International Journal of Thermal Sciences 146 (2019) 106067 Available online 13 September 2019 1290-0729/© 2019 Elsevier Masson SAS. All rights reserved. On thermal performance of serpentine silicon microchannels Dungali Sreehari a, b , Apurbba Kumar Sharma b, * a Department of Mechanical Engineering, National Institute of Technology, Uttarakhand, Srinagar, Pauri (Garhwal), Uttarakhand, 246174, India b Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, 247667, India A R T I C L E INFO Keywords: Micro-USM Serpentine Microchannel Simulation Thermal performance ABSTRACT In the present study, three different serpentine microchannels (Rectangular, U and V) of rectangular cross-section with a channel span 24 mm were fabricated on a 0.525 mm thick (100) silicon substrate using micro-ultrasonic machining (micro-USM) technique. Thermal performance of the microchannels was experimentally investigated by making the working fuid (water) to fow through them at different Reynolds numbers (100–400) and at different heat fuxes (10 kW/m 2 , 20 kW/m 2 and 30 kW/m 2 ). Similar microchannels were modeled and analysed numerically simulating the experimental conditions. The performances of the microchannels obtained with the experimental as well as numerical results were compared in terms of pressure drop, substrate and fuid tem- peratures and heat transfer coeffcient. The results indicate that the overall thermal performance of the micro- channel heat sink mostly depends on the type of pattern as the fuid-substrate interaction area, defned by the Sink Area Factor (SAF), changes appreciably with the pattern. It was found that the U-serpentine microchannel exhibited the best thermal performance while compared to the other two serpentine microchannels. The sharp bends of the microchannel patterns and the surface roughness of the microchannel walls adversely affect the overall thermal performance of the microchannels. The study also outlines the need for a compromise in the Reynolds number, as higher Reynolds number tends to lower the overall thermal performance of the microchannels. 1. Introduction Increase in the functional speed of electronic devices results in generation of high heat fuxes. Dissipation of these high heat fuxes from the micro-electronic devices is the major concern for the manufacturers. The use of traditional air-cooling technologies are not suffcient for dissipation of high heat fuxes and hence considered ineffective. In order to maintain the temperature below a safe/optimal operating tempera- ture and to increase the performance of the components, the micro- channel heat sink technology is being explored [1]. The frst microchannel was fabricated by Tuckerman and Pease [1] directly on the back side of a silicon chip. They have fabricated straight rectangular microchannels of width 50 μm and depth 300 μm using an orientation dependent etching technique. Experimental investigations were carried out by Xu et al. [2] to study the fow friction in the microchannels by varying the hydraulic diameter and Reynolds number. Qu and Mudawar [3] conducted experimental and numerical in- vestigations on rectangular cross-section microchannels to study the pressure drop and heat transfer characteristics. Poh and Ng [4] numerically investigated the effect of microchannel length, depth, width and fow inlet velocity on the performance of rectangular micro- channels. Hao et al. [5] experimentally investigated the fow charac- teristics such as pressure drop and velocity profles in the trapezoidal silicon microchannels. Thus, several experimental and numerical in- vestigations were carried out on straight/parallel microchannels with different cross-sections to understand the effect of various parameters such as length, width, depth, pattern, cross-section, surface roughness, etc. on their performance [6–8]. However, the commonly employed straight microchannels are incapable of proper mixing due to increase in the velocity and thermal boundary layers along the fow direction which leads to reduction in heat transfer performance. In general, active/- passive mixers are used to disrupt the boundary layer and to improve the mixing in order to enhance the heat transfer. Active mixers uses an external force or mechanical power, while in passive mixers, geomet- rical patterns (serpentine, zigzag/wavy) are used to increase the surface area to obtain the desired mixing of fuids [9]. Rosaguti et al. [10] numerically studied the fuid fow in the periodic serpentine microchannels with constant heat fux in comparison with straight microchannel of similar cross-section and path length. They * Corresponding author. E-mail address: akshafme@iitr.ac.in (A.K. Sharma). Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: http://www.elsevier.com/locate/ijts https://doi.org/10.1016/j.ijthermalsci.2019.106067 Received 23 January 2019; Received in revised form 23 August 2019; Accepted 27 August 2019