Experimental investigation of heat transfer, thermal efficiency, pressure drop, and flow characteristics of Fe3O4-MgO magnetic hybrid nanofluid in transitional flow regimes

This study investigates the heat transfer characteristics of Fe 3 O 4 -MgO/DIW Magnetic Hybrid Nanofluids (MHNFs) compared to deionized water (DIW) across turbulent, laminar and transition flow regimes. Results reveal that the transition of MHNFs begins at significantly higher Reynolds numbers than DIW, contradicting previous findings. This disparity may be due to the specific characteristics of MHNFs, such as altered thermal conductivity and viscosity. Heat transfer results demonstrate enhancement within the fully developed transition regime, with improvements observed for MHNF concentrations from 0.3 to 0.00625 vol%. Volume fraction significantly impacts nanofluids' convective heat transfer characteristics, with higher volume fractions corresponding to higher critical Reynolds numbers. Even at 0.00625 % vol, the transition begins at a lower Reynolds number than DIW. The maximum enhancements in heat transfer were 26 % for 0.3 vol%, 25.8 % for 0.2 vol%, 25.7 % for 0.1 vol%, 17.9 % for 0.05 vol%, 25.6 % for 0.025 vol%, 31.6 % for 0.0125 vol%, and 30.2 % for 0.00625 vol% MHNFs. The optimum enhancement was observed with MHNF concentrations of 0.0125 vol% and 0.00625 vol%. Higher volume fractions led to increased pressure drops, indicating a complex interplay between fluid dynamics and nanofluid properties. The study highlights notable enhancements in thermal efficiency across transition and laminar flow regimes. • Transition at higher Reynolds numbers for MHNFs (Fe 3 O 4 -MgO/DIW) begin at higher Re than DIW, contradicting previous findings. • Highest enhancement of 31.6 % observed at 0.0125 % vol in the transition regime. • Higher volume fractions lead to higher critical Re; even 0.00625 % vol starts transitioning at a lower Re than DIW. • Higher volume fractions result in increased pressure drops, highlighting the trade-off between thermal efficiency and pressure drop.