Investigations of Effect of Dimple Depth on Heat Transfer and Fluid Flow within Rectangular Channel

The numerical analysis is carried out to study the flow physics of effect of dimple depth on heat transfer and fluid flow. The dimple diameter is 5 cm kept constant. While dimple depth is varied as 10 mm, 15 mm and 20mm, so that dimple depth to dimple diameter ratio is maintained as 0.2, 0.3 and 0.4. The channel is having aspect ratio of 4 kept constant. The numerical analysis is carried out at Reynolds number based on hydraulic diameter of 20,000. Fluent 6.3.26, a finite volume flow solver is used for solving governing equations for present geometry. The cell count is based on grid independence study and y+ value. Appropriate boundary conditions are imposed under forced heat convection mode.. The fluid flow characteristics are presented in the form of velocity contours. The numerical analysis clarifies the flow structure due to dimple surface. The heat transfer enhancement because of dimple surface is due to flow separation at the leading edge and reattachment at the trailing edge of the dimple. For the dimple depth 6/D=0.3, the augmented strength and intensity of secondary vortices increases the rate of heat transfer enhancement compared to dimple depth 6/D=0.2 and 6/D=0.4. The heat transfer enhancement rate for dimple depth 6/D=0.4 decreases due to strong recirculation zone within the dimple and some fluid is trapped at the bottom of the dimple. (C) 205 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ICCHMT - 2015