Experimental Investigation of a Low-Profile Heat Pipe with Wickless Wettability-Patterned Condenser

Heat pipes (HP) are metal-wick equipped cooling devices that circulate a phase-changing liquid to transfer heat over long distances more efficiently than solid-metal heat sinks. Metal wicks are commonly used in heat pipes, but also have capillary limits such as high pressure drop and pore-clogging issues. Wettability patterned (WP) surfaces do not face these limitations and as shown here, could effectively substitute metal wicks in HPs. WP surfaces facilitate the collection and efficient transport of condensates, therefore enhancing heat transfer from the hot (evaporator) to the cold (condenser) side. In this study, a 10 cm long 5 mm-thin HP with an axially graded wick-lined evaporator and a wickless WP condenser is designed, fabricated, and tested. Condensation is controlled on the wickless side of the system via juxtaposed superhydrophilic/hydrophobic areas to regulate both dropwise and filmwise condensation, to collect and return the condensate to the evaporator's wick, thus increasing the maximum allowable heat load and lowering the device's thermal resistance (lowest 0.16 K/W at 105 W). Additionally, an axially graded wick improved condensate transport from the cold to the hot side of the system. Finally, the effect of wettability patterning and the wick’s pore size were examined