Twisted helical Tape's impact on heat transfer and friction in zinc oxide (ZnO) nanofluids for solar water heaters: Biomedical insight

Abstract

This study explores the influence of Zinc Oxide (ZnO) nanofluids on solar water heaters with Dimple Tubes and Helical Twisted Tape (DTHTT) surfaces. The helical twisted tape design enhances turbulence, improving nanofluid mixing and thermal exchange. Computational fluid dynamics (CFD) validates the efficiency of the parabolic trough solar water heater (PTSWH) with emphasis on solar light concentration and feed water flow velocity. Optimal conditions include a 0.3% ZnO nanofluid volume concentration, mass flow rates between 1.0 kg/min and 5.0 kg/min, and copper-type twisted helical tapes. Experimental results reveal Nusselt number enhancements of 15.1% and 20.96% at H/D = 10, and 16.72% and 32.12% at H/D = 3, for 0.3% ZnO nanofluid, at Reynolds numbers from 3000 to 8000. The twisted tape arrangement at H/D = 3 exhibits increased fluid mixing, leading to higher convective heat transfer. Friction factor enhancements at Reynolds numbers 3000 and 8000 are 0.26% and 0.38%, respectively, compared to the base fluid. At a 3.0 kg/min mass flow rate, thermal efficiency increases to 39.25%, a 13.25% gain over plain tapes. The model shows a ±3.24% deviation from the expected friction factor, with a total ±1.2% discrepancy between experimental and simulated findings, remaining within an acceptable range.