Thermal management of double-pipe air to water heat exchanger

In this study, turbulent flow and heat transfer in an air to water double-pipe heat exchanger is investigated experimentally. The working fluids were air, flowing in the annular pipe, and water through the inner circular tube. To attain fully developed conditions, the heat exchanger was built with additional lengths before and after the test section. The inner tube was made from copper. The external tube was made of an industrial plastic which was insulated from the environment. In this manner, the outer surface of the annular channel can be considered adiabatic. The experiments are conducted in the range of flow rate of water from 120 to 200 (L/h) and in the temperature of water in upper tank range from 70 to 90 °C. Correlations for Nusselt number and friction factor are presented for according to experimental data. Results show that velocity boundary layer thickness in air side increases with increase of the temperature of the water in the upper tank and flow rate of water on heat transfer. Nusselt number in water side is an increasing function of inlet temperature and inlet velocity of water while opposite tend is observed for Nusselt number in air side. Inserting agitator improves the rate of heat transfer. Enhancement of heat transfer has reverse relationship with Reynolds number.