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non isothermal heat transfer in room

Posted 07.05.2012, 12:42 GMT-4 Fluid & Heat, Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD) Version 4.2a 2 Replies

Pedro Torres
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Hello,

I am trying to model a simple room 4 m x 3 m, 2.90 m high with:
- open door (to large volume of air) - outdoor = open boundary, 20°C
- open window (to large volume of air) - indoor = open boundary, 20°C
- a heat source in the room = gas furnace, 100 m3/hr of fluid, temp 1000°C = inlet, laminar inflow 100 m^3/hr, temperature 1000°C
- gravity (-g_const*nitf.rho), defined as volume force

Physics is nitf, non isothermal transfer in fluid.

My problem is that it never converges although I reduced and improved a lot mesh size.
If I change the "open boundary" condition with "outlet", it can converge but setting a temperature at the outlet is not realist.

Does air density variation with temperature is automatic in 4.2 o do I have to introduce a formula to take this in account?

Thanks for any help you can provide,

Pedro
2 Replies Last Post 07.05.2012, 15:26 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 07.05.2012, 14:07 GMT-4
Hi

I'm not sure how "unique" the solution to your equations are if you have large "open" boundaries for a small volume, but I'm no CFD expert ;)

On the other hand, if you use library material properties and your rho is defined as a function of T and p, then yes rho will depend on the pressure and the temperature (or just one of the two). Check your material data

--
Good luck
Ivar
Hi I'm not sure how "unique" the solution to your equations are if you have large "open" boundaries for a small volume, but I'm no CFD expert ;) On the other hand, if you use library material properties and your rho is defined as a function of T and p, then yes rho will depend on the pressure and the temperature (or just one of the two). Check your material data -- Good luck Ivar
Pedro Torres
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Posted: 1 decade ago 07.05.2012, 15:26 GMT-4
Hi,

Thanks Ivar.

I tried to reduce open boundary without success. Should I leave a huge volume of air (like an envelope) at the open boundaries of my model?

Yes rho is defined as function of T, gas is "Air" from mat lib.

thanks
Pedro
Hi, Thanks Ivar. I tried to reduce open boundary without success. Should I leave a huge volume of air (like an envelope) at the open boundaries of my model? Yes rho is defined as function of T, gas is "Air" from mat lib. thanks Pedro

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