Investigation of self-similar heat sinks for liquid cooled electronics Flavio Brighenti a, * , Natrah Kamaruzaman a, b , Juergen J. Brandner a a Karlsruhe Institute of Technology, Institute for Micro Process Engineering, Campus North, Hermann-von-Helmholz Platz 1, 76344, Germany b Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Malaysia article info Article history: Received 14 December 2011 Accepted 4 January 2013 Available online xxx Keywords: Microchannel Developing boundary layer Heat sink Liquid cooling Diffusion bonding abstract Electronic systems require cooling devices that are able to deal with high heat-flux capabilities. For this purpose, microchannels are attractive for direct cooling, due to their superior performances. A study on self-similar heat sinks for liquid cooled electronics is presented in this work, where the devices are made from copper, designed for industrial application and for large scale production. Self-similarity refers to the fact that there is a certain similarity and repeatability (or pattern) of the substructures compared with the overall structure. The internal structures, the so called overflow structures (or microchannels), have been designed in order to achieve high heat transfer coefficients. To validate the design and describe the flow characteristics inside the device via analytical solutions is almost impossible, therefore a well known numerical code was employed to have an insight of the thermal-fluid distributions. As can be seen clearly from the simulation, most of the heat is removed in the overflow-structure, on the side of the device adjacent to the source of heat. This paper attempts to analyse a comprehensive list of data as well as plots in a critical manner in order to illustrate the significant characteristics of this type of device. A clear lack in a proper common definition of the heat flux may lead to a misinterpretation of the results, in fact depending on the chosen area where the heat exchange takes place (namely the internal area of the microstructures or the separation surface between the device and the heating source), we can achieve a maximum heat flux of either about 200 W/cm 2 or about 700 W/cm 2 . A very low pressure drop together with a good heat removal capability, make this device suitable for cooling of IGBT chips in power electronic applications. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction In electronic devices, thermal management issues play an increasingly prominent role in microelectronic system design, as do the difficulties. The constraints on heat removal are a major factor limiting the performance of a microelectronic system, but the high heat transfer coefficients achievable in microchannels are attractive for direct cooling of electronic systems. The use of microchannels as a viable cooling solution was first proposed 30 years ago by Tuckerman and Pease [1]. They showed that a single layer microchannel etched directly on a silicon wafer is highly effective for dissipating heat. Using water as a working fluid they demonstrated that these microchannels can remove up to 790 W/cm 2 of heat. The effectiveness of a microchannel device for high heat flux cooling lies in its increased heat transfer coefficient and in a large surface area to volume ratio, and micro heat exchangers have been widely implemented in different sectors of research and industry [2]. State of the art micro-scale convective heat transfer techniques are presented for use in heat sinks. In chemistry and biological sciences microchannels are used in various microsystems such as micro heat sinks and microreactors, because of their different superior performances compared to conventional size devices. The recent attention on micro devices has favoured not only the research in the thermal-fluid-dynamics, but also in the field of micro-fabrication techniques, i.e. among others this includes hot- embossing, lithography, etching, micro-mechanical machining and diffusion-bonding. Several researchers have investigated the possibility of imple- menting different shapes for the microchannels, ranging from rect- angular, to semi-circular, to triangular and so on, both from a fluid- dynamic as well as a manufacturing point of view [2]. Even though, many have been oriented to using simple, easily obtainable shapes. In this work we are presenting the results of a study on self-similar heat sinks for liquid cooled electronics, made from copper, designed * Corresponding author. Tel.: þ49 (0)72160824201; fax: þ49 (0)72160823186. E-mail address: flavio.brighenti@kit.edu (F. Brighenti). Contents lists available at SciVerse ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.applthermaleng.2013.01.001 Applied Thermal Engineering xxx (2013) 1e8 Please cite this article in press as: F. Brighenti, et al., Investigation of self-similar heat sinks for liquid cooled electronics, Applied Thermal Engineering (2013), http://dx.doi.org/10.1016/j.applthermaleng.2013.01.001