Effects of uniform magnetic induction on heat transfer performance of aqueous hybrid ferrofluid in a rectangular cavity

Abstract

Utilization of hybrid nanoparticles to formulate nanofluids is one of the ways to improve nanofluids’ thermal and fluid properties. This work attempted to study the free convection heat transfer performance of aqueous Fe2O3-Al2O3 (75:25) nanofluids in a rectangular cavity under magnetic induction. The thermal properties of the aqueous hybrid ferrofluids (AHFs) were measured for volume concentrations of 0.05–0.3 vol% and temperatures of 20–40 °C. Also, the stability and morphology of AHFs were examined. On charging the AHF and base fluid samples into the cavity, the two opposite vertical walls were subjected to temperature gradients ranging from 20 to 35 °C to create buoyancy. Parameters such as Nuav, hav, Ra and Qav were determined for each AHF sample and the base fluid. The AHF with the highest heat transfer performance was exposed to magnetic induction to investigate its convective heat transfer. With Ra range of 1.65 × 108–3.80 × 108, the Nuav was observed to intensify with increasing Ra. Without the magnetic induction, the improvements in hav, Nuav, and Q̇av were observed for 0.05–0.2 vol% AHFs in comparison with the base fluid. Optimum heat transfer enhancement of 10.79% was achieved for 0.10 vol% HF at ΔT = 35 °C. By inducing magnetic field (118.4 G) vertically on the side wall of the cavity, a maximum enhancement of Nuav (4.91%) was achieved compared to the case without magnetic induction. Additionally, increasing the magnetic field strength (48.9–219.5 G) was noticed to further enhance heat transfer of 0.10 vol% AHF. Correlations were proposed for predicting viscosity, thermal conductivity and Nuav of AHF in a rectangular cavity. The use of hybrid nanofluid was revealed to have better heat transfer performance than mono-particle nanofluids. Conclusively, the heat transfer performance was observed to depend on φ, ΔT, AHF deployment, magnetic induction, strength and direction.