Proceedings of the 15th International Heat Transfer Conference, IHTC-15 August 10-15, 2014, Kyoto, Japan IHTC15-9230 MODIFIED ENDWALL FLUID FLOW IN A DIMPLED PIN FIN ARRAY FOR HEAT TRANSFER ENHANCEMENT S.M. Roux, ∗ G. Mahmood, J.P. Meyer Department of Mechanical and Aeronautical Engineering, University of Pretoria, Pretoria, South Africa, 0041 ABSTRACT By adding dimples to pin-fins it is possible to enhance the heat transfer, however, all of the work on dimpled pin-fins has been done on either a single pin-fin or one row of pin-fins and no work so far has been done on an array of dimpled pin fins. It was the purpose of this study to experimentally measure the flow field within a staggered array of short dimpled pin-fins and use the results to predict possible heat transfer enhancement on the endwall. Measurements were conducted in a wind tunnel on a scale model with 13 staggered rows of 50 mm diameter pin-fins with a height of 64 mm and streamwise and spanwise spacing of 100 mm. The dimples were 5.2 mm in diameter, had a depth of 0.82 mm and were machined asymmetrically with an offset of 3.87 mm. For comparison purposes measurements were also taken on smooth pin-fins of the same dimensions. Re- sults were obtained for a Reynolds numbers of 40 000 using a L-shaped five-hole probe. The results showed an increase in vorticity for the dimpled configuration, greater streamwise velocity acceleration, and the de- velopment of additional secondary flows between the endwall and bulk flow. All three conclusions predict an increase in endwall heat transfer for a dimpled pin-fin array. KEY WORDS: thermodynamics, convection, heat transfer enhancement, gas turbines, heat exchanger 1. INTRODUCTION The use of short pin-fins in cooling applications is well documented due to the wide range of its use including internal cooling of turbine blades and pin-fin heat sinks in electronic component applications. Since their initial implementation, copious numbers of papers have been written on the subject testing numerous arrays, configurations, and modifications with varying degrees of effectiveness. Metzger et al. [10–13], Van Fossen [18] and Simoneau and Van Fossen [15] focused primarily on the effect of pin spacing on the heat transfer and pressure drop as well as developing flow conditions. Heat transfer showed high dependency on the streamwise pin spacing with the closest spaced pins having heat transfer rates twice as high as the most widely spaced array at a Reynolds number of 1 000. This dependency decreased with increasing Reynolds number. Metzger et al.’s correlations [12] are regularly being used for a wide range of pin geometries. Research was extended to square [3], elliptic [7, 17], and diamond [16] shaped pin-fins which were tested in staggered and inline configurations. Staggered cubic elements [3] showed the most promise with a 30-80% increase in heat transfer over the test range. Goldstein et al. [5] tested pins with stepped diameters which showed a 5% increase in heat transfer. Various other papers were published concentrating on the flow field [1, 17, 19] and heat transfer [2, 14, 19] mechanisms. ∗ Corresponding S.M. Roux: stephan.roux@up.ac.za 1