Experimental investigation into heat transfer performance of water-based magnetic hybrid nanofluids in a rectangular cavity exposed to magnetic excitation

Abstract

This paper addressed the scarcity of experimental studies on the duo effect of magnetic excitation and hybrid nanofluid on the thermo-convection characteristics in enclosures. Novel Fe2O3-MWCNT (80:20)/deionized water (DIW) nanofluids with volume concentrations (φ) of 0.05–0.4 vol% were employed in a rectangular cavity exposed to magnetic excitation (4.89–21.95 mT) to examine the thermo-convection heat transfer behavior. The prepared hybrid magnetic nanofluids (HMNFs) were characterized for their stability, viscosity, thermal conductivity, and morphology. The DIW and stable HMNFs were charged into the cavity and differentially heated at ΔT of 20–35 °C under steady conditions. The results showed that without magnetic excitation, the average Nusselt number (Nuav) were observed to augment as Rayleigh number (Ra) and ΔT increased. Nuav and average heat transfer (Q̇av) were augmented for φ ≤ 0.2 vol% but they depreciated with φ > 0.2 vol% when compared with DIW. As the viscosity of HMNFs and φ increased heat transfer was noticed to depreciate. At ΔT = 35 °C, highest Nuav (11.33%) and Q̇av (11.21%) were achieved with φ = 0.05 vol%. With the magnetic excitation of 4.89–21.95 mT applied to the bottom, side (vertically and horizontally) and top (perpendicular and parallel to ΔT direction) walls of the cavity containing 0.05 vol% HMNF at ΔT = 35 °C, Q̇av was enhanced by 0.86%–1.46% and 1.72%–5.02% for the bottom and side walls when compared with the case of no magnetic excitation. Highest Q̇av (2.69%–5.02%) was recorded when the magnetic excitation was applied vertically on the side wall. Conclusively, the obtained results were observed to be strongly related to φ, ΔT, strength of magnetic excitation, use of HMNFs, position, and configuration of magnetic excitation.