Parametric Effects on Heat Transfer of Impingement on Dimpled Surface

Abstract

Jet impingement on a dimpled surface is investigated experimentally for Reynolds numbers in the range 5000–11500, and jet-to-plate spacing from 1 to 12 jet-diameters. These include spatially resolved local Nusselt numbers with impingement both on the dimpled itself and on the flat portion between dimples. Two dimple geometries are considered: hemispherical dimples and double or cusp elliptical dimples. All experiments were carried under maximum crossflow that is the spent air exits along one way. At the narrow jet-to-plate spacing such as H/Dj=2, a vigorous recirculation occurred, which prevented the dimpled plate to enhance heat transfer. The effect of impinging jet positions meant that impinging onto dimples generated more and higher energetic vortices, and this led to better heat transfer performance. Cusped elliptical dimples increase the heat transfer compared to a flat plate less than the hemispherical geometry. The influence of dimple depth was also considered, the shallower dimple, d/Dd=0.15, improves significantly the heat transfer by 64% compared to that of the flat surface impingement at H/Dj=4; this result was 38% higher than that for a deeper dimple of d/Dd=0.25. The very significant increase in average heat transfer makes dimple surface impingement a candidate for cooling applications. Detailed pressure measurements will form a second part of this paper, however, plenum pressure measurements are illustrated here as well as a surface pressure measurement on both streamwise and spanwise directions.

Features of heat transfer at interaction of an impact swirl jet with a dimple

“…One strategy here implies modification of the surface onto which the jets impinge with obstacles. The authors of [3][4][5] examined heat transfer in narrow channels in which a system of jets impinging onto a surface modified with cavities was organized. It was shown that such systems exhibit good performance characteristics and can be used, in particular, for cooling turbine blades from inside.…”

Experimental investigation of impingement heat transfer on a flat and dimpled plate with different crossflow schemes

“…Kanokjaruvijit and Martinez-Botas [9] made a comparison of the averaged heat transfer coefficient with and without edges, but they simply use a same edge area for each dimple. The results showed that the heat transfer values illustrate no significant reduction when edges are taken out of consideration.…”

Numerical investigation of an axi-symmetric laminar jet impinging on a dimpled surface under uniform heat flux using a finite element method

“…Ekkad and Controvitz [6] reported that the presence of dimples resulted in a lower heat transfer for Re = 4,800-14,800. Kanokjaruvijit and MartinezBotas [7][8][9] showed enhanced heat transfer in the presence of dimples with strong crossflows for Re = 5,000-11,500. None of these works gave detailed information on flow visualization.…”

“…Using the flat plate impingement results as baseline cases, dimple impingement was studied together with various parametric effects, such as Re, jet-to-plate spacing (H/D j ), dimple depth (d/D d ), and ratio of nozzle exit diameter to dimple projected diameter (D j /D d ). Due to the scarcity of information on heat transfer and flow of a laminar jet impinging onto a dimple, this study intends to provide computational data for better understanding of the experimental results found by previous researchers [5][6][7][8][9]. Fig.…”