Why does the temperature of the fluid generally decrease after throttling?
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This post was last edited by crjgood on 2011-11-28 at 20:14. Why does the temperature of the fluid generally decrease after throttling?
After throttling, the fluid volume decreases, and the effective heat exchange area increases relative to that before throttling, which will result in a temperature drop.
Things related to fluid thermodynamics. For compressible fluids, the principles of throttling, expansion, cooling, and refrigeration are as follows.
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In other words, gasification and heat absorption occur after throttling!
After throttling, the fluid volume decreases, and the effective heat exchange area increases relative to that before throttling, which will result in a temperature drop. Hydrogen is different; its temperature increases after throttling. That is also why the risk of hydrogen leakage is relatively high. Because an increase in the throttling temperature of hydrogen can cause a flame or explosion. Whether the temperature of a gas decreases or increases during throttling depends on the gas conditions (P, V) before throttling. For more detailed information, please refer to relevant thermodynamics textbooks on the Joule-Thomson coefficient.
The pressure of a liquid decreases after throttling. As the pressure drops, part of the liquid vaporizes due to phase equilibrium, and vaporization requires heat, which in turn causes the temperature of the system to drop. Gas throttling can be approximated by the gas equation of state
When a gas is throttled, the pressure decreases, causing the gas volume to expand. As a result, the distance between molecules increases, the potential energy between them rises, while their kinetic energy decreases. Since the magnitude of a molecule’s kinetic energy reflects the temperature, in general, the temperature of a gas always drops after it is throttled.
Gas expansion can be isentropic, while throttling is generally considered isenthalpic. However, in reality, it is impossible to have processes that are entirely isentropic or entirely isenthalpic. The temperature usually decreases after pressure reduction through throttling, especially if a jetting process is involved, in which case the temperature drop is even more significant
After throttling, the volume expands, work is done on the surroundings, and the temperature drops; however, this does not apply to gases such as hydrogen and helium. This is what I found on Baidu, and I think it’s correct; I hope it helps you understand.