CN114812476A - Low-temperature rapid temperature change test device and method for blade tip clearance sensor - Google Patents
Low-temperature rapid temperature change test device and method for blade tip clearance sensor Download PDFInfo
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
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- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
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Abstract
The invention discloses a low-temperature rapid temperature change test device and a method of a blade tip clearance sensor, wherein the device comprises a test box (1), a sensor mounting part (5), a temperature sensor (6), a working medium supply assembly, a working medium replacement assembly, an exhaust pipeline (22) and a controller (23); the simulation blade (29), the tip clearance sensor (25) and the temperature sensor are arranged in the test box through sensor mounting pieces; a plurality of working medium inlets with different apertures are formed on the test box, an air supply pipeline of the working medium supply assembly is communicated with the test box through the working medium inlets through electromagnetic valves, and low-temperature nitrogen is input into the test box; the exhaust pipeline and the working medium replacement assembly are connected with the test box, and the controller is connected with the temperature sensor, the working medium supply assembly and the working medium replacement assembly. The invention can realize low-temperature rapid temperature change of a test environment so as to accurately simulate the working environment of the blade tip clearance sensor, thereby effectively verifying the working performance of the blade tip clearance sensor before the blade tip clearance sensor is put into application.
Description
Technical Field
The invention relates to a blade tip clearance measuring device and method, in particular to a low-temperature rapid temperature change testing device and method of a blade tip clearance sensor.
Background
In rotary machines such as aero-engines, gas turbines, steam turbines, and compressors, the minute distance between the tip of a rotor blade and the inner wall of a casing is called the tip clearance, which is one of the important parameters affecting the performance of the rotary machine. The smaller tip clearance can reduce the gas leakage at the tip of the blade and obviously improve the operation efficiency of the rotary machine, but the too small tip clearance can cause the collision and friction between the blade and the casing, and seriously endanger the operation safety of the rotary machine. The temperature change caused by variable working conditions causes the blades and the casing to expand and contract, thereby directly causing the change of the blade tip clearance.
The application environment of the rotary machine is complex and various, wherein the working environment temperature of the industrial low-temperature compressor is-50 ℃ to-170 ℃, and the temperature of a part of area can be rapidly reduced even at the speed of 4 ℃/s due to the influence of variable working condition operation and rapid inflow of cooling working media, which brings great challenge to the temperature adaptability of the blade tip clearance measuring system. In order to ensure that the tip clearance sensor can normally work under the severe condition, corresponding test verification is carried out on the performance condition of the tip clearance sensor under the condition of low temperature and rapid temperature change.
At present, the scheme for the low-temperature rapid temperature change test of the blade tip clearance sensor comprises the following steps:
1. by adopting the high-low temperature test box, the cooling speed of the high-low temperature test box in the prior art is low, generally lower than 10 ℃/min, the requirement of rapid temperature change is difficult to meet, and the temperature adaptability of the blade tip clearance sensor in the actual working condition cannot be accurately verified. And the cooling working medium of the high-low temperature test box is generally a mixture of liquid nitrogen and nitrogen, and the existence of the liquid nitrogen can seriously affect the working performance of the blade tip clearance sensor, thereby further aggravating the error of the test result.
2. The tip clearance sensor is directly inserted into liquid nitrogen to realize rapid cooling, but the cooling rate of the liquid nitrogen is difficult to control accurately and effectively, the experimental simulation environment is not consistent with the actual environment, and the temperature adaptability of the tip clearance sensor in the actual working condition cannot be verified accurately. Also, the working performance of the tip gap sensor under the influence of liquid nitrogen cannot be guaranteed.
Disclosure of Invention
One of the purposes of the invention is to provide a low-temperature rapid temperature change test device for a blade tip clearance sensor, which can accurately simulate the low-temperature rapid temperature change working environment of the blade tip clearance sensor, so that the working performance of the blade tip clearance sensor is verified before the blade tip clearance sensor is put into application.
One of the purposes of the invention is to provide a low-temperature rapid temperature change test method for a tip clearance sensor, which can implement a rapid temperature change test with an accurately controllable cooling rate, wherein the temperature change speed can reach 4 ℃/s, and the temperature change requirement of a verification test of the working performance of the tip clearance sensor is met.
The invention is realized by the following steps:
a low-temperature rapid temperature change test device of a tip clearance sensor comprises a test box, a sealing element, a sensor mounting part, a temperature sensor, a working medium supply component, a working medium replacement component, an exhaust pipeline and a controller; a cable hole is reserved in the test box and can be sealed through a sealing element, the simulation blade, the blade tip clearance sensor and the temperature sensor are installed in the test box through the sensor installation part, and a cable of the blade tip clearance sensor is led out of the test box through the cable hole and is externally connected with test acquisition equipment; a plurality of working medium inlets with different calibers are formed on the test box, and a plurality of air supply pipelines of the working medium supply assembly are respectively communicated with the test box through a plurality of working medium inlets through electromagnetic valves, so that the working medium supply assembly inputs low-temperature nitrogen into the test box; the exhaust pipeline is communicated with the test box, a pneumatic valve is arranged on the exhaust pipeline, and the working medium replacement assembly is communicated with the test box; the controller is electrically connected with the temperature sensor, the working medium supply assembly and the working medium replacement assembly.
The working medium supply assembly comprises a double-layer Dewar flask, a first air supply pipeline, a first electromagnetic valve, a second air supply pipeline, a second electromagnetic valve, a third air supply pipeline and a third electromagnetic valve; the lower layer of the double-layer Dewar bottle is filled with liquid nitrogen through a liquid storage tank, the upper layer of the double-layer Dewar bottle is filled with low-temperature nitrogen through a gas storage tank, and a liquid nitrogen pipeline spirally surrounding the outside of the gas storage tank is formed on the liquid storage tank, so that the gas storage tank is filled with low-temperature nitrogen formed by vaporization; the first air supply pipeline is connected between the air storage tank and the test box through a first electromagnetic valve, the second air supply pipeline is connected between the air storage tank and the test box through a second electromagnetic valve, and the third air supply pipeline is connected between the air storage tank and the test box through a third electromagnetic valve.
