Experimental study of the turbulent convective heat transfer of titanium oxide nanofluid flowing inside helically corrugated tubes

The convective heat transfer for the turbulent flow of water/TiO2 nanofluid inside helically horizontal corrugated tubes is investigated in this paper using experimental techniques. The tube boundary condition is a uniform wall temperature. The test apparatus was designed and assembled with a test section containing 93 cm copper tubes with internal and external diameters of 7.71 mm and 9.52 mm, respectively. First, the heat transfer characteristics of the distilled water turbulent flow in a plain copper tube were measured preliminarily. Second, various test runs were performed for nanofluids with two nanoparticle concentrations (0.1% and 0.5%), two corrugation depth to diameter ratios (0.0648 and 0.103), two corrugation pitch to diameter ratios (0.917 and 1.297), and two corrugation width to diameter ratios (0.363 and 0.492) that were all within the range of turbulent Reynolds numbers (3000 < Re < 15000). The experimental results reveal that the Nusselt number augments the dual increments in corrugation depth and width and with the decrements in corrugation pitch, particularly for high Reynolds numbers. The nanoparticles have a stronger effect on the heat transfer in helically corrugated tubes with higher corrugation depths and widths as well as lower corrugation pitches. A correlation for the Nusselt number in terms of the helically corrugated tubes is introduced based on the linear regression analysis of the experimental data.