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As we all know a large-volume high low temperature test box can contain more test products, and a small-volume test box can contain fewer and smaller test products. When we test products, should we keep the two racks fully packed? This is not correct. According to the standard, the volume of the working chamber of the high low temperature test chamber should be at least 3 to 5 times the volume of the test product. The reasons are as follows:
1. The accuracy indicators of the environmental parameters in the working chamber of the high low temperature test chamber are the results of testing under no-load conditions. As long as the tested product is placed, the uniformity of the environmental parameters in the working chamber of the test chamber will be affected. The larger the space the tested products occupy, the more impact it will cause to the environmental parameters. The actual test data shows that the temperature difference between the windward side and the leeward side of the flow field can reach 3~8℃, and can reach more than 10℃ in severe cases. Therefore, we should try to meet the requirements specified in the standard to ensure the uniformity of the environmental parameters around the product being tested.
2. The product under test occupies a smooth channel after being placed in the box. The narrowing of the channel will increase the flow rate of the airflow and accelerate the heat exchange between the airflow and the test product. This is inconsistent with the reproduction of environmental conditions, because the relevant standards stipulate that the airflow around the test sample in the high low temperature test chamber should not exceed 1.7m/s for temperature and environmental tests, so as to prevent the test sample and the surrounding in line with the actual heat conduction. The average wind speed in the test chamber is 0.6~0.8m/s when there is no-load, and not exceed1m/s. When the space and area ratio specified is within the above requirements, the wind speed of the flow field may increase (50~ 100)%, and the average maximum wind speed is (1~1.7) m/s, which meets the requirements of the standard. If the volume of the test product or the area of the windward section increase without restriction during the test, the airflow wind speed during the actual test will exceed the maximum wind speed specified by the test standard. As a result, the validity of the test results will be questioned.
3. According to the principle of heat conduction, the temperature of the airflow near the box wall is usually 2~3℃ different from the temperature of the center of the flow field, and it may reach 5℃ for maximum. The temperature of the box wall and the temperature of the flow field near the box wall are different by 2~3℃ (depending on the structure and material of the box wall). The greater the difference between the test temperature and the external atmospheric environment temperature, the greater the above temperature difference will be. Therefore, you can't use the space within the distance of 100~150mm of the box wall.