Experimental investigation of magnetic hybrid nanofluids for enhancing heat transfer in forced convection internal flow through transition and turbulent regimes

Abstract

Efficient heat transfer is critical for optimizing the performance and safety of industrial and engineering systems. While nanofluids have demonstrated Outstanding heat transfer efficiency juxtaposed to deionized water (DIW), the exploration of Magnetic Hybrid Nanofluids (MHNFs) in forced convection heat transfer within transition and turbulent flow regimes remains limited. This study investigates the thermal and hydrodynamic characteristics of MHNFs, specifically Fe_3 O_4/TiO_2, Fe_3 O_4/MgO, and Fe_3 O_4/ZnO, flowing through a heated pipe. The research examines their performance across laminar, transition, and turbulent flow regimes, with suspension concentrations between 0.00625% and 0.3%. The study was conducted in four phases, addressing critical aspects of MHNFs stability, thermophysical properties, and heat transfer dynamics under varied conditions. In the first phase, the effects of hybridization mixing ratio (HMR), nanoparticle size, and temperature on the stability and thermophysical properties of Fe_3 O_4/TiO_2-DIW, Fe_3 O_4/MgO-DIW, and Fe_3 O_4/ZnO-DIW were evaluated. Results showed that Fe_3 O_4/ZnO-DIW at an 80:20 HMR demonstrated the highest thermal conductivity enhancement (31.28%) and lowest viscosity at 50°C, achieving the best thermal conductivity-viscosity balance. Fe_3 O_4/TiO_2 (18 nm)-DIW exhibited the highest electrical conductivity (4.23 mS/cm) at 50°C. Temperature emerged as the most influential factor on thermal conductivity, emphasizing the potential of MHNFs for advanced cooling applications, such as in proton exchange membrane (PEM) fuel cells. The second phase analysed the heat transfer capabilities of Fe_3 O_4/TiO_2 fluids across Reynolds numbers and volume fractions. Significant improvement in the convective heat transfer coefficient (CHT) were observed, particularly at lower concentrations; at 0.3 vol.% is 11.42% , at 0.2 vol.%, is 14.03% , at 0.1 vol.% is 18.04%, at 0.05 vol.% is 19.98%, at 0.025 vol.% is 22.91%, peaking at at 0.0125 vol.% is 26.33%, and at 0.00625 vol.% is 24.30%. at 0.3 vol.% (21% at Reynolds number 5019) the pressure drops were highest and progressively reduced with lower concentrations: 13.10% at 0.2 vol.%, 11.94% at 0.1 vol.%, 9.82% at 0.05 vol.%, and minimal at 0.0125% and 0.00625 vol.%. The Total Efficiency Index (TEI) was maximized at 0.0125 vol.%, indicating the optimal balance between heat transfer enhancement and minimal hydraulic resistance. The third phase focused on Fe_3 O_4/MgO MHNFs, revealing unique thermal transport behavior in the transition region. Results indicated delayed transition at higher Re juxtaposed to DIW. The thermal transport enhancements were observed across volume fractions, with increases of 26% at 0.3 vol.%, at 0.2 vol.% is 25.8%, at 0.1 vol.% is 25.7%, at 0.05 vol.% is 17.9%, at 0.025 vol.% is 25.6%, at 0.0125 vol.% is 31.6%, and at 0.00625 vol.% is 30.2%. Optimal performance was achieved at 0.0125% and 0.00625 vol.%. However, higher concentrations resulted in increased pressure drops, demonstrating the intricate relationship between fluid dynamics and thermophysical characteristics. In the final phase, the effects of magnetic field strength and waveforms parameters were investigated for Fe_3 O_4/TiO_2 nanofluids. Magnetic waveforms sine, square, and triangular enhanced heat transfer, with increases of 27.87%, 28.21%, and 26.74%, respectively, at 0.0125 vol.%. Magnetic field frequency (40 Hz to 1000 Hz) and voltage (2V to 12V) demonstrated a direct correlation with thermal performance, with optimal results achieved at 60 Hz and 4V. These findings advance the understanding of MHNFs in forced convection heat transfer, offering practical insights for thermal management in power generation, HVAC systems, and chemical processing. The demonstrated ability of MHNFs to optimize heat transfer efficiency while minimizing pressure losses at lower concentrations presents a promising avenue for improving energy efficiency in heat exchangers and thermal systems.