[Fat shady]

Hello everyone,
Hope the community can assist to solve a problem I have faced. At the moment, I am trying to conduct an turbo expander modeling using "natural gas",which is mixture of the methane/ethane/propane/nitrogen/pentane/i pentane/i butene/helium/water/H2S/CO2.(0.964/0.0136/0.0038/0.0074/0.0013/0.0004/0.0031/0.0001//0.00009/0.00001/0.0062Mass Fraction)
It works as follows :
Natural gas flows into the nozzle inlet of the turbo expander and performs the first expansion process through the nozzle flow path. When the gas flows out of the nozzle, the speed increases and the pressure decreases. Then it flows into the impeller for a second expansion process, flows out through the impeller outlet, the gas pressure decreases again, and the speed increases again.
Fluid Setup:
1.Generate pure substance RGP files from the NIST-REFPROP library for methane, ethane and other fluids mentioned above.
2.Created a material "natural gas" (gas) as a fixed composition mixture, liquid state. Since I have no data, the mixture thermodynamic and transport properties were set to "Ideal Mixture"
Problem:
After creating a mixed component fluid similar to natural gas, an error is reported when solving with CFX.Some mistakes are:

ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Floating point exception: Zero divide
ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Stopped in routine FPX: C_FPX_HANDLER
An error has occurred in cfx5solve: |
| |
| The ANSYS CFX solver exited with return code 1. No results file |
| has been created.
End of solution stage.
+--------------------------------------------------------------------+
| The following user files have been saved in the directory |
| D:/RJLX/LXCFX/6.7_pending/dp0_CFX_Solution/CFX_001: |
| |
| trace, mon |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| For CFX runs launched from Workbench, the final locations of |
| directories and files generated may differ from those shown. |
+--------------------------------------------------------------------+
This run of the ANSYS CFX Solver has finished.


My purpose is to simulate the components of natural gas as the working fluid to simulate the turbo expander, but it cannot be solved now. I don't know what the problem is. Is the fluid setting incorrect?

[ghorrocks]

You are getting a divide by zero error - the error message says so. So your challenge is to find it.

You have some complex material models and the source of the problem is likely to be there. So I would do a series of simulations to work out which one:
1) Make the fluid air ideal gas
2) Make the fluid a fixed composition mixture with all the components ideal gases
3) One gas at a time, change the component gasses over tot he real gas model you have.

If (1) runs OK then the basic simulation is OK. And from there where the simulation starts giving divide by zero errors will tell you which component has the problem.

[Opaque]

Glenn's summary:
1 - Crawl
2 - Stand
3 - Walk
4 - Run

You must get familiar with mixtures if you have not worked with them before. The more materials you add to your mixture, the more checking you have to do that ALL the data is input CORRECTLY.

You will make some mistakes at each step, but that is part of the learning process. If you avoid the small steps, you will be searching for a needle in a haystack.

[Fat shady]

I'm so happy to receive your reply!Thank you for your adivice! Next, I will try it according to your suggestion.

[Fat shady]

Thank you Opaque!I'll learn more about the use of fixed composion mixture.