Numerical exploration of optimal microgroove shape in loop-heat-pipe evaporator

A loop heat pipe (LHP) is a heat transport device driven by capillary pressure in porous media and the vapor–liquid phase change of a working fluid. LHPs are widely used in the electronic cooling systems of spacecraft (Okamoto et al., 2016), insulated gate bipolar transistors (Dupont et al., 2013), laptops (Lin et al., 2013), and other thermal engineering applications. As shown in Fig. 1, an LHP consists of an evaporator, a condenser, a vapor line, a liquid line, and a compensation chamber (CC). Unlike conventional heat pipes, the wick is enclosed in the evaporator, enabling long transport lengths and large radiation areas. The operating characteristics and working mechanisms of LHPs are reviewed in Maydanik (2005), Ku (1999), and Launay et al. (2007). The wick shape as well as porous materials and capillary structures critically affects the evaporator performance, but the design of the wick shape is complicated, which is focused in this paper. Some papers have attempted enhancement of the evaporator heat-transfer coefficient by parametric studies with respect to the shape (e.g., contact surface area between casing and wick, groove number, groove width, groove pitch, groove cross-sectional shape, groove location (in a wick or casing) and wick thickness) with a cylindrical or flat evaporator (North et al., 1997; Riehl et al., 2008; Kiseev et al., 2010; Yakomaskin et al., 2013; Yakomaskin, 2016; Kuroi and Nagano, 2012; Hodot et al., 2013; Wu et al., 2014; Uchida, 2014; Zhang et al., 2012). Especially, the heat-transfer coefficient was significantly improved by forming microgrooves on the wick surface (North et al., 1997; Riehl et al., 2008; Kiseev et al., 2010; Yakomaskin et al., 2013; Yakomaskin, *Department of Mechanical Engineering, Toyohashi Univ. of Tech. 1-1, Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan **currently at Panasonic Co. 1006, Oaza Kadoma, Kadoma-shi, Osaka 571-8501, Japan ***Department of Mechanical Engineering, Worcester Polytechnic Inst. 100 Institute Road, Worcester, MA, 01609, USA E-mail: nishikawara@me.tut.ac.jp