Effect of Plate Characteristics on Axial Dispersion and Heat Transfer in Plate Heat Exchangers

Abstract

A new mathematical model of singleblow transient testing technique is proposed for the determination of heat transfer and dispersion coefficients in plate heat exchangers (PHEs) in which the flow maldisrtibution effects are separated from the fluid backmixing. The fluid axial dispersion is used to characterize the backmixing and other deviations from plug flow. Singleblow experiments are carried out with different number of plates for various flow rates with three different plate geometries of 30 deg, 60 deg, and mixed (30 deg/60 deg) chevron angles. The outlet temperature response to an exponential inlet temperature variation is solved numerically using finite difference method. In the present work, the whole curve matching technique is used to determine the values of Nusselt number and dispersive Peclet number. Since the maldistribution effects are separated, these data are independent of test conditions and hence using a regression analysis, general correlations are developed for Nusselt number and Peclet number of the present plate heat exchangers. The applicability of the singleblow test data is validated using a twofluid experiment. Twofluid experiments are conducted on the same plate heat exchanger with smaller and larger number of plates and the results have been compared with its simulation which used the Nusselt number and Peclet number correlations developed by the new model of singleblow test as the inputs.