I am solving the natural convection heat transfer problem within an enclosure with few heat generating components using Fluent.Around this enclosure,I have considered the fluid domain. To consider the solar effect, i have used the solar model ( No radiation model).Will this problem converge? Energy will be conserved? . I have a thought the since this solar load is applied as heat source (heat flux) on the outer surface of the enclosure, It is pumping the heat to the inside fluid. Because of this fact, inside fluid temperature may keep going and resulting in no convergence. Will that be true.
Please share your views.
Are you considering it an unsteady or steady problem? There are basically two approaches to solve natural convection problems. I think it will be difficult to get convergence in your case if you will consider it as a steady problem. However, problem is still not clear from your explanation. So it is difficult to give any specific comment.
Thanks for your comment Uday, It is steady state problem.
@ Mohammad, I agree with your point. But Some how, we have to introduce the solar load on enclosure. As you pointed out,Heat flux boundary condition is not possible.Is there any other alternate way to impose this boundary condition i.e. to see the effect of solar heat load on inside air temperature and internal components temperature of an enclosure. This enclosure is completely sealed off , Ambient air can not enter inside.
Dear Balasubramaniam Vadivel,
I think that you have to consider some wall to ambient losses with an external air flow or a heat transfer coefficient but this is not possible to work if a heat flux condition is applied on all the external walls.
You may could apply this ''solar heat flux'' condition to some external surfaces and the losses condition on the rest, but again this is not what really happens on the enclosure.
If fluent does not cover you I definitely suggest you try Solidworks Flow Simulation environment. I have conducted natural convection in the air gap of a solar flat plate collector applying solar radiation with this tool and it works.
If you intend solving the problem as a steady problem, Calculate the solar flux on each wall for the day (sunrise to sunset), average it with the number of sunshine hours(varies with month, and latitude) and treat this as a constant flux. This will be steady state, representing, the 'average' solar flux effect. The night, switch off the solar flux, and treat as a specified temperature, similar to the first approximation, you may assume average temperature ( from say, sunset to sunrise). OR, choose small time intervals (say, 15 min) when you can assume the solat flux to be constant.the converges solution will be an initial condition for the next time step. I believe, you have to make the choice depending on the application and the accuracy needed.
Dear Dimitrios Korres, and V. V. Satyamurty,
Thanks for your suggestions and valuable inputs.
As you suggested solar heat flux boundary condition on wall and roof , I have estimated solar load following ASHRAE STD guidelines and applied this heat load on outer surface of the enclosure. The problem is solved for the worst case condition ( Peak temperature).
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