# A real challenge: real gas isothermal delta h

1. Feb 11, 2012

### Harry-cy

1. The problem statement, all variables and given/known data
Using any software, create the enthalpy table for the following two cases of superheated steam:

1. Isobaric process at a chosen pressure in 100 spaces of 5 degrees celcius.
2. Isothermal process at a chosen temperature, given Vg from the book, in 1000 spaces of 0.1 bar

2. Relevant equations

The 4 maxwell equations
Pv=zRT, Pv=RT(IDEAL)
du=Tds-pdv, dh = Tds-vdp
dh=CpdT + [v-T*(∂V/∂T)p]dP <---- MAIN EQUATION
Can use many more though

3. The attempt at a solution

Hi guys (and girls). I just created my account, this is my first threat. I came across this very difficult problem and I am IN NEED for some help. I managed to solve relatively easy the first part. I integrated the Cp function since dP=0 and voila, I was done. I use FORTRAN, but I can use Excel if necessary.The problem is the second part. Since the process is isothermal, CpdT=0. But I cannot use ideal gas equations. I chose a temperature and found the Vg from my book. Then I integraded both sides and ended up with:
hf-hi = v(Pf-Pi) - T*???(Pf-Pi), where '???' is the integrated (∂V/∂T)p part. I tried it as an ideal gas, as a compressibility factor Z equation, I even put various values in Excel and plotted the V(T) at a constant pressure equation, but the answers are definitely wrong. I triple checked the programming code. Any help from some experts?

Last edited: Feb 11, 2012