The liquid storage tank is communicated with a liquid nitrogen tank through a pipeline and a fourth electromagnetic valve, and the liquid nitrogen tank is filled with liquid nitrogen; the gas storage tank is connected to the low-temperature nitrogen tank through a fifth electromagnetic valve through a pipeline, and the low-temperature nitrogen tank is filled with low-temperature nitrogen.
The working medium replacement assembly comprises a vacuum pump and a normal-temperature nitrogen tank; the vacuum pump is communicated with the test box through a pipeline, the normal-temperature nitrogen tank is communicated with the test box through a sixth electromagnetic valve through a pipeline, and the normal-temperature nitrogen tank is filled with normal-temperature nitrogen; the vacuum pump and the normal temperature nitrogen tank are respectively and electrically connected with the controller.
The inner wall of the test box is provided with a heat insulation layer, the test box is of an open-cover box structure, a top cover sealing cover with a cable hole is reserved on the test box, and the sensor mounting piece is mounted on the inner wall of the top cover.
A low-temperature rapid temperature change test method for a blade tip clearance sensor comprises the following steps:
step 1: setting temperature change parameters according to the rapid temperature change requirement of the test; the temperature change parameters comprise the times s of the temperature change stages and the initial temperature T in each temperature change stage 1 End temperature T 2 Time of temperature change H d And holding time H hold ；
Step 2: setting a test process of the rapid temperature change of the test box in each rapid temperature change stage;
and step 3: installing a tip clearance sensor and a simulation blade on a top cover of a test box, connecting the tip clearance sensor to test acquisition equipment, and checking the working state of the tip clearance sensor;
and 4, step 4: confirming whether the air tightness of the test box is good or not, if so, executing the step 5, and if not, sealing the test box again;
and 5: starting a rapid temperature change test, calculating to obtain an actual cooling speed U ' through a temperature sensor and a controller, and judging whether the actual cooling speed U ' of the rapid temperature change test is consistent with an ideal cooling speed U, namely U ' ═ U; if yes, executing step 6; if not, resetting the heat absorption coefficient k and returning to the step 2;
step 6: monitoring and recording temperature and pressure data in the test box, pressure data in the double-layer Dewar flask, opening and closing of the electromagnetic valve and opening data of the electromagnetic valve through a controller, and recording clearance signal data of the leaf clearance sensor in the rapid temperature change process, which is acquired by test acquisition equipment, through a computer;
and 7: and 6, evaluating the working performance of the leaf gap sensor under the low-temperature rapid temperature change condition according to the data in the step 6.
The step 1 further comprises:
step 1.1: setting the critical value of the air pressure in the test chamber as P 0 When the air pressure in the test chamber exceeds the air pressure critical value P 0 When the valve is opened, the air pressure valve is opened automatically and exhausts air through the exhaust pipeline;
step 1.2: the temperature of the low-temperature nitrogen input into the test chamber is T N Pressure of P N Density of rho N The diameter of the working medium inlet is set as d, and the calculation formula of the low-temperature nitrogen mass flow Q in unit time is as follows:
Q＝π*d 2 *[ρ N *(P N -P 0 )/2] 0.5 formula 1;
wherein, P N ≥P 0 ；
The inlet area of the low-temperature gas is pi x d 2 */4；
Step 1.3: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Required cooling time H d The calculation formula is as follows: h d ＝(T 2 -T 1 ) the/U formula 3;
wherein U is an ideal temperature change speed.
The step 2 further comprises:
step 2.1: calculating the volumes V of the sensor mounting piece and the blade tip clearance sensor;
step 2.2: calculating the start temperature T of the sensor mounting part and the tip clearance sensor 1 Cooling to the termination temperature T 2 Heat quantity H to be released out The calculation formula is as follows:
H out ＝c s *ρ s *V*(T 2 -T 1 ) Formula 4;
wherein, c s Specific heat capacity, p, for sensor mount and tip clearance sensor s Density of sensor mounts and tip clearance sensors;
step 2.3: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Heat H to be absorbed by low-temperature nitrogen in The calculation formula is as follows:
H in ＝k*H out equation 5;
wherein k is a heat absorption coefficient, k is a constant, and k is>>1; at the start of the test, k is set to k 0 ；
k 0 ＝a*S 1 /S 0 Wherein a is an empirical coefficient, S 1 Is the surface area of the test chamber (1), S 0 Is the surface area of the sensor mount (5);
step 2.4: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Mass flow Q of low temperature nitrogen 2 The calculation formula is as follows:
Q 2 ＝H in /[H d *c N *(T 2 -T 1 )]equation 6;
wherein, c N The specific heat capacity of the low-temperature nitrogen;
step 2.5: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 The required air inlet area S of the low-temperature nitrogen is calculated by the following formula:
S＝Q 2 /[2*ρ N *(P N -P 0 )] 0.5 equation 7.
Step 2.6: and selecting the number and the caliber of the working medium inlets according to the required air inlet area S.
In the step 4, the method for detecting the air tightness of the test chamber comprises the following steps: the working medium replacement assembly is controlled by the controller to operate, so that the vacuum pump of the working medium replacement assembly vacuumizes the test box, and the vacuum degree in the test box reaches P 0 And below, and at least for a retention time H v If the test chamber has good air tightness, inputting normal-temperature nitrogen into the test chamber through a normal-temperature nitrogen tank; otherwise, the airtightness of the test chamber is considered to be not satisfactory.
In step 5, the method for resetting the heat absorption coefficient k is as follows: if U' > U, reset k ═ k 1 ＝k 0 U/U', and k 1 ＜k 0 (ii) a If U' < U, reset k 2 ＝k 0 U/U', and k 2 ＞k 0 。
Compared with the prior art, the invention has the following beneficial effects:
1. the device can realize the accurate control of the temperature change speed of the test environment in the test box, is used for simulating the working environment of the blade tip clearance sensor so as to meet the test requirement of the blade tip clearance sensor and solve the problem of the verification of the low-temperature performance of the blade tip clearance sensor.
2. The device of the invention controls and collects data through the controller, the computer and other equipment, ensures the judgment accuracy of the working performance of the blade tip clearance sensor, and also provides reliable data support for subsequent field application.
3. The method can realize the rapid temperature change in the experimental box and the accurate control of the temperature change speed thereof by controlling the pressure of the low-temperature nitrogen and the air inlet area, has simple control method, less setting parameters, higher operability and universality, and is suitable for the low-temperature rapid temperature change test of various sensors.
