Short communication Optimization of a microchannel heat sink with temperature dependent fluid properties Afzal Husain, Kwang-Yong Kim * Department of Mechanical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Gu, Incheon 402-751, Republic of Korea Received 17 November 2007; accepted 3 December 2007 Available online 8 December 2007 Abstract The present study deals with the numerical optimization of microchannel heat sink with the help of surrogate analysis and evolution- ary algorithm. Two design variables related to the microchannel depth, width and fin width are chosen and their ranges are decided through preliminary calculations of three-dimensional Navier–Stokes and energy equations. Objective functions related to the heat trans- fer and pressure drop i.e., thermal resistance and pumping power are formulated to analyze the performance of the heat sink. Water with temperature dependent thermal properties is used as coolant for steady, laminar fully developed flow in the silicon microchannels. Using the numerically evaluated objective function, polynomial response surface is constructed for each objective function. Evolutionary algo- rithm for multiobjective optimization is performed to obtain global Pareto optimal solutions. Trade off between objectives is found and analyzed with the design variables and flow constraints. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Microchannel; Thermal properties; Electronic cooling; Evolutionary algorithm; Multiobjective optimization 1. Introduction Downscaling of MEMS devices and advances in micro fabrication processes have helped to satisfy the growing demand for higher dissipation of heat flux from electronic devices. The progress in micro-electro-mechanical systems (MEMS) and power required to drive cooling devices inte- grated in electronics robotics, avionics, and medicine industry have opened the doors for optimization. Micro- channel heat sink, as an integrated part of silicon based electronic device, has been a potential microcooling device having a high surface area to volume ratio. Microchannel heat sink has been long studied since its advent by Tuckerman and Pease [1] who performed exper- iments on silicon based microchannel heat sink for elec- tronic cooling. Sobhan and Garimella [2] carried out comparative analysis of studies on fluid flows and heat transfer in microchannels. They figured out some discrep- ancies existed in these results may be due to some experi- mental and/or scaling effects. Toh et al. [3] carried out a detailed numerical study of variation of local thermal resis- tance and friction factor along the flow direction in micro- channels by solving three-dimensional Navier–Stokes equations using temperature dependent fluid properties. Some researchers claimed that conventional Navier–Stokes equations are not adequate to study fluid flow and heat transfer mechanism in microchannels. Whereas many stud- ies [4–6] supports that common theoretical basis for macro- and micro-flows can be used to understand the fluid flow and heat transfer mechanism. Herwig and Hausner [4] sug- gested that certain scaling effects can be of different impor- tance for micro systems. Xu et al. [5] investigated liquid flows in microchannels and found that viscous dissipation effects tend to be significant due to higher velocity gradients exited in channel with small hydraulic diameters. They pro- posed a criterion for the significance of the viscous dissipa- tion effects in microchannel flows. Koo and Kleinstreuer [6] numerically investigated the viscous dissipation effects on 1359-4311/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2007.12.001 * Corresponding author. Tel.: +82 32 872 3096; fax: +82 32 868 1716. E-mail address: kykim@inha.ac.kr (K.-Y. Kim). www.elsevier.com/locate/apthermeng Available online at www.sciencedirect.com Applied Thermal Engineering 28 (2008) 1101–1107