Thermo-Hydraulic Performance Of Nanofluids Under Adjustable Magnetic Field

The effects of an adjustable magnetic field on convective heat transfer performance and flow resistance coefficient of water-based Fe3O4 nanofluids under varying Reynolds numbers (800-10,000) are experimentally investigated. Additionally, the effects of Reynolds number, mass fractions, magnetic field strengths, electromagnets arrangement modes and pitch curvature ratios are discussed. The obtained results indicate that the convective heat transfer performance is directly related to the mass fraction, magnetic field strength and pitch curvature ratio. The Nusselt number and friction resistance coefficient can be increased by 25.0% and 8.1% at best by the use of ferrofluid. The maximum enhancement ratio of heat transfer is 13.8% by increasing magnetic field strength. The spiral tube with P/D = 1.5 can improve the Nusselt number by 57.8% at best when compared with the spiral tube with P/D = 0.6. To effectively reveal the relation between convective heat transfer and flow resistance, a thermal efficiency index is applied to analyze the thermo-hydraulic performance of spiral tubes, thermal efficiency index decreases with Reynolds number in laminar flow, and then increases until reaching peak value at Re = 8000, finally decreases slightly. Our findings are useful for optimizing the enhanced heat transfer mechanism of ferrofluids and improving heat exchanger heat transfer efficiency.