Investigations of the turbulent thermal-hydraulic performance in circular heat exchanger tubes with multiple rectangular winglet vortex generators

Abstract

This work explores the turbulent thermal-hydraulic performance in circular heat exchanger tubes with multiple rectangular winglet vortex generators. Numerical simulations demonstrate that multi-longitudinal vortices are induced, which enhances fluid mixing in the tubes. The effects of geometric parameters including the circumferential number of rectangular winglets (N = 4, 6, 8), height ratio (HR = 0.05, 0.1, 0.2), and pitch ratio (PR = 1.57, 3.14, 4.71), are examined experimentally. The results demonstrate that both the friction factor and Nusselt number increase with the height ratio and the number of rectangular winglets due to the better fluid mixing performance caused by multi-longitudinal vortices with higher turbulent kinetic energy. For the considered Reynolds numbers, the friction factor and Nusselt number ratios are in the range of 1.46–11.63 and 1.15–2.32, respectively. An increase in the number of rectangular winglets improves the thermal enhancement factor (TEF) for HR = 0.05, while the opposite trend is found for the other cases. The maximum TEF is up to 1.27. Moreover, correlations for the friction factor and Nusselt number are derived based on the experimental results for practical applications.