A system and method for detecting inner and outer leakage of a plate-fin heat exchanger at low temperature

Abstract

The application discloses a system and method for detecting the inner and outer leakage rate of a plate-fin heat exchanger at low temperature, which comprises a cryogenic treatment system for conveying low-temperature pre-cooling working medium, a helium filling system for storing low-temperature working medium for leakage detection, a vacuum cold box system, a test system for vacuum pumping and leakage detection, and a recovery system for high-pressure recovery of helium; the cryogenic treatment system, the helium filling system, the test system and the recovery system are connected with the vacuum cold box system respectively and sequentially form a cryogenic treatment passage, a helium filling passage, a test passage and a recovery passage, and a passage valve is arranged on each passage; the tested piece is arranged in the vacuum cold box system in a detachable mode. The application can more accurately test the leakage rate of the plate-fin heat exchanger under different low-temperature working conditions, is especially suitable for detecting the inner and outer leakage rate of a multi-cavity container or multiple containers such as the plate-fin heat exchanger, and simultaneously realizes the recovery and recycling of helium.

Description

TECHNICAL FIELD

[0001] The present application relates to a system and method for detecting the internal and external leakage rate of a plate-fin heat exchanger, in particular to a system and method for detecting the internal and external leakage rate of a plate-fin heat exchanger at low temperature. BACKGROUND

[0002] Large helium liquefaction, hydrogen liquefaction and other devices use low-temperature cold boxes, which are usually designed with vacuum insulation. Plate-fin heat exchangers, as important components of large helium liquefaction, hydrogen liquefaction and other devices, are placed in the vacuum cold box. The vacuum degree of the cold box determines whether the heat insulation effect of the cold box can meet the requirements. The external leakage rate needs to be kept below 10 Pa·L / s at room temperature and low temperature. At the same time, due to the different working media and pressures in different channels of the plate-fin heat exchanger, the micro-leakage of the working media in the flow channel will also cause the impurity of the low-temperature working medium or leakage, thereby affecting the performance of the entire low-temperature system, and even affecting the safe operation of the system. Therefore, the internal leakage rate also needs to be kept below 10 Pa·L / s at room temperature and low temperature. -6 -5

[0003] Generally speaking, plate-fin heat exchangers and other equipment or devices are brazed in a high-temperature vacuum brazing furnace. The brazing seam is dense and has many welds, which are prone to micro-leakage. Although internal pressurized water bubble visual leak detection at room temperature and helium mass spectrometry leak detection with external helium at room temperature can detect micro-leakage, the previously defective parts are prone to become new leak holes during the cooling process of the plate-fin heat exchanger to low temperature due to material, welding environment, stress and other reasons. This will increase the leakage rate at low temperature by several orders of magnitude, causing the plate-fin heat exchanger to be unable to function normally at low temperature. The repair work will be very tedious, and even the situation of high leakage rate at low temperature and normal leakage rate after returning to room temperature may occur. The previous testing device or method for testing the heat exchanger after cooling and returning to room temperature cannot effectively detect the leakage. Therefore, a leakage detection system capable of real-time detection at room temperature and low temperature must be developed.

[0004] Patent 202110801347.6 discloses a plate-fin heat exchanger multi-channel internal and external leak detection and recovery purification device and method. The invention solves the problems of tedious helium detection work and long time for multi-cavity containers or multiple containers, and recovers the helium used for leak detection. However, this device and method use a plastic film cover for detection, which cannot achieve high-pressure helium detection of large equipment or devices at low temperature. Therefore, the invention needs to be improved to achieve high-pressure helium detection of plate-fin heat exchangers and other multi-cavity containers or multiple containers at room temperature and low temperature. SUMMARY

[0005] The present application aims to provide a system and method for detecting the internal and external leakage rate of a plate-fin heat exchanger at low temperature.​​

[0006] Technical solution: The system for detecting the inner and outer leakage rate of the plate-fin heat exchanger at low temperature comprises a cryogenic treatment system for conveying pre-cooling low-temperature working medium, a helium filling system for storing leakage detection low-temperature working medium, a vacuum cold box system, a test system for vacuumizing and leakage detection, and a recovery system for high-pressure recovery of helium; the cryogenic treatment system, the helium filling system, the test system, and the recovery system are connected with the vacuum cold box system respectively and sequentially form a cryogenic treatment path, a helium filling path, a test path, and a recovery path, and each path is provided with a path valve; the tested piece is detachably arranged in the vacuum cold box system.

