Experimental study on the heat transfer and flow properties of γ-Al2O3/water nanofluid in a double-tube heat exchanger

Double-tube heat exchanger is primarily adapted to high-temperature, high-pressure applications due to their relatively small diameters. An experimental study performed to investigate the effects of Al2O3/water nanofluid on the hydrodynamics and convective heat transfer of a counter flow double-tube heat exchanger. The nanofluid was used as hot fluid and passed through the inner tube of the heat exchanger considering fully developed turbulent flow regime. Experiments were conducted at the nanofluid flow rates of 7, 9, and 11 L min(-1), nanofluid inlet temperatures of 45, 55, and 65 A degrees C, and dilute nanoparticle concentrations of 0.05 and 0.15 vol%. Local convective heat transfer coefficient in double-tube heat exchanger has been measured experimentally for the first time. Results showed that nanofluids had higher Nusselt number than pure water. Also, the Nusselt number increased by increasing particles volume fraction, flow rate as well as temperature of nanofluid. However, increasing the convective heat transfer coefficient of the nanofluids was not sensible with increasing the concentration. In addition, the ratio of the heat transfer coefficient of nanofluid to that of the base fluid decreased by increasing Reynolds number. Adding gamma-Al2O3 nanoparticles to the base fluid increased the friction factor. In this study, the greatest enhancement in the heat transfer coefficient and the friction factor obtained at 0.15 vol% concentration of nanoparticles which were 23 and 25 %, respectively.