4. The method of the invention provides the low-temperature nitrogen with stable temperature as the cooling working medium through the double-layer Dewar flask, further improves the control precision of the temperature in the test box and the cooling speed thereof, enables the cooling speed to reach 4 ℃/s, and simultaneously avoids the influence of liquid nitrogen on the working performance of the blade tip clearance sensor.
The invention can realize low-temperature rapid temperature change of a test environment so as to accurately simulate the working environment of the blade tip clearance sensor, thereby effectively verifying the working performance of the blade tip clearance sensor before the blade tip clearance sensor is put into application.
Drawings
FIG. 1 is a schematic diagram of a main structure of a low-temperature rapid temperature change test device of a blade tip clearance sensor according to the present invention;
FIG. 2 is a layout diagram of an air supply pipeline in the low-temperature rapid temperature change test device of the blade tip clearance sensor of the invention;
FIG. 3 is a schematic diagram of a liquid nitrogen pipeline of a Dewar flask in the low-temperature rapid temperature change test device of the blade tip clearance sensor of the invention;
FIG. 4 is a flow chart of a low-temperature rapid temperature change test method of a blade tip clearance sensor according to the invention.
In the figure, 1 test box, 2 heat preservation layer, 3 top cover, 4 sealing element, 5 sensor mounting part, 6 temperature sensor, 7 double-layer Dewar flask, 71 liquid nitrogen pipeline, 72 gas storage tank, 73 liquid storage tank, 8 first gas supply pipeline, 9 first electromagnetic valve, 10 second gas supply pipeline, 11 second electromagnetic valve, 12 third gas supply pipeline, 13 third electromagnetic valve, 14 liquid nitrogen tank, 15 fourth electromagnetic valve, 16 low-temperature nitrogen tank, 17 fifth electromagnetic valve, 18 vacuum pump, 19 sixth electromagnetic valve, 20 normal-temperature nitrogen tank, 21 pneumatic valve, 22 exhaust pipeline, 23 controller, 24 touch screen, 25 apex gap sensor, 26 cable, 27 test acquisition equipment, 28 computer, 29 simulation blade, 30 cable hole.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
Referring to fig. 1, a low-temperature rapid temperature change test device for a blade tip clearance sensor comprises a test box 1, a sealing part 4, a sensor mounting part 5, a temperature sensor 6, a working medium supply assembly, a working medium replacement assembly, an exhaust pipeline 22 and a controller 23; a cable hole 30 is reserved in the test box 1 and can be sealed through a sealing element 4, the simulation blade 29, the tip clearance sensor 25 and the temperature sensor 6 are installed in the test box 1 through the sensor installation part 5, and a cable 26 of the tip clearance sensor 25 is led out of the test box 1 through the cable hole 30 and is externally connected with a test acquisition device 27; referring to fig. 2, a plurality of working medium inlets with different apertures are formed on a test chamber 1, a plurality of air supply pipelines of a working medium supply assembly are respectively communicated with the test chamber 1 through a plurality of working medium inlets by electromagnetic valves, so that the working medium supply assembly inputs nitrogen (i.e. test working medium) with low temperature (-196 ℃) into the test chamber 1; the exhaust pipeline 22 is communicated with the test box 1, the exhaust pipeline 22 is provided with a pneumatic valve 21, and the working medium replacement assembly is communicated with the test box 1; the controller 23 is electrically connected with the temperature sensor 6, the working medium supply assembly and the working medium replacement assembly.
Preferably, the controller 23 may adopt a PLC control device in the prior art, and the controller 23 is provided with a touch screen 24 to facilitate human-computer interaction. The test acquisition device 27 may employ a sensor driving and acquisition conditioning module matched with the blade tip clearance sensor 25, and the sensor driving and acquisition conditioning module may be connected to the computer 28 through a serial port harness, so as to facilitate acquisition, transmission and storage of sensor data.
Preferably, the temperature sensor 6 should be installed near the tip clearance sensor 25 and far away from the working medium inlet when being installed, so that the accuracy of the temperature sensor 6 measuring the temperature near the tip clearance sensor 25 is ensured, and meanwhile, the interference caused by direct air flow injection is avoided to the greatest extent.
Referring to fig. 3, the working medium supply assembly includes a double-layer dewar flask 7, a first air supply pipeline 8, a first solenoid valve 9, a second air supply pipeline 10, a second solenoid valve 11, a third air supply pipeline 12 and a third solenoid valve 13; the lower layer of the double-layer Dewar flask 7 is filled with liquid nitrogen through a liquid storage tank 73, the upper layer of the double-layer Dewar flask 7 is filled with low-temperature nitrogen through a gas storage tank 72, a plurality of liquid nitrogen pipelines 71 are formed on the liquid storage tank 73, the liquid nitrogen pipelines 71 spirally surround the outside of the gas storage tank 72, and the gas storage tank 72 is filled with low-temperature (-196 ℃) nitrogen formed by vaporization; the first air supply line 8 is connected between the air tank 72 and the test chamber 1 through a first solenoid valve 9, the second air supply line 10 is connected between the air tank 72 and the test chamber 1 through a second solenoid valve 11, and the third air supply line 12 is connected between the air tank 72 and the test chamber 1 through a third solenoid valve 13. The number of the air supply pipeline and the electromagnetic valves thereof can be determined according to the requirement of the cooling speed, the size of the air supply pipeline can be determined according to the size of the working medium inlet, the electromagnetic valves are opened, low-temperature (-196 ℃) nitrogen enters the test box 1 through the air supply pipeline through the working medium inlet, the flow of the nitrogen entering the test box 1 can be adjusted by combining the caliber of the working medium inlet through the control of the electromagnetic valve switch, the number and the opening degree of the electromagnetic valve switch, and therefore the cooling speed of the low-temperature (-196 ℃) nitrogen on the internal test environment of the test box 1 is controlled. The liquid nitrogen pipeline 71 can increase the heat exchange area between the liquid nitrogen and the external environment, accelerate the vaporization process of the liquid nitrogen, enable the liquid nitrogen to pass through the liquid nitrogen pipeline 71 upwards and be converted into gaseous nitrogen, and meanwhile, can absorb the heat of the nitrogen in the gas storage tank 72 in the vaporization process, so that the nitrogen in the gas storage tank 72 is always kept at the critical temperature. Meanwhile, a plurality of air supply pipelines are respectively communicated with the air storage tank 72, so that nitrogen input into the test box 1 is kept at-196 ℃, and the accurate control of the cooling speed is facilitated. Since vaporized nitrogen and liquefied nitrogen exist simultaneously at the interface between the upper and lower layers of the double-layer dewar flask 7, the temperature of the nitrogen gas in the gas storage tank 72 is about-196 ℃, which is the critical temperature of the nitrogen gas.