[0007] Preferably, the cryogenic treatment system is sequentially connected with a first low-temperature liquid storage tank, a vaporizer, and a first mixer; the first low-temperature liquid storage tank stores liquid nitrogen or liquid helium; the first mixer is provided with a heater, collects low-temperature pre-cooling working medium and normal-temperature pre-cooling working medium vaporized by the vaporizer, and obtains the pre-cooling working medium at the target low-temperature working condition with the assistance of the heater.

[0008] Preferably, the cryogenic treatment path comprises a first cryogenic treatment path and a second cryogenic treatment path; the first cryogenic treatment path comprises the first low-temperature liquid storage tank, the vaporizer, the first mixer, and a first cryogenic treatment switching valve in sequence; and the second cryogenic treatment path comprises the first low-temperature liquid storage tank, the vaporizer, the first mixer, and a second cryogenic treatment switching valve in sequence.

[0009] Preferably, the helium filling system comprises a leakage detection helium gas source, a leakage detection nitrogen gas source, a second low-temperature liquid storage tank, a heat exchange coil, and a second mixer, and the above components are sequentially connected to form a helium filling path; the second low-temperature liquid storage tank stores liquid nitrogen or liquid helium; the heat exchange coil is spirally arranged in the tank body of the second low-temperature liquid storage tank from top to bottom; and the second mixer is provided with a heater.

[0010] Preferably, the test system is sequentially connected with a test reheating coil, a vacuumizing system, and a helium mass spectrometer leakage detector; and the vacuumizing system is a molecular pump group.

[0011] Preferably, the test path comprises an evacuation path and a leakage detection path; the evacuation path comprises the test reheating coil, a pump group control valve, and the vacuumizing system in sequence; and the leakage detection path comprises the test reheating coil, a leakage detection control valve, and the helium mass spectrometer leakage detector in sequence.

[0012] Preferably, the recovery system comprises a first recovery reheating coil, a second recovery reheating coil, an air bag, a recovery compressor, and a dirty helium gas cylinder group; and the recovery compressor is a multi-stage piston compressor or a diaphragm compressor.

[0013] Preferably, the recovery path comprises a first recovery path and a second recovery path; the first recovery path comprises in sequence a first recovery reheat coil, a first recovery switching valve, a helium recovery control valve, a gas bag, a recovery compressor, and a set of dirty helium gas cylinders; the second recovery path comprises in sequence a second recovery reheat coil, a second recovery switching valve, the helium recovery control valve, the gas bag, the recovery compressor, and the set of dirty helium gas cylinders, and a nitrogen venting control valve is connected to the helium recovery control valve through a pipeline.

[0014] Preferably, the vacuum cold box system comprises a first manifold, a first set of channel connecting pipes, a vacuum cold box, a second set of channel connecting pipes, and a second manifold; the vacuum cold box is a sealing device for covering and vacuum sealing the plate-fin heat exchanger; the first set of channel connecting pipes and the second set of channel connecting pipes are respectively connected to two ends of the channels of the test piece and have the same number of channels; each of the connecting pipes of the first set of channel connecting pipes and the second set of channel connecting pipes is provided with a valve, and the valves respectively form a first channel valve group and a second channel valve group; the first set of channel connecting pipes is connected to a first cryogenic treatment path, a helium filling path, and a first recovery path through the first manifold; the second set of channel connecting pipes is connected to a second cryogenic treatment path, a test path, and a second recovery path through the second manifold.

