GB/T 18443.6-2010Testing method of performance for vacuum insulation cryogenic equipment - Part 6: Heat-leak rate measurement (English PDF)

4.2 Surface temperature measurement method

4.2.1 Test principle and method Measure the outer surface temperature of the vacuum insulation pipe and the corresponding ambient temperature. Calculate the heat-leak rate into the vacuum insulation pipe according to the natural convection in the large space. Calculate the heat conduction heat-leak rate of the joint according to the difference between the measured temperature of the air side of the joint and the temperature of the liquid. Or establish the finite element heat transfer model of the joint to solve the heat-leak rate of the joint. The schematic diagram of the test device is shown in Figure 1.

b) The rated flow rate of the flowmeter shall be compatible with the gas flow rate evaporated by the tested vacuum insulation cryogenic pipe;

c) There shall be ambient temperature, ambient atmospheric pressure and flowmeter inlet temperature and pressure measurement devices.

7.2 Surface temperature measurement method

7.2.1 Liquid nitrogen is generally used as the test medium. The actual delivered cryogenic liquid can be used as the test medium.

7.2.2 Open valve

10.Use the cryogenic container 11 to continuously deliver cryogenic liquid to the test vacuum insulation pipe and its pipe fittings until they are full. When the liquid level in the auxiliary test section drops to half, it shall be refilled with liquid. Ensure that the test vacuum insulation pipe is filled with test medium liquid.

7.2.3 The data can be recorded only after the vacuum insulation pipe and its fittings have been continuously conveying cryogenic liquid for 24h.

7.2.4 The data recording shall be based on the time interval of not more than 10min, collection surface and ambient temperature, until the relative error of the collected data within 1h is less than ± 5%. Where, Q0 - Total heat-leak rate of the joint pair, in watts (W) D1 - The outer diameter of the outer pipe of the male joint, in meters (m); D2 - The inner diameter of the outer pipe of the male joint, in meters (m); delta1 - The outer pipe wall thickness of the male joint, in meters (m); delta2 - The inner pipe wall thickness of the female joint, in meters (m); Twj1 - The average temperature of the outer surface of the male joint in contact with the environment, in Kelvin (K); Twj2 - The average temperature of the outer surface of the female joint in contact with the environment, in Kelvin (K); T2 - The saturation temperature of the cryogenic liquid corresponding to the average pressure in the test piece during the test, in Kelvin (K); lambda1 - The average thermal conductivity of the outer pipe material of the male joint in the temperature zone from Twj1 to T2, in watts per meter Kelvin (W/m·K); lambda2 - The average thermal conductivity of the inner pipe material of the female joint in the temperature zone from Twj2 to T2, in watts per meter Kelvin (W/m·K); L1 - The length of the outer pipe of the male joint, in meters (m); L2 - The length of the inner pipe of the female connector, in meters (m).

b) When calculating the heat-leak rate of other joint pairs in the pipeline, consider the heat conduction structure of the actual size. The temperature difference is the difference between the measured surface temperature and the saturated liquid temperature. For complex structures, it shall use finite element thermal analysis and calculation.

8.2 Calculation of heat-leak rate Q20 of standard state (standard ambient condition)

8.2.1 The heat-leak rate Q20 of high vacuum multi-layer insulation of the standard state shall be calculated according to formula (9). Where, Q20 - The heat-leak rate of standard state, in watts (W); Q0 - The total heat-leak rate of the joint pair, in watts (W); Ts - The cryogenic liquid saturation temperature under standard atmospheric pressure (101.325kPa), in Kelvin (K); T1 - The average ambient temperature during the test, in Kelvin (K); T2 - The saturation temperature of the cryogenic liquid corresponding to the average pressure in the test piece during the test, in Kelvin (K).

8.2.2 The powder or fiber vacuum insulation heat-leak rate Q20 of the standard state shall be calculated according to formula (10). Where, Q20 - The heat-leak rate of the standard state, in watts (W); Q0 - The total heat-leak rate of the joint pair, in watts (W); Ts - The cryogenic liquid saturation temperature under standard atmospheric pressure (101.325kPa), in Kelvin (K); T1 - The average ambient temperature during the test, in Kelvin (K); T2 - The saturation temperature of the cryogenic liquid corresponding to the average pressure in the test piece during the test, in Kelvin (K).