Design of Multipass Heat Exchangers: An Alternative Approach

Multipass heat exhangers are often designed according to the reule of thumb F{sub T} {ge} 0.75. The F{sub T} correction factor is usually correlated in terms of two dimensionless ratios, the thermal effectiveness of the exchanger (P) and the ratio of the two heat capacity flow rates (R). This criterion can give rise to poor designs. It is the slope of ({partial derivative}F{sub T}/{partial derivative}P){sub R} that is important, not just the absolute value of F{sub T}. Furthermore, in multishell arrangements, the number of shells required is usually evaluated by trial and error. This paper introduces an approach based on a new parameter that is an alternative to F{sub T} factors. The method is fully compatible with established design practice, takes accoutn of the F{sub T} slope, and evaluates the number of shells explicitly in multishell cases.