Experimental investigation on thermo-hydraulic performance of water-based fly ash–Cu hybrid nanofluid flow in a pipe at various inlet fluid temperatures

The objective of the present work is to evaluate the experimental convective heat transfer coefficient and friction factor of the nanofluids flowing through a copper tube under a uniform heat flux of 7962 W/m². Water-based stable fly ash and fly ash– Cu (80:20% by vol.) hybrid nanofluids were used as working fluids in the concentration range of 0.5 to 2.0 vol%. Experiments in the Reynolds number range of 6800 to 45,200 were performed at fluid inlet temperatures in the temperature range of 30 to 60 °C. The findings suggest that compared to water and fly ash nanofluid, thermal conductivity, viscosity, and the heat transfer rate of hybrid nanofluid is higher. At fluid inlet temperature of 60 °C, the maximum Nusselt number augmentation for fly ash-Cu hybrid nanofluid is 15.6% and 93.5% was observed at a concentration of 2.0% compared to fly ash nanofluid and water, respectively. A maximum thermal performance factor of 1.65 and 1.87 is observed for fly ash and hybrid nanofluid respectively at 60 °C with a 2.0% volume concentration. Correlations for evaluating the Nusselt number and friction factor of hybrid nanofluid were developed with the experimental data.