Effect of Surface Curvature on Heat Transfer and Hydrodynamics Within a Single Hemispherical Dimple

Abstract

Turbulent heat transfer and hydrodynamics have been studied in concavely and convexly curved dimples with Reynolds numbers ranging from 1.3×105 to 3.1×105. The large-scale single hemispherical dimple 50 mm in diameter and 25 mm in depth was arranged on the smooth concave or convex wall of a curved rectangular-shaped passage. The fluid flow and heat transfer measurements, and surface streamline observations were performed within the flow curvature parameter δ**/R ranged from 0.002 to 0.007. The “tornado-like” oscillating vortex bursting periodically out of the dimple was registered in the experiments with a “curved” dimple. This vortex structure is similar to that earlier observed in a “flat” dimple. The surface curvature considerably influences the dimple heat transfer rate in both cases. It enhances heat transfer in a “concave” dimple and reduces it in a “convex” one; however, the more remarkable effect occurred in a concavely curved dimple. The correction factors describing the effect of curvature on average heat transfer in a “curved” dimple have been obtained as a result of experimental study.