Interface engineering to enhance thermal contact conductance of evaporators in miniature loop heat pipe systems Jeehoon Choi a, b, * , Byungho Sung a,1 , Chulju Kim c, 2 , Diana-Andra Borca-Tasciuc b, 3 a Zalman Tech Co., Ltd., Seoul, South Korea b Mechanical, Aerospace, and Nuclear Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 30308, USA c School of Mechanical Engineering, Sungkyunkwan University, Suwon, South Korea highlights  The mLHPs have received attention from academic and industrial communities.  But the complicated fabrication and system integration lead to high cost devices.  Thus these have stunted the advent of commercialization.  We introduce a novel low-cost sintering method for fabricating evaporators.  The mLHP with new evaporator can provide overall cooling at a lower temperature. article info Article history: Received 17 December 2012 Accepted 30 June 2013 Available online 18 July 2013 Keywords: Miniature loop heat pipe Evaporator Sintering Contact conductance Thermal resistance abstract While miniature loop heat pipes (mLHP) have significant potential for electronic cooling, they are only used in a narrow niche of applications, such as space or military. Complicated fabrication and system integration leading to high cost devices are the main culprit. To this end, this paper explores a low-cost sintering method for fabricating evaporators for mLHP that have increased heat transfer performance. Through this method, the porous wick of the evaporator is fabricated to partially fill the vapor collection channels embedded in the base plate of the evaporator. The sintering method employs an organic ma- terial used to define the vapor collection channels, which is sublimated at the end of the sintering process. Interpenetrating these two, otherwise distinctive, parts of the evaporator results in an increased contact area and thermal conductance. The heat transfer performance of an mLHP employing the new evaporator is compared to that of a system using a standard evaporator configuration, where the porous wick is rested against a flat base plate. It is found that the thermal contact conductance increases about 25%, depending on the applied heat load, while the total thermal resistance of the mLHP with the new evaporator decreases approximately by a factor of two. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Active cooling heat sinks combined with conventional heat pipes have been traditionally used in personal computers (PC) to efficiently control the temperature of multi-core central and graphic processing units (CPU and GPUs). However, in high-end computers and PCs with CPU over-clocking, the cooling capacity must be over 130 W, pushing the limits of existing cooling tech- nologies [1]. In this context, miniature loop heat pipes (mLHP) are receiving increased attention from academic and industrial com- munities, being explored as potential candidates for electronics’ cooling. The mLHP consists of an evaporator, a condenser, vapor and liquid transport lines as in the conventional heat pipes, but differs in having a porous wick only within the evaporator [2]. This unique feature of the mLHP allows the separation of heat absorption and rejection sites, enabling the fitting of the small evaporator inside the confined space of modern PC [3]. The condenser can be placed away at a relatively large distance from electronics box, since fluid transport is ensured by ordinary tubes that can be easily bent. All these unique * Corresponding author. Mechanical, Aerospace, and Nuclear Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 30308, USA. Tel.: þ1 518 423 0735. E-mail addresses: choijeehoon@gmail.com, jhchoi@zalman.co.kr (J. Choi), bh03@chol.com (B. Sung), cjkim@me.skku.ac.kr (C. Kim), borcad@rpi.edu (D.-A. Borca-Tasciuc). 1 Tel.: þ82 70 4480 7875. 2 Tel.: þ82 031 290 7434. 3 Tel.: þ1 518 276 2010. Contents lists available at 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.2013.06.060 Applied Thermal Engineering 60 (2013) 371e378