Three dimensional aspects of droplet coalescence during dropwise condensation on superhydrophobic surfaces

Rykaczewski, Konrad; Scott, John Henry J.; Rajauria, Sukumar; Chinn, Jeff; Chinn, Amy M.; Jones, Wanda

doi:10.1039/c1sm06219k

Cited by 94 publications

(107 citation statements)

References 43 publications

Supporting

Mentioning

104

Contrasting

Order By: Relevance

“…In principle, any sub-microscale structures with a small feature size (tip size and interspace) and a certain height (or depth) can become effective candidates for creating CMDSP surfaces. In fact, except for arrays of closely packed nanotips, including nanocones, [22,27,50,69,70] nanoneedles, [21,28,31,66,71] nanopencils, [23] and tip-like nanotubes, [72,73] other architectures such as nano wires, [24,74] nanosheet arrays, [20,29,62,75] nanorod-capped nano pores, [68,76] the porous structure of nanoparticles, [67] nanoparticle aggregates, [73,[77][78][79][80] and two-tier structures [25,57,63,[81][82][83][84][85][86][87][88][89] have all been verified to be effective in endowing material surfaces with the desired CMDSP functionality as long as they follow these basic construction rules.…”

Section: Construction Rules Of Bionic Cmdsp Surfacesmentioning

confidence: 99%

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

2017

View full text Add to dashboard Cite

interest has focused on utilizing the lowadhesivity nature of superhydrophobic surfaces for the rapid removal of condensate microdrops, as this has significance in fundamental research and technological innovation. Example applications are the enhancement of condensation heat transfer for high-efficiency thermal management and energy utilization, [20][21][22][23][24][25] energy-effective antifreezing for airconditioner heat exchangers and aircraft wings, [26][27][28] and electrostatic energy harvesting. [29] In general, condensate drops on typical flat hydrophobic surfaces are only shed off under gravity when their sizes are comparable to the capillary length (≈2.7 mm for water), [30] which creates undesirable effects such as large thermal resistance [20][21][22][23][24][25] and the freezing of subcooled drops. [26][27][28] Clearly, a great challenge is the timely removal of condensate drops at the microscale where the gravitational effect does not work. The latest research has indicated that these small-scale condensate microdrops may self-remove via mutual coalescence as long as the coalescence-released excess surface energy is larger than the interface adhesion-induced energy dissipation. [31] Much effort has been devoted to exploring the utilization of knowledge of bionic low-adhesivity superhydrophobicity to develop innovative condensate microdrop self-propelling (CMDSP) surfaces. Different from traditional superhydrophobic surfaces, which are characterized by the bouncing or rolling off of deposited millimeter-size large drops, [32,33] CMDSP surfaces support the self-removal capability of smallscale condensate microdrops. It has been reported that classical superhydrophobic lotus leaves (Figure 1a), [34][35][36][37] as well as artificial surfaces consisting of hierarchical micro-and nanostructures, [38] one-tier microstructures, [39][40][41][42][43] or nanostructures [44,45] with larger characteristic interspaces, present a low-adhesivity property to the deposited water macrodrops, but become highly adhesive to condensed microdrops (Figure 1b). This is because moisture easily penetrates the microscale valleys or cavities. Clearly, superhydrophobic surfaces with irrationally designed surface structures can enhance the solid-liquid interfacial adhesion instead of promoting the rapid removal of condensed drops. Accordingly, it is still a challenge to design and fabricate very effective low-adhesivity superhydrophobic surfaces with the self-removal ability of condensate microdrops. Recently, there has been a large breakthrough in understanding the mechanism and construction rules of bionic CMDSP surfaces, leading to the exploration of fabrication methods for the surface functionalization of widely used metal materials and the Bionic condensate microdrop self-propelling (CMDSP) surfaces are attracting increased attention as novel, low-adhesivity superhydrophobic surfaces due to their value in fundamental research and technological innovation, e.g., for enhancing heat transfer, energy-effective antifreezing, and...

show abstract

Section: Construction Rules Of Bionic Cmdsp Surfacesmentioning

confidence: 99%

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

2017

View full text Add to dashboard Cite

show abstract

“…While a considerable amount of work has focused on understanding and fabricating superhydrophobic surfaces for potential enhancements in condensation 29,52,54,67,68,74,75,[86][87][88][89][90] , heat transfer measurements that quantify the improvