How to calculate flux across the patch
 

Hello.

My field variable is a scalar (concentration). I need to calculate the flux (which is -grad(C)) across one of the patches. I could use patchIntegrate utility for integration over the patch but I need gradient field for that.

foamCalc utility can calculate div(U) but only for vector fields. Is there a way to automatically calculate the field of gradients having the field of scalar?

Thank you,
Eugene