pipelines is not more than-76.0 ℃ dp, and the dew point value is maintained for a certain time, and the maintaining time is set and issued by a liquid nitrogen supply system master controller.
In the liquid nitrogen precooling stage, firstly, the dead weight of liquid nitrogen in the liquid nitrogen in a storage tank is utilized to precool a low-temperature centrifugal pump 16 and a back-pump return pipeline, when the temperature of the low-temperature centrifugal pump 16 and the back-pump return pipeline reaches the saturated steam temperature and the dew point meets the requirement, the low-temperature centrifugal pump 16 is started at 20Hz frequency, normal-pressure liquid nitrogen is boosted to 0.3MPa, the liquid nitrogen is utilized to precool a supply return pipeline, a supply pipeline and an injection pipeline in sequence, precooled tail liquid is discharged into the atmosphere through a gas-liquid separator 18, when the temperature of each loop reaches the saturated steam temperature and the dew point meets the requirement, the liquid nitrogen is switched to flow back to a liquid nitrogen storage tank 15, and liquid nitrogen precooling of the next loop is started until the temperature and the dew point of all the pipelines meet the liquid nitrogen precooling requirement, and liquid nitrogen precooling work of a supply system is completed. The dew point qualification standard under the liquid nitrogen precooling flow is that the dew point value of all the loops after precooling reaches-76.0 ℃ dp, and the temperature reaches-190 ℃ or below.
In the variable working condition supply stage, normal-pressure liquid nitrogen is boosted to a supply pressure of 0.54-1.5 MPa by the low-temperature centrifugal pump 16, and the low-temperature centrifugal pump 16 controls the liquid nitrogen to be boosted and then sequentially passes through a system pipeline, a supply pipeline and the test cabin body 17, so that the liquid nitrogen is sprayed into the test cabin body 17. In the variable working condition supply process, dew point monitoring values of two dew point monitoring points at the inlet of the supply pipeline and the tail end of the supply reflux pipeline are obtained in real time, if the dew point monitoring values do not meet the variable working condition supply requirement, a flow valve at the upstream of a liquid nitrogen injection port in the test cabin body 17 is closed, and a flow valve on the injection reflux pipeline is opened, so that liquid nitrogen directly flows into the supply reflux pipeline through the injection reflux pipeline, and the low-temperature centrifugal pump 16 is controlled to stop running. And after the medium is switched back to the gas-liquid separator, fault detection is carried out. When fault detection is carried out, the dew point monitoring device sequentially obtains the dew point monitoring values of all the dew point monitoring points at equal time intervals, if the dew point monitoring value of a certain dew point monitoring point falls to be more than 12 ℃ dp in the monitoring time, the dew point of the pipeline is normal, and if the dew point monitoring value of a certain dew point monitoring point does not fall, rises or falls to be less than 12 ℃ dp in amplitude, the dew point fault of the pipeline where the dew point monitoring point is located is judged. And under the variable working condition supply flow, the dew point qualification standard is that the dew point monitoring value of all the related dew point monitoring points is not higher than-76 ℃ dp, and the rise in each minute is not higher than 5 ℃ dp.
In the safe parking stage, the low-temperature centrifugal pump 16 stops running, the flow valve at the upstream of the injection port on the injection pipeline in the test cabin body 17 is closed, the low-temperature centrifugal pump 16, the post-pump return pipeline, the supply pipeline, the injection return pipeline and the supply return pipeline are all communicated with the liquid nitrogen storage tank 15, liquid nitrogen is kept in all pipelines, the low-temperature state is maintained, and the next injection command is waited. In the safe parking process, the dew point monitoring value of each dew point monitoring point position is obtained in a timing and circulating way, when the dew point monitoring value of a certain dew point monitoring point position rises to exceed 5 ℃ dp in one minute, the dew point abnormality of the dew point monitoring point position is judged, polling monitoring is stopped, the 'parking dew point abnormality' is sent to a master controller, after the master controller receives information, a flow valve at the inlet of a liquid nitrogen storage tank 15 is turned off, an audible and visual alarm is sent, fault detection is prompted, if the dew point monitoring value is continuously normal, after the preset monitoring time of five minutes is timed, the pipeline is closed, and the dew point monitoring of the next pipeline is carried out.