[0015] The method for detecting the internal and external leakage rates of the plate-fin heat exchanger under low-temperature working conditions by the detection system comprises the following steps:

[0016] S1: passing low-temperature pre-cooling working medium into at least one channel of the plate-fin heat exchanger of the test piece through the cryogenic treatment system to cryogenically treat the plate-fin heat exchanger to a required working condition; the low-temperature pre-cooling working medium is low-temperature nitrogen or low-temperature helium. Specifically, the method comprises:

[0017] S1-1: passing the low-temperature pre-cooling working medium flowing out of the first mixer through the cryogenic treatment path to pre-cool the test piece;

[0018] S1-2: during the pre-cooling process, when the temperature of one end of the test piece is reduced below the working temperature, the low-temperature pre-cooling working medium filling channel is switched through the control of the first cryogenic treatment switching valve and the second cryogenic treatment switching valve to rapidly reduce the temperature of the other end with a higher temperature until the temperatures of both ends are reduced below the working temperature; the rapid temperature reduction rate should not be higher than 4 K / min;

[0019] S1-3: The low-temperature pre-cooling working medium after the cryogenic treatment is recovered or discharged after being warmed up through the recovery pipeline, corresponding to step S1-2 at the same time, and the low-temperature pre-cooling working medium exhaust passage is switched through the control of the first recovery switch valve and the second recovery switch valve. When the low-temperature pre-cooling working medium is low-temperature nitrogen, the nitrogen venting control valve is opened to vent the nitrogen for cryogenic treatment; when the low-temperature pre-cooling working medium is low-temperature helium, the helium recovery control valve is opened to recover the helium for cryogenic treatment to the gas bag.

[0020] S2: The vacuum cold box system and each channel of the tested piece are pumped using a test system; when the vacuum of the vacuum cold box system and each channel of the tested piece reaches below 5 Pa, the pump group control valve is closed, the leak detection control valve is opened, the helium mass spectrometer leak detector is connected, and the background leak rate of the vacuum cold box is recorded at the same time.

[0021] S3: The low-temperature leak detection working medium is sequentially filled into the test channels of the tested piece through a helium filling system, and the test channels of the tested piece are sequentially subjected to internal and external leak detection using a test system. Specifically, it includes:

[0022] S3-1: The low-temperature leak detection working medium flowing out of the second mixer is sequentially filled into the test channels of the tested piece through the helium filling path; the low-temperature leak detection working medium is low-temperature helium or low-temperature helium-nitrogen mixed gas;

[0023] S3-2: When the channel pressure reaches the working pressure, the filling of the low-temperature leak detection working medium is stopped, and the test channels of the tested piece are sequentially subjected to internal and external leak detection using the helium mass spectrometer leak detector;

[0024] S3-2-1: First, measure the external leak of the test channel, connect the vacuum cold box to the helium mass spectrometer leak detector, and continuously measure and record the data, which is the external leak rate of the channel;

[0025] S3-2-2: Then, measure the internal leak of the channel, sequentially connect the helium mass spectrometer leak detector to the other non-test channels, continuously measure and record the data, which is the internal leak rate of the channel;

[0026] S3-2-3: After completing the internal and external leak detection of the channel, the next channel is subjected to internal and external leak detection by repeating step S3, until the internal and external leak detection of all channels is completed.

[0027] S4: The helium for leak detection is recovered at high pressure using a recovery system. Specifically, it includes:

[0028] S4-1: The low-temperature leak detection working medium after the leak detection is recovered after being warmed up through the second recovery pipeline, the helium recovery control valve is opened, and the helium for leak detection is recovered to the gas bag;

[0029] S4-2: The helium in the gas bag is pressurized and stored in the contaminated helium steel cylinder group by the recovery compressor, so as to realize high-pressure recovery of the helium.

