Hi

I have few queries
*I have design data of water-cooled condenser but it is for R-12 can I use it for R-22.
Also when I get surface area required for heat transfer should I calculate length by this formulae
Pi x dia x length x no of tubes x= surface area calculated

*2 we are designing shafts for fans and problem we are facing is fracture of shafts the material used for shaft is Mild steel and total static is 5.5 in wc. What uis reason for material failure. If we use carbon steel shaft will it solve problem?
*what is leak check method of air handling units(proper performa to be filled for test)?

Regards

Ali