Referring to the attached drawings, the dew point monitoring method of the liquid nitrogen supply system of the low-temperature test chamber comprises the following steps:
The first dew point monitoring point position 40, the second dew point monitoring point position 41, the third dew point monitoring point position 42, the fourth dew point monitoring point position 43 and the fifth dew point monitoring point position 44 are sequentially connected with the five fluid inlets 12; powering up a liquid nitrogen master controller in a liquid nitrogen supply system, and enabling self-detection to pass through without abnormality; the dew point monitoring device is electrified, the control unit 14 automatically detects no abnormality, the touch screen inputs the outlet pressure of the pressure reducing piece 7 to be 0.2MPa, the outlet temperature of the heating piece 3 to be 15 ℃, the polling time is 5 minutes, and the five-way sampling hand valve 1 is opened.
And in the nitrogen cleaning stage, the air source is kept dry, and the pressure is stably output to 0.6MPa. The nitrogen purging at least comprises the steps of opening a purge path air source according to purge steps, controlling a purge path valve, and controlling a monitoring device valve, and specifically: the total controller in the liquid nitrogen supply system binds the qualified standard of nitrogen cleaning dew point to be the dew point measured value of minus 76 ℃ dp, and the duration is 30 minutes; the overall controller issues a "start nitrogen purge" command to the dew point monitoring device. After the first flow valve 23, the second flow valve 24 and the fourth flow valve 26 are opened, the master controller receives the in-place signals of the first flow valve 23, the second flow valve 24 and the fourth flow valve 26, opens the first power valve 20 to introduce nitrogen, and simultaneously instructs the dew point monitoring device to open the electromagnetic valve 2 corresponding to the first dew point monitoring point position 40 and the second dew point monitoring point position 41 in the box 11 of the dew point monitoring device. The monitoring value of the dew point meter 9 is lower than-76 ℃ dp for 30 minutes, the electromagnetic valve 2 corresponding to the first dew point monitoring point position 40 and the second dew point monitoring point position 41 is closed, and the master controller is returned to the 'first loop cleaning is qualified'. After receiving the "first circuit cleaning pass" information, the overall controller closes the first flow valve 23, the second flow valve 24, the fourth flow valve 26 and the first power valve 20. After the master controller receives the closing signals of the first flow valve 23, the second flow valve 24, the fourth flow valve 26 and the first power valve 20 for a period of time, opening the fifth flow valve 27, the fifteenth flow valve 37 and the flow rate valve 22 which is arranged corresponding to the fifteenth flow valve 37 by 100 percent and the seventeenth flow valve 39; after the master controller receives the opening signals of the fifth flow valve 27, the fifteenth flow valve 37 and the seventeenth flow valve 39 and the opening feedback of the flow rate valve 22 is 100%, the second power valve 21 is opened to introduce nitrogen, and the dew point monitoring device is instructed to open the electromagnetic valve 2 corresponding to the fourth dew point monitoring point 43; the monitoring value of the dew point meter 9 is lower than-76 ℃ dp for 30 minutes, and the master controller is returned to be qualified in the second loop cleaning; the master controller receives the second loop cleaning qualification information, closes the fifteenth flow valve 37 and closes the opening of the flow rate valve 22 to 0%; the master controller receives the fifteenth flow valve 37 closing signal, the opening feedback of the flow rate valve 22 is 0%, and after timing for a period of time, the sixth flow valve 28, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35 and the fourteenth flow valve 36 are opened; after receiving the signals of opening the sixth flow valve 28, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35 and the fourteenth flow valve 36 in place, the master controller commands the dew point monitoring device to open the electromagnetic valve 2 corresponding to the third dew point monitoring point 42; the monitoring value of the dew point meter 9 is lower than-76 ℃ dp for 30 minutes, the electromagnetic valve 2 corresponding to the first dew point monitoring point position 40, the third dew point monitoring point position 42 and the fourth dew point monitoring point position 43 is closed, and the total controller is returned to 'third loop cleaning is qualified'; the overall controller receives the third loop cleaning qualified information and closes the sixth flow valve 28, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35, the fourteenth flow valve 36, the seventeenth flow valve 39 and the second power valve 21; the master controller receives and the sixth, eleventh, twelfth, thirteenth, and fourteenth flow valves 28, 33, 35, 36, seventeenth, and second power valves 39, 21 close in place signals and the liquid nitrogen supply system records a "nitrogen purge complete" message.
