Views: 234 Author: Wendy Publish Time: 2023-08-10 Origin: Site
Environmental testing has grown in importance as industry and information technology have developed, and it is now frequently used by companies and scientific research facilities to evaluate the quality of their output. The utilization of temperature and humidity test chambers is increasing as one of the most crucial supporting pieces of equipment for environmental testing and research. The primary technical parameters of temperature and humidity deviation, fluctuation, temperature rise and fall rate, wind speed, etc., were covered in earlier literature and standard standards.Many people talk about humidity test chambers, but uniformity studies are scarce.
Due to the different inner wall structures of the temperature and humidity test chamber, the temperature and humidity of each section of the inner wall are also different. This affects the thermal convection in the studio, leading to different internal temperature and humidity uniformity and deviation.
The uniformity of interior temperature and humidity will be impacted by some light and heating loads placed inside the test chamber or test samples that affect the total internal heat convection. The temperature and humidity uniformity of the temperature and humidity test chamber should, by default, be measured under no-load, per the applicable requirements.
There will be heat dissipation and heat transfer in some parts of the test chamber due to the different heat transfer coefficients of the front, back, left, upper, and lower six surfaces of the inner wall of the chamber, as well as the detection holes, threading holes, and test holes on the side of some chamber walls. This uneven temperature in the chamber and uneven convective heat transfer radiated by the chamber wall have a significant impact on the test results.
It is challenging to achieve the required level of uniformity and symmetry when designing the space and internal structure of the test chamber, which will inevitably result in uneven temperature and humidity levels inside the chamber. Examples of this include the placement of the heating pipe and the design, power, and position of the air duct.
The test sample's improper placement or excessive volume will obstruct air heat convection in the chamber, which will impact the uniformity of temperature and humidity. The thermal cycle in the chamber will be significantly impacted, for instance, if the sample is placed near to an inner wall or air duct on one side, resulting in an uneven temperature and humidity. The volume of the heat dissipation samples used in the test must not exceed 1/5 of the test chamber's total volume, as specified by the test standard.
The door and chamber are not impenetrably tight. For instance, the consistency of temperature and humidity in the temperature and humidity test chamber will be impacted if the sealing strip is torn and the door leaks.
Generally speaking, the wind speed in the temperature and humidity chamber shouldn't be greater than 1.7 m/s during the environmental test. If the wind speed is too high, it will hasten the heat transfer from the test piece's surface to the moving air in the chamber and hasten the evaporation of moisture from the wet ball gauze, which is bad for the test and results in false humidity readings. Therefore, for the test, a lower wind speed is preferable. Air must be circulated in the test chamber, nevertheless, to guarantee the consistency of the chamber's temperature and humidity. The average wind speed in the chamber is 0.6 to 0.8 m/s for the no-load test.
Because the heat divergence is not perfectly uniform, there will be a certain fluctuation once the test chamber achieves the desired temperature and humidity condition. The temperature deviation can be decreased by enhancing the test chamber's control precision and lowering temperature fluctuation. For the low-temperature test chamber, the temperature fluctuation is typically controlled through heat balance, which means that after the test chamber reaches the set temperature, the refrigerator is still typically open and the controlled heating power is used to balance the excess refrigeration capacity. For the high temperature test chamber, the temperature fluctuation can be reduced by PID continuous adjustment of heating power.