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Cool system ,Convection + Radiation problem.

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Old   February 20, 2001, 01:35
Default Cool system ,Convection + Radiation problem.
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Hi guys,

I am trying to model a cooling system in a cavity. That is, a 2D model with a solid region containing different materials and a fluid region inside. In the solid region there exists a cool surface , say at about 260 K while the outer the environment is at 290 K. I am trying to find out the flow inside due to convection, radiation and bouyant forces.Also the heat transfer rates due to conduction and finally the temperature distribution in the model..

I used a mapped and fine 2D mesh of quadrilateral elements., segregated solver,steady state analyis, k-e modelling. When I choose bousinesq for the density of the fluid in the region, the code hangs up. .?? Firs order discretization for momentum and turbulence params. Standart handling for presusre and SIMPLE for velocity-pressure coupling.

Now, for the operating conditions, I defined a gravitaional accel. But for the operating temp, pressure and density, which values should I choose.

I have applied the case in the tutorials but it seems to be very brief..

Anybody has any experience with such a case.. Any suggestions are welcome!!!


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Old   February 21, 2001, 03:39
Default Re: Cool system ,Convection + Radiation problem.
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Try to calculate density of air using ideal gas most of the time. If the temperature difference is very small, Ra no. is small then Boussinesq method is advisable. Pressure can be atmospheric pressure. Operating temp can be kept at average temperature( use defaults initially, if ambient is not different from default 300K). For radiation you have to choose one method out of four depending on the optical thickness. Most complex method is DO method which even captures radiation through semi-transparent material( like glass). You need to specify the surface emissivities of all boundaries, emissivity etc. Material Properties have to be changed for DO Radiation-model. Start solution with default solution parameters. You will see it works. Ashutosh

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