Operation of a Throttling Valve
Propylene gas at 100 bar and 373.15 K is throttled to a lower pressure selected by the slider. The process does not produce any shaft work. In addition, there are no appreciable changes in the kinetic or potential energies. Thus, if the process is adiabatic, we get a reduction of pressure at constant enthalpy (or ). This means that for an ideal gas , since the enthalpy of an ideal gas is a function of temperature only. For most real gases, a reduction in pressure at constant enthalpy leads to a reduction in temperature (i.e. ). Indeed, this situation corresponds to a positive Joule–Thompson coefficient, .[more]
In this Demonstration, we compute the temperature change using either the Soave–Redlich–Kwong or the Peng–Robinson equation of state based on the methodology described in . In addition, we compare our results (red curve) with the data obtained (blue dots) with the Aspen-HYSYS process simulator . As can be seen from Snapshots 3 and 4, excellent agreement is observed between the results derived from both methods.[less]
 J. M. Smith, H. C. Van Ness and M. M. Abbott, Introduction to Chemical Engineering Thermodynamics, 7th ed., Boston: McGraw-Hill, 2005.
 Aspentech. "Aspen-HYSYS." (Dec 15, 2016) www.aspentech.com/products/aspen-hysys.