Convective and Radiative heat B.C. in Free surface modelling during solidification
 

I am trying to model solidification in an ingot. I am using a multiphase model with air and molten metal. I need to define the top surface as a free surface thus i did define the top surface as a pressure outlet boundary condition with 0 gauge pressure.

but now i need to define certain thermal boundary conditions also, such as convective and radiative heat loss from top of the melt. There isn't any option regarding that in fluent.
what can i do in this case? Do i have to write a udf for that?