Parametric study on the combined thermal and hydraulic performance of single phase micro pin-fin heat sinks part I: Square and circle geometries

This paper is the first part of a three paper series studying the overall performance of a micro pin-fin heat sink with single phase liquid flow and different pin-fin geometries operating under and similar conditions. Two different heat sinks, one with square shaped pin-fins and the other with circular pin-fins are selected for study in this paper. The paper focuses on studying the effect of thermal resistance and pressure drop of micro heat sinks when subjected to various factors such as pitch distance in axial and transverse directions, aspect ratio of the pin-fin, hydraulic diameters of the pin-fin, and the liquid flow rate through the device. A figure of merit (FOM) involving both the thermal resistance and pressure drop across the heat sink is introduced in the paper and the performance is evaluated on the basis of this FOM. The heat sinks are subjected to uniform heat flux at the bottom of the heat sink and the characteristic study is based on constant Reynolds number of liquid flow at the entrance of the channel. Water is used as the fluid in this study. The study is conducted over the Reynolds number range of 50-500. The characteristic study is carried out with the help of simulations developed using commercially available computational fluid dynamics software CoventorWar (TM). The characteristic study carried out in this paper is divided into four cases. In the first case the axial pitch distance is varied between 350 mu m and 650 mu m by keeping the aspect ratio of the pin-fin structure constant at 0.5. For the second case the transverse pitch distance is varied between 150 mu m and 300 mu m and the aspect ratio is kept the same as in the first case. Third case studies the effect of varying the aspect ratio (between 0.33 and 1) of the pin-fin structures by keeping both pitches constant. Case four studies the variation in the performance of the heat sink with the change in the hydraulic diameter of the pin-fins. The study conducted in this paper reveals the importance of considering the pressure drop along with the thermal resistance in evaluating the overall performance of the micro pin-fin heat sink. At low Reynolds number (below 300) the heat sinks with circular pin-fins shows better performance compared with heat sinks with square pin-fins and vice versa at high Reynolds number (above 300). FOM varies considerably with the change in the parameters like axial pitch distance, transverse pitch distance, aspect ratio and hydraulic diameter of the pin-fins. (C) 2010 Elsevier Masson SAS. All rights reserved.