Physics Help Forum Enthalpy-thermo problem

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

 Feb 16th 2015, 06:24 PM #1 Junior Member   Join Date: Feb 2015 Posts: 2 Enthalpy-thermo problem Hi, I have a practice problem in thermo that I have some difficulties with: The PVT relation for helium is given by the following equation of state: P=RT/V-b, where b=2.3*10^5 m^3/mol Through an isenthalpic (H=0) throttling process, the gas is let to expand from a pressure of 10^8 Pa at 300 K to a pressure of 10^5 Pa. Calculate the final temperature of the gas. Cp canbe considered constant at a value of 5/2R. I started by using the eq. for enthalpy dH=0=CpdT + (V-T(dV/dT))dP and finding (dV/dT) from the PVT relation given which resulting in R/P Replacing R/P in the dH eq. we get: 0=CpdT + (V-T(R/P))dP Wouldn't this cancel the dP term since TR/P =V. Or should I not cancel them and just integrate? I'm a bit confused and could use some help. Thank you in advance
 Feb 17th 2015, 10:31 AM #2 Senior Member   Join Date: Jun 2010 Location: NC Posts: 405 Hi, Looks like you have the answer... Having 0=CpdT + (V-T(R/P))dP and P=RT/V-b or TR/p = V-b Then 0=CpdT + b dP So integrate this. TSH for PHF
 Feb 22nd 2015, 06:22 PM #3 Junior Member   Join Date: Feb 2015 Posts: 2 Thank you

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