Hi,

Recently I am running a model to study the heat transfer effect. The model is a hot object in a room. The B.C. for the hot object is fixed temperature, the B.C. for the room surfaces is 0 heat-flux. The s2s radiation model is on. After I got the result, I found the convection heat transfer is extremely high. The wall.-func.-heat-trans.-coeff. is couple of hundreds at many surfaces. If I turn off the rad model, the wall.-func.-heat-trans.-coeff. is back to normal (10~100). Could anybody tell me what's the reason that the wall.-func.-heat-trans.-coeff becomes so high after the radiation model is on? Thanks very much.

D. L.

Hi!

I am modelling a production hall with hot mashines in it, I think the problem is comparable to yours. But I use a heat-flux B.C. for the machines. What I found out is that without using a radiation model, the surface temperatures of the machines are much higher than with using radiation. So if you use a fixed temperature B.C., the heat flux with radiation will be much higher than without radiation, which results in a higher heat transfer coefficient. Have you tried other radiation models than s2s?

The variable "wall func. heat trans. coeff." depends on T*, a dimensionless temperature. T* depends of the heat flux at the wall. Look at the equations in the user guide, you should find an answer to your question. For my version (6.3.26) the variable "wall func. heat trans. coeff." is define here: "30.4 Alphabetical Listing of Field Variables and Their Definitions" and T* is define here: "12.10.2 Standard Wall Functions"

check the reference values (i suffered from same problem but with some other context)(and i hope you have calculated you are calculating/reading shape factors) your case looks to be natural convection the value 10-100 itself is objectionable

research scholar ashish