[@nkur]

Sir, I am new to ansys
Instead of modeling complete shell and circular finned tube heat exchanger consisting of number of tube rows in both horizontal and vertical directions, i have modeled only a small 3D portion of it considering its symmetry and carried out the simulations. I have considered air as fluid on the shell side and given constant temperature for the tubes.

Now should i calculate the different dimensionless nos such as Reynolds Nusselt etc. and hydraulic diameter ( focussing on the shell side) for that small 3D portion only or should i consider the whole heat exchanger for calculating those things