[0030] Beneficial effects: Compared with the prior art, the leak detection system has the following remarkable advantages: the sealing structure is more reliable, the leak rate of the plate-fin heat exchanger under different low-temperature working conditions can be more accurately tested, and in particular, the plate-fin heat exchanger or other multi-cavity containers or multiple containers can be tested under different low-temperature working conditions in a simulated vacuum cold box environment, and the actual internal and external leak rates can be tested, so that the reliability of the tested piece under the liquid nitrogen and liquid helium temperature zone can be effectively ensured. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The figure is a schematic diagram of the system of the application. DETAILED DESCRIPTION

[0032] The technical solutions of the application will be further described below with reference to the drawings.

[0033] Figure 1 The reference signs in the drawings are as follows:

[0034] 1 - cryogenic treatment system; 11 - first low-temperature liquid storage tank; 12 - vaporizer; 13 - first mixer; 101 - first cryogenic treatment switching valve; 102 - second cryogenic treatment switching valve;

[0035] 2 - helium filling system; 21 - leak detection helium gas source; 22 - leak detection nitrogen gas source; 23 - second low-temperature liquid storage tank; 24 - heat exchange coil; 25 - second mixer;

[0036] 3 - vacuum cold box system; 31 - first manifold; 32 - first channel connecting pipe group; 33 - vacuum cold box; 34 - second channel connecting pipe group; 35 - second manifold; 301 - first channel valve group; 302 - second channel valve group; 303 - cold box evacuation valve;

[0037] 4 - test system; 41 - test reheat coil; 42 - vacuum pumping system; 43 - helium mass spectrometer leak detector; 401 - pump group control valve; 402 - leak detection control valve;

[0038] 5 - recovery system; 51 - first recovery reheat coil; 52 - second recovery reheat coil; 53 - gas bag; 54 - recovery compressor; 55 - contaminated helium steel cylinder group; 501 - first recovery switching valve; 502 - second recovery switching valve; 503 - nitrogen venting control valve; 504 - helium recovery control valve.

[0039] The present application relates to a system and method for detecting the internal and external leakage rate of plate-fin heat exchangers at low temperatures, which can be used to test the leakage rate of plate-fin heat exchangers under different low-temperature conditions, and is particularly suitable for internal and external leak detection of multi-cavity containers or multiple containers such as plate-fin heat exchangers. The following will be described and explained in detail taking the liquid nitrogen temperature zone as an example.

[0040] As shown in Figure 1 A system for detecting the internal and external leakage rate of plate-fin heat exchangers at low temperatures, comprising a cryogenic treatment system 1, a helium filling system 2, a vacuum cold box system 3, a test system 4, a recovery system 5, and a plurality of passage valves; the cryogenic treatment system 1, the helium filling system 2, the test system 4, and the recovery system 5 are connected with the vacuum cold box system 3, and form a cryogenic treatment passage, a helium filling passage, a test passage, and a recovery passage in sequence; the cryogenic treatment system 1 passes low-temperature pre-cooling working medium into one or more channels of the tested piece, and cryogenically treats it to the required working condition; the helium filling system 2 fills low-temperature leak detection working medium into each channel of the tested piece; the test system 4 is used for vacuumizing each channel of the vacuum cold box 33 and the tested piece, and for low-temperature helium mass spectrometric leak rate detection; and the recovery system 5 is used for high-pressure recovery of helium.

[0041] The cryogenic treatment system comprises a first low-temperature liquid storage tank 11, a vaporizer 12, and a first mixer 13. The first low-temperature liquid storage tank 11 stores liquid nitrogen; the first mixer 13 is provided with a heater; and the first mixer 13 collects low-temperature liquid nitrogen and normal-temperature nitrogen gas vaporized by the vaporizer 12, and obtains pre-cooling nitrogen gas at the target low-temperature working condition with the assistance of the heater.

[0042] The cryogenic treatment passage comprises a first cryogenic treatment passage and a second cryogenic treatment passage; the first cryogenic treatment passage comprises the first low-temperature liquid storage tank 11, the vaporizer 12, the first mixer 13, and a first cryogenic treatment switching valve 101 in sequence; and the second cryogenic treatment passage comprises the first low-temperature liquid storage tank 11, the vaporizer 12, the first mixer 13, and a second cryogenic treatment switching valve 102 in sequence.