The liquid storage tank 73 is connected to the liquid nitrogen tank 14 through a pipeline via a fourth electromagnetic valve 15 for communication, and liquid nitrogen is filled in the liquid nitrogen tank 14 and can be supplied to the liquid storage tank 73 in a supplementing manner.
The gas storage tank 72 is connected to the low-temperature nitrogen tank 16 through a pipeline through a fifth electromagnetic valve 17, low-temperature (-196 ℃) nitrogen is filled in the low-temperature nitrogen tank 16, the low-temperature nitrogen in the gas storage tank 72 can be supplied, and the temperature and the pressure of the nitrogen which is input into the test box 1 and has the temperature of-196 ℃ can be controlled more accurately, so that the control of the cooling speed in the test box 1 is facilitated.
The working medium replacement assembly comprises a vacuum pump 18 and a normal-temperature nitrogen tank 20; the vacuum pump 18 is communicated with the test box 1 through a pipeline, the normal-temperature nitrogen tank 20 is communicated with the test box 1 through a sixth electromagnetic valve 19 through a pipeline, and the normal-temperature nitrogen is filled in the normal-temperature nitrogen tank 20; the vacuum pump 18 and the normal temperature nitrogen tank 20 are electrically connected to a controller 23, respectively. The controller 23 controls the vacuum pump 18 to start and stop, so that the vacuum pump 18 can pump the test box 1 to a vacuum state, and water vapor contained in the air in the test box 1 is prevented from being condensed into ice in a rapid cooling and low-temperature state, so that the problem that the blade tip gap sensor 25 fails due to the influence of icing on a test result on the surface of the blade tip gap sensor 25 is avoided. And opening the sixth electromagnetic valve 19 after the test box 1 is vacuumized, and injecting the normal-temperature nitrogen in the normal-temperature nitrogen tank 20 into the test box 1 to realize the replacement of the working medium in the test box 1, so that the test box 1 is in a nitrogen environment suitable for the test.
The inner wall of the test box 1 is provided with a heat preservation layer 2, the test box 1 is of an open-cover box structure, a top cover 3 with a cable hole 30 reserved is covered on the test box 1 in a sealing mode, and a sensor mounting part 5 is mounted on the inner wall of the top cover 3. Before experimental, pull down top cap 3, apex clearance sensor 25 that will need experimental verification passes through sensor mounting spare 5 to be fixed on top cap 3, will simulate blade 29 simultaneously and fix on sensor mounting spare 5, make simulate blade 29 just to the detection terminal surface of sensor mounting spare 5, cover top cap 3 again, cable 26 draws forth the back through sealing member 4 with the hole seal closure through cable hole 30, ensure that the experimental environment in proof box 1 keeps apart with external environment completely, the convection heat transfer of the inside and outside gas of separation proof box 1, thereby realize the accurate control of temperature in proof box 1.
Referring to fig. 4, a low-temperature rapid temperature change test method for a tip clearance sensor includes the following steps:
step 1: and setting temperature change parameters through a touch screen 24 of the controller 23 according to the rapid temperature change requirement of the test. The temperature variation parameters comprise the number s of temperature variation stages and the initial temperature T in each temperature variation stage 1 End temperature T 2 Time of temperature change H d And holding time H hold 。
Aiming at the test requirements of a larger temperature change range and a higher temperature change rate, a plurality of(s) temperature change stages can be set for step-by-step temperature reduction, and the initial temperature T 1 And a termination temperature T 2 Can be set according to the temperature change test requirement of each stage, and T 1 ≥T 2 . Holding time H hold Can be set according to specific test requirements.
Step 1.1: setting the critical value of the air pressure in the test chamber 1 as P 0 When the air pressure in the test chamber 1 exceeds the air pressure critical value P 0 At this time, the air pressure valve 21 is automatically opened and exhausted through the exhaust pipe 22, so that the air pressure in the test chamber 1 is always kept in a safe range. P 0 Is constant and can be set by the air pressure valve 21 according to the safety performance requirement of the test chamber 1.
Step 1.2: the temperature of the low-temperature nitrogen input into the test box 1 by the gas storage tank 72 on the upper layer of the double-layer Dewar bottle 7 is T N Pressure of P N Density of rho N Setting the diameter of the working medium inlet as d and the mass flow rate Q of low-temperature nitrogen in unit time (neglecting the gas supply pipeline)On-way resistance loss) is calculated as:
Q＝π*d 2 *[ρ N *(P N -P 0 )/2] 0.5 equation 1.
Wherein, P N ≥P 0 。
The inlet area of the low-temperature gas is pi x d 2 */4。
The opening number and the caliber of the working medium inlet can be selected according to the temperature change speed requirement. Referring to FIG. 2, if the bottom of the test chamber 1 has three apertures d 1 、d 2 、d 3 When the three working medium inlets are fully opened, the temperature change speed in the test box 1 is the maximum, the test box is suitable for a rapid temperature change stage, and the mass flow Q of the low-temperature nitrogen entering the test box 1 in unit time is equal to the mass flow Q of the low-temperature nitrogen 1 Comprises the following steps:
π*(d 1 2 +d 2 2 +d 3 2 )*[ρ N *(P N -P 0 )/2] 0.5 equation 2.
The inlet area of the low-temperature gas is pi (d) 1 2 +d 2 2 +d 3 2 )/4。
According to the formulas 1 and 2, the mass flow rates Q and P of the low-temperature nitrogen entering the test box 1 through the working medium inlet in unit time N -P 0 Is in direct proportion.
Step 1.3: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Required cool-down time H d The calculation formula is as follows: h d ＝(T 2 -T 1 ) the/U equation 3.
