Experimental study of thermo-convection performance of hybrid nanofluids of Al2O3-MWCNT/water in a differentially heated square cavity

Abstract

Hybrid nanofluids as a new class of nanofluids known for their improved thermal and flow properties over single-particle nanofluids. However, experimental studies on the natural convection of hybrid nanofluids in enclosures are very scarce in the public domain. This paper investigates the natural convection of Al2O3−MWCNT/water nanofluids at various bi-nanoparticles’ percent weights (Al2O3:MWCNT; 80:20, 60:40, 40:60, and 20:80) for 0.1 vol% in a square cavity. The Nuav, hav, Ra and Qav at varying temperature gradients (20 °C–50 °C) were considered. The viscosity and thermal conductivity of the stable nanofluids and base fluid were experimentally measured at a temperature range of 20 °C–50 °C. The obtained experimental data for these properties were engaged in the study. The range of Ra considered in this work was 1.65 × 108–3.80 × 108. A direct relationship was noticed between Ra and Nuav. Temperature gradient and percent weight of bi-nanoparticles in the nanofluids were observed to augment Nuav, hav, and Qav. The hybrid nanofluid with 60:40 wt% of Al2O3 and MWCNT nanoparticles was identified to have the highest value for Ra, Nuav, hav, and Qav at various temperature gradients. Furthermore, maximum enhancements of 16.2%, 20.5%, and 19.4% were recorded for Nuav, hav, and Qav, respectively, at ΔT = 50 °C, in relation to the base fluid. The engagement of Al2O3−MWCNT/water nanofluids in a square cavity has shown improved natural convection performance. A new correlation as related to Ra and bi-nanoparticles ratio has been developed for predicting Nuav. Results from this study further corroborate the advantage afforded by hybrid nanofluids over single-particle nanofluids.