HVAC - Radiation Boundary Conditions

alex_gtz · July 25, 2016, 05:32

Hi everyone,

I am trying to model an entrance hall will a window-wall on one side. Other walls (including floor and ceillings) are considered adiabatic.

My questions concerns the boundary conditions I should enter at walls and window-wall. For the window-wall I know that, by convention heat transfer coeff is 8 W/m^2.K at the inside and 23 W/m^2.K at the outside. Which one should I put in FLUENT for the window-wall ?

Free stream temperature is the temperature of the outside. BUT, what is external radiation temperature ? I did put the same temp than the free stream temp but I am not sure at all if I'm right...

For walls, is the free stream temp the temp of the inside (fluid-domain) ? And external radiation temp the temp of the exterior environment ?

Last question, I put 0.006m as the wall thickness (for the window-wall) but it doesn't seem to change anything, does anybody know how wall thickness work ?

I know that all of these questions are not really related to FLUENT, it is related to radiation knowlegde in general but I can't find good documents on the internet, If somebody could enlighten me that would be very helpful !

Thank you. Alex.

cturutoglu · July 27, 2016, 04:35

You should use the inside heat transfer coefficient value for convection. I have no idea about radiation temp but i guess you can use the free stream temp which is the temp of the outside.
Wall thickness is only meaningfull when you work on a heat conduction problem.

nvarma · July 27, 2016, 16:01

You cannot specify heat transfer coefficient or free flow temperature on wall side facing the fluid. this is taken care by the fluent code and turbulence model.

so the values you enter are for the outside (no fluid zone, ie. end of domain)

alex_gtz · August 2, 2016, 08:10

Quote:

Originally Posted by nvarma

You cannot specify heat transfer coefficient or free flow temperature on wall side facing the fluid. this is taken care by the fluent code and turbulence model.

so the values you enter are for the outside (no fluid zone, ie. end of domain)

If I follow your idea then FLUENT will compute the heat transfer by conduction depending on the thickness of the wall...

July 25, 2016, 05:32	HVAC - Radiation Boundary Conditions	#1
alex_gtz New Member Alex Gtz Join Date: Jun 2016 Location: Paris Posts: 15 Rep Power: 9	Hi everyone, I am trying to model an entrance hall will a window-wall on one side. Other walls (including floor and ceillings) are considered adiabatic. My questions concerns the boundary conditions I should enter at walls and window-wall. For the window-wall I know that, by convention heat transfer coeff is 8 W/m^2.K at the inside and 23 W/m^2.K at the outside. Which one should I put in FLUENT for the window-wall ? Free stream temperature is the temperature of the outside. BUT, what is external radiation temperature ? I did put the same temp than the free stream temp but I am not sure at all if I'm right... For walls, is the free stream temp the temp of the inside (fluid-domain) ? And external radiation temp the temp of the exterior environment ? Last question, I put 0.006m as the wall thickness (for the window-wall) but it doesn't seem to change anything, does anybody know how wall thickness work ? I know that all of these questions are not really related to FLUENT, it is related to radiation knowlegde in general but I can't find good documents on the internet, If somebody could enlighten me that would be very helpful ! Thank you. Alex.

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July 27, 2016, 04:35		#2
cturutoglu Member CT Join Date: May 2016 Location: Turkey Posts: 32 Rep Power: 9	You should use the inside heat transfer coefficient value for convection. I have no idea about radiation temp but i guess you can use the free stream temp which is the temp of the outside. Wall thickness is only meaningfull when you work on a heat conduction problem.

July 27, 2016, 16:01		#3
nvarma Senior Member nm Join Date: Mar 2013 Posts: 100 Rep Power: 13	You cannot specify heat transfer coefficient or free flow temperature on wall side facing the fluid. this is taken care by the fluent code and turbulence model. so the values you enter are for the outside (no fluid zone, ie. end of domain)