Improvement on device performance in multi-pass heat transfer through a parallel-plate channel with external recycle

A new external-recycle device of multi-pass heat exchangers with uniform wall temperature, resulting in a considerable heat-transfer efficiency improvement, has been designed and studied theoretically. The theoretical analysis on the temperature profile and heat-transfer efficiency improvement has been developed by using an eigenfunction expansion in power series. The analytical predictions are represented graphically and compared with that in single-pass devices and the previous work [C.D. Ho, H.M. Yeh, Y.C. Tsai, Improvement in performance of multi-pass laminar counterflow heat exchangers with external refluxes, Int. J. Heat Mass Transfer 45 (2002) 3529–3547]. A substantial heat-transfer efficiency improvement is obtained by employing such a new recycle type with a suitable adjustment of the impermeable-sheet position and recycle ratio, instead of using the single-pass device without external recycle for Gz>10Gz>10 and the recycle type of the previous study for Gz>30Gz>30.