A real challenge: real gas isothermal delta h

[Harry-cy]

Homework Statement

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

Homework 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

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?

 

[KataKoniK]

Thank you for posting your question here. I am a scientist with experience in thermodynamics and I would be happy to assist you with this problem.

Firstly, let me commend you on your efforts in solving the first part of the problem. It seems like you have a good understanding of the equations involved and how to use them. However, for the second part, there are a few things to consider.

Since the process is isothermal, the temperature remains constant throughout. This means that the internal energy (u) and enthalpy (h) also remain constant. Therefore, the equation you have used, hf-hi=v(Pf-Pi)-T*?(Pf-Pi), may not be applicable in this case.

Instead, you can use the equation dh=CpdT+[v-T*(∂V/∂T)p]dP, as you have mentioned in your post. However, in this case, since the temperature is constant, the term CpdT will be zero. This leaves us with the following equation:

dh=[v-T*(∂V/∂T)p]dP

Since you have already chosen a temperature and found the corresponding Vg from your book, you can substitute those values in the equation and integrate it to find the change in enthalpy (hf-hi). This will give you the enthalpy table for the isothermal process at the chosen temperature.

I hope this helps you in solving the problem. If you have any further questions or need clarification, please do not hesitate to ask. Good luck with your calculations!