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-   -   Openning Outlet (http://www.cfd-online.com/Forums/cfx/19372-openning-outlet.html)

David December 13, 2002 07:23

Openning Outlet
 
For a multiphase multicomponent flow, CFX requires to specify "Fluid Values" including volume fraction, mass fraction and temperature at outlet. Could anybody tell me how to specify them? For example, a pipe. Thanks.

David

ribeiro@feq.unicamp.br December 13, 2002 08:06

Re: Openning Outlet
 
David

It depends on the physics of the problem. The openning boundary works for outlets that you don't know if the flow is fully developed. As the flow is not fully developed, the fluid can recirculate in the outlet region. Thus, the solver will need values for this recirculating (or, in other words, entering) fluid all its specifications but the velocity. This is calculated by the pressure drop.

it means that you should guess these values in the opennings unless you have a physical situation where you know exactly what is happening. The the case of pipes, I'd make theses values identical to the inlet. But this is just a guess.

I hope this helps Ribeiro

David December 13, 2002 08:55

Re: Openning Outlet
 
Hi Ribeiro

Thank you very much for your so quick response. It's very helpful. So I can specify it as you said. Since I don't know the values for opening outlet, guess values have to be adpoted. Will the guesses affect the results? I mean different guess has different solutions? Thanks again.

David

Ribeiro December 17, 2002 13:31

Re: Openning Outlet
 
David

If the problem has just one Steady State, the initial guess will not affect the results. But if there are many steady states, the initial guess can be important. As a chemical engineer, I know that in some Continuous Reactors can occur multiple SS. In the case of pipe flows, I don't know.

I hope this helps.

Ribeiro


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