Approximate solutions for metallic regenerative heat exchangers

An analytical model to calculate the temperature profiles and the effective ness of regenerative heat exchangers in counterflow is presented. It is lim ited to cases where the storage matrix has a small wall thickness so that n o temperature variation in the matrix perpendicular to the flow direction h as to be considered. This is usually the case for metallic matrices but can also be fulfilled for ceramic matrices in the form of a thin-wailed monoli th. Starting from a two-phase model for the gas and storage matrix an appro ximate solution is derived for the limiting case where the period of the ho t and cold process stream becomes infinitesimally small. Using series expan sions of this solution the equations to calculate the temperature profiles and the regenerator effectiveness are obtained. Contrary to already publish ed correlations the presented analytical approach considers the heat conduc tivity in the storage matrix parallel to the flow direction. The range wher e these equations can be applied is shown by comparing the approximate solu tion with a numerical solution of the complete set of governing dynamic ene rgy balance equations. The effect of important process parameters on the pe rformance of a countercurrent regenerative heat exchanger is discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.