An experimental study on hydraulic and thermal performances of hybrid nanofluids in mini-channel A new correlation for viscosity of hybrid nanofluids

In the present work, the thermo-physical properties and hydraulic and thermal performances of alumina/water, silica/water, and alumina-silica/water nanofluids were experimentally investigated. The thermal conductivity and dynamic viscosity of nanofluids were measured for the volume fractions in the range of 0-2% and the temperature in the range of 10-40 degrees C. Some new correlations were proposed for the hybrid nanofluid. Single and hybrid nanofluids at the volume fractions of 0.05%, 0.1%, and 0.2% and the Reynolds number in the range of 490-3100 were tested in a mini-channel. Measurements of the thermo-physical properties indicated that the hybrid nanofluid provided larger values of the thermal conductivity and viscosity in comparison with the single ones. The results also showed that the Nusselt number increased with increasing the Reynolds number and volume fraction of the nanoparticles for all nanofluids. Hybrid nanofluid with 75% alumina-25% silica and volume fraction of 0.2% and the single alumina nanofluid with volume fraction of 0.2% provided the highest and the lowest increments in the Nusselt number with the mean increment values of 46% and 11%, respectively. The hydraulic performance assessment revealed that adding nanoparticles to the base fluid increased the friction factor in the mini-channel from 10.4 to 65.2% based on the values of the volume fraction. However, the thermal performance evaluation criteria are always above the unity regardless the type of the nanofluid and among the nanofluids considered in this study, and the maximum performance evaluation criterion was recorded for the hybrid nanofluid with the value of 1.23 at volume fraction of 0.2%.