Experimental studies on the heat transfer characteristics of alumina/water nanofluid inside a helical coil tube

Laminar convective heat transfer and pressure drop characteristics of Al2O3-water nanofluid were experimentally investigated inside a horizontal Helical-Coil Tube (HCT) under constant heat flux boundary conditions for Dean numbers between 400 and 1600. The experiments have been performed using Al2O3-water nanofluid of three mass concentrations and heat fluxes at different flow rates. Thermal conductivity and viscosity of the fluids are measured experimentally, and a proper agreement was observed with the new model predictions for thermo-physical properties of nanofluids. Based on the experimental results, the thermal conductivity and viscosity of Al2O3-water nanofluid were almost 2.12% and 3.1% higher than water in 1 wt% concentration. According to the observations, the heat transfer coefficients in the fully developed region increases by 6.4%, 19%, and 23.7% under 2283, 3774, and 4975 W/m(2)heat fluxes, respectively, at 1 wt% concentration of Al2O3-water nanofluid with respect to pure water.Besides, it has been noticed that pressure drop through the helical coil is increased with adding nanoparticles, enhancement of heat flux, and De number. Finally, based on the thermal performance factor, it has been concluded that using nanofluids in the helical coil is a feasible method for improving energy efficiency.