Source term UDF including face area
 

I am working on developing a UDF in an axisymmetric configuration for the following source term within an Eulerian flow for liquid phase. The source term acts as a mass sink in a specific zone.

S=-(rhol*alphal*ux,l)/(delta x)-(rhol*alphal*vr,l)/(delta r)-(rhol*alphal*vr,l)/(r)

Source term is defined at the cell level, but I need to consider delta r and delta x which act on a face. Can you help me figure out how to add delta x and delta r to my code?

Thank you