Wherein, U is an ideal temperature change speed and can be determined according to the requirement of the test on the rapid temperature change speed.
Step 2: and setting the test process of the rapid temperature change of the test box 1 in each rapid temperature change stage.
Step 2.1: the volume V of the sensor mount 5 and the tip clearance sensor 25 is calculated. The dimensions of the sensor mounting part 5 and the tip clearance sensor 25 may be measured first and calculated according to a volume calculation formula corresponding to the shape thereof, which is not described herein again.
Step 2.2: calculating the starting temperature T of the sensor mount 5 and the tip clearance sensor 25 1 Cooling to the termination temperature T 2 Heat quantity H to be released out The calculation formula is as follows:
H out ＝c s *ρ s *V*(T 2 -T 1 ) Equation 4.
Wherein, c s Specific heat capacity, ρ, of the sensor mount 5 and the tip clearance sensor 25 s Is the density of the sensor mount 5 and the tip clearance sensor 25.
Step 2.3: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Heat H to be absorbed by low-temperature nitrogen in The calculation formula is as follows:
H in ＝k*H out equation 5.
Wherein, k is the heat absorption coefficient, and k is the constant, and k > >1, and low temperature nitrogen gas is used for cooling the heat that sensor installed part 5 and apex clearance sensor 25 absorbed only for very little partly, and the vast majority absorbs the heat and all is used for cooling the quick temperature change of test environment in test box 1, even has not taken place the temperature change effect promptly through exhaust pipe 22 discharge test box 1.
At the start of the test, k may be set to k 0 ，k 0 ＝a*S 1 /S 0 Wherein a is an empirical coefficient, a is more than or equal to 1 and less than or equal to 1.5, the empirical coefficient a reflects the sealing and heat-insulating properties of the test box 1, if the sealing and heat-insulating properties of the test box 1 are good, a is appropriately smaller, otherwise, a is larger, S is S 1 Is the outer surface area of the test chamber 1, S 0 Is the surface area of the sensor mount 5.
Step 2.4: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Mass flow Q of the required cryogenic nitrogen 2 The calculation formula is as follows:
Q 2 ＝H in /[H d *c N *(T 2 -T 1 )]equation 6.
Step 2.5: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Of nitrogen at low temperatureThe required air inlet area S is calculated by the following formula:
S＝Q 2 /[2*ρ N *(P N -P 0 )] 0.5 equation 7.
Wherein, c N The specific heat capacity of low temperature nitrogen.
From equation 7, the intake area S and the pressure P of the low-temperature nitrogen gas N As variables, by controlling the pressure P of the cryogenic nitrogen in the reservoir 72, with other parameters determined N And the mass flow Q of the low-temperature nitrogen input into the test chamber 1 can be controlled by changing the air inlet caliber of the low-temperature nitrogen and the opening degree of the electromagnetic valve of the corresponding air supply pipeline 2 And the accurate control of different temperature change speeds of the test box 1 can be realized.
Step 2.6: and selecting the number and the caliber of the working medium inlets according to the required air inlet area S. The required air inlet area S and the air inlet area pi x d of the test chamber 1 2 4 or pi (d) 1 2 +d 2 2 +d 3 2 ) And the/4 is equivalent, so that the number and the caliber of the working medium inlets can be calculated.
And step 3: the tip clearance sensor 25 and the simulation blade 29 are installed on the top cover 3 of the test box 1, the cable 26 of the tip clearance sensor 25 is led out through the cable hole 30 and is connected to the test acquisition equipment 27, the test acquisition equipment 27 is connected with the computer 28, the test acquisition equipment 27 is opened, the working state of the tip clearance sensor 25 is checked, if the voltage signal acquired by the test acquisition equipment 27 is a direct current signal or a slowly-changed signal, the working state of the tip clearance sensor 25 is normal, otherwise, the working state is abnormal, and the tip clearance sensor 25 needs to be repaired or replaced.
And 4, step 4: and (3) covering the top cover 3, sealing the cable hole 30 through the sealing piece 4, confirming whether the air tightness of the test box 1 is good or not, if so, executing the step 5, and if not, re-sealing the top cover 3 of the test box 1 and the cable hole 30.
The method for detecting the air tightness of the test chamber 1 comprises the following steps: the operation of the working medium replacement assembly is controlled by a touch screen 24 of the controller 23, so that a vacuum pump 18 of the working medium replacement assembly vacuumizes the test box 1, and the vacuum in the test box 1 is enabledDegree reaches P 0 And below, and at least for a retention time H v If the air tightness of the test box 1 is good, normal-temperature nitrogen is input into the test box 1 through a normal-temperature nitrogen tank 20; otherwise the airtightness of the test chamber 1 is considered to be unsatisfactory.
And 5: starting a rapid temperature change test, calculating to obtain an actual cooling speed U ' through the temperature sensor 6 and the controller 23, and judging whether the actual cooling speed U ' of the rapid temperature change test is consistent with an ideal cooling speed U, namely U ' ═ U; if yes, executing step 6; if not, resetting the heat absorption coefficient k and returning to the step 2.
The resetting method of the heat absorption coefficient k comprises the following steps: if U' > U, reset k ═ k 1 And k is 1 ＜k 0 (ii) a If U' < U, reset k 2 And k is 2 ＞k 0 。
The resetting method of the heat absorption coefficient k comprises the following steps: if U' ≠ U, then reset k ═ k 0 *U/U’。
Step 6: the controller 23 monitors and records the temperature and pressure data in the test chamber 1, the pressure data in the double-layer Dewar flask 7, the opening and closing of the electromagnetic valve and the opening data thereof, and the computer 28 records the gap signal data of the leaf gap sensor 25 in the rapid temperature change process, which is acquired by the test acquisition equipment 27.
And 7: and evaluating the working performance of the leaf clearance sensor 25 under the low-temperature rapid temperature change condition according to the data in the step 6.