[0043] The helium filling system comprises a leak detection helium gas source 21, a leak detection nitrogen gas source 22, a second low-temperature liquid storage tank 23, a heat exchange coil 24, and a second mixer 25; the second low-temperature liquid storage tank 23 stores liquid nitrogen; the heat exchange coil 24 is arranged in a spiral shape from top to bottom in the tank body of the second low-temperature liquid storage tank 23; the second mixer 25 is provided with a heater; and the second mixer 25 collects normal-temperature helium-nitrogen mixed gas and low-temperature helium-nitrogen mixed gas cooled by the heat exchange coil 24, and obtains helium-nitrogen mixed gas at the target low-temperature working condition with the assistance of the heater.

[0044] The helium filling passage comprises in sequence a leak detection helium source 21, a leak detection nitrogen source 22, a second low-temperature liquid storage tank 23, a heat exchange coil 24 and a second mixer 25.

[0045] The test system comprises a test reheat coil 41, a vacuum pumping system 42 and a helium mass spectrometer leak detector 43; the vacuum pumping system is a molecular pump vacuum pump set.

[0046] The test passage comprises a vacuuming passage and a leak detection passage; the vacuuming passage comprises in sequence the test reheat coil 41, a pump set control valve 401 and the vacuum pumping system 42; the leak detection passage comprises in sequence the test reheat coil 41, a leak detection control valve 402 and the helium mass spectrometer leak detector 43.

[0047] The recovery system comprises a first recovery reheat coil 51, a second recovery reheat coil 52, an air bag 53, a recovery compressor 54 and a contaminated helium steel cylinder set 55; the recovery compressor is a multi-stage piston compressor or a diaphragm compressor; the contaminated helium steel cylinder set can be connected with a helium purifier, and high-purity helium gas can be obtained after crude helium passes through the helium purifier.

[0048] The recovery passage comprises a first recovery passage and a second recovery passage; the first recovery passage comprises in sequence the first recovery reheat coil 51, a first recovery switching valve 501, a helium recovery control valve 504, the air bag 53, the recovery compressor 54 and the contaminated helium steel cylinder set 55; the second recovery passage comprises in sequence the second recovery reheat coil 52, a second recovery switching valve 502, the helium recovery control valve 504, the air bag 53, the recovery compressor 54 and the contaminated helium steel cylinder set 55, and a nitrogen venting control valve 503 is provided in the pipeline before the helium recovery control valve 504.

[0049] The vacuum cold box system comprises a first manifold 31, a first channel connecting pipe set 32, a vacuum cold box 33, a second channel connecting pipe set 34 and a second manifold 35. The vacuum cold box 33 is a sealing device for covering and vacuum sealing the plate-fin heat exchanger. The first channel connecting pipe set 32 and the second channel connecting pipe set 34 are respectively connected with both ends of the channels of the plate-fin heat exchanger. The number of connecting pipes in the first channel connecting pipe set 32 and the second channel connecting pipe set 34 is the same as the number of channels of the plate-fin heat exchanger. A first channel valve group 301 is provided on each connecting pipe of the first channel connecting pipe set 32, and a second channel valve group 302 is provided on each connecting pipe of the second channel connecting pipe set 34. The first channel connecting pipe set 32 is connected with a first cryogenic treatment passage, a helium filling passage and a first recovery passage through the first manifold 31 respectively; the second channel connecting pipe set 34 is connected with a second cryogenic treatment passage, a test passage and a second recovery passage through the second manifold 35 respectively.

[0050] A method for detecting the inner and outer leakage of a plate-fin heat exchanger at low temperature, comprising the following steps:

[0051] S1: passing low-temperature nitrogen into at least one channel of the plate-fin heat exchanger to be tested through the cryogenic treatment system 1, and cryogenically treating the plate-fin heat exchanger to a required working condition.

