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Title: Experimental investigation on natural convection of hybrid-water nanofluids in cavity flow
Authors: Scott, Temiloluwa Olatunji 
Keywords: Heat transfer;Volume concentration;Hybrid nanofluids;Natural convection;Cavity flow;Convective heat transfer
Issue Date: May-2023
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.
A thesis submitted in fulfillment of the academic requirements for the degree of Master of Engineering: Mechanical Engineering, Durban University of Technology, Durban, South Africa, 2022.
Appears in Collections:Theses and dissertations (Engineering and Built Environment)

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