Coupled effects of hydrophobic layer and vibration on thermal efficiency of two-phase closed thermosyphons

Tong W.L., Tan M.K., Chin J.K., Ong K.S., Hung Y.M., RSC Advances 5 (2015) 10332 -10340, 2015

Condensed droplets in a two-phase closed thermosyphon (TPCT) are subject to two competing forces:contact line pinning force between the droplet and the wall of the TPCT and the body force due togravity. Either reducing the contact line pinning force or increasing the body force can lead to significantenhancement in the heat transport capability. This study aims to scrutinize the coupled effects ofhydrophobic surface coating at the condenser wall and high-acceleration induced vibration on thethermal efficiency of a TPCT. We explore an approach to reduce the contact line pinning force byapplying a thin layer of hydrophobic coating, which also facilitates dropwise condensation to furtherincrease the heat transport capability. The body force of the condensed droplets can be increased byintroducing a low-frequency (f  102 Hz) high-acceleration (€x  103 m s2) vibration. The formation ofelongated liquid jets and entrainment of droplets induced by the high-acceleration vibration counteractsthe enhancing effect from the increased body force of condensed droplets. Nanofluid with distinguishedthermo-physical properties is charged to the TPCT to further enhance the thermal efficiency. Byincorporating the coupled effects of hydrophobic layer and vibration, we can obtain a maximumaugmentation in the heat transfer coefficient exceeding 47.7%. The factors contributing to theenhancement of thermal efficiency of a TPCT are identified and the underlying physical significance ofthe coupled effects is delineated.

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