He, HongbinYamada, MasayukiHidaka, SumitomoKohno, MasamichiTakahashi, KojiTakata, Yasuyuki2017-09-192017-09-192017http://hdl.handle.net/2263/62436Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .Heat transfer characteristic of a closed two-phase thermosiphon with enhanced boiling surface is studied and compared with that of a copper mirror surface. Two-phase cooling improves heat transfer coefficient (HTC) a lot compared to singlephase liquid cooling. The evaporator surfaces coated with a pattern of hydrophobic circle spots (non-electroplating, 0.5  2 mm in diameter and 1.5  3 mm in pitch) achieve very high heat transfer coefficient and lower the incipience temperature overshoot using water as the working fluid. Sub-atmospheric boiling on the hydrophobic spot-coated surface shows a much better heat transfer performance. Tests with heat loads (30 W to 260 W) revealed the optimum thermosiphon performance. Hydrophobic circle spots coated surface with diameter 1 mm, pitch 1.5 mm achieves the maximum heat transfer enhancement with the boiling thermal resistance as low as 0.03 K/W.4 pagesPDFenUniversity of PretoriaHydrophobic circle spots evaporatorLooped thermosiphonBoiling surfacePresentation