Experimental investigation of natural convection Al₂O₃-MWCNT/water hybrid nanofluids inside a square cavity

ABSTRACT

The use of nanofluids for convectional heat transfer has become a spry area of research in recent years with the aim of improving heat transfer efficiency. Hybrid nanofluids have attracted significant attention and are advancing research and industrial applications since they involve employing more than one type of nanoparticle(s) in a base fluid. They enhance heat transfer by combining the chemical and physical properties of several nanoparticles concurrently and providing the properties in a homogeneous state. However, few experimental studies have focused on natural convective heat transfer using hybrid nanofluids. In this study, the natural convection of alumina – multiwalled carbon nanotube/water hybrid nanofluids formulated using a two-step method at a percentage weight ratio of 10:90 Al₂O₃: MWCNT at various nanoparticles volume concentrations of 0.00, 0.05, 0.10, 0.15, and 0.20 vol% was studied inside a square cavity (AR = 1) 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 (Nu_av), heat transfer coefficient (h_av), heat transfer (Q_av), 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 h_av,Q_av, and Nu_av. 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 44%, 49%, and 42% were noted for h_av,Q_av, and Nu_av, respectively, at ∆T = 50 °C, in comparison with the base fluid. Al₂O₃-MWCNT/water hybrid nanofluids application in a square cavity demonstrated enhanced natural convection. This present study concluded that hybrid nanofluids as heat transfer fluid significantly improved heat transfer performance compared to the base fluid.

KEYWORDS:

• Hybrid nanofluids
• heat transfer enhancement
• natural convection
• cavity flow
• convective heat transfer

Highlights

• Heat transfer performance of Al₂O₃-MWCNT/deionized water hybrid nanofluids is investigated.

• Hybrid nanofluids were prepared at various volume concentrations.

• Reduction in Ra as both the thermal conductivity and viscosity of the hybrid nanofluids increased.

• Maximum heat transfer enhancement of 43.98% was recorded at φ =0.10 vol%

Nomenclature

Table

Acknowledgments

The authors acknowledge the financial support provided by the Durban University of Technology and appreciate Prof Josua Meyer, Prof Mohsen Sharipfur, Dr Suseel Krishman, and Mr Modaser Momin of the Nanofluids Research Laboratory at the University of Pretoria for the use of the laboratory and their technical support during the experiments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Durban University of Technology [Emerging Researchers’ Grant].