Evaluation of thermal efficiency for heat regenerators in periodic operation by approximate methods

Abstract

Thermal efficiency of heat regenerators in periodic operation is one of the most important quantities to the designer and plant engineer. The current procedures for calculation of efficiency are model dependent numerical algorithms which require considerable computational time. In this work approximate formulae, applicable to all model types, have been developed for quick calculation, by algebraic means, of the regenerator efficiency in single pass, cocurrent or countercurrent operation. The formulae require only the knowledge of the variance of the impulse response of a model based on the assumed heat transfer mechanisms in the regenerator. A method is introduced for utilizing the representation of the regenerator thermal impulse response by a gamma probability density function in obtaining the solution and efficiency for cocurrent periodic operation. An analogy to countercurrent heat recuperators and the intergral of the impulse response are used to develop a formula for efficiency for the countercurrent case. The accuracy of the developed approximations is discussed and shown to be well within the accuracy of the parameters of the system.