calculation of cooling rate
 

I need to calculate cooling rate i.e. dT/dt. I suppose I need to write a udf for this as i couldn't find any variable for cooling rate predefined in fluent.

The simple formula I am thinking of applying is (T(x+1)-T(x))/time step. where, x is the position of node.
can anybody tell me how can i implement in a UDF. C_T(c,t) is used for getting the temperature at a particular cell in a particular thread.
But how can i get temperature values at cells adjacent to the cell?

Any Ideas?
Please guide.