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-   -   how to maintain constant presure in a tank? (http://www.cfd-online.com/Forums/fluent/48893-how-maintain-constant-presure-tank.html)

 JB July 29, 2008 09:32

how to maintain constant presure in a tank?

Hello everyone,

I'm modelling the rise in temperature of a 'sealed' air tank, from 300K to 450K, over about 20 minutes.

In reality, the tank is not 100% sealed, but according to theoretical calculations, the velocity magnitude through the leakage zone is very small compared to the rest of the tank (flow driven by free convection).

Is there a simple way to account for the leakage without geometrically representing the leakage zones? (i.e. pressure remains constant in the tank, even if the temperature increases and the tank is 'sealed'.) A mass sink maybe? any successful experience?

 chouki July 29, 2008 17:46

Re: how to maintain constant presure in a tank?

You can use DEFINE_PROFILE UDF (UDF manual, Chapter 2, 2.3.13 DEFINE_PROFILE ) Chouki

 JB July 30, 2008 05:07

Re: how to maintain constant presure in a tank?

Thanks Chouki.

I will try to implement something with a UDF on a simpler model, and see how it behaves (I'm not familiar with UDFs.)

/JB

 Tepin Joe July 30, 2008 08:25

Re: how to maintain constant presure in a tank?

Hi, I feel you need not require any special care to maintain constant pressure inside the tank. For natural convection problems with density formulation by Boussinesq approximation the pressure variations remain almost the same. Regards,

 JB July 30, 2008 10:07

Re: constant presure in a tank? - CONFUSED

Thanks Joe.

I went through the user's guide, and now I'm just totally confused:

How can Rho=Pop/((R/Mw)xT) for Incompressible Ideal Gas flows?? That would mean that if I have a 100% sealed tank, and I heat it up, the overall density will drop... M[kg]=rho[kg/m3]xV[m3], right?? If the volume of the tank is constant, that means a fraction of the mass initially contained in my volume will just disapear as the temperature increases?