Isenthalpic expansion of hydrogen gas 2

[scarlet27]

I've read with interest several of the threads on this or similar subject.

I'm trying to determine the resulting temperature drop of hydrogen gas (99% purity) when a steady flow is expanded from 125psig at 60F to 80psig through a pressure regulator and then from 80psig to approximately 1psig through a safety valve.
Someone suggested using a Mollier chart for hydrogen and, using the enthalpy at inlet conditions, reading the corresponding temperatures for the downstream pressures of interest.
Where would a person find a Mollier chart for hydrogen on the internet? I've searched for it in Perry's Chemical Handbook and Matheson's Gas Data Handbook but came up empty handed.

Can anyone provide a link to one?

Thanks,
Jacques

 

[vzeos]

There is a free thermodynamic properties program available on the University of Idaho’s webpage (link attached.) Download ALLPROPS for Windows (v1.0). This program is deceptively sophisticated. You can use it to generate a Mollier diagram or to obtain the Joule-Thompson coefficient.

After you start the program, access the Options menu to select the properties to display and to select your units. Then access the Fluids menu to select your fluid. You can calculate properties at a point by supplying your state variables and pressing Enter or, from the Tools menu you can define Tables or Graph to be generated. You can use the Graph feature to generate a Mollier diagram.

But in your case, I would simply choose to display Joule-Thompson coefficient and then use it to calculate the temperature increase.

http://www.webpages.uidaho.edu/~cats/software.htm

 

[vzeos]

scarlet27

How did you make out? Were you able to get that program?

 

[scarlet27]

Thank you for the link to the program, RGasEng. I was able to install it and generate some numbers. Aside from a few difficulties with printing tables or generating a Mollier chart, this should be a great help.

Thanks again

 

[cryotechnic]

Very nice program! Thanks, I was also looking for something like this.
I have to find out how it exactly works, but the first impression is very good. (and I don't have that often)

Thanks
Cryotechnic

 

[vzeos]

I also have trouble printing tables. What I do is; after generating tables, from the Edit menu- Select All- then Copy- then Paste into an Excel spreadsheet.

 

[scarlet27]

That is also also what I did to print a table, but the Mollier diagram comes up blank. Tried the help menu but it's pretty basic.

 

[vzeos]

scarlet27:
The graph facility works but I don't find it useful. Notice the Note at the bottom of the Graph Settings. Once you establish your graph settings, you will get a blank graph. The tables you generate thereafter will be plotted on the graph. I find it more useful to generate graphs in Excel. At least in Excel you can curve fit as well as plot.

 

[Montemayor]

Jacques:

There is no need for a Hydrogen Mollier Diagram or much less for calculating the Joule-Thomson coefficient or any other Thermodynamics correlations in order to solve your problem. The answers are:

1) The temperature resulting from adiabatically expanding Hydrogen from 125 psig & 60 oF down to 80 psig is 60 oF. In other words, there is essentially no temperature change. I would expect this (or perhaps a slight heatup instead, with Hydrogen or Helium).
2) The resulting temperature of expanding the 80 psig Hydrogen through a relief valve down to 1 psig is approximately 61 oF – a slight heatup.

These answers can be confirmed through the use of the free Thermodynamic database for 34 gaseous compounds found at:

http://webbook.nist.gov/chemistry/fluid/

This free NIST database is not only authoritative since it is sponsored by our Federal Government, is furnishes the following properties:
Density
CP
Enthalpy
Internal energy
Viscosity
Joule-Thomson coefficient
Specific volume
CV
Entropy
Speed of Sound
Thermal conductivity
Surface tension (saturation curve only)

You shouldn’t have to break a leg generating a Mollier Diagram when the authoritative basic Thermodynamic data is available free to you at your discretion. I am not detailing the procedure to apply an isenthalpic expansion to this database because I'm assuming if you can use a Mollier Diagram, you know enough Thermodynamics to be spared a lecture. I hope this helps you out accurately and efficiently.

Art Montemayor

 

[scarlet27]

Thank you all for your responses. I was able to obtain the required information using the ALLPROPS program suggested by RGasEng.

 

[sailoday28]

The original question was:
"Resulting temp drop....when a steady flow is expanded from 125psig at 60F to 80psig through a pressure regulator and then from 80psig to approximately 1psig through a safety valve."

If the process is adiabatic, and the difference of source and exit kinetic energy is small, then constant enthalpy is a reasonable approximation for determining the temperature change.