Experimental investigation on natural convection of hybrid-water nanofluids in cavity flow

Abstract

The heating and cooling of fluid play a crucial role in many industries, such as transportation, electronics, and manufacturing; however, among other concerns like size, weight, and cost reduction of cooling and heating systems, heat transfer enhancement is a primary concern in many industrial applications. As a result, a large number of researchers have carried out numerous studies to find alternatives to enhance heat transfer. The research on nanofluids has proliferated in the past decade, and reports indicate that nanofluids can be used for heat transfer applications in engineering and in general and/or commercial industries. Nevertheless, a growing area of research in recent years has involved employing more than one type of nanoparticles in a base fluid, known as hybrid nanofluids. Studies showed that hybrid nanofluids exhibited improved rheological and thermal characteristics than single nanoparticle nanofluids. In this study, the natural convection of alumina – multiwalled carbon nanotube /water hybrid nanofluid formulated using a two-step technique at a percentage weight ratio of 10:90 Al2O3: MWNCT at various nanoparticles volume concentrations of 0.00, 0.05, 0.10, 0.15, and 0.20 vol% was studied inside a square cavity with two vertical walls which are isothermal, aimed at the Rayleigh number (Ra) range of 2.81 × 108 to 8.58 × 108 . The average Nusselt number (Nuav), heat transfer coefficient (hav), heat transfer (Qav), and Rayleigh number (Ra) were considered at varying temperature gradients of 20 °C – 50 °C. Al2O3- MWCNT/water hybrid nanofluid with 0.10 vol% volume concentration was discovered to have the maximum value for hav, Qav, and Nuav. However, it was also observed that a further increase in the hybrid nanoparticles' volume concentration led to their deterioration at various temperature gradients. The maximum enhancements of 43.98%, 49.27%, and 42.20% were noted for hav, Qav, and Nuav, respectively, at ∆T = 50 °C, in comparison with the base fluid. Al2O3-MWCNT/water hybrid nanofluid application in a square cavity demonstrated enhanced free convection. Several results from this study indicate that hybrid nanofluids offer an advantage over mono-particle nanofluids and base fluids.