Hello
I recently am suffering calculation of temperature change resulted from the Joule-Thomson effect when propylene gas at 35 oC at 2 bar passes through a membrane to vacuum pressure (~ 0 bar) in an insulated system. The Joule-Thomson coefficient can be calculated from the equation: uJT= ( 𝜕 T/ 𝜕 P)H. the problem is how to calculate the Joule-Thomson coefficient.
Could anyone please help me to figure it out?
Thank you!
The easiest way is use a process simulator, and set up with one component propylene, and equation of state - say Peng Robinson. Define a feed stream as 1 mol/s propylene at 2 bar a and 35C feeding a valve with a pressure drop of say 1 bar. The valve is isenthalpic, so the outlet stream's temperature shows the J-T effect.
I did this using DWSim6 and obtained a temp drop of 1.462 C through the valve, so the J-T coefficient at low pressures and ambient temperature is 1.462 C/bar. For your case with the membrane and 2 bar DP the temperature drop would be about 2.9 deg C. In practice you would not expand to a complete vacuum, but away from the vapour-liquid phase boundary the J-T coefficient at 'room temperature' and moderate pressure of a few bar is not sensitive to pressure.
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