The particular solution we are trying to calculate is a natural convection problem in an enclosed space. We are primarily concerned with solution convergence in a sub-region/sub-domain of the solution which is around the area of interest. I have been trying to follow the equations given in the Definition of Residuals for the Pressure-Based Solver section (28.15.1.1 in ANSYS 18.2), and exporting the relevant data to post-process in another application. It appears, however, that in order to calculate the globally scaled residuals, I need the cell center coefficient for each cell. I have been unable to find a way to export this coefficient or export the variables that calculate it (a_nb, b). What is the best way to either get this cell center coefficient value from Fluent or to generally calculate the scaled residual for a sub-region of the solution?

Using ANSYS 18.2 on Windows 10, 64-bit machine.