An experimental system is established to investigate the thermo-hydraulic performance of Fe3O4-water nanofluids in a corrugated tube under various magnetic fields. The influences of magnetic induction intensities (B=0 G, 100 G, 200 G, 300 G), nanoparticle mass fractions (ω=0.0%, 0.1%, 0.3%, 0.5%), electromagnet arrangement modes (one-side electromagnet and two-side staggered electromagnet), kinds of tubes (smooth tube and corrugated tube), Reynolds numbers (Re=800-12000) on flow and heat transfer characteristics are discussed. It is obtained that the augmentation of heat transfer is more sensitive to high nanoparticle mass fraction, high magnetic induction intensity, two-side staggered electromagnet and corrugated tube. A Comprehensive evaluation index is applied to estimate the thermo-hydraulic performance. It can be discovered that the comprehensive evaluation index increases with the increasing Reynolds number at first and then decreases, and the rough surface of corrugated tube delays the appearance of critical Reynolds number.

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Convective heat transfer and resistance coefficient of nanofluids upward flowing through helical tubes are experimentally researched in this paper.The effects of three factors (thread pitches [s = 10, 12.5, and 15 cm], inclination angles [β = 0°, 45°, and 90°], and nanoparticle mass fractions [ω = 0.0, 0.1, 0.3, and 0.5 wt.%]) on the heat transfer and flow characteristics are discussed. A thermal efficiency evaluation plot is applied to evaluate the thermo-hydraulic performance of nanofluids. Results show that Nusselt number and resistance coefficient increase with the increasing nanoparticle mass fraction and the decreasing thread pitches. It is also found that helical tube with inclination angle β = 45°shows the best heat transfer performance and that with inclination angle β = 90°shows the worst heat transfer performance. In addition, it is found from the thermal efficiency evaluation plot that the experimental data almost locate in Regions I and II and nanofluids in helical tubes can improve the heat transfer under the same pressure drop. The helical tube with s = 10 cm and β = 45°at the range of Reynolds number (Re > 8,000) shows the largest thermal efficiency.