natural ventilation

ritmat · June 8, 2011, 04:30

hello all,
I want to determine my required opening size for natural ventilation in a closed building. Inside there is a source of heat that I modeled as a rectangle and heat flux BC. In reality that surface is isolated so the temperature should not be more than building temperature but I cant set heat flux and temp. at the same time.
My outside temperature is 25C, and I want to be able to keep 50C max in my building.
I have tried many things but I dont get any convergence or realistic results(boussinesq, transient...).
my inlet at the bottom is pressure inlet at 0barg and my outlet at the top is pressure outlet at also 0barg ( I am also a bit confused if I should put or not the hydrostatic pressure corresponding to rho*g*h at the outlet for taking account the 21m of my building or fluent take that into account....).
I tried to have as a start a rough structured mesh with edge size of 0.2 all over my geometry.
After calculatin of Ra, and boussinesq condition, i thought i could use laminar and boussinesq in steady to calculate, but since i dont get anything which looks right, I have a doubt on my way to determine those numbers.
I would be gratefull, if anyone with experience on this type of problem could help me.
Thanks

ritmat · June 9, 2011, 04:22

hi,
In fact my Ra is probably over 10^10, so I am running my model in transient with a k-epsilon model. But I would really like to have some advice about my BC and my previous questions.
thanks a lot

June 8, 2011, 04:30	natural ventilation	#1
ritmat New Member henri Join Date: Jun 2011 Posts: 2 Rep Power: 0	hello all, I want to determine my required opening size for natural ventilation in a closed building. Inside there is a source of heat that I modeled as a rectangle and heat flux BC. In reality that surface is isolated so the temperature should not be more than building temperature but I cant set heat flux and temp. at the same time. My outside temperature is 25C, and I want to be able to keep 50C max in my building. I have tried many things but I dont get any convergence or realistic results(boussinesq, transient...). my inlet at the bottom is pressure inlet at 0barg and my outlet at the top is pressure outlet at also 0barg ( I am also a bit confused if I should put or not the hydrostatic pressure corresponding to rhogh at the outlet for taking account the 21m of my building or fluent take that into account....). I tried to have as a start a rough structured mesh with edge size of 0.2 all over my geometry. After calculatin of Ra, and boussinesq condition, i thought i could use laminar and boussinesq in steady to calculate, but since i dont get anything which looks right, I have a doubt on my way to determine those numbers. I would be gratefull, if anyone with experience on this type of problem could help me. Thanks

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June 9, 2011, 04:22		#2
ritmat New Member henri Join Date: Jun 2011 Posts: 2 Rep Power: 0	hi, In fact my Ra is probably over 10^10, so I am running my model in transient with a k-epsilon model. But I would really like to have some advice about my BC and my previous questions. thanks a lot