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-   -   different mass flow rates (http://www.cfd-online.com/Forums/fluent/35727-different-mass-flow-rates.html)

michael February 14, 2005 05:35

different mass flow rates
 
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.

Robin February 14, 2005 13:48

Re: different mass flow rates
 
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

michael February 15, 2005 04:24

Re: different mass flow rates
 
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

Robin February 15, 2005 21:47

Re: different mass flow rates
 
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

George February 21, 2005 04:48

Re: different mass flow rates
 
I think that you just need to use a Custom Field Function, not a UDF.

Regards George


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