How to Correctly Select the Volume of Environmental Test Chamber?

When putting the tested products (components, components, parts, or complete machine) into the environmental test chamber for the test, to ensure that the surrounding atmosphere of the tested products can meet the environmental test conditions specified in the test specifications, the following rules shall be followed between the working size of the environmental test chamber and the overall size of the tested products:

Rules

1. Volume of tested product (W) × D × H) It shall not exceed 20 -35% of the effective working space of the small environmental test chamber. It is recommended that no more than 10% of the products heated in the test be selected.

2. The ratio of the windward sectional area of the tested product to the total area of the environmental test chamber on the section shall not be greater than 35 -50%.

3. The distance between the outer surface of the tested product and the wall of the environmental test chamber shall be at least 100 -

To sum up the above three points, the working room volume of the small environmental test chamber shall be at least 3 - 5 times the outer volume of the tested product.

The reasons are as follows:

After the tested product is placed in the environmental test box, it occupies the smooth channel. The narrowing of the channel will increase the airflow rate and accelerate the heat exchange between the airflow and the tested product. This is inconsistent with the reproduction of environmental conditions because it is stipulated in relevant standards for environmental tests involving temperature that the air velocity around the test sample in the environmental test chamber shall not exceed 1.7m/s, to prevent the test sample and the surrounding atmosphere from generating unrealistic heat conduction. When no-load, the average wind speed in the test chamber is 0.6 - 0.8m/s, not exceeding 1m / s.

When the space and area ratio specified in the above requirements are met, the wind speed of the flow field may increase by (50 - 100)%, and the average z-high wind speed is (1 - 1.7) m / s, which meets the requirements specified in the standard. If the volume or windward cross-sectional area of the tested product is increased without restriction in the test, the air velocity will increase to Z high wind velocity specified in the test standard during the actual test, and the validity of the test results will be questioned.

The accuracy indicators of the environmental parameters in the working room of the environmental test chamber are the results of the detection under the no-load state. Once the tested product is placed, it will have an impact on the uniformity of the environmental parameters in the working room of the environmental test chamber. The larger the space occupied by the tested product, the more serious the impact will be.

The measured test data show that the temperature difference between the windward side and the leeward side in the flow field can reach 3 - 8℃, and it can be more than 10℃ in severe cases. Therefore, several requirements outlined above must be met as far as possible to ensure the uniformity of environmental parameters around the tested product.

According to the principle of heat conduction, the temperature of the airflow near the wall of the environmental test chamber is usually 2-3℃ different from the center temperature of the flow field and may reach 5℃ at the upper and lower limits of high and low temperature. The difference between the temperature of the small environmental test chamber wall and the temperature of the flow field near the chamber wall is 2-3℃ (depending on the structure and material of the chamber wall). The greater the difference between the test temperature and the external atmospheric environment, the greater the above temperature difference. Therefore, the space within the distance from the environmental test chamber wall (100- 150mm) is unusable.

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