liquid side pressure drop in finned tube

Dear all, good day,

FYI, I am currently doing some projects on finned tube heat exchanger where hot air is travel outside the fin and cool water is inside the tube. It is an air cooled water heated heat exchanger.


My question is that how we calculate the pressure drop of the water inside the tube which is usually measured in mmwg @ mmH2o?

Could any experts here show me the way/formula/equation to calculate it?or is there any link, pdf file that can share to help me in calculating the liquid side pressure drop for the finned tube?

Thank you very much