Electrowetting‐Controlled Dropwise Condensation with Patterned Electrodes: Physical Principles, Modeling, and Application Perspectives

Abstract

Patterning the wettability of solid surfaces is a successful strategy to control the dropwise condensation of vapor onto partially wetting solid surfaces. The condensation of water vapor onto electrowetting‐functionalized surfaces is studied with structured co‐planar electrodes. A detailed analysis of the experimental distribution of millions of drops reveals that despite the presence of contact angle hysteresis and the occurrence of random drop coalescence events, the preferential drop positions closely follow the numerically calculated local minima of the electrostatic energy for variable drop size. Even subtle transitions between competing preferred locations are properly reproduced by the model. Based on this quantitative understanding of the condensation patterns, a series of important follow‐up steps that need to be taken to demonstrate a reliable performance gain in various applications focusing in particular on enhanced heat transfer is discussed.

Interaction of Potential Sources in Infinite 2D Arrays: Diffusion through Composite Membranes, Micro‐Electrochemistry, Entrance Resistance, and Other Examples

“…[35] We will consider elliptical discs. Their electrical capacity has been shown to be proportional to 2𝜋a e ∕K(k) where a e is the length of the larger axis of the ellipse, K(k) is the complete elliptic integral of the first kind, and k ≡ √ 1 − (b e ∕a e ) 2 , where b e is the length of the smaller axis. Actually, in electrostatics the capacity is two times larger.…”

“…In a number of cases, such processes occur in highly heterogeneous structures. Examples are as diverse as evaporation of multiple sessile drops, water-vapor condensation on structured surfaces, [1,2] dissolution of nano-bubbles or nano-droplets attached to surfaces, [3] plant transpiration via stomata, [4] currentinduced concentration polarization of arrays of microelectrodes, [5][6][7] solvent and solute flows in thin-film composite membranes, [8] soil drainage using perforated tubes, [9,10] or fluid flows in composite materials containing perforated layers. [11,12] A useful mathematical idealization of such structures is impervious domains alternating with zones of extremely high "conductivity" (or permeability or diffusivity depending on the process).…”

Interplay of Drop Shedding Mechanisms on High Wettability Contrast Biphilic Stripe-Patterned Surfaces

“…To further enhance drop shedding, recent investigations have revealed that surfaces that are biphilic (i.e., surfaces with both hydrophilic and hydrophobic patterns) increase water and fog collection rates. ,− The innovation of these surfaces was inspired by nature, , such as cacti, , Namib desert beetles, , and Moloch Horridus lizards, which have unique microstructured surfaces increasing favorable contact angle hysteresis on their skin to collect and transport water efficiently for ingestion. The fabrication of the bioinspired interfaces is of great importance to enhancing water harvesting efficiencies, and emerging advanced manufacturing techniques have shed light on biomimicry potential with varying degrees of success.…”