Numerical study of thermal enhancement in micro channel heat sink with secondary flow Navin Raja Kuppusamy a , R. Saidur a,⇑ , N.N.N. Ghazali a , H.A. Mohammed b,⇑ a Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia b Department of Thermofluids, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia article info Article history: Received 10 April 2014 Received in revised form 19 June 2014 Accepted 24 June 2014 Available online 17 July 2014 Keywords: Micro channel heat sink Numerical analysis Secondary flow Slanted passage Heat transfer enhancement abstract Secondary flow is employed in micro channel heat sink (MCHS) by introducing slanted passage in the channel wall between the adjacent channels in alternating orientation. The intervallic passage causes disruption in the hydrodynamic boundary layer and redevelopment at the leading edge of the following wall. This phenomenon decreases the average thermal boundary layer thickness, thus enhances the heat transfer performance with minor pressure drop due to combined effect of thermal boundary layer re-development and flow mixing. The data presented in comparison of simple MCHS. The results showed that the overall performance of MCHS with alternating slanted passage (MASP) increased by 146% and thermal resistance reduced to 76.8% when compared with simple MCHS. It has to be highlighted that contradicting from the usual phenomenon where improvement in heat transfer accompanied with incre- ment in pressure loss, thermal enhancement in present study comes together with reduction in pressure drop up to 6% compared to the simple one. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction With the rapid increment of heat dissipation from various electronic components such as central processing unit (CPU) and graphic card in computers, there is an imperative demand for supe- rior cooling technology. Micro channel heat sink MCHS is one of the widely used devices for the cooling of tiny but extremely heated electronics components. There are several advantages in MCHS such as compactness, light weight and higher heat transfer surface area to fluid volume ratio which makes it more attractive favorable compared to macro-scale systems. The first idea of MCHS was introduced by Tuckerman and Pease [1] in 1981. The silicon MCHS has a very small volume and can achieve a heat flux of 7.9  10 6 W/m 2 with the maximum temperature difference of 71 °C between the substrate and inlet water. However, the penalty of pressure drop was very high; 200 kPa and 380 kPa using plain micro channels and pin fin enhanced micro channels respectively. Numerous reaches were conducted from thereon to study the thermal and flow performance of the MCHS. The analyses were focused on optimizing the geometry of the micro channel such as the height, width and aspect ratios [2–4]. Besides, the micro channel is also analyzed using various shapes such circular and trapezoidal channel [5–11]. Nonino et al. [12] conducted on numerical investigation on the difference type of cross-sectional shapes of micro channel for their flow behavior and wall heat flux. Morini [13] reviewed the experimental results of single phase heat transfer in micro channel. It was also observed that numbers of numerical study was to investigate the developed flow behavior in micro channel. Lee et al. [14] experimentally investigated rect- angular micro channel to validate the classical correlations and it was found that the numerical results matched well with the exper- imental data. Liu and Garimella [15] proposed five approximate analytical models for predicting the convective heat transfer in micro channel heat sinks. A modified thermal boundary condition is proposed to correctly characterize the heat flux distribution in the end. Tao et al. [16] suggested a few methods such as shortening the thermal boundary layer; increasing flow interruptions and increas- ing the velocity gradient near the heated surface for the single- phase heat transfer enhancement. Sui et al. [17] revealed that Dean Vortices were generated when liquid coolant flows through the wavy micro channel that significantly enhance the heat transfer with acceptable pressure drop. In the review of enhancement in single phase heat transfer, Steinke and Kandlikar [18] recommended that placing smaller sec- ondary channels with an angle between the mainstream channels in micro channel application will induce the secondary flow that will move from one channel to another through these channels. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.06.072 0017-9310/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding authors. E-mail addresses: saidur@um.edu.my, saidur912@yahoo.com (R. Saidur), hussein.dash@yahoo.com (H.A. Mohammed). International Journal of Heat and Mass Transfer 78 (2014) 216–223 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt