heat source on surface ??
 

i want to demonstrate the water flow inside a porous media under heat on the surface. i have only one cell which is porous. but in the cell zone condition, i can just choose for the source term or fixed values which make the cell zone heat averagely. but i want the heat is come from outside, which the center should remain the initial for quite a long time while the outer part of the cell should be nearly to the certain temperature. i just can't find a option to do this. do i need a UDF to do this? and may i ask how? thank you so much.