The liquid nitrogen pre-cooling stage at least comprises a manual stop valve 19 for opening an outlet of the liquid nitrogen storage tank 15, and the valves on all pre-cooling paths are controlled according to the pre-cooling step to control the valve of the dew point monitoring device, in particular: the master controller binds liquid nitrogen precooling dew point qualification standard: the dew point measurement value is not higher than-76 ℃ dp, and the monitoring temperature of the first temperature monitoring point 45 and the second temperature monitoring point 46 is not higher than-190 ℃. Opening a manual cut-off valve for liquid supply at the outlet of the liquid nitrogen storage tank 15, and issuing a command of 'starting liquid nitrogen precooling' to a dew point monitoring device by the master controller, and simultaneously opening a first flow valve 23, a second flow valve 24 and a fourth flow valve 26; the master controller receives the signals of opening the first flow valve 23, the second flow valve 24 and the fourth flow valve 26, and commands the dew point monitoring device to open the electromagnetic valve 2 correspondingly communicated with the first dew point monitoring point position 40, the second dew point monitoring point position 41 and the fifth dew point monitoring point position 44. The monitoring value of the dew point meter 9 is lower than-76 dp, the temperature value of the first temperature monitoring point position 45 is not higher than-190 ℃, the electromagnetic valve 2 communicated with the second dew point monitoring point position 41 in the dew point monitoring device is closed, and the total controller is returned to 'the first loop pre-cooling is qualified'. The master controller receives the information of 'first loop precooling is qualified', closes the fourth flow valve 26 and opens the third flow valve 25; the master controller receives the signals that the fourth flow valve 26 is closed and the third flow valve 25 is opened, after timing for a period of time, the low-frequency 20Hz starts the low-temperature centrifugal pump 16, opens the fifth flow valve 27, the fifteenth flow valve 37 and the seventeenth flow valve 39, and controls the opening of the flow rate valve 22 which is arranged corresponding to the fifteenth flow valve 37 to 100 percent; after the master controller receives the feedback of the operating frequency 20Hz of the low-temperature centrifugal pump 16, the fifth flow valve 27, the fifteenth flow valve 37 and the seventeenth flow valve 39 are opened to the right signals, and the opening degree of the flow rate valve 22 is fed back by 100 percent, the dew point monitoring device is instructed to open the electromagnetic valve 2 correspondingly communicated with the fourth dew point monitoring point 43; the monitoring value of the dew point instrument 9 is lower than-76 ℃ dp, the temperature value of the second temperature monitoring point position 46 is not higher than-190 ℃, and the master controller is returned to be 'qualified for the second loop precooling'; the master controller receives the second loop pre-cooling qualification information and opens the sixth flow valve 28, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35 and the fourteenth flow valve 36; after receiving the signals of opening the sixth flow valve 28, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35 and the fourteenth flow valve 36 in place, the master controller commands the dew point monitoring device to open the electromagnetic valve 2 correspondingly communicated with the third dew point monitoring point 42; the monitoring value of the dew point instrument 9 is lower than-76 ℃ dp, the temperature value of the second temperature monitoring point position 46 is not higher than-190 ℃, and the master controller is returned to be 'qualified in third loop precooling'; the master controller receives the "third loop dew point pass" information, opens the sixteenth flow valve 38, and closes the seventeenth flow valve 39; the third circuit dew point pass information is received, the sixteenth flow valve 38 is opened, the seventeenth flow valve 39 is closed, and the liquid nitrogen supply system records the liquid nitrogen precooling completion.
