How to Choose Temperature Humidity Test Chamber

The temperature and humidity environmenttest chamber, also known as the high and low temperature humid heat test chamber, temperature and humidity cycle test chamber, etc., is a commonly used environmental simulation system and equipment in laboratories and factories.

 

The temperature and humidity environment test chamber is used to simulate natural environments such as high temperature, low temperature, humidity, and dryness to test the performance stability of materials or products in various environments. So how to choose a suitable temperature and humidity environment test chamber? Here, I will specifically explain how to choose a temperature and humidity environment test chamber from several aspects such as volume, temperature, humidity, and control methods.

 

1. Capacity selection

Place the tested product (component, assembly, part or whole machine) in a climate environment test chamber for testing to ensure that the surrounding environment of the tested product meets the environmental testing conditions specified in the testing specifications. The following points should be followed between the size of the climate chamber and the size of the tested product.

 

The volume of the test product shall not exceed 20~35% (recommended 20%) of the effective working space in the laboratory.

 

1.2 The proportion of the windward area of the test product to the total area of the laboratory workshop shall not exceed (35-50)% (recommended 35%).

 

1.3 The distance between the outer contour of the test product and the inner wall of the test chamber should be at least 100-150mm (recommended 150mm).

 

The main reason for this regulation is that placing the test piece in a crowded channel inside the test chamber, narrowing the channel will lead to an increase in airflow, which will affect the uniformity of environmental parameters inside the test chamber and occupy more space. The more severe the impact on the specimen.

 

According to the principle of heat conduction, the temperature of the airflow around the inner wall of the experimental space is generally 2 ℃~3 ℃ different from the center of the flow field, and the high or low temperature can even reach 5 ℃. The greater the difference between the experimental temperature and the external atmospheric environment, the greater the temperature difference mentioned above. Therefore, the space within a distance of 100-150mm from the inner wall of the cavity is unusable. Experimental data shows that the temperature difference between the windward and leeward sides of the flow field can reach 3 ℃~8 ℃, and in severe cases, it can exceed 10 ℃. Therefore, it is necessary to meet the requirements of 1.1 and 1.2 as much as possible to ensure the consistency of the environmental parameters around the tested product.

 

For example, the relevant standards for temperature related environmental testing include that the air flow around the test chamber should not exceed 1.7m/s to avoid creating a sense of unreality between the test product and the surrounding environment. Spread heat. If there are no restrictions on the volume or windward cross-sectional area of the test product, the actual test airflow speed will increase to the maximum wind speed exceeding the test standard, and the validity of the test results will be questioned

 

2. Selection of Temperature Range

At present, the temperature range of the temperature and humidity environment test chamber is generally -40 ℃~130 ℃, and some test equipment can reach a low temperature of -70 ℃ and a high temperature of 150 ℃ or even 180 ℃. For temperatures ranging from -40 ℃ to 130 ℃, unless there are special requirements such as installation near a heat source outside the engine or other commercial products, it can meet the temperature detection needs of most military and civilian products. Do not blindly increase the upper temperature limit.

 

The higher the upper temperature limit, the greater the temperature difference between inside and outside the chamber, the worse the uniformity of the flow field inside the chamber, and the smaller the available working chamber volume. On the other hand, the higher the upper limit temperature value, the higher the cost of the production chamber, because the higher the temperature, the higher the heat resistance requirements for insulation materials (such as glass wool) need to be.

 

3. Selection of humidity range

The humidity index given by the temperature and humidity environment test chamber is mostly 20%~98% or 30%~98%. If the temperature and humidity environment test chamber does not have a dehumidification system, then the test chamber with a humidity range of 60% to 98% can only perform high humidity tests.

 

To achieve high temperature and high humidity, simply spray water vapor or atomized water droplets into the chamber air for humidification. Low temperature and humidity are relatively difficult to control. Due to the low absolute moisture content at this time, sometimes much lower than the absolute moisture content in the atmosphere, it is necessary to dehumidify the indoor air to make it dry.

 

Relative humidity is directly related to temperature, the higher the temperature, the lower the relative humidity, of course, this is under the same absolute moisture content. For example, an absolute moisture content of 5g/Kg (referring to 1kg of dry air containing 5g of water vapor). When the temperature is 29 ℃ and the relative humidity is 20%, when the temperature is 6 ℃ and the relative humidity is 90%, and when the temperature is below 4 ℃ and the relative humidity is above 100%, condensation will occur inside the cavity.

 

4. Selection of Control Modes

There are two types of temperature and humidity environment test chambers: constant test chamber and alternating test chamber.

In general, the high and low temperature environment test chamber refers to a constant temperature high and low temperature environment test chamber, and its control method is to set a target temperature. The test chamber has the ability to automatically maintain a constant temperature to the target temperature point. The control method of the constant temperature and humidity environment test chamber is similar, with a target temperature and humidity point set, and the ability to automatically maintain a constant temperature to the target temperature and humidity point.

 

The high and low temperature alternating test chamber can be set with one or more high and low temperature change and cycle programs. The test chamber has the ability to complete the test process according to the preset program, and can accurately control the heating and cooling speed within the maximum temperature rise range and cooling speed, that is, it can control the heating and cooling speed according to the slope of the set curve. Of course, the alternating test chamber has the function of a constant test chamber, but the manufacturing cost of the alternating test chamber is relatively high. Due to the need for automatic curve recording equipment, program controllers, and opening the refrigerator at high temperatures in the alternating test chamber.

 

5 Fluctuations in temperature and humidity

In order to more accurately simulate the actual environmental conditions that products experience in nature, it is necessary to ensure that the surrounding environment of the tested product is at the same temperature during environmental testing. Therefore, the temperature gradient and temperature fluctuation chamber in the test must be limited. Temperature fluctuation is a relatively easy parameter to implement, and the actual temperature fluctuation in most manufacturers' test chamberes is within the range of ± 0.3 ℃.

 

The relative humidity deviation inside the temperature and humidity environment test chamber should be -3% to+2%. To meet the requirements of humidity control accuracy, the temperature control accuracy inside the environmental test chamber is relatively high, and the temperature fluctuation is generally less than ± 1 ℃, otherwise it is difficult to achieve the humidity control accuracy requirements.


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