Experimental investigation of optimum thermal performance and pressure drop of water-based Al₂O₃, TiO₂ and ZnO nanofluids flowing inside a circular microchannel

This paper presents thermal performance and pressure drop characteristics of water-based nanofluids flowing through a horizontal circular microchannel under the constant surface temperature condition, experimentally. Al₂O₃ (13 nm), TiO₂ (10–25 nm) and ZnO (18 nm) nanoparticles with 0.5, 0.7 and 1.0% volume concentrations were used in order to prepare nanofluid. The thermal conductivity and viscosity values needed for the calculations were obtained by measuring separately. For the experiments, the microchannels made by both the different materials (Stainless steel, PEEK) and the different inner diameter (400, 750, 1000 μm) were tested for the different surface temperatures (283, 298, 313 K). In the tests, the nanofluids had the different inlet temperature (323–333 K), the volume flow rates (20, 35, 50 mL min⁻¹) and the concentrations. Heat transfer rate, Nusselt number, pressure drop and friction factor results were calculated. The optimum conditions were determined by using Taguchi approach. The thermal performance and the pressure drop of the fluids were compared. The results showed that the best thermal performance was obtained for Al₂O₃ nanofluid with 1.0% vol. concentration. A heat transfer enhancement of 15.3% was achieved using nanofluid instead of deionized water as the base fluid. Moreover, it has been seen no considerable pressure drop.