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Mass Flow Rate is not converging

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Old   December 7, 2010, 04:08
Default Mass Flow Rate is not converging
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Ghulam Destgeer
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I'm analyzing heat transfer and pressure drop in a heat exchanger. All the residuals are converging up till (at least) 10^-3. But some residuals' lines do not go below 10^-3 mark.
After completion of solution, when I check Mass Flow Rate at the Inlet which I initially assigned as Inlet Boundary Condition, do not remain same. In fact, Mass Flow Rate becomes significantly low. In addition, if I apply velocity as the Inlet condition, velocity remains same at the inlet, but again when I calculate mass flow rate, it gives very low value.

I need to know, how can I make Mass Flow rate to converge. At least mass flow rate should remain same at the inlet as I assign as a boundary condition.

Your help would be highly appreciated.

Thanks,
Ghulam
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Old   December 7, 2010, 18:48
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Glenn Horrocks
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http://www.cfd-online.com/Wiki/Ansys...gence_criteria
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Old   December 9, 2010, 08:55
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Ghulam Destgeer
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Thanks a lot ghorrocks... It was really helpful...
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Old   December 10, 2010, 08:18
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Ghulam Destgeer
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I have followed the instructions and the solution converged to 1e-4 in 50 iterations. But the mass flow rate which I applied as the inlet boundary condition (i.e. value 0.02 kg/s) do not remain same after the solution. As Mass Flow rate is a boundary condition, it should remain same, but the mass flow rate turns out to be 0.0001 kg/s when I calculate it in post processing (Mass Flow over area average ~0.0001kg/s). what should I do to make it remain same as I specify it in the beginning.

Regards,
ghulam Destgeer

Last edited by destgir448; December 10, 2010 at 09:01.
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Old   December 11, 2010, 06:13
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Glenn Horrocks
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Something is not right in your simulation setup when that happens. Do you have warnings about reverse flow?

Also, how are you calculating mass flow rate? Use the mass flow rate calculator in CFD-Post. Mass Flow over area average is not the correct way of calculating it.
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Old   December 11, 2010, 06:55
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Ghulam Destgeer
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Thank you so much for your reply.

You are right, i was not calculating mass flow rate in the right way... now it is OK. I got my results.

Thanks,
Ghulam Destgeer
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