hi, We are simulating heat transfer in a stirred tank using Fluent5. The tank is heated from outside (walls). When the solution is obtained, the shaft and the impeller keep the same initial temeprature (since the are walls). Is there a way to make the heating process include the shaft and the impeller (non constant boundries) ? may be by using UDF (how?)? Best regards Mounir

You can use a UDF to make a varying boundary conditions. If you ask Fluent they will send you an example - one of their standard examples does just this.

You might also consider meshing the shaft and impeller and solve heat-conduction in those solids to represent the physics better. I don't know if this is what you want but it doesn't cost much and usually works very well.