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Old   February 14, 2005, 04:35
Default different mass flow rates
  #1
michael
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hi anybody! I have problem with calculating the mass flow rate. I used the Turbo postprocessing panel for calculation mass flow rate (oultet) boundary. I was suprised when I calculated the mass flow rate using 'report-> surface integrals'. Calculated mass flow rate:

Density(average)*Velocity(radial,average)*Area =mass flow rate.

Obtained mass flow rate using area- and mass-weighted average report types gave different m.f.rates than one calculated by turbo post. panel. Is my formulation of m.f.rate wrong, or just turbo post. panel has some bugs. Please help, I don't know which value is correct.
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Old   February 14, 2005, 12:48
Default Re: different mass flow rates
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Robin
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Hi Micheal,

You should not average the values first. Rather, calculate the sum of Density*Velocity_normal*Area_normal. Fluent should have a function to calculate Mass Flow's directly, since the IP mass flows will differ slightly from this calculation.

-Robin
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Old   February 15, 2005, 03:24
Default Re: different mass flow rates
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michael
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Thanks a lot Robin. You have right. I have one question more: My problem is unsteady, so I would like to save mass flow rates through the inlet and outlet boundaries every time step. It is easy to save some quantities using

solve->monitors->surface-> and so on…

But there is no possibility to monitor mass flow rate through the selected zone. Is there any easy possibility to do that without writing UDF (unfortunately T am not so familiar in UDFs)?

best regards
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Old   February 15, 2005, 20:47
Default Re: different mass flow rates
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Robin
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I haven't the foggiest idea of how to do this in Fluent. I can tell you the expression for CFX-5, but that isn't going to help you much.

Regards, Robin
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Old   February 21, 2005, 03:48
Default Re: different mass flow rates
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George
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I think that you just need to use a Custom Field Function, not a UDF.

Regards George
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