A GENERAL ANALYTICAL APPROACH FOR DEFINING EFFECTIVENESS IN IDEAL TWO FLUID HEAT EXCHANGERS

摘要

A general analytical development, based on the first and second laws of thermodynamics, is used to define the maximum possible heat transfer in an ideal two-fluid exchanger as well as the maximum possible temperature differences for both fluid streams. It is shown that the conventional expression for the maximum possible heat transfer in ideal two-fluid heat exchangers is a special case of the general expressions. The application of both the first and second laws of thermodynamics in defining the maximum possible heat transfer and maximum possible temperature difference provides only one expression (instead of two different expressions) for either stream which is a measure of both thermal and temperature effectiveness of the particular stream. Differences between the conventional and proposed effectiveness values are presented as functions of the capacity ratio and NTU. These data are used to demonstrate the advantages of the new definitions for maximum heat transfer and maximum temperature difference in ideal two-fluid heat exchangers.