The criteria utilized for determination of the number of passes in a heat exchanger relates to the basic thermal design. The mass-velocity of tube side fluid (sensible heating/cooling applications) directly determine the film coefficient. Once a reasonable velocity has been determined to give adequate heat transfer on the tube side, the total mass flow of tube side fluid, area required and tube length determine the number of passes required. There will be a correction to the standard LMTD calculation when the number of passes exceeds one. See Process Heat Transfer by Hewitt, Shires & Bott or Perry’s Chemical Engineers Handbook for references.