Water-to-water heat transfer in tube-tube heat exchanger: Experimental and analytical study

Tube-tube heat exchanger (TTHE) is a low cost, vented double wall heat exchanger which increases reliability by avoiding mixing of fluids exchanging heat. It can be potentially used for heat recovery from engine cooling circuit, oil cooling, desuperheating in refrigeration and air conditioning, dairy, and pharmaceutical industry, chemical industry, refinery, etc. These tube-tube heat exchangers are successfully demonstrated for superheat recovery water heating applications, condenser and evaporator in heat pumps, lube oil cooler for shipboard gas turbines, milk chilling and pasteurizing application. This paper presents an experimental study on various layouts of TTHE for water-to-water heat transfer. The theoretical and experimental results on this type of heat exchanger configuration could not be located in literature. Overall heat transfer coefficient and pumping power were experimentally determined for a fixed tube length and surface area of serpentine layouts with different number of bends and results are compared with straight tube TTHE. In the case investigated, serpentine layout TTHE with seven bends has shown optimum performance, with overall heat transfer coefficient 17% higher than straight tube TTHE. Two out of five serpentine layout TTHE have shown poor heat transfer performance than straight tube TTHE. The experimental results also indicate that there is a definite optimum for a number of bends in serpentine layout TTHE. An analytical model for prediction of thermo-hydraulic performance of straight layout has been developed and validated experimentally. (c) 2005 Published by Elsevier Ltd.