Thomson Joule calculation

[athompson27]

I am trying to calculate the temperature drop through a back pressure regulator I intend on using. The inlet to the valve is 332 K, and 3548.7 kPa. The media is air. the outlet of the valve will be 963.2 kPa, and I am looking for the temperature. I understand this is a Thomson-joule calculation, but I have not been able to find good data on this. Can anyone help?

 

[iainuts]

I get 327.3 K.

 

[iainuts]

oh... assuming air and pressures are gage pressure.

 

[athompson27]

The pressures given were absolute pressures, not gauge pressures but I imagine that wouldn't make a huge difference. Do you know of any calculators for this type of problem, or could you explain your basic methodology for solving this?

Thanks.

 

[iainuts]

If you don't have some kind of fluids database, I don't know how you would do it. I have a computerized database similar to REFPROP

http://www.nist.gov/data/nist23.htm

This is just an isenthalpic expansion from one pressure to another (ie: enthalpy is constant). But without a database of enthalpy or at least the Joule Thompson coefficient, I don't know how you'd do this.

If you do much thermodynamic work, you should consider purchasing the database from NIST.

 

[25362]

I think Perry's Chemical Engineering Handbook has tabulated thermophysical properties for compressed air. Assuming you have an isenthalpic expansion to the lower pressure you'd be able to find the air's temperature at this pressure with the same enthalpy.

 

[mbeychok]

athompson27:

I think you would find it most useful to read this article on the Joule-Thomson effect:

http://en.citizendium.org/wiki/Joule-Thomson_effect

The reponse you got from 25362 is correct in that Perry's Handbook has relevant data, but the above article will help you understand how and why the Joule-Thomson effect works.

Milton Beychok
(Visit me at www.air-dispersion.com)
.