An analytical study of laminar counterflow double-pass heat exchangers with external refluxes

A new device of inserting an insulation sheet or an impermeable sheet with negligible thermal resistance to divide an open duct into two channels with uniform wall temperature and with external refluxes at the ends, resulting in substantially improving the heat transfer, has been studied and investi gated by an orthogonal expansion technique. The analytical results are repr esented graphically and compared with that in an open conduit of the same s ize without recycle. Considerable improvement in heat transfer is obtainabl e by employing double-pass operations with an impermeable sheet of negligib le thermal resistance instead of using double-pass operations with an insul ation sheet inserted and single-pass operations. The effect of sheet locati on on the enhancement of heat transfer efficiency as well as on the increme nt of power consumption, has been also discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.