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Droplets on micro/nano hierarchical structures exhibit extraordinary hydrophobic properties, such as large contact angles, low dynamic hysteresis, and high mobility. Vapor condensation on such the surface may potentially achieve rapid condensate removal and surface cleaning, therefore significantly enhancing the heat transfer coefficient. This article reports novel conical hierarchical structures (CHS) and their mechanisms for enhancing vapor/moisture condensation. Through a normal optical tomography, visualization images show, in spite of ultrahigh surface structure, condensate droplets are able to rapidly precipitate under capillary forces and maintain at the stable Cassie state in a dynamic condensation environment. Within CHS, the major condensation is advanced at where the incident moisture is cooled to its dew point. Compared with the traditional dropwise condensation, CHS reduces the mass transport resistance when moisture must diffuse through the entire noncondensable gas (NCG) layer. The stable Cassie state in dynamic condensation environment, as well as the CHS structural tolerance to NCG, enables high efficient vapor/moisture condensation in a complicated industrial environment.

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To mitigate temperature overshoot and dissipate highly concentrated heat from high-power electronic components, it is important to develop an ultrathin vapor chamber/heat spreader to fit in a compact 3D electronic system. As a semiconductor material, silicon is highly thermal conductive, micromachinable and process-compatible with microelectronic manufactures. Thus, a silicon based vapor chamber (SVC) can be directly integrated with microelectronic devices to achieve hot spot cooling, without introducing an additional thermal interface. In this article, development of SVC is initiated from analyses of structural safety, followed by numerical simulations of the liquid and vapor flows. Advanced multiscale wick structures are implemented to balance the heat and mass transports of high heat flux under a gravitational force. On these bases, SVC with structural reinforcement of a 13×8 pillar array is developed through a triple bonding approach. The successful development of the SVCs results in the emergence of a large scale (50mm×70mm) and ultrathin (1mm thick) phase change heat transfer device, with the effective density less than 1.510 3 kg/m 3. Using water as the operating fluid, high effective thermal conductivity over 10,000W/m.K is experimentally demonstrated in both 1D and 2D heat transfer modes.