[0052] S2: using the test system 4 to vacuumize the vacuum cold box system 3 and each channel of the plate-fin heat exchanger to be tested;

[0053] S3: using the helium charging system 2 to sequentially charge low-temperature helium-nitrogen mixed gas into the test channels of the plate-fin heat exchanger to be tested, and using the test system 4 to sequentially perform inner and outer leak detection on the test channels of the plate-fin heat exchanger to be tested;

[0054] S4: using the recovery system 5 to recover the helium used for leak detection at high pressure.

[0055] In step S1, the following steps are included:

[0056] S1-1: the low-temperature nitrogen flowing out of the first mixer 13 pre-cools the plate-fin heat exchanger to be tested through the cryogenic treatment passage.

[0057] S1-2: during the pre-cooling process, when the temperature of one end of the plate-fin heat exchanger to be tested is reduced to below the working temperature of 80-100K, the low-temperature nitrogen charging passage is switched through the control of the first cryogenic treatment switching valve 101 and the second cryogenic treatment switching valve 102, so that the other end with a higher temperature is rapidly cooled until the temperatures of both ends are reduced to below the working temperature, and the cryogenic treatment passage is closed; the rapid cooling rate should not be higher than 4K / min.

[0058] S1-3: the nitrogen venting control valve 503 is opened, the helium recovery control valve 504 is closed, and the low-temperature nitrogen after cryogenic treatment is discharged after being warmed up through the recovery pipeline, which corresponds to step S1-2, and the low-temperature nitrogen discharge passage is switched through the control of the first recovery switching valve 501 and the second recovery switching valve 502.

[0059] In step S2, the following steps are included:

[0060] S2-1: all channel valves in the second channel valve group 302 and the cold box evacuation valve 303 are opened, the pump group control valve 401 is opened, the vacuum cold box 33 and each channel of the plate-fin heat exchanger to be tested are vacuumized to below 5Pa, the vacuumization system 42 is closed, the pump group control valve 401 is closed, the leak detection control valve 402 is opened, the helium mass spectrometer leak detector 43 is connected, and the background leakage rate of the vacuum cold box 33 is recorded.

[0061] In step S3, the following steps are included:

[0062] S3-1: open each channel valve in the first channel valve group 301 in turn, and the low-temperature helium-nitrogen mixed gas flowing out of the second mixer 25 is filled into the test channel of the test piece through the helium filling channel in turn.

[0063] S3-2: when the channel pressure reaches the working pressure of 0.02-5 MPa, stop filling the low-temperature helium-nitrogen mixed gas, and use the helium mass spectrometer leak detector 43 to sequentially perform internal and external leak detection on the test channel of the test piece.

[0064] In step S3-2, the following steps are included:

[0065] S3-2-1: first measure the external leakage of the test channel, open the cold box evacuation valve 303, connect the vacuum cold box 33 to the helium mass spectrometer leak detector 43, and the leak detector continuously measures and records data, which is the external leakage rate of the channel.

[0066] S3-2-2: then measure the internal leakage of the channel, sequentially open other non-test channel valves in the second channel valve group 302, sequentially connect other non-test channels to the helium mass spectrometer leak detector 43, and the leak detector continuously measures and records data, which is the internal leakage rate of the channel.

[0067] S3-2-3: after completing the internal and external leak detection of the channel, continue to repeat step S3 to perform internal and external leak detection on the next channel, until the internal and external leak detection of all channels is completed.

[0068] In step S4, the following steps are included:

[0069] S4-1: open the second recovery switching valve 502, and the low-temperature helium-nitrogen mixed gas after leak detection is recovered after being warmed up through the second recovery pipeline, open the helium recovery control valve 504, and recover the helium used for leak detection to the gas bag.

[0070] S4-2: the helium in the gas bag is stored in the contaminated helium cylinder group through the effect of pressure increase by the recovery compressor, thereby realizing high-pressure recovery of helium, and the recovery pressure is as high as 15-20 MPa, and the recovery rate is greater than 99%.

