I am designing a system that is constantly flowing compressed air through a valve which is open to the atmosphere. I would like to size a heater to keep the valve at a constant temperature and prevent it from freezing due to the heat loss from the fluid expanding through the valve, is there an approximation I can use to estimate the heat loss?

As an example, the air is flowing at 0.01 kg/s, expanding from 24.1 MPa / 60 C to ambient conditions (0.1 MPa, 20C)

  • $\begingroup$ The temp of the expanded gas is almost absolute zero according to the equations, so what you're trying to figure out is what heat transfer to the valve is. I suggest that this level of cooling is going to be off of the charts, and you will need to do this empirically. $\endgroup$
    – Tiger Guy
    Oct 12, 2023 at 18:42
  • $\begingroup$ Had to stop welding when the gas cylinder pressure regulator froze as it had a ball of frost from condensation about the size of a basketball around it - warmed up as the solution was a cup of coffee... $\endgroup$
    – Solar Mike
    Nov 11, 2023 at 14:55

1 Answer 1


To determine the maximum possible heat needed you can try the following

  1. first determine density of fluid at the starting conditions.
  2. determine volume flow rate (Vdot) by dividing by density.
  3. Use formula dP*Vdot to determine heat power loss. Where dP is (mains pressure - ambient)

If you would like to take it further , you would have to know how much heat is being added the system under ambient conditions under radiation and convection and get a Heat Transfer coefficient. You need advanced software I think to do such a thing, an experiment or if you are lucky you might find a table somewhere in a paper.


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