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franzdrs September 30, 2009 05:06

Heat loss through walls
 
Hi all,
I am quite an CFD beginner, and need some urgent help to simulate heat loss through the walls of my system. It is a simple geometry, a cubic space with thin metallic walls, one small horizontal inlet at one side, and one vertical, much wider outlet. The thing is, air enters the system at about 10 m/s and with 30 to 40 C above ambient (surrounding) temperature. What I want to see is the energy loss through the walls due to the lower surrounding temperature and how this affects the temperature distribution at the outlet. How should this be done? Do I need to include in the geometry the room where my actual system sits and define there the temperature of the surroundings? I am guessing not. In the Thermal tab of the Wall panel there appears different thermal conditions (heat flux, temperature, convection, etc) but I do not know which is appropriate, if any. So, to make it short, my problem is, how to simulate the loss of heat through the walls of my system.
I appreciate your help.
Franz

Ahmed September 30, 2009 05:37

Quote:

Originally Posted by franzdrs (Post 230951)
Hi all,
I am quite an CFD beginner, and need some urgent help to simulate heat loss through the walls of my system. It is a simple geometry, a cubic space with thin metallic walls, one small horizontal inlet at one side, and one vertical, much wider outlet. The thing is, air enters the system at about 10 m/s and with 30 to 40 C above ambient (surrounding) temperature. What I want to see is the energy loss through the walls due to the lower surrounding temperature and how this affects the temperature distribution at the outlet. How should this be done? Do I need to include in the geometry the room where my actual system sits and define there the temperature of the surroundings? I am guessing not. In the Thermal tab of the Wall panel there appears different thermal conditions (heat flux, temperature, convection, etc) but I do not know which is appropriate, if any. So, to make it short, my problem is, how to simulate the loss of heat through the walls of my system.
I appreciate your help.
Franz

You seem to be using a commercial solver, Can you tell us what? You might get more responses if you post in that particular forum,
Returning to your guess, You are absolutely wrong, why?
If you knew any of these values at the walls, then there is no need to go for a CFD analysis, a SINDA model or even careful hand calculations would do the job.
You do not know the surface temperature-> let the solver find it.
You know the ambient temperature far away from the walls, but how far?
Think in terms of a light bulb as an example, you need to place your system inside a bigger mesh and specify the known ambient temperature at the boundaries of that big mesh.
Good luck

franzdrs September 30, 2009 06:33

Hi Ahmed,
thanks for your answer. I am using FLUENT.
In a couple of past threads they say one can simulate this using a heat transfer coefficient BC and an external temperature. I think this would be done in FLUENT with the Convective Heat Transfer thermal condition for the walls. Wouldnt this be a possible approach? Unfortunately if I place my system inside a bigger mesh, my computer will not be able to handle it, I am afraid.
Thanks
Franz


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