Example 1:
the bottom of test box 1 is equipped with three working medium imports, is respectively: diameter d 1 And connected to the working medium inlet of the first gas supply line 8, the diameter of which is d 2 And connected to the working medium inlet of the second gas supply line 10 and having a diameter d 3 And is connected to the working medium inlet of the third gas supply line 12. The mass flow Q of the low-temperature nitrogen gas entering the test chamber 1 per unit time according to the formula 2 1 Is pi (d) 1 2 +d 2 2 +d 3 2 )*[ρ N *(P N -P 0 )/2] 0.5 . Wherein d is 1 ＝d 2 ＝d 3 ＝20mm，ρ N ＝802.6993kg/m 3 ，P 0 ＝1bar。
The leaf gap sensor 25 is an optical fiber sensor, and the low-temperature rapid temperature change test requirements are as follows: the temperature range is-50 ℃ to-170 ℃, the average speed reduction rate needs to reach 4 ℃/s, namely U is 4 ℃/s.
Because the temperature change range is large, the cooling speed is high, and the rapid temperature change is completed in two stages, namely s is 3.
In a first phase: the temperature change range is-50 ℃ (T) 1 )～-90℃(T 2 ). The specific temperature change steps are as follows:
I. the temperature in the test box 1 is conventionally reduced to minus 50 ℃, and the temperature is preserved for 10min at minus 50 ℃, so that the blade tip clearance sensor 25 realizes sufficient heat exchange, and the internal and external temperatures of the blade tip clearance sensor 25 and the sensor mounting part 5 thereof are ensured to be uniform.
II. Time of temperature reduction H d ＝(T 2 -T 1 ) Cooling rapidly for 10s and making the temperature in the test chamber 1 from-50 ℃ (T ═ 10s 1 ) Reduced to-90 ℃ (T) 2 ) And keeping the temperature at-90 ℃ for 10 min.
In the first stage, the round corners, the threads, the fastening screws, and the like are omitted, and the sensor mount 5 and the tip clearance sensor 25 may be considered to be cylindrical structures having a volume V of 0.0012m 3 (ii) a Known as ρ s ＝8900kg/m 3 ，c s 390J/(kg K), from the initial temperature T of the sensor mount 5 and the tip clearance sensor 25, is calculated by equation 4 1 Cooling to the termination temperature T 2 Heat quantity H to be released out 163 kJ; given that the chamber of test chamber 1 is approximately cylindrical, with a cross-sectional diameter of approximately 0.5m and a height of approximately 0.5m, the internal surface area of test chamber 1 is approximately 0.1963m 2 Assuming that the initial value of the heat absorption coefficient k is the ratio of the surface areas of the test chamber 1 and the sensor mounting member 5, the empirical coefficient a is 1, that is, k 0 25. According to equation 6: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Mass flow Q of the required cryogenic nitrogen 2 ＝H in /[H d *c N *(T 2 -T 1 )]＝5.1089kg/s。
According to equation 7: from the starting temperature T 1 Cooling to the termination temperature T 2 Required intake area of low-temperature nitrogen gas (S ═ Q) 2 /[2*ρ N *(P N -P 0 )] 0.5 ＝5.1/(P N -P 0 ) 0.5 ＝4*10 -4 m 2 Therefore, during the temperature change process of the first stage, the first solenoid valve 9 and the second solenoid valve 11 can be fully opened, so that the low-temperature nitrogen enters the test chamber 1 through the first air supply pipeline 8 and the second air supply pipeline 10, and the pressure P of the low-temperature nitrogen is N The temperature reduction speed and temperature requirement of the first stage can be met by controlling the pressure to be 1 bar.
In a second phase: the temperature change range is-90 ℃ (T) 1 )～-130℃(T 2 ). The specific temperature change steps are as follows:
I. the test box 1 is kept at-90 ℃ for 10min, so that the blade tip clearance sensor 25 can realize sufficient heat exchange, and the uniform internal and external temperatures of the blade tip clearance sensor 25 and the sensor mounting piece 5 thereof are ensured.
II. Time of temperature reduction H d ＝(T 2 -T 1 ) and/U is 10s, and the temperature is quickly reduced by 10s to reduce the temperature in the test box 1 from minus 90 ℃ to minus 130 ℃.
In the second stage, the round corners, the threads, the fastening screws, and the like are omitted, and it is considered that the sensor mount 5 and the tip clearance sensor 25 have cylindrical structures, and the volume V is 0.0012m 3 (ii) a From equation 4, the starting temperature T of the sensor mount 5 and the tip clearance sensor 25 is calculated 1 Cooling to the termination temperature T 2 Heat quantity H to be released out 163 kJ; with the continuous reduction of the temperature in the rapid temperature change test box, the heat exchange between the rapid temperature change test box and the external environment is increased, then in the second stage, the initial value of the heat absorption coefficient k is set as the ratio of the surface area of the test box 1 to the surface area of the sensor mounting part 5 multiplied by the empirical coefficient, and a is 1.5, namely k is 1.5 0 38. According to equation 6: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Mass flow Q of the required cryogenic nitrogen 2 ＝H in /[H d *c N *(T 2 -T 1 )]＝7.7655kg/s。
According to equation 7: from the starting temperature T 1 Cooling to the termination temperature T 2 Required admission of cryogenic nitrogenArea S ═ Q 2 /[2*ρ N *(P N -P 0 )] 0.5 ＝7.7/(P N -P 0 ) 0.5 ＝6.1*10 -4 m 2 Therefore, during the temperature change process of the second stage, the second solenoid valve 11 and the third solenoid valve 13 can be fully opened, so that the low-temperature nitrogen enters the test chamber 1 through the second air supply pipeline 10 and the third air supply pipeline 12, and the pressure P of the low-temperature nitrogen is N The temperature reduction speed and temperature requirements of the second stage can be met by controlling the pressure to be 1 bar.
In the third stage: the temperature change range is-130 ℃ (T) 1 )～-170℃(T 2 ) The specific temperature change steps are as follows:
I. the test box 1 is kept at-130 ℃ for 10min, so that the sensor realizes sufficient heat exchange and ensures uniform internal and external temperatures.
