Heat radiation and heat transfer principle of high and low temperature test chamber

When discussing the conditions of high and low temperature test chamber for heat dissipation test sample, radiation heat transfer can not be ignored When the test sample and test chamber wall are hot black (radiation coefficient is about 1), from test sample to test chamber About half of the heat transfer of the wall is conducted by means of thermal radiation If the heat dissipation test sample is subjected to a certain temperature test in a high and low temperature test chamber with a hot white wall or a hot black wall, the surface temperature of the test sample will be significantly different Therefore, if you want to get reproducible test results, the relevant specifications should limit the radiation coefficient and temperature of the chamber wall 　　 Between the test sample and the box wall, if there are other test samples, heating or cooling components, mounting brackets, etc., the thermal radiation between the test sample and the box wall will be affected, and the thermal color and temperature of the test box wall will not meet the requirements The visual angle factor of the modified point is determined by the percentage of the "visible" part of the box wall at a specific point on the test sample Each point of the test sample The "viewing angle factor" of is not suitable to be disturbed by some devices that do not meet the requirements for the thermal color and temperature of the box wall 　　 Under the ideal "free air" condition, the heat transferred from the test sample to the surrounding air is completely absorbed by the surrounding air, which is caused by the complete absorption of the heat of free convection and radiation exchange Generally, most devices (including equipment and components) operate in a very hot black rather than hot white environment, making the inner wall of the high and low temperature test chamber similar to that of the hot black Hot black is easier than hot white, because most coatings and (unpolished) materials are closer to hot black than hot white At the same time, due to the aging effect of materials over time, it is particularly difficult to keep the box hot white for a long time 　　 If the temperature change of the box wall is within 3% of the specified test temperature, and the radiation coefficient of the box wall is between 0.7-1.0, the change of the surface temperature of the test sample is usually less than 3K The factor radiation heat transfer is directly proportional to the difference between the fourth power of the surface temperature of the test sample and the fourth power of the box wall temperature The radiation heat transfer at low temperature is less significant than that at high temperature, so the low temperature test The requirements for the color and temperature of the box wall are not strict The heat exchange through thermal radiation mainly depends on the temperature of the chamber wall This dependence is the main reason why when the difference between the surface temperature of the test sample and the ambient air temperature is very large, the test sample temperature can not be corrected by forced air circulation without following the standard procedures.