Experimental study on thermo-hydraulic performance of nanofluids upward flowing through helical tubes of heat exchanger system based on thermal efficiency

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 [beta = 0 degrees, 45 degrees, and 90 degrees], and nanoparticle mass fractions [omega = 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 beta = 45 degrees shows the best heat transfer performance and that with inclination angle beta = 90 degrees 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 beta = 45 degrees at the range of Reynolds number (Re > 8,000) shows the largest thermal efficiency.