Claims

1. A system for detecting inner and outer leakage rates in a plate-fin heat exchanger at low temperature, characterized by: The cryogenic treatment system (1) for conveying low-temperature working medium, the helium filling system (2) for storing low-temperature working medium for leak detection, the vacuum cold box system (3), the test system (4) for vacuumizing and leak detection, and the recovery system (5) for high-pressure recovery of helium; the cryogenic treatment system (1), the helium filling system (2), the test system (4), and the recovery system (5) are connected with the vacuum cold box system (3) respectively and sequentially form a cryogenic treatment path, a helium filling path, a test path, and a recovery path, and each path is provided with a path valve; the tested piece is detachably arranged in the vacuum cold box system (3); The cryogenic treatment path comprises a first cryogenic treatment path and a second cryogenic treatment path; the first cryogenic treatment path comprises a first low-temperature liquid storage tank (11), a vaporizer (12), a first mixer (13), and a first cryogenic treatment switching valve (101) in sequence; the second cryogenic treatment path comprises the first low-temperature liquid storage tank (11), the vaporizer (12), the first mixer (13), and a second cryogenic treatment switching valve (102) in sequence; The recovery path comprises a first recovery path and a second recovery path; the first recovery path comprises a first recovery reheat coil (51), a first recovery switching valve (501), a helium recovery control valve (504), a gas bag (53), a recovery compressor (54), and a dirty helium gas cylinder group (55) in sequence; the second recovery path comprises a second recovery reheat coil (52), a second recovery switching valve (502), the helium recovery control valve (504), the gas bag (53), the recovery compressor (54), and the dirty helium gas cylinder group (55) in sequence, and a nitrogen venting control valve (503) is connected with the helium recovery control valve (504) through a pipeline; The vacuum cold box system (3) comprises a first manifold (31), a first channel connecting pipe group (32), a vacuum cold box (33), a second channel connecting pipe group (34), and a second manifold (35); the vacuum cold box (33) is a sealing device; the first channel connecting pipe group (32) and the second channel connecting pipe group (34) are respectively connected with both ends of the channel of the tested piece, and the number of channels of the three is the same; each connecting pipe of the first channel connecting pipe group (32) and the second channel connecting pipe group (34) is provided with a valve, and respectively constitutes a first channel valve group (301) and a second channel valve group (302); the first channel connecting pipe group (32) is connected with the first cryogenic treatment path, the helium filling path, and the first recovery path through the first manifold (31); the second channel connecting pipe group (34) is connected with the second cryogenic treatment path, the test path, and the second recovery path through the second manifold (35).

2. The system for detecting the internal and external leak rate as claimed in claim 1 wherein: The deep cooling treatment system (1) is sequentially connected with a first low-temperature liquid storage tank (11), a vaporizer (12) and a first mixer (13). The first low-temperature liquid storage tank (11) stores liquid nitrogen or liquid helium. The first mixer (13) is provided with a heater. The first mixer (13) collects low-temperature pre-cooling working medium and normal-temperature pre-cooling working medium after vaporization, and obtains pre-cooling working medium at a target low-temperature working condition with the assistance of the heater.

3. The system for detecting the internal and external leak rate as claimed in claim 1 wherein: The helium filling system (2) comprises a leak detection helium gas source (21), a leak detection nitrogen gas source (22), a second low-temperature liquid storage tank (23), a heat exchange coil (24) and a second mixer (25). The above components are sequentially connected to form a helium filling passage. The second low-temperature liquid storage tank (23) stores liquid nitrogen or liquid helium. The heat exchange coil (24) is spirally arranged in the tank body of the second low-temperature liquid storage tank (23) from top to bottom. The second mixer (25) is provided with a heater. The second mixer (25) collects normal-temperature leak detection working medium and low-temperature leak detection working medium after cooling by the heat exchange coil (24), and obtains leak detection working medium at a target low-temperature working condition with the assistance of the heater.

4. The system for detecting the internal and external leak rate as claimed in claim 1 wherein: The test system (4) is sequentially connected with a test reheat coil (41), a vacuum pumping system (42) and a helium mass spectrometer leak detector (43). The vacuum pumping system (42) is a molecular pump group.

