Discussion Forum

Dear all,

I am having a general question about the boundary condition in natural convection. I am starting with a really simple 2-D model, one rectangular box set as high temperature metal, and outside is another box set as air at room temperature. I would like to see the temperature change when metal is set to 100 C and air is 20 C.

However, I find many ways to set boudary conditions in this case, for example: convective cooling, heat flux, inflow heat flux, and boundary heat source. To me, all the govening equations mentioned above are the same, because they all need to input heat flux amount or heat convection coefficient. It also works if I do not set any boundary condition between the air and metal, I guess the default setting may be heat conduction.

I am not able to set the boundary as "convective cooling" or "heat flux" when I was setting the material as air in the outside box. If I delete the air box, I am able to obtain a reasonable temperature distribution profile by choosing "air" and "external natural convection" in "convective cooling" condition.

Could anybody give me a introduction what is the difference between all these conditions I listed above, and what is the most appropriate one I should choose for a natural convection boundary condition between metal and air? Also, is there any difference between setting the air as "heat transfer in solid" and "heat transfer in liquid" if velocity is not given?

Thanks in advance!!!