Condensation is a common phenomenon and is widely exploited in power generation and refrigeration devices. Although drop‐wise condensation offers high heat and mass transfer rates, it is extremely difficult to maintain and control. In this study, the ability to spatially control heterogeneous nucleation on a superhydrophobic surface by manipulating the free energy barrier to nucleation through parameterizing regional roughness scale on the Si nanowire array‐coated surface is reported. Water vapor preferentially condenses on the designed microgrooves on the Si nanowire surface and continuous shedding of the drop‐wise condensate is observed on the surface. The nucleation site density can also be manipulated by tailoring the density of the microgroove on the surface. Moreover, the cycle time on the Si nanowire array with microgrooves is approximately ten times smaller than that on a plain Si surface. This suggests that potentially high heat and mass transfer rates can be achieved on the surface. The insight from this study has implications in enhancing energy efficiency in a wide range of thermal energy conversion systems.

Evaporation from nanopores plays an important role in various natural and industrial processes that require efficient heat and mass transfer. The ultimate performance of nanopore-evaporation-based processes is dictated by evaporation kinetics at the liquid–vapor interface, which has yet to be experimentally studied down to the single nanopore level. Here we report unambiguous measurements of kinetically limited intense evaporation from individual hydrophilic nanopores with both hydrophilic and hydrophobic top outer surfaces at 22 °C using nanochannel-connected nanopore devices. Our results show that the evaporation fluxes of nanopores with hydrophilic outer surfaces show a strong diameter dependence with an exponent of nearly −1.5, reaching up to 11-fold of the maximum theoretical predication provided by the classical Hertz–Knudsen relation at a pore diameter of 27 nm. Differently, the evaporation fluxes of nanopores with hydrophobic outer surfaces show a different diameter dependence with an exponent of −0.66, achieving 66% of the maximum theoretical predication at a pore diameter of 28 nm. We discover that the ultrafast diameter-dependent evaporation from nanopores with hydrophilic outer surfaces mainly stems from evaporating water thin films outside of the nanopores. In contrast, the diameter-dependent evaporation from nanopores with hydrophobic outer surfaces is governed by evaporation kinetics inside the nanopores, which indicates that the evaporation coefficient varies in different nanoscale confinements, possibly due to surface-charge-induced concentration changes of hydronium ions. This study enhances our understanding of evaporation at the nanoscale and demonstrates great potential of evaporation from nanopores.

Given the self-unbridging phenomenon, the confined liquid-film thickness, and the dragging motion observed on the 3D hybrid surfaces, enhanced condensation heat transfer on the 3D hybrid surface over a large subcooling (DT sub) range was achieved. In addition, the obtained heat flux of 655 G 10 kW$m À2 at DT sub $18 K exceeded the values in the literature regarding state-of-the-art micro/ nanostructured surfaces. This suggests that the 3D hybrid surface can be applied to enhance the condensation in various applications.

Micro/nano (two-tier) structures are often employed to achieve superhydrophobicity. In condensation, utilizing such a surface is not necessarily advantageous because the macroscopically observed Cassie droplets are usually in fact partial Wenzel in condensation. The increase in contact angle through introducing microstructures on such two-tier roughened surfaces may result in an increase in droplet departure diameter and consequently deteriorate the performance. In the meantime, nanostructure roughened surfaces could potentially yield efficient shedding of liquid droplets, whereas microstructures roughened surfaces often lead to highly pinned Wenzel droplets. To attain efficient shedding of liquid droplets in condensation on a superhydrophobic surface, a Bond number (a dimensionless number for appraising dropwise condensation) and a solid-liquid fraction smaller than 0.1 and 0.3, respectively, are suggested.