There are two design methods of Compact Heat Exchangers (CHE)(eg Tube, Tube-fin, Plate or Plate-fin Heat Exchangers):
1) Rating or performance method: the CHE are fully given (sizes, arrangements, shape of the surfaces, etc.)and the designer is looking for the performances (Power, Pressure Drops) at the nominal flow rates, and inlet temperatures.
2) Sizing or design method: the inputs are the flow rates, the primary (or secondary) inlet-outlet temperatures, the outputs are the sizes, the arrangements, etc. Even if the "Design Method" seems more appropriate and straigth on, the "Rating Method" is preferable because it is faster, when the designer has a little of experience.
See: R. K. Shah, "Heat Exchangers Design Methodology - An Overview" and "Compact Heat Exchangers Design Procedures", in Heat Exchangers, Hemisphere Pub. Corp., 1981.