A model of the rotary heat exchanger accounting for axial heat dispersion and longitudinal matrix conduction is developed. The heat conservation equations are solved using a finite difference approach. The heat exchanger effectiveness is then predicted and the effect of axial heat dispersion on the exchanger performance is studied. ;ij 1998 Published by Elsevier Science Ltd. All rights reserved. Nomenclature Ag cross-sectional fluid area for dispersion in a zone (with subscript) Ag* ratio of Ag, to Ag,, A,v cross-sectional matrix area for conduction in a zone (with subscript) AS* ratio of As, to As, C thermal capacity rate (with appropriate subscript) D fluid dispersion coefficient E, effectiveness without dispersion El effectiveness with dispersion hA heat transfer coefficient times area for a zone hA* ratio of hA, to hA,,, k matrix thermal conductivity L matrix length NTU no. of fluid transfer units (with subscript) NTCIo no. of overall transfer units Pe-' overall fluid Peclet number Pe, ' overall matrix Peclet number R matrix radius r fluid temperature, dimensionless T matrix temperature, dimensionless z length coordinate z* dimensionless length coordinate, z/L. Greek symbols 8" zone n dispersion parameter