Recycle effect on heat transfer enhancement in double-pass heat exchangers under asymmetric isotherm conditions

The mathematical formulation of a heat transfer flow problem in the recycling parallel-plate heat exchanger under asymmetric wall temperatures was developed theoretically with ignoring axial conduction, and the analytical solution was obtained using a superposition principle and an orthogonal expansion technique in extended power series. The influences of the design parameters of the impermeable-sheet position (Delta), and the operating parameters of the Graetz number (Gz), wall temperature ratio (sigma) and recycle ratio (R) are examined. Significant heat transfer improvement is obtainable by employing double-pass devices instead of using single-pass ones for a larger Graetz number system. A technical feasibility of the new double-pass device was investigated in terms of the Nusselt number and device performance improvement under the effect of wall temperature ratios. (C) 2015 Elsevier Ltd. All rights reserved.