No heat transfer in air

thomasyangfly · April 18, 2013, 00:07

Hello guys:

I am doing the numerical simulation using Ansys CFX to simulate natural convection in duct with both ends open. The square duct is put in a big champer filled with air at 25 deg C, and one of the outer surface of the square duct is fixed at constant heat flux boundary (1000W/m2), the other three outer surfaces are kept adiabatic. The air inlet is opening boundary with static pressure at 0 atm and the air outlet is outlet boundary with static pressure at 0 atm. The inner surfaces of the square duct (fluid-solid interface) are automatically set as conservatic heat flux.

After it reached convergence, the fluid has velocity but only the boundary layer of fluid near the inner surface of the squar duct has temperature gradient, the main stream has no heat transfer. I do not know what happened. I tried to check all the mesh (quality is 0.9) and the boundary condition settings, but nothing can I found.

There is a very confusing results: when all of the outer surfaces of the square duct are kept at constant heat flux, there is heat transfer in the main stream. Why with one face kept at constant heat flux, no heat transfer in air?

Could you help me solve this problem? I am suffering this problem for quite a long time. Thanks very much for your kindly help.

ghorrocks · April 18, 2013, 07:35

Can you post an image of what you are modelling and the CCL?

April 18, 2013, 00:07	No heat transfer in air	#1
thomasyangfly New Member Xiaohu Yang Join Date: Sep 2011 Posts: 5 Rep Power: 15	Hello guys: I am doing the numerical simulation using Ansys CFX to simulate natural convection in duct with both ends open. The square duct is put in a big champer filled with air at 25 deg C, and one of the outer surface of the square duct is fixed at constant heat flux boundary (1000W/m2), the other three outer surfaces are kept adiabatic. The air inlet is opening boundary with static pressure at 0 atm and the air outlet is outlet boundary with static pressure at 0 atm. The inner surfaces of the square duct (fluid-solid interface) are automatically set as conservatic heat flux. After it reached convergence, the fluid has velocity but only the boundary layer of fluid near the inner surface of the squar duct has temperature gradient, the main stream has no heat transfer. I do not know what happened. I tried to check all the mesh (quality is 0.9) and the boundary condition settings, but nothing can I found. There is a very confusing results: when all of the outer surfaces of the square duct are kept at constant heat flux, there is heat transfer in the main stream. Why with one face kept at constant heat flux, no heat transfer in air? Could you help me solve this problem? I am suffering this problem for quite a long time. Thanks very much for your kindly help.

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April 18, 2013, 07:35		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	Can you post an image of what you are modelling and the CCL?