Thermal Design Theory of Three-Fluid Heat Exchangers

The thermal and hydraulic design theory of a direct-transfer-type two fluid heat exchanger (tubular, plate-type, and extended-surface exchangers) is well developed and is available in standard heat transfer literature. The well-established algorithm for thermal design of a two-fluid heat exchanger, however, has no adequate equivalent when the physical situation implies more than one thermal communication. This chapter outlines only the effectiveness- NTU (number of heat transfer units) approach and corresponding rating and sizing problems for the determination of the effectiveness or NTU for a three-fluid heat exchanger. The thermal design theory of multifluid heat exchangers (having more than three-fluid streams) and multistream plate-fin heat exchangers and the study of nonlinear problems are not considered in this chapter.