A Comprehensive Model of Electric-Field-Enhanced Jumping-Droplet Condensation on Superhydrophobic Surfaces

Abstract

Superhydrophobic micro/nanostructured surfaces for dropwise condensation have recently received significant attention due to their potential to enhance heat transfer performance by shedding positively charged water droplets via coalescence-induced droplet jumping at length scales below the capillary length, and allowing the use of external electric fields to enhance droplet removal and heat transfer, in what has been termed electric-field-enhanced (EFE) jumping-droplet condensation. However, achieving optimal EFE conditions for enhanced heat transfer requires capturing the details of transport processes that is currently lacking. While a comprehensive model has been developed for condensation on micro/nanostructured surfaces, it cannot be applied for EFE condensation due to the dynamic droplet-vapor-electric field interactions. In this work, I developed a comprehensive physical model for EFE condensation on Furthermore, the results suggest that EFE electrodes can be optimized such that the work input is minimized depending on the condensation heat flux. To analyze overall efficiency, I defined an incremental coefficient-of-performance and showed that it is very high (~10 6 ) for EFE iii condensation. I finally proposed mechanisms for condensate collection which would ensure continuous operation of the EFE system, and which can scalably be applied to industrial condensers. This work provides a comprehensive physical model of the EFE condensation process, and offers guidelines for the design of EFE systems to maximize heat transfer.iv ACKNOWLEDGMENTS

How Surface Orientation Affects Jumping-Droplet Condensation

“…11 This passive jumping mechanism serves to decrease the maximum droplet departure size of the condensate by several orders of magnitude compared to gravitationally driven dropwise condensation. [11][12][13][14] As a result, the heat transfer coefficient of jumping-droplet condensation is at least 30% higher than classical dropwise [15][16][17] and can be even higher when using electric fields, 18,19 tall and interconnected nanowires, 20 or overlaying hydrophilic features. 21,22 The mechanism for out-of-plane droplet jumping is the impact of the coalescing liquid bridge against the low-adhesion substrate.…”

Laplace Pressure Driven Single-Droplet Jumping on Structured Surfaces

“…Droplet transport on and shedding from a surface is vital to the cleaning of plants leaves and insect wings, antibacterial function of animal skins, and spreading of basidiomycete ballistospores . In the industrial world, rapid shedding of droplets from solid surfaces has become the primary bottleneck hindering the enhancement of a plethora of applications including self-cleaning, antifogging, antifrosting, − water harvesting, and condensation heat transfer. − In an effort to enhance droplet shedding, various approaches have been proposed to realize passive or active droplet transport enabled by external electric, − vapor cushion, and capillary and gravitational forces. Among them, droplet self-transport induced by surface chemistry and/or structural properties including wettability gradients, ,, charge density gradients, structure variations, − and diverging tracks ,− have received increasing attention due to their passive nature.…”

Dropwise Condensation on Advanced Functional Surfaces – Theory and Experimental Setup

“…Further investigations aimed to optimize the surface structure of hierarchical SHS or one‐tier nanostructured SHS , to enhance jumping DWC. The jumping drops have also been found to be electrostatically charged , a property that was further investigated for its potential use in electric power generation and for its potential to enhance DWC via an external electric field , , .…”