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[siretb]

I am expanding pure gazeous ammonia (temp around 40°C), 3.3 atm absolute though a metallic porous media, down to about 1.0 atmospheric

I am trying to figure out the resulting temperature. Should this be considered as an isenthalpic process, like a discharge through a valve ?

[Art Montemayor]

siretb:

The expansion through a porous plug (or sintered metal) is the same physical process as the expansion through a valve. It should be an isenthalpic process. In fact, if I remember my history correctly, Joule performed his famous experiments based on the expansion of gases across a porous plug. I recall being curious how Joule was able to come up with a porous plug during his era, but I have never found out. If I learned anything about the early scientists and engineers that gave us so much about Thermodynamics, it was that they were resourceful and self-reliant. I'm sure he figured it all out and made it all work out the way we have it today.

I figure your ammonia gas ought to enter the porous plug at 3.3 atm and 40 oC while exiting out the other side at 1.0 atm and approximately 35 oC. The NIST database gave me an enthalpy of 6.9604 kcal/mole at 40 oC & 3.3 atm, which I held constant until getting to 1.0 atm.

Art Montemayor
Spring, TX