Second Law Analysis of Heat Exchangers

Abstract

This paper further explores the topic of an ideal heat exchanger, which is still an open question. It is shown that the minimization of entropy production or exergy destruction should not be an objective in heat exchanger design. It is further proven that heat exchanger effectiveness does not correlate with irreversibility. A new performance measure, entropy flux, is introduced and a general expression for its evaluation is presented. It is shown that entropy flux captures many desirable attributes of heat exchangers. For a given effectiveness, a single stream heat exchanger has the absolute maximum entropy flux, and for capacity ratios greater than zero, counterflow has the highest entropy flux, parallel flow the lowest, and the shell and tube heat exchangers are somewhere in between.