Investigation of turbulent flow and heat transfer in an air to water double-pipe 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 are air, flowing in the annular pipe, and water through the inner circular tube. To achieve 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 pipe can be considered adiabatic. The experiments are conducted in the range of water flow rate (water inlet velocity) from 120 to 200 (L/h) and temperature of water in upper tank range (water inlet temperature) from 70 to 90 °C. Correlations for Nusselt number and friction factor are presented according to experimental data. Results show that velocity boundary layer thickness in air side increases with increase in the water inlet temperature and water flow rate. Nusselt number in water side is an increasing function of water inlet temperature, and water inlet temperature while opposite tend is observed for Nusselt number in air side.