The Effect of Longitudinal Heat Conduction on Periodic-Flow Heat Exchanger Performance

Abstract

A numerical finite-difference method of calculating the effectiveness for the periodic-flow type heat exchanger accounting for the effect of longitudinal heat conduction in the direction of fluid flow is presented. The method considers the metal stream in crossflow with each of the gas streams as two separate but dependent heat exchangers. To accommodate the large number of divisions necessary for accuracy and extrapolation to zero element area, use was made of a general purpose digital computer. The values of the effectiveness thus obtained are good to four significant figures while those values for the conduction effect are good to three significant figures. The exchanger effectiveness and conduction effect have been evaluated over the following range of dimensionless parameters. 1.0 ≥ Cmin/Cmax ≥ 0.901.0 ≤ Cr/Cmin ≤ ∞1.0 ≤ NTU0 ≤ 1001.0 ≥ (hA)* ≥ 0.251.0 ≥ As* ≥ 0.250.01 ≤ λ ≤ 0.32