Numerical investigation of condensation on microstructured surface with wettability patterns

Ke, Zhaoqing; Shi, Junxiang; Zhang, Bo; Chen, Chung‐Lung

doi:10.1016/j.ijheatmasstransfer.2017.08.121

Cited by 22 publications

(10 citation statements)

References 34 publications

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“…In particular, the effects of a pillar microstructure on droplet dynamics (especially droplet coalescence jump, pillar squeezing droplet jump, and droplet dragging by wettability gradients) were investigated. 28 In this work, we go beyond analyzing well-known condensation modes, and we explore sophisticated surface designs that can lead to unique condensation outcomes. Using a computational framework coupling a three-dimensional (3D) volume of fluid (VOF) model with the continuity and momentum equations, 29,30 we propose a novel strategy for enhanced condensate droplet jumping.…”

Section: ■ Introductionmentioning

confidence: 99%

Out-of-Plane Biphilic Surface Structuring for Enhanced Capillary-Driven Dropwise Condensation

et al. 2023

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Rapid and sustained condensate droplet departure from a surface is key toward achieving high heat-transfer rates in condensation, a physical process critical to a broad range of industrial and societal applications. Despite the progress in enhancing condensation heat transfer through inducing its dropwise mode with hydrophobic materials, sophisticated surface engineering methods that can lead to further enhancement of heat transfer are still highly desirable. Here, by employing a threedimensional, multiphase computational approach, we present an effective out-of-plane biphilic surface topography, which reveals an unexplored capillarity-driven departure mechanism of condensate droplets. This texture consists of biphilic diverging microcavities wherein a matrix of small hydrophilic spots is placed at their bottom, that is, among the pyramid-shaped, superhydrophobic microtextures forming the cavities. We show that an optimal combination of the hydrophilic spots and the angles of the pyramidal structures can achieve high deformational stretching of the droplets, eventually realizing an impressive "slingshot-like" droplet ejection process from the texture. Such a droplet departure mechanism has the potential to reduce the droplet ejection volume and thus enhance the overall condensation efficiency, compared to coalescenceinitiated droplet jumping from other state-of-the-art surfaces. Simulations have shown that optimal pyramid-shaped biphilic microstructures can provoke droplet self-ejection at low volumes, up to 56% lower than superhydrophobic straight pillars, revealing a promising new surface microtexture design strategy toward enhancing the condensation heat-transfer efficiency and water harvesting capabilities.

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Section: ■ Introductionmentioning

confidence: 99%

Out-of-Plane Biphilic Surface Structuring for Enhanced Capillary-Driven Dropwise Condensation

et al. 2023

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“…For instance, it is very difficult to measure the variation of pressure water drops in the impacting process. In recent years, some researchers have resorted Volume of Fluid (VOF) method, a fixed-mesh method, in which the interface between immiscible fluids is modelled as the discontinuity in characteristic function (such as volume fraction) to simulate water droplet impacted on the structured surface [26,27].…”

Section: Introductionmentioning

confidence: 99%

Dynamic behaviours of water droplets impacting on laser ablated surfaces

Cai

Luo

Tian

et al. 2019

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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In order to reveal the underlying mechanism of surface microstructure-determined wetting states, this paper adopted Volume of Fluid (VOF) method to investigate the dynamic behaviours of water droplets impacting on surfaces with different structures at low and high Weber numbers. The simulation results showed that the high and stable pressure of air pockets is critical for the formation of the superhydrophobicity. A superhydrophobic substrate will result in shorter recoiling time and longer rebound time for water droplet than the hydrophobic substrate. Furthermore, superhydrophobic surface resulted in higher kinetic energy for water droplet than hydrophobic surfaces, which is the underlying mechanism of microstructureenabled self-cleaning function. High-speed camera tests of laser processed surface microstructures were conducted to validate the observation in dynamic impacting simulation. The results in both high-speed camera testing and VOF simulation proved that water droplet will have a lower adhesion force when impacting superhydrophobic surface than hydrophobic surface.

