Introduction of the principle of climatic environmental test chamber

The working volume of the climatic environmental test chamber should be at least 3 to 5 times the volume of the tested product.

The working volume of the climatic environmental test chamber should be at least 3 to 5 times the volume of the tested product. The reasons for this provision are as follows:

After the tested product is placed in the climatic chamber, it squeezes a smooth channel. The narrowing of the channel will increase the flow rate of the airflow and accelerate the heat exchange between the airflow and the tested product.This is inconsistent with the reproduction of environmental conditions, because in the relevant standards, as follow:

a) For temperature-related environmental tests, the air velocity around the test specimen in the test chamber should not exceed 1.7 m/s to prevent the test specimen and surrounding climate from generating unrealistic heat conduction.

b) The average wind speed in the test chamber is 0.6-0.8m/s, not exceeding 1m/s.

When meeting the space and area ratios specified in two points a) and b) , the wind speed of the flow field may increase by (50~100)%. The average maximum wind speed of the constant damp heat test chamber is (1~1.7) m/s, which meet the requirements of the standard.

If the volume or upwind cross-sectional area of the test piece is increased without restrictions during the test, the airflow wind speed during the actual test will increase to exceed the maximum wind speed specified by the test standard, and the validity of the test results will be doubted.

The accuracy indexes of the environmental parameters (such as temperature, humidity, salt fog settling rate, etc.) in the working chamber of the climate chamber are the results of testing under no-load conditions. Once the tested product is placed, it will affect the uniformity of the environmental parameters in the working chamber of the test chamber, and the larger the space occupied by the tested product, the more serious this effect will be.

The actual test data shows that the temperature difference between the windward and leeward surfaces in the flow field can reach 3-8℃, and in severe cases it can be as high as 10℃. Therefore, the two requirements a) and b) must be met as much as possible to ensure the uniformity of the environmental parameters around the tested product.

According to the principle of heat conduction, the temperature of the air flow near the wall of the chamber usually differs from the center temperature of the flow field by 2 to 3℃, and may reach 5℃ at the upper and lower limits of high and low temperatures.

The temperature of the test chamber wall of the high and low temperature chamber is different from the temperature of the flow field near the chamber wall by 2 to 3℃ (depending on the structure and material of the test chamber wall). The large the difference between the test temperature and the external atmospheric environment, the large the above temperature difference. Therefore, the space within a distance of 100-150 mm from the test chamber wall is unusable space.

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