# Convective heat transfer using Fluent

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 August 27, 2015, 04:22 Convective heat transfer using Fluent #1 New Member   Lamboram Join Date: Jul 2011 Location: Munich Posts: 16 Rep Power: 8 Sponsored Links Hello all, I am starting to work with Fluent for convection heat transfer (Natural convection) between a solid which is generating heat and a surrounding volume of air (the volume is fixed). I have tried two methods so far 1. defining these two bodies as a single part and by doing so I get a conjucate mesh on the boundry (between solid and fluid) 2. deining these two bodies as a individual parts, the individual faces of the solid as a named selection, upon updating it in Fluent I get respective shadow walls. Now, in both cases I have no success so far. I know there is a problem in wall BC definition. Now I have the basic settings right. Can you tell me some material where I could understand the wall BC definitions better. one more question. I have worked relatively a lot in Ansys Thermal, can I model the fixed volume of air around the body as a 3D Model and simulate it in FEM? Will it make good sense? because the air in our case is not moving around and the volume might also be same because its a closed environment. Looking forward your suggestions! Ram

 August 27, 2015, 12:22 #2 Senior Member   Lucky Tran Join Date: Apr 2011 Location: Orlando, FL USA Posts: 1,879 Rep Power: 26 Method #2 is the correct way. You should have two cell zones, one for the solid and one for the fluid. You should have a coupled wall (an interface) between at the solid-fluid boundary. A shadow wall will be automatically generated when you create this coupled wall. There are no boundary conditions on this interface (it is not a boundary). You need to specify the correct heat generation rate in your solid domain. Then finally you need to specify sensible boundary conditions for the outside of the fluid domain. Air is moving if it's natural convection, it's driven by density gradients instead of being forced but it is still a type of bulk motion. If you have truly stagnate problem then you could treat it as a solid body but you should confirm first whether or not you expect there to be any bulk motion.

September 2, 2015, 05:13
Thanks
#3
New Member

Lamboram
Join Date: Jul 2011
Location: Munich
Posts: 16
Rep Power: 8
Thanks LuckyTran,

I ran a simulation with reasonable results with the Method #2. You are right regarding the air bulk. I think it is sensible to simulate using the CFD method. But I have simulated using Pressure-based. I am running one using Density-based now. I will compare the results and keep you posted.

Do you know any materials where I can read in detail about these walls (Shadow, interface, coupled)?

Cheer,
Ram

Quote:
 Originally Posted by LuckyTran Method #2 is the correct way. You should have two cell zones, one for the solid and one for the fluid. You should have a coupled wall (an interface) between at the solid-fluid boundary. A shadow wall will be automatically generated when you create this coupled wall. There are no boundary conditions on this interface (it is not a boundary). You need to specify the correct heat generation rate in your solid domain. Then finally you need to specify sensible boundary conditions for the outside of the fluid domain. Air is moving if it's natural convection, it's driven by density gradients instead of being forced but it is still a type of bulk motion. If you have truly stagnate problem then you could treat it as a solid body but you should confirm first whether or not you expect there to be any bulk motion.

 Tags ansys thermal, cfd, fluent, natural convection, wall boundary conditions

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