Temp And Humidity Chamber-Influence Factors Of Uneven Temperature Distribution

When choosing a temp and humidity chamber, pay special attention to its performance parameters. These parameters, including temperature range, temperature uniformity, fluctuation, and heating and cooling rates, are key factors in evaluating whether the test chamber can meet the specific experimental needs, ensure that the test chamber can operate stably under set conditions, and obtain accurate and reliable experimental results. In addition, the selection of the appropriate test chamber should also consider its energy consumption, material quality and maintenance convenience to ensure long-term use of economy and durability.
Among many performance parameters, uniformity is particularly important and deserves our special attention. During the test, uniformity problems often occur, which directly affects the overall performance of the constant temperature and humidity chamber. According to the national standard, the temperature uniformity of the constant temperature and humidity box should be controlled at ±2℃, however, with the progress of environmental simulation test equipment technology, the temperature uniformity of today's constant temperature and humidity box has been able to reach ±0.5℃ to ±0.2℃. Next, we will explore the reasons for the uneven temperature phenomenon of the temp and humidity chamber.

Influence of test samples

If the test sample placed in the chamber of the temperature humidity chambers is enough to affect the overall heat convection inside, it will inevitably affect the uniformity of the internal temperature to a certain extent, that is, the temperature uniformity. For example, if LED lighting products are placed, the product itself emits light and heat, becoming a thermal load, then there is a great impact on temperature uniformity.

Thermal insulation material

The insulation material is the key factor to ensure the temperature uniformity inside the constant temperature humidity chambers. If the manufacturer has problems in the treatment of thermal insulation materials, it will directly lead to a significant deviation in the temperature uniformity in the box. Usually, we choose a combination of polyurethane insulation material and glass fiber to achieve a better insulation effect.

Air circulation system

Temp and humidity chamber through air circulation to improve the internal temperature uniformity. At the rear of the test area is provided with an air conditioning duct. The air heated by a heating tube is evenly stirred by a stainless steel multi-wing centrifugal wind wheel driven by a high-temperature long-axis motor, and finally discharged through an adjustable louver outlet to achieve a uniform distribution of temperature.

Differences in internal structure of the chamber

In the internal structure and spatial layout of the temp and humidity chamber, it is often difficult to achieve a complete symmetrical design, which may affect the indoor heat convection, resulting in temperature uniformity errors. This problem is mainly reflected in sheet metal design and treatment, such as the layout of the air duct, the location of the heating tube and the power of the fan, which will affect the temperature uniformity inside the box.

Difference in heat transfer coefficient of the inner wall of the chamber

Test chamber air convection condition

When conducting the test, if the volume of the test object is too large, or its placement and manner are improper, the air convection will be blocked, resulting in significant temperature uniformity deviation. For example, placing the test product next to the air duct will not only seriously affect the air circulation, but also have a significant impact on temperature uniformity. It is usually required that the cross section area of the test sample does not exceed 1/3, and appropriate spacing should be maintained between the samples to ensure that the surrounding air and the internal air can effectively convection. In addition, the sample should not block the outlet, and should be kept at a certain distance to avoid being placed around the air duct, so as not to affect the circulation of the wind. The test sample should be firmly placed to ensure the balance of the wind wheel and uniform air discharge.

Solution

1.During the test, attention must be paid to the volume, weight and placement of the test product in the working space of the test chamber. The relevant standards stipulate that the total volume of the test should be less than 1/5 of the studio to ensure adequate ventilation space. In addition, on each windward surface, the area of the test should be controlled within 1/3 of the windward section area to promote air flow. These requirements help to maintain the uniformity of the temperature in the box and ensure that the temperature deviation is in accordance with the standard regulations.

2.Reduce the supply air temperature difference and increase the supply air volume. Reducing the supply air temperature difference can reduce the influence of air flow on the temperature field in the working room, so as to maintain the temperature uniformity more effectively. At the same time, increasing the supply air volume can not only reduce the temperature difference of the supply air, but also effectively eliminate the indoor air flow dead zone.

3.Reduce the supply air temperature difference and increase the supply air volume. By reducing the supply air temperature difference, the influence of air flow on the temperature field in the working room can be reduced, and the temperature difference can be stabilized more effectively. At the same time, increasing the supply air volume not only helps to reduce the supply air temperature difference, but also effectively eliminates the indoor air flow dead zone.

4.If the test method allows, increasing the wind speed can enhance the flow of air in the box and eliminate the dead zone, so as to achieve a uniform distribution of temperature in the box.

5.Improve the control accuracy of the temperature humidity chambers and reduce temperature fluctuations, which can effectively reduce the temperature deviation. During the heating process of the test chamber, the temperature fluctuation can be reduced by PID continuous adjustment of the heating power. In the cooling process, the heat balance control method is usually used: after the set temperature is reached, the refrigerator is still running, but the excess cooling capacity is balanced by the controlled heating power. In order to avoid excessive heat shock and waste of energy, the cooling capacity is usually adjusted to reduce the cooling capacity in the constant temperature state, so as to reduce the need for balance of heat, which not only saves energy, but also improves the control accuracy. In addition, the position of the temperature sensor has a significant influence on the control accuracy. In order to improve temperature sensitivity, the sensor is usually placed near the air outlet to enhance control accuracy and reduce temperature fluctuations, ultimately reducing temperature deviation.

6.By adjusting the set value of the temperature field, the temperature deviation can be effectively reduced. The upper and lower deviations of temperature are often asymmetrical. If the upper or lower deviation exceeds the allowable range, but half of the difference between them is still within the allowable range, the temperature setting value of the equipment can be adjusted appropriately to ensure that the adjusted temperature deviation is less than the allowable value.

The above content summarizes the main factors leading to the uneven temperature in the temp and humidity chamber and its countermeasures. We hope that when facing relevant problems, we can examine these key factors one by one, so as to find a solution in time. Through systematic analysis and adjustment, we can not only improve the performance of the test chamber, but also ensure the reliability and accuracy of the experimental results, so as to better meet the actual needs.