Abstract
In this work, we propose the concept to use the hydrophilic or neutral surface for condensation heat transfer and to use the superhydrophobic surface for enhancement by self-shedding and sweeping of condensate. Molecular dynamics simulation results show that no matter the vapor condenses on the solid surface in dropwise or filmwise mode, the grown-up condensate self-sheds and falls off the superhydrophobic surface, sweeping the growing condensate on the condensing surface downstream. We characterize the dynamics of condensate that the continuous self-shedding and sweeping effectively remove the droplets from the solid surface in dropwise mode or thin the condensate film on the solid surface in filmwise mode, which significantly enhances the condensation heat transfer. We reveal that the mechanism for self-shedding is two-fold: (1) that the external force on condensate bulk defeats the adhesive force between the condensate and the solid surface triggers the self-shedding; (2) the release of the surface free energy of condensate promotes the self-shedding. We also reveal that the mechanism of heat transfer enhancement is essentially due to the timely suppression over the growing condensate bulk on the condensing surface through the self-shedding and sweeping. Finally, we discuss the possible applications.
Highlights
Condensation is a common physical phenomenon that plays an important role in many applications
We use molecular dynamics (MD) simulation to carry out the investigation of condensation on vertically composite nano-surface
In the dual-β cases with β = (0.35,0.10) and β = (0.45,0.10), the density profiles apparently show droplets existing near the condensing surface (x/lx = 0.1~0.2) at t = 5000 τ while the droplets disappears at t = 7000 τ
Summary
Condensation is a common physical phenomenon that plays an important role in many applications (see refs 1 and 2 and references therein). The superhydrophobicity is achieved by physically or chemically reducing the surface free energy, which leads to the coalescence-induced droplet jumping[14, 15]. It has been demonstrated from the molecular level that superhydrophobicity generally serves as a remarkable interfacial thermal resistance due www.nature.com/scientificreports/. The superhydrophobicity leads to very large contact angle (normally above 150°)[6] and reduces the effective heat transfer area (solid-liquid contact area)[20] Considering these aspects, it is necessary to focus on the sustainability and the heat transfer performance of DWC on superhydrophobic surface. We report a new method, using a composite nano-surface, to sustain and enhance condensation heat transfer under external force field and we reveal the microscopic mechanism
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