The variable working condition supply stage at least comprises the steps of closing a back return pipeline of the pump and closing an injection return pipeline, indirectly controlling the flow of liquid nitrogen in the supply pipeline by controlling the return flow of the regulation and control pipeline, and finally achieving the aim of controlling the temperature of the test cabin body 17, and specifically: the master controller binds liquid nitrogen supply dew point reject standard: the dew point measurement rose above 5 ℃ dp within one minute. The master controller issues a command of starting variable working condition supply to the dew point monitoring device, and closes the second flow valve 24, the third flow valve 25, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35 and the fourteenth flow valve 36 to command the dew point monitoring device to close the electromagnetic valve 2 correspondingly communicated with the second dew point monitoring point 41; after receiving the signals of closing the second flow valve 24, the third flow valve 25, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35 and the fourteenth flow valve 36, the master controller manually issues the target supply pressure; the cryogenic centrifugal pump 16 increases the frequency according to the set value of the supply pressure, and the flow rate valve 22 on the regulating pipeline starts to control the opening in a closed loop manner so as to stabilize the supply pressure monitored at the pressure monitoring point 47 to the set value of the supply pressure; sequentially opening a seventh flow valve 29, an eighth flow valve 30, a ninth flow valve 31 and a tenth flow valve 32, injecting liquid nitrogen into the test cabin body 17 for cooling, and controlling injection flow by changing a supply pressure set value in real time according to the temperature change condition; when the variable-working-condition operation is stopped, the seventh flow valve 29, the eighth flow valve 30, the ninth flow valve 31 and the tenth flow valve 32 are sequentially closed, and the liquid nitrogen is controlled to fully reflux to the liquid nitrogen storage tank 15 by adopting an adjusting pipeline, so that the liquid nitrogen injection is finished. In the variable working condition supply operation process, once the dew point monitoring device sends a dew point disqualification signal to the master controller, the following steps are executed: the overall controller opens the eleventh, twelfth, thirteenth, fourteenth and seventeenth flow valves 33, 34, 35, 36 and 39; after receiving the feedback signals of opening the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35, the fourteenth flow valve 36 and the seventeenth flow valve 39, the master controller closes the seventh flow valve 29, the eighth flow valve 30, the ninth flow valve 31, the tenth flow valve 32 and the sixteenth flow valve 38 to stop the operation of the cryogenic centrifugal pump 16; the master controller receives the closing signals of the seventh flow valve 29, the eighth flow valve 30, the ninth flow valve 31, the tenth flow valve 32 and the sixteenth flow valve 38, and the frequency feedback of the low-temperature centrifugal pump 16 is 0Hz, and commands the dew point monitoring device to close the electromagnetic valve 2 communicated with the first dew point monitoring point position 40, the third dew point monitoring point position 42 and the fourth dew point monitoring point position 43, and starts timing. After the polling time is 5 minutes, if the measured value of the dew point meter 9 falls below 12 ℃ dp within 5 minutes, the dew point of the liquid nitrogen storage tank 15 is not qualified, if the measured value of the dew point meter 9 falls below 12 ℃ dp within 5 minutes, the dew point of the liquid nitrogen storage tank 15 is qualified, the electromagnetic valve 2 communicated with the fifth dew point monitoring point position 44 is closed, the electromagnetic valve 2 communicated with the first dew point monitoring point position 40 is opened, and timing is started; after the polling time is 5 minutes, if the measured value of the dew point meter 9 is reduced to less than 12 ℃ dp, the dew point of the system pipeline is unqualified, if the measured value is reduced to more than 12 ℃ dp, the dew point of the system pipeline is qualified, the electromagnetic valve 2 communicated with the first dew point monitoring point position 40 is closed, the electromagnetic valve 2 communicated with the third dew point monitoring point position 42 is opened, and timing is started; after the polling time is 5 minutes, if the measured value of the dew point meter 9 is lowered to less than 12 ℃ dp, the dew point of the supply pipeline is failed, if the measured value is lowered to more than 12 ℃ dp, the dew point of the supply pipeline is failed, the electromagnetic valve 2 communicated with the third dew point monitoring point position 42 is closed, the electromagnetic valve 2 communicated with the fourth dew point monitoring point position 43 is opened, and timing is started; after 5 minutes of polling time, if the dew point measurement by the dew point meter 9 drops below 12 ℃ dp, this indicates that the supply return line dew point is unacceptable, and if it drops above 12 ℃ dp, this indicates that the supply return line dew point is acceptable.
