Novel self-join winglet vortex generators for enhanced heat transfer of turbulent airflow in round tubes

Abstract

Novel self-join winglet vortex generators (SWVGs) consisting of multiple pairs of connected V-shaped rectangular winglets were put forward for enhanced heat transfer of turbulent airflow in round tubes. Numerical results firstly confirmed the generation of longitudinal swirl flows, which improved the air mixing and reduced the synergy angle between flow and thermal fields in the tube. Besides, increasing the winglets' included angle (α) and height ratio (HR) resulted in more intense swirl flows and uniform temperature distributions. Additive manufacturing was applied to fabricate the vortex generators using nylon, and experimental tests were carried out. The results showed that the Nusselt number ratio was 1.50–3.49 over the smooth tube, demonstrating the high capability for enhanced heat transfer of the proposed SWVGs. However, pressure loss was accompanied meanwhile. The overall thermal performance in terms of thermal enhancement factor displayed a decreasing tendency with the Reynolds number. The maximum thermal enhancement factor value of 1.27 was found at HR = 0.05 and α = 120°. In addition, the empirical correlations for friction factor and Nusselt number regarding α, HR, and Reynolds number were achieved by nonlinear regression to reference industrial applications.