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The temperature and thermal expansion

The expansion coefficient of solid similar dependencies and heat on the temperature. However, when the temperature is far lower than the debye temperature, the expansion coefficient ( 一) Is small, difficult to measure. In order to solve this problem, but with the aid of Greg's resistance type. Actually use the total linear shrinkage rate to estimate the thermal stress is more convenient. Expansion coefficient of the data can be used in the temperature between the reference temperature T and a general linear shrinkage and the ratio of the length of the reference temperature.

1 most metal materials from cold room temperature to liquid nitrogen temperature, their length contraction 0. 2% - 0. Below 4%, such as from liquid nitrogen temperature liquid helium temperature region, the material of cabernet didn't continue to shrink, as a result, from the liquid nitrogen temperature of liquid helium temperature shrinkage only 1/10 from room temperature to liquid nitrogen temperature shrinkage. If a rough estimate thermal stress or stress test, just considering the liquid nitrogen temperature.

2 copper and stainless steel of the thermal expansion rate is almost the same, brass and deutsche bank are very similar, with these two kinds of materials in low temperature when connected to match, the thermal stress may be smaller.

3 if the same material temperature, thermal conductivity values of specific heat hours cooling may produce larger around the middle of the engineering stress. When such as plastic cooling, often due to uneven cooling, shrinkage is different, each part internal stress too big to rupture.

but the teflon is a plastic at low temperature and malleable, people often use it to do the piston seal ring, but have to take special measures to add inside the elastic ring. Such as when used as a seat, cold shrink equipment using liquid nitrogen.

4 a few root is commonly used in cryogenic system support rod or fit problem such as suspension, if the material is different, low temperature could be caused by cold deformation device tilt, sometimes even internal temperature is lower part of the tilt is too much, so that the external vacuum and high temperature contact short-circuit envelope, excessive heat.
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