II. Time of temperature reduction H d ＝(T 2 -T 1 ) Cooling rapidly for 10s from-130 deg.C (T) in test chamber 1 1 ) Reducing the temperature to-170 ℃ (T) 2 )。
In the third stage, the round corners, the screw threads, the fastening screws, and the like are omitted, and it is assumed that the sensor mount 5 and the tip clearance sensor 25 have a cylindrical structure, and the volume V is 0.0012m 3 (ii) a From equation 4, the starting temperature T of the sensor mount 5 and the tip clearance sensor 25 is calculated 1 Cooling to the termination temperature T 2 Heat quantity H to be released out 163 kJ; with the continuous reduction of the temperature in the rapid temperature change test box, the heat exchange between the rapid temperature change test box and the external environment is increased, and in the third stage, the initial value of k is set as the ratio of the surface areas of the test box 1 and the sensor mounting part 5 multiplied by an empirical coefficient, where a is 3, that is, k is 0 75. According to equation 6: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Mass flow Q of the required cryogenic nitrogen 2 ＝H in /[H d *c N *(T 2 -T 1 )]＝15.3266kg/s。
According to equation 7: from the starting temperature T 1 Cooling to the termination temperature T 2 Required intake area of low-temperature nitrogen gas (S ═ Q) 2 /[2*ρ N *(P N -P 0 )] 0.5 ＝10.2/(P N -P 0 ) 0.5 ＝12*10 -4 m 2 Therefore, in the temperature change process of the third stage, the first solenoid valve 9, the second solenoid valve 11 and the third solenoid valve 13 can be fully opened, so that the low-temperature nitrogen enters the test box 1 through the first air supply pipeline 8, the second air supply pipeline 10 and the third air supply pipeline 12, and the pressure P of the high-temperature low-temperature nitrogen is higher N And the temperature is controlled to be 2bar, so that the requirements of the cooling speed and the temperature in the third stage can be met.
The tip clearance sensor 25 and the simulation blade 29 are installed on the top cover 3 of the test box 1, the cable 26 of the tip clearance sensor 25 is led out through the cable hole 30 and is connected to the test acquisition equipment 27, the test acquisition equipment 27 is connected with the computer 28, and after inspection, the voltage received by the test acquisition equipment 27 is larger than 0.2V, and the working state of the tip clearance sensor 25 is normal. The top cover 3 is covered, the cable hole 30 is sealed through the sealing piece 4, the vacuum pump 18 is controlled through the touch screen 24 of the controller 23 to vacuumize the test box 1, the vacuum degree in the test box 1 reaches 0.020bar and below and can be kept for more than 10min, the air tightness of the test box 1 is good, normal-temperature nitrogen is input into the test box 1 through the normal-temperature nitrogen tank 20, and the air in the test box 1 is completely replaced by the normal-temperature nitrogen.
The controller 23 based on the PLC technology automatically controls or manually controls each electromagnetic valve of the vacuum pump 18 through the touch screen 24, the three stages of rapid temperature change tests are sequentially started, in the temperature change process of each stage, the temperature sensor 6 sends the real-time temperature in the test box 1 to the controller 23, the controller 23 calculates the actual cooling speed U 'of the rapid temperature change test of the stage according to the temperature change condition, and the temperature change test is carried out according to the setting, wherein the result U' is 4 ℃/s.
The controller 23 monitors and records the temperature and pressure data in the test chamber 1, the pressure data in the double-layer Dewar flask 7, the opening and closing of the electromagnetic valve and the opening data thereof, and the computer 28 records the gap signal data of the leaf gap sensor 25 in the rapid temperature change process, which is acquired by the test acquisition equipment 27. And evaluating the working performance of the leaf clearance sensor 25 under the low-temperature rapid temperature change condition according to the data, namely whether the leaf clearance sensor 25 can work circularly in a low-temperature environment.
The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The utility model provides a quick temperature change test device of apex clearance sensor's low temperature which characterized by: the device comprises a test box (1), a sealing element (4), a sensor mounting part (5), a temperature sensor (6), a working medium supply assembly, a working medium replacement assembly, an exhaust pipeline (22) and a controller (23); a cable hole (30) is reserved in the test box (1) and can be sealed through a sealing element (4), the simulation blade (29), the blade tip clearance sensor (25) and the temperature sensor (6) are installed in the test box (1) through the sensor installation part (5), and a cable (26) of the blade tip clearance sensor (25) is led out of the test box (1) through the cable hole (30) and is externally connected with a test acquisition device (27); a plurality of working medium inlets with different calibers are formed on the test box (1), and a plurality of air supply pipelines of the working medium supply assembly are respectively communicated with the test box (1) through a plurality of working medium inlets through electromagnetic valves, so that the working medium supply assembly inputs low-temperature nitrogen into the test box (1); the exhaust pipeline (22) is communicated with the test box (1), the exhaust pipeline (22) is provided with a pneumatic valve (21), and the working medium replacement assembly is communicated with the test box (1); the controller (23) is electrically connected with the temperature sensor (6), the working medium supply assembly and the working medium replacement assembly.
2. The low-temperature rapid temperature change test device of the blade tip clearance sensor according to claim 1, which is characterized in that: the working medium supply assembly comprises a double-layer Dewar flask (7), a first air supply pipeline (8), a first electromagnetic valve (9), a second air supply pipeline (10), a second electromagnetic valve (11), a third air supply pipeline (12) and a third electromagnetic valve (13); the lower layer of the double-layer Dewar flask (7) is filled with liquid nitrogen through a liquid storage tank (73), the upper layer of the double-layer Dewar flask (7) is filled with low-temperature nitrogen through a gas storage tank (72), and a liquid nitrogen pipeline (71) spirally surrounding the outside of the gas storage tank (72) is formed on the liquid storage tank (73), so that the gas storage tank (72) is filled with the low-temperature nitrogen formed by vaporization; the first air supply pipeline (8) is connected between the air storage tank (72) and the test box (1) through a first electromagnetic valve (9), the second air supply pipeline (10) is connected between the air storage tank (72) and the test box (1) through a second electromagnetic valve (11), and the third air supply pipeline (12) is connected between the air storage tank (72) and the test box (1) through a third electromagnetic valve (13).
3. The low-temperature rapid temperature change test device of the blade tip clearance sensor according to claim 2, which is characterized in that: the liquid storage tank (73) is connected to the liquid nitrogen tank (14) through a pipeline and a fourth electromagnetic valve (15) to be communicated, and liquid nitrogen is filled in the liquid nitrogen tank (14); the gas storage tank (72) is connected to the low-temperature nitrogen tank (16) through a fifth electromagnetic valve (17) through a pipeline, and the low-temperature nitrogen tank (16) is filled with low-temperature nitrogen.
