Does reducing steam pressure lower the temperature?
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Today I saw a steam pipeline; the pressure as it entered the plant was around 1 MPaG. The thermometer on site indicated a temperature of just under 200°C. After passing through a pressure reducing valve, the pressure dropped to around 0.2 MPaG, and the thermometer then showed a temperature of only a little over 100 degrees Celsius. The steam only has its pressure reduced; its temperature doesn’t drop. Why then does the temperature decrease by so much? Is there anyone who can do the calculations? Is this temperature drop reasonable?
It will definitely cool down; just check the table and you’ll see
After being depressurized by a pressure reducing valve, does the temperature of superheated steam decrease? https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1068146&shareuid=4554153 Check out this post; it explains things quite clearly.
This post was last edited by Zhongyuanren on 2022-8-21 at 11:21. According to thermodynamics: PV=nRT; if the pressure is reduced, the volume increases so that the temperature can remain constant. If the volume decreases, the temperature must change.
In my understanding, at the moment of pressure reduction, the temperature remains constant; at this point, saturated steam turns into superheated steam. However, as pressure decreases, the temperature rises rapidly as heat is released around it. Especially since the steam contains moisture, which requires a large amount of heat to be converted into gas, the temperature will soon reach that corresponding to the saturated steam pressure.
The temperatures corresponding to saturated vapors at different pressures are not the same.
When saturated steam is depressurized through a valve, it undergoes isenthalpic throttling; the expansion of its volume results in work being done on the outside, and of course internal energy is consumed, causing the temperature to drop. Let’s review the Joule-Thomson effect again.
In the vast majority of cases, a decrease in steam pressure leads to a decrease in temperature, which is determined by its thermodynamic properties — temperature and pressure are directly related to each other.