5. The system for detecting the internal and external leak rate as claimed in claim 1 wherein: The test passage comprises a vacuum pumping passage and a leak detection passage. The vacuum pumping passage sequentially comprises the test reheat coil (41), a pump group control valve (401) and the vacuum pumping system (42). The leak detection passage sequentially comprises the test reheat coil (41), a leak detection control valve (402) and the helium mass spectrometer leak detector (43).

6. The system for detecting the internal and external leak rate as claimed in claim 1 wherein: The recovery system (5) comprises a first recovery reheat coil (51), a second recovery reheat coil (52), an air bag (53), a recovery compressor (54) and a dirty helium gas cylinder group (55). The recovery compressor (54) is a multi-stage piston compressor or a diaphragm compressor.

7. A method for detecting the inner and outer leakage of a plate-fin heat exchanger in a low temperature environment by using the system according to any one of claims 1 to 6. The method comprises the following steps: S1: passing low-temperature pre-cooling working medium into at least one channel of the plate-fin heat exchanger of the tested piece through the deep cooling treatment system (1) to deep cool the tested piece to a required working condition; S1-1: low-temperature pre-cooling working medium flowing out of the first mixer is used to pre-cool the tested piece through the deep cooling treatment passage; S1-2: during the pre-cooling process, when the temperature of one end of the tested piece is reduced below the working temperature, the low-temperature pre-cooling working medium filling passage is switched through the control of the first deep cooling treatment switch valve and the second deep cooling treatment switch valve, so that the other end with a higher temperature is rapidly cooled until the temperatures of both ends are reduced below the working temperature. The rapid cooling rate should not be higher than 4K / min; S1-3: low-temperature pre-cooling working medium after deep cooling is recovered or discharged after being warmed through the recovery pipeline. Corresponding to step S1-2, the low-temperature pre-cooling working medium exhaust passage is switched through the control of the first recovery switch valve and the second recovery switch valve. When the low-temperature pre-cooling medium is low-temperature nitrogen, a nitrogen venting control valve is opened to vent the nitrogen for cryogenic treatment; when the low-temperature pre-cooling medium is low-temperature helium, a helium recovery control valve is opened to recover the helium for cryogenic treatment into a gas bag; S2: using the test system (4) to vacuumize each channel of the vacuum cold box system (3) and the tested piece; after the vacuum of each channel of the vacuum cold box system and the tested piece reaches below 5 Pa, the pump group control valve is closed, the leak detection control valve is opened, the helium mass spectrometric leak detector is connected, and the background leak rate of the vacuum cold box is recorded at the same time; S3: through the helium filling system (2), the low-temperature leak detection medium is filled into the test channels of the tested piece in turn, and the test system (4) is used to perform internal and external leak detection on the test channels of the tested piece in turn; S3-1: the low-temperature leak detection medium flowing out of the second mixer is filled into the test channels of the tested piece in turn through the helium filling path; the low-temperature leak detection medium is low-temperature helium or low-temperature helium-nitrogen mixed gas; S3-2: after the channel pressure reaches the working pressure, the filling of the low-temperature leak detection medium is stopped, and the helium mass spectrometric leak detector is used to perform internal and external leak detection on the test channels of the tested piece in turn; S3-2-1: first, the external leak of the test channel is measured, the vacuum cold box is connected to the helium mass spectrometric leak detector, the leak detector continuously measures and records data, and the external leak rate of the channel is obtained; S3-2-2: then, the internal leak of the channel is measured, and the helium mass spectrometric leak detector is connected to each non-test channel in turn, the leak detector continuously measures and records data, and the internal leak rate of the channel is obtained; S3-2-3: after the internal and external leak detection of the channel is completed, the next channel is subjected to internal and external leak detection by repeating step S3, until the internal and external leak detection of all channels is completed; S4: using the recovery system (5) to perform high-pressure recovery on the helium for leak detection.

8. The method of inner and outer leak rate detection of claim 7, wherein: In step S1, the low-temperature pre-cooling medium is low-temperature nitrogen or low-temperature helium.

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