about using the udf to impose dt/dz=0 boundary

FengYun

Dear All, Now I am using the FLUENT to simulate a case about the solidification process. I have read the FLUENT tutorial guide about the modelling solidification. In the example, a velocity inlet is used with the velocities pointing outwards as the boundary conditions for the outlet because the solid is pulled out with a specified velocity. In my case, it is like this but unfortunately the pulled Temperature is not a constant value and the turbulent model is used. I want to use the similar method and it seems that I need to write a UDF code to impose the boundary, the convective flux (i.e. dT/dx=0 for this case) is zero as the outlet boundary. Could you tell me how to write the udf code for the kind of boundary conditions? Thanks a lot in advance.