Friction factor and Nusselt number correlations for forced convection in helical tubes

摘要

Helical tubes are widely used in heat exchangers in various industries. Due to the secondary flow caused by centrifugal forces, flow and heat transfer characteristics in helical tubes are more complicated than that in straight tubes. The centrifugal effects depend on Reynolds number, curvature ratio and the helical pitch. In the current investigation, friction factors of laminar and turbulent flows in helical tubes are measured to validate the correlations in the literature. Friction factor correlations for laminar and turbulent flows with large applicable ranges of Reynolds numbers and curvature ratios are recommended. Friction factor correlation of Zhao et al. (2016) for rough helical tube is recommend when Reynolds number is higher than 105. By relating pressure drops and heat transfer coefficients, new Nusselt number correlations for laminar and turbulent convections in helical tubes are obtained by regression analysis of experimental data in the literature. The new correlations show good prediction with wide ranges of Reynolds numbers and curvature ratios.