Chapter 3 - Steady-state characteristics of heat exchangers

Abstract

The energy equations of the fluids are applied to different flow arrangements, leading to analytical expressions for the calculation of temperature changes in heat exchangers. The degree of performance is expressed with an effectiveness ɛ, defined as the ratio of actual heat load to maximal possible heat load. As a measure of heat exchanger size or potential, the number of transfer units NTU is used, defined with the lower capacity rate in this analysis. Analytical relationships between NTU and ɛ are given for the following flow arrangements: parallel and counterflow including the case of phase change in one fluid; shell-and-tube heat exchangers with one shell-side and one to four tube-side passes; one-pass unmixed-unmixed, mixed-unmixed, and mixed-mixed crossflow; various multipass crossflow arrangements; parallel and counterflow spiral plate heat exchangers; and plate-fin heat exchangers. Multistream arrangements are considered for plate heat exchangers, shell-and-tube heat exchangers, and plate-fin heat exchangers. Heat transfer and pressure drop correlations are also given for the previous constructions. To facilitate the application of the equations, five rating and sizing examples are presented.