UDF Outputs dont match exactly for volumetric heat generation.
 

I checked and crosschecked and backcalculated and everything.

I have a volumetric heat generation rate set as a function of coordinates. If I manually calculate the numbers (which I have set in the udf) I get say 10kW exact. But when it comes to udf, the total volume integral is only 9500W.

The contour plot makes sense. Heat balance is exact. But the 500W difference?

Anybody?

Are you calculating heat generation at the nodes or cell centres? What is the UDF you are using to calculate the volume integral?

Based on cell centres.

I have come to the conclusive assumption that this is the discretization error from the mesh?

The mesh would need to be quite coarse to be missing 5 % of the heat generation (try mesh refinement). What is the UDF you are using, are you sure it's calculating across the full volume?