Experimental investigation of heat transfer and drag on surfaces coated with dimples of different shape

Abstract

The results of an experimental investigation of the heat transfer and the drag on surfaces coated with dimples are presented. The dimples of six different shapes were considered, namely, spherical, oval, and teardrop dimples, spherical dimples with rounded edges, turned teardrop dimples, and dimples obtained by milling a sphere along a circular arc. The distinctive feature of the study is that the relative drag and heat transfer coefficients were simultaneously recorded during the same run of the experimental setup. The drag coefficients were determined by directly weighing the models under study using a one-component strain gauge balance. The heat transfer coefficients were determined by means of the unsteady heat transfer method using the IR camera. The Reynolds number based on the boundary layer length ranged from 0.2·106 to 7·106. The two-dimensional fields of the heat transfer coefficient on the dimpled surfaces are presented, together with the data of the flow visualization. The Reynolds number effect on the heat transfer enhancement, the drag increase, and the heat-hydraulic efficiency is determined. The average values of the above-mentioned parameters are presented for all the surfaces considered.