The safe parking stage at least comprises a back flow pipeline and an injection back flow pipeline after a pump is opened, each loop of the system is communicated with a liquid nitrogen storage tank 15, the pressure stability of a liquid nitrogen supply system is maintained through the liquid nitrogen storage tank 15, no air is broken, air is prevented from entering a pollution system, after the next working of the test cabin body 17 directly enters pre-cooling, the operation under a variable working condition is started, and the test preparation time is shortened. The master controller issues a "safe parking" command to control the cryogenic centrifugal pump 16 to operate at a frequency of 5Hz per minute down to the cryogenic centrifugal pump 16 to stop operating, with the liquid nitrogen supply pressure automatically matching the cryogenic centrifugal pump 16 frequency. The overall controller receives pump frequency feedback of 0Hz, opening the second flow valve 24, the third flow valve 25, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35, and the fourteenth flow valve 36; after receiving the signals of opening the second flow valve 24, the third flow valve 25, the eleventh flow valve 33, the twelfth flow valve 34, the thirteenth flow valve 35 and the fourteenth flow valve 36 in place, the master controller closes the electromagnetic valve 2 communicated with the first dew point monitoring point position 40, the third dew point monitoring point position 42 and the fourth dew point monitoring point position 43, and the dew point monitoring device starts to monitor the sampling points according to the polling time issued by the master controller; starting to count time for 5 minutes, stopping polling monitoring when the measured value of the dew point meter 9 rises to more than 5 ℃ dp within 5 minutes, sending 'abnormal parking dew point' to a master controller, and after the master controller receives the information, turning off a third flow valve 25 and a sixteenth flow valve 38, sending out audible and visual alarm and prompting fault detection. If the detected dew point is normal, closing the electromagnetic valve 2 communicated with the fifth dew point monitoring point position 44, opening the electromagnetic valve 2 communicated with the first dew point monitoring point position 40, starting timing for 5 minutes, stopping polling monitoring when the measured value of the dew point meter 9 rises to more than 5 ℃ dp within one minute within 5 minutes, sending a 'parking dew point abnormality' to a master controller, and after the master controller receives the information, closing the third flow valve 25 and the sixteenth flow valve 38, sending an audible and visual alarm to prompt fault detection; if normal, closing the electromagnetic valve 2 communicated with the first dew point monitoring point position 40, and opening the electromagnetic valve 2 communicated with the second dew point monitoring point position 41; starting timing for 5 minutes, stopping polling monitoring when the measured value of the dew point meter 9 rises to more than 5 ℃ dp within one minute within 5 minutes, sending 'parking dew point abnormality' to a master controller, after the master controller receives the information, turning off a third flow valve 25 and a sixteenth flow valve 38, sending out audible and visual alarms, prompting fault investigation, and if normal, turning off the electromagnetic valve 2 communicated with the second dew point monitoring point position 41 and turning on the electromagnetic valve 2 communicated with the third dew point monitoring point position 42; timing for 5 minutes, stopping polling monitoring when the measured value of the dew point meter 9 rises to more than 5 ℃ dp within one minute within 5 minutes, sending 'abnormal parking dew point' to a master controller, after the master controller receives the information, turning off a third flow valve 25 and a sixteenth flow valve 38, sending out audible and visual alarms, prompting fault investigation, if normal, turning off an electromagnetic valve 2 communicated with a third dew point monitoring point position 42, and turning on an electromagnetic valve 2 communicated with a fourth dew point monitoring point position 43; and (3) timing for 5 minutes, stopping polling monitoring when the measured value of the dew point meter 9 rises to more than 5 ℃ dp within one minute within 5 minutes, sending 'abnormal park dew point' to a master controller, after the master controller receives the information, turning off the third flow valve 25 and the sixteenth flow valve 38, sending out audible and visual alarm to prompt fault investigation, if the measured value is normal, turning off the electromagnetic valve 2 communicated with the fourth dew point monitoring point position 43, re-opening the electromagnetic valve 2 communicated with the fifth dew point monitoring point position 44, and performing circulation. It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (10)
1. The dew point monitoring device of the low-temperature test chamber liquid nitrogen supply system is characterized in that the low-temperature test chamber liquid nitrogen supply system comprises a liquid nitrogen storage tank (15), a system pipeline, a supply pipeline, a test chamber body (17) and a supply reflux pipeline which are circularly communicated, wherein an outlet of the supply reflux pipeline is communicated with an inlet of the liquid nitrogen storage tank (15);
a low-temperature centrifugal pump (16) is arranged on the system pipeline, and a post-pump return pipeline is arranged on the system pipeline at the downstream of the low-temperature centrifugal pump (16);
The dew point monitoring device includes:
The system comprises a fluid inlet (12), at least five system pipeline inlets, a back-pump return pipeline inlet, a supply return pipeline tail end and dew point monitoring points arranged at the top of a liquid nitrogen storage tank (15), wherein the dew point monitoring points are suitable for being communicated with the fluid inlet (12) in a one-to-one correspondence manner;
and the fluid inlets (12) are communicated with the measuring pipeline, and the heating part (3), the pressure reducing part (7) and the dew point monitoring part are sequentially arranged on the measuring pipeline.
