Oct 27 , 2021
How to solve the large deviation of the temperature uniformity of the constant temperature and humidity testing machine?
What should I do if the temperature uniformity error of the constant temperature and humidity testing machine is large?
1) The structure of the constant temperature and humidity test box harms the uniformity of the intermediate temperature in the work to a very large level, because the structure is difficult to be completely symmetrical, and the uniformity of the temperature is harmful. Common low temperature test box or constant temperature and humidity test box (cold and wet aging test box) structure.
The front door is in the front, the central air-conditioning room is behind the box, and the upper and lower air are exhausted. Obviously, this kind of structure is symmetrical up and down, and it is easy to make the left and right temperature symmetrical, but the structure is different from the top and bottom, and the front and the left are completely different, which causes unevenness in the temperature of the indoor space during work. Even so, this kind of single air duct structure is properly solved in the design scheme, and the practical experience personal studio can be applied from 0.1 to 300m3, and the temperature error can be considered in the specification.
2) Because the thermal conductivity of the six sides of the box wall is different, some have heat conduction such as wire holes. Make the box wall temperature uneven, and then make the box wall radiation uneven heat transfer to the widespread flow, which endangers the temperature field uniformity. 3) Thermal damage such as heat leakage (high and low temperature test chamber) or cold leakage (low temperature test chamber) is caused by the heat conduction of the box wall. In order to better compensate for the heat damage, there must be a difference in exhaust air temperature, the exhaust of the high temperature box The temperature is higher than the operating temperature in the box, and the exhaust temperature of the ultra-low temperature box is lower than the operating temperature in the box. Because there must be a difference in exhaust air temperature, the temperature in the room is uneven during work.
How does the constant temperature and humidity test box ensure the humidification effect?
It is selected by the Meteorological Bureau to compile an environmental humidity look-up table at this stage.
The whole process of humidification of the constant temperature and humidity test chamber is actually to increase the working pressure of water vapor. The first method of humidification is to spray water on the wall of the environmental test chamber to control the saturation pressure of the water surface according to the operating temperature.
The water on the surface of the box wall produces a large surface. On this surface, the water vapor pressure is added to the box according to the method of diffusion outside the box to increase the air humidity in the environmental test box. This method appeared in the 1950s. Because at that time, the control of the environmental humidity was mainly carried out by using the liquid mercury electric contact conductivity meter to carry out simple on-off adjustments. The control adaptability to the large and backward boiling water tank temperature was weak, so the whole process of control connection was longer. It should not be considered that the alternating cold and humidity have more requirements for humidification. More importantly, in the case of self-spraying on the box wall, it is inevitable that water drops on the sample will cause different levels of environmental pollution to the sample. . In addition, there are also certain regulations for the drainage pipes in the tank.
This method was quickly replaced by steam humidification and shallow water zone humidification. However, this approach still has some advantages. Although its operation and connection process is relatively long, the environment humidity fluctuates less after the system software is stable, which is more suitable for stable cold and wet experiments.
In addition, in the whole process of humidification, water vapor but heat is not easy to increase the additional calorific value in the system software. Also, when the self-spraying temperature is manipulated to be less than the key point temperature specified in the experiment, the self-spraying water has the effect of dehumidification.
In-depth analysis of the ineffectiveness of the constant temperature and humidity box circulation system test
1. Analysis of the characteristics of the ground stress of the temperature cycle system: In the temperature cycle system test, the cyclone symmetry in the alternating high and low temperature test is a very important main parameter, which will harm the temperature transformation speed of the product. This requires that when several test products are being tested separately, there must be a moderate distance between the test product, between the test product and the test chamber wall, so that the cyclone can circulate the system freely between the test product, between the test product and the chamber wall.
2. The principle of ineffectiveness caused by ground stress in temperature circulation system and photoresistors: The temperature circulation system makes different raw materials with different thermal expansion coefficients different in swelling conditions, resulting in detachment, cracking, and the photoresistor such as paint coating Layers, etc.; the temperature circulation system makes the screw butt or riveted loose joints loose, and its photosensitive resistors such as screws, riveting components, etc.; the temperature circulation system makes the press-fitted joints that lack mechanical equipment support slack; high The low temperature test alternately changes the temperature cycle system of the test chamber to increase the resistance of the fiber welding with poor material or cause the lead path, the photosensitive resistor such as resistor components, etc.; the temperature cycle system causes contact erosion and environmental pollution, and the photosensitive resistor Appliances such as alloy products.