When discussing the conditions of the high and low temperature test chambers used for testing the heat test samples, the radiation heat transfer cannot be ignored. In the case where the test sample and the test chamber wall are hot black (radiation coefficient is about 1), from the test sample to the test chamber wall. About half of the heat transfer is transmitted by thermal radiation. If the heat test sample is subjected to a temperature test in a high-temperature test chamber where the wall is hot white or the wall is hot black, the surface temperature of the test sample will be It will be significantly different, so if you want to get reproducible test results, the relevant specifications should limit the emissivity and temperature of the test box wall.
Between the test sample and the tank wall, if there are other test samples, heating or cooling components, mounting brackets, etc., the thermal radiation between the test sample and the tank wall will be affected, and the thermal color and temperature of the test chamber wall will be If the requirements are not met, the percentage of the wall portion of the test sample that can be “seen†on the test sample determines the viewing angle factor of the change point. The “view factor†of each point of the test sample is not suitable for some non-conformity to the thermal color of the box wall. The temperature required device interferes.
Under ideal "free air" conditions, the heat transferred from the test sample to the surrounding air is completely absorbed by the surrounding air, which is due to the complete absorption of free convection and radiation exchange heat, usually most devices (including equipment and components) It is operated in an environment that is very similar to hot black rather than hot white. It is easier to make the inner wall of the high and low temperature test chambers close to hot black than to be hot white, because most paints and (unpolished) materials It is closer to hot black than hot white, and at the same time, it is particularly difficult to keep the inside of the box hot white due to the aging effect of the material over time.
If the wall temperature change is within 3% of the specified test temperature, and the emissivity of the tank wall varies between 0.7 and 1.0, the change in the surface temperature of the test sample is usually less than 3K, and the factor radiative heat transfer is related to the test sample. The difference between the fourth-order surface temperature and the fourth-order wall temperature is proportional to the difference between the fourth-order temperature and the box wall temperature. The radiation heat transfer at low temperature is not so significant at high temperatures, so the requirements for the color and temperature of the box wall are not so strict during the low-temperature test. .
The heat exchange by thermal radiation mainly depends on the temperature of the test chamber wall. This dependence is why the temperature of the test sample is not corrected according to the standard procedures when the difference between the surface temperature of the test sample and the ambient air temperature is large. The main reason why the forced air circulation cannot be used for testing.
Waist Massager
Waist massager
Waist massager
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