UDF to access interior surface to calculate mass flow rate
 

Hi All

I am working to adjust counter current boundary condition for an absorber model in which gas inlet is acting as liquid outlet.

I studied forum and conclude scheme to work for counter current boundary conditions that I should calculate mass flow rate of liquid near bottom boundary and then adjust my bottom boundary through this calculated mass flow rate.

problem I am facing that I could not access interior surface (that is actually a line in case of 2D geometry) thorugh UDF to calculate mass flow rate.

Can any body help to sort out this problem?