How to Place Samples When Using Temperature Test Chamber?

How to place the test product when using a high and low temperature test chamber? It is well known that a high and low temperature test chamber with a large capacity can accommodate more test products, while a small capacity test chamber can accommodate fewer and fewer test products.

When we test the product, should we pack the two racks completely? This is incorrect. According to the standard, the working chamber volume of the high and 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 index of the environmental parameters in the working room of the high and low temperature test chamber is the test result under no-load conditions. As long as the tested product is placed, it will affect the uniformity of the environmental parameters in the working room of the test chamber.

The larger the space occupied by the tested product, the greater the impact on 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 in severe cases it can reach more than 10℃.

Therefore, as a test chamber manufacturer, we should try our best to meet the requirements specified in the standard to ensure the consistency of the environmental parameters around the tested product.

2. The tested product 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 air flow temperature around the test sample in the high and low temperature test chamber and the environmental test should not exceed 1.7m/s to prevent the test sample from being in line with the actual heat conduction around the surrounding.

The average wind speed in the test chamber when unloaded is 0.6~0.8m/s, not more than 1m/s. When the specified space area ratio is within the above requirements, the flow field wind speed can be increased by (50~100)%, and the average maximum wind speed is (1~1.7)m/s, which meets the standard. If the volume or windward section area of the test product increases unrestricted during the test, the air flow wind speed during the actual test will exceed the maximum wind speed specified in the test standard. Therefore, the validity of the test results will be questioned.

3. According to the principle of heat conduction, the air flow temperature near the box wall is usually 2~3℃ different from the center temperature of the flow field, and the maximum can reach 5℃.

The box wall temperature is 2~3℃ different from the flow field temperature near the box wall (depending on the box wall structure and material). The greater the difference between the test temperature and the external atmospheric ambient temperature, the greater the above temperature difference. Therefore, the space within 100~150mm of the box wall cannot be used.