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“…chemically treating surfaces) to form hybrid regions. Ke et al [30] numerically studied droplet dynamics and condensation enhancement on microstructure surfaces using electrowetting to form different wettability patterns. Inspired by this study, Yan et al [79] proposed an active approach to achieve a similar objective via EWOD for water harvesting studies.…”

Section: Discussionmentioning

confidence: 99%

“…They also reported the electrowetting transport of liquid droplets over a multiscale-roughness-induced superhydrophobic surface and identified a substantial reduction in pressure loss associated with a superhydrophobic surface composed of carbon nanotubes. In 2017, Ke et al [30] conducted numerical analysis of condensation on microstructured surfaces with wettability patterns. They explored the droplet dynamics and heat transfer performance of four wettability patterns: a hydrophilic case, a superhydrophobic case, a hybrid wettability case, and a dynamic wettability case.…”

Section: Motivations For Present Work and Applicationsmentioning

confidence: 99%

“…The paper discussed by Ke et al [30] indicated strong potential to actively control the wettability on hydrophobic surfaces of EWOD devices and achieve higher watercapturing capability, droplet-shedding frequency, and heat transfer rate. This approach would carry great significance for water harvesting systems, and heat transfer systems such as power plants, heat exchangers, and waste heat recovery systems.…”

Section: Motivations For Present Work and Applicationsmentioning

confidence: 99%

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Water harvesting and condensation heat transfer enhancement induced with electrowetting-on-dielectric

Yan¹

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As demand for the world's natural resources continues to rise, energy saving has become an urgent topic. Water harvesting and condensation heat transfer enhancement represent two vital energy-saving objectives. Many researchers have focused on alternating surface wettability by employing advanced materials or complex surface structures to achieve such goals; however, most of these approaches operate in a passive manner. In terms of active methods, electrowetting-on-dielectric (EWOD) has become a popular option owing to its excellent contact angle reversibility, switching speed, and long-term reliability in altering surface wettability. This dissertation presents a study of the EWOD effect on water harvesting and condensation heat transfer. It describes experimental and analytical studies concerning various characteristics such as EWOD-induced droplet dynamics, water capture capability, and heat transfer performance. It also quantifies water harvesting and condensation heat transfer enhancement. This dissertation is divided into four main studies, each of which considers different aspects of the effects of EWOD on water harvesting and condensation heat transfer. The first part of this dissertation (Chapter 2) describes microfabrication technologies to obtain EWOD devices, including low-pressure chemical vapor deposition, photolithography, sputtering deposition, and lift-off and spin coating. Mask designs with different electrode configurations and a device microfabrication protocol are also described. The second part of this dissertation (Chapter 3) presents an experimental investigation of EWOD-induced water harvesting enhancement. EWOD devices were tested in a high-humidity environment under mist flow. Compared with an uncharged EWOD device, the water capture capability of charged devices improved significantly. These results are of great importance, as they indicate strong potential for improvement in water-harvesting applications. The third part of this dissertation (Chapter 4) describes a visualization study of EWOD-regulated condensation droplet distribution. Side-by-side experiments were performed to compare charged and uncharged devices. Charged devices exhibited a regulated droplet distribution, faster droplet growth, more dispersed droplet distribution, and more large droplets. These experimental results introduced a novel approach to actively influence droplet distribution on microfabricated condensing surfaces and showed promise for improving the condensation heat transfer rate via EWOD. The fourth part of this dissertation (Chapter 5) discusses the EWOD effect on the condensation heat transfer coefficient and heat flux. The heat transfer coefficient and heat flux were compared on uncharged and charged (40V DC) EWOD devices. Experimental results demonstrated a positive effect of EWOD on condensation heat transfer. This approach could be incorporated into many industrial applications (e.g., heat exchanger fin surfaces, condensing surfaces of waste heat recovery systems, and components of electronic cooling packages) requiring high-efficiency heat dissipation. In summary, this work makes valuable contributions to the field of water harvesting and condensation heat transfer, proposing a new approach to research in these areas. Findings also detail a new tool to achieve water harvesting and condensation heat transfer enhancement via an active EWOD method.

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Numerical investigation of condensation on microstructured surface with wettability patterns

Cited by 22 publications

References 34 publications

Out-of-Plane Biphilic Surface Structuring for Enhanced Capillary-Driven Dropwise Condensation

Out-of-Plane Biphilic Surface Structuring for Enhanced Capillary-Driven Dropwise Condensation

Dynamic behaviours of water droplets impacting on laser ablated surfaces

Water harvesting and condensation heat transfer enhancement induced with electrowetting-on-dielectric

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