(227g) Thermohydraulic Characteristics of TIO2-Water Nanofluids in MICRO-Fin Tubes Fitted with Twisted-Tapes

This paper presents heat transfer enhancement, friction factor and thermal performance characteristics of TiO₂-water nanofluids in the micro-fin tubes equipped with twisted tapes. The major functions of the nanoparticles (TiO₂) in the nanofluids, the micro-fin tubes and the twisted tapes are respectively enhancing the thermal conductivity of the base fluid (water), intensifying turbulence near tube walls, and generating swirl flows.  The experiments were performed using Nanofluids with TiO₂ concentrations varied between 0.1% and 0.3% by volume,  the twisted-tapes with three different twist ratios, y/W = 2.0, 3.0, and 4.0, for Reynolds numbers between 5000 and 15,000, under a constant wall heat flux (UHF) boundary condition.  The experimental results are reported in terms of Nusselt number (Nu), friction factor (f) and thermal performance factor (h). The experimental results indicate that Nusselt number and friction factor increase with decreasing tape twist ratio and increasing TiO₂ concentration. Thermal performance tends to decrease with the rise of Reynolds number and becomes almost constant for the Reynolds numbers beyond 12000.  For the studied range, the use of TiO₂-water nanofluids in the micro-fin tubes equipped with twisted tapes results in thermal performance factors above unity, reflecting the potential of the combined technique for energy saving. In addition, the empirical correlations of Nusselt number, friction factor and performance factor associated with the use of the combined technique, were also developed.