4. The low-temperature rapid temperature change test device of the blade tip clearance sensor according to claim 1, which is characterized in that: the working medium replacement assembly comprises a vacuum pump (18) and a normal-temperature nitrogen tank (20); the vacuum pump (18) is communicated with the test box (1) through a pipeline, the normal-temperature nitrogen tank (20) is communicated with the test box (1) through a sixth electromagnetic valve (19) through a pipeline, and the normal-temperature nitrogen tank (20) is filled with normal-temperature nitrogen; the vacuum pump (18) and the normal temperature nitrogen tank (20) are respectively and electrically connected with the controller (23).
5. The low-temperature rapid temperature change test device of the blade tip clearance sensor according to claim 1, which is characterized in that: the inner wall of the test box (1) is provided with a heat preservation layer (2), the test box (1) is of an open-cover box structure, a top cover (3) with a cable hole (30) reserved is covered on the test box (1) in a sealing mode, and the sensor mounting piece (5) is mounted on the inner wall of the top cover (3).
6. A low-temperature rapid temperature change test method of a low-temperature rapid temperature change test device adopting the blade tip clearance sensor of claim 1 is characterized in that: the method comprises the following steps:
step 1: setting temperature change parameters according to the rapid temperature change requirement of the test; the temperature change parameters comprise the times s of the temperature change stages and the initial temperature T in each temperature change stage 1 End temperature T 2 Time of change of temperatureRoom H d And holding time H hold ；
Step 2: setting a test process of the rapid temperature change of the test box (1) in each rapid temperature change stage;
and 3, step 3: installing a blade tip clearance sensor (25) and a simulation blade (29) on a top cover (3) of a test box (1), connecting the blade tip clearance sensor (25) to test acquisition equipment (27), and checking the working state of the blade tip clearance sensor (25);
and 4, step 4: confirming whether the air tightness of the test box (1) is good or not, if so, executing the step 5, and if not, re-sealing the test box (1);
and 5: starting a rapid temperature change test, calculating to obtain an actual cooling speed U ' through a temperature sensor (6) and a controller (23), and judging whether the actual cooling speed U ' of the rapid temperature change test is consistent with an ideal cooling speed U, namely U ' ═ U; if yes, executing step 6; if not, resetting the heat absorption coefficient k and returning to the step 2;
step 6: temperature and pressure data in the test box (1), pressure data in the double-layer Dewar flask (7), opening and closing of the electromagnetic valve and opening degree data of the electromagnetic valve are monitored and recorded through a controller (23), and gap signal data of the leaf gap sensor (25) in the rapid temperature change process, which is acquired by a test acquisition device (27), is recorded through a computer (28);
and 7: and 6, evaluating the working performance of the leaf gap sensor (25) under the low-temperature rapid temperature change condition according to the data in the step 6.
7. The method of claim 6, wherein the method comprises: the step 1 further comprises:
step 1.1: setting the critical value of the air pressure in the test chamber (1) as P 0 When the air pressure in the test chamber (1) exceeds the air pressure critical value P 0 When the air pressure valve (21) is opened automatically, the air is exhausted through the exhaust pipeline (22);
step 1.2: the temperature of the low-temperature nitrogen input into the test chamber (1) is T N Pressure of P N Density of rho N Setting the diameter of the working medium inlet as d, and the low-temperature nitrogen in unit timeThe formula for calculating the mass flow Q is:
Q＝π*d 2 *[ρ N *(P N -P 0 )/2] 0.5 formula 1;
wherein, P N ≥P 0 ；
The inlet area of the low-temperature gas is pi x d 2 */4；
Step 1.3: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Required cooling time H d The calculation formula is as follows: h d ＝(T 2 -T 1 ) the/U formula 3;
wherein U is an ideal temperature change speed.
8. The method of claim 6, wherein the method comprises: the step 2 further comprises:
step 2.1: calculating the volume V of the sensor mounting part (5) and the blade tip clearance sensor (25);
step 2.2: calculating the starting temperature T of the sensor mount (5) and the tip clearance sensor (25) 1 Cooling to the termination temperature T 2 Heat quantity H to be released out The calculation formula is as follows:
H out ＝c s *ρ s *V*(T 2 -T 1 ) Formula 4;
wherein, c s Specific heat capacity, rho, of the sensor mount (5) and the tip clearance sensor (25) s Density of the sensor mount (5) and tip clearance sensor (25);
step 2.3: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Heat H to be absorbed by low-temperature nitrogen in The calculation formula is as follows:
H in ＝k*H out equation 5;
wherein k is a heat absorption coefficient, k is a constant, and k is>>1; at the start of the test, k is set to k 0 ；
k 0 ＝a*S 1 /S 0 Wherein a is an empirical coefficient, S 1 Is the surface area of the test chamber (1), S 0 Is the surface area of the sensor mount (5);
step 2.4: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 Mass flow Q of low temperature nitrogen 2 The calculation formula is as follows:
Q 2 ＝H in /[H d *c N *(T 2 -T 1 )]equation 6;
wherein, c N The specific heat capacity of the low-temperature nitrogen;
step 2.5: calculating the temperature T from the start 1 Cooling to the termination temperature T 2 The required air inlet area S of the low-temperature nitrogen is calculated by the following formula:
S＝Q 2 /[2*ρ N *(P N -P 0 )] 0.5 equation 7.
Step 2.6: and selecting the number and the caliber of the working medium inlets according to the required air inlet area S.
9. The method of claim 6, wherein the method comprises: in the step 4, the method for detecting the air tightness of the test box (1) comprises the following steps: the working medium replacement assembly is controlled to operate by the controller (23), so that the vacuum pump (18) of the working medium replacement assembly vacuumizes the test box (1) to ensure that the vacuum degree in the test box (1) reaches P 0 And below, and at least for a retention time H v If the air tightness of the test box (1) is good, normal-temperature nitrogen is input into the test box (1) through a normal-temperature nitrogen tank (20); otherwise, the airtightness of the test chamber (1) is considered to be not satisfactory.
10. The method of claim 6, wherein the method comprises: in step 5, the method for resetting the heat absorption coefficient k is as follows: if U' > U, reset k ═ k 1 ＝k 0 U/U', and k 1 ＜k 0 (ii) a If U' < UThen, reset k to k 2 ＝k 0 U/U', and k 2 ＞k 0 。
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