Effects of Reynolds number on thermal wake in conjugate heat transfer between a sphere and its surrounding fluid

Abstract

Unsteady conjugate heat transfer between an aluminum sphere and its surrounding water was investigated. The mass, momentum and energy equations were solved, and for Reynolds number greater than 400, the large eddy simulation with the Smagorinsky–Lilly model was used. 3D transient simulations were carried out for the sphere Reynolds numbers ranging from 1 to 10,000 (6.99 ≤Pe ≤ 69,900). This study particularly focuses on the effect of Reynolds numbers on the thermal wake phenomenon. The simulation results showed that under the condition of the conductivity ratio of 337.33 and the heat capacity ratio of 0.567, thermal wake exists when 1≤ Re <8000 (6.99 ≤ Pe < 55,920). The Reynolds number of 8000 (Pe = 55,920) was determined as the turning point that thermal wake disappears. Two modes of reverse heat transfer, laminar and vortical were identified. For laminar thermal wake, the thermal inversion point starts from the rear stagnation, while for vortical thermal wake, it occurs near the separation point.