An experimental investigation of the flow characteristics and heat transfer properties of a heated and an unheated vertically positioned circular cylinder at different Reynolds numbers

Abstract

This study investigated flow characteristics and heat transfer properties simultaneously around a heated circular cylinder vertically immersed in a water channel at different Reynolds (Re) numbers. The channel water temperature and heat flow were kept constant during the experiments. The results included time-averaged vorticity contours (<ω>), streamlines (<Ѱ>), turbulent kinetic energy (<TKE>), the root mean square value of the velocity component in the streamwise direction 〈Urms〉, and the root mean square value of the spanwise velocity component 〈Vrms〉. Thermal buoyancy forces disrupt the periodic vortex formation around the cylinder. Depending on the increased Richardson number, the dead flow zone grew significantly smaller and was eliminated at the value of Re=500 in such a way that it prevented flow separation. In the unheated condition, however, a higher turbulent kinetic energy (TKE) emerged around the junction in the wake region. In contrast, a high TKE was formed in the region closer to the cylinder wall with the cylinder being heated. At the Reynolds number of 5000, the effects of thermal buoyancy forces on the flow properties in the wake of the heated cylinder were found to be negligible. Even though the effects of the oscillations caused by thermal buoyancy forces persisted on the vortex formation due to the increased Reynolds number, the oscillation amplitudes significantly declined. It was noted that, at lower Reynolds numbers (especially Re=500, Re=1000, and Re=1500), the difference between the Nusselt (Nu) distribution around the cylinder was small and that the Nu distribution tended to form almost a straight line as a result of the increased thermal boundary layer thickness. The difference between the maximum and minimum Nusselt values around the cylinder increased directly to the rise in the Reynolds number. It, therefore, appeared that the higher the Reynolds numbers, the more the turbulence in such a way as to improve the heat transfer.