2. The device according to claim 1, characterized in that a non-return valve (10) is mounted on the measuring tube downstream of the dew point monitoring element.
3. The cryogenic test chamber liquid nitrogen supply system dew point monitoring device according to claim 1 or 2, characterized in that a filter (5) is mounted between the heating element (3) and the pressure reducing element (7).
4. A method for monitoring dew point of a cryogenic test chamber liquid nitrogen supply system, characterized by being based on the cryogenic test chamber liquid nitrogen supply system dew point monitoring device according to any one of claims 1 to 3.
5. The method for monitoring dew point of cryogenic test chamber liquid nitrogen supply system according to claim 4, comprising the steps of:
And (3) adopting normal-temperature dry nitrogen to sequentially clean a low-temperature centrifugal pump (16), a back-pump return pipeline, a supply return pipeline and a supply pipeline, stopping nitrogen cleaning of the pipeline after the dew point monitoring value of the dew point monitoring point on the previous pipeline is not more than-76.0 ℃ dp and the preset cleaning time is kept, and switching to the next pipeline until the dew point monitoring values of all the dew point monitoring points are all more than-76.0 ℃ dp, thereby completing the nitrogen cleaning work.
6. The method for monitoring dew point of a cryogenic test chamber liquid nitrogen supply system of claim 5, comprising:
The liquid nitrogen in the liquid nitrogen storage tank (15) precools the low-temperature centrifugal pump (16) and the back-pumping return pipeline under the action of self gravity, when the temperature of the back-pumping return pipeline is not more than-190 ℃, the low-temperature centrifugal pump (16) is started to boost the pressure of the liquid nitrogen, the low-temperature centrifugal pump (16) is used for controlling the liquid nitrogen to flow so as to precool the supply return pipeline and the supply pipeline in sequence, after the temperature of the previous pipeline is not more than-190 ℃, the liquid nitrogen precooling of the next pipeline is started until the temperatures of all pipelines are not more than-190 ℃, and the liquid nitrogen precooling work is completed.
7. The method for monitoring dew point of a cryogenic test chamber liquid nitrogen supply system of claim 6, comprising:
The low-temperature centrifugal pump (16) controls the liquid nitrogen to be boosted and then sequentially passes through the system pipeline, the supply pipeline and the test cabin body (17), liquid nitrogen is sprayed into the test cabin body (17), and liquid nitrogen wake flows into the supply return pipeline;
And acquiring dew point monitoring values of two dew point monitoring points at the inlet of the supply pipeline and the tail end of the supply reflux pipeline in real time, closing a liquid nitrogen jet orifice in the test cabin body (17) if the dew point monitoring values do not meet the supply requirement of the variable working condition, enabling liquid nitrogen to directly flow into the supply reflux pipeline, controlling the low-temperature centrifugal pump (16) to stop running, and performing fault detection.
8. The method for monitoring dew point of a cryogenic test chamber liquid nitrogen supply system of claim 7, comprising:
When the liquid nitrogen stops spraying, the system enters a safe parking state, the low-temperature centrifugal pump (16) stops running, a spraying valve in the test cabin body (17) is closed, the low-temperature centrifugal pump (16), a back-pump return pipeline, a supply pipeline and a supply return pipeline are all communicated with the liquid nitrogen storage tank (15), and the liquid nitrogen is statically arranged in the pipeline;
And (3) periodically acquiring the monitoring values of all the dew point monitoring points, and when the change rate of the monitoring value of a certain dew point monitoring point is higher than a safety early warning value, switching the communication with the liquid nitrogen storage tank (15) into the communication with the gas-liquid separator (18) for fault detection.
9. The cryogenic test chamber liquid nitrogen supply system dew point monitoring method of claim 7, wherein the variable regime supply requirement comprises: the dew point monitoring value is not higher than-76 ℃ dp, and does not rise by more than 5 ℃ dp per minute.
10. A cryogenic test chamber liquid nitrogen supply system dew point monitoring method according to any of claims 7 to 9, wherein the fault detection step comprises: and sequentially and isochronously acquiring the dew point monitoring values of the related dew point monitoring points, and judging that the pipeline where the dew point monitoring point is located is faulty if the drop of the dew point monitoring value of a certain dew point monitoring point within the monitoring time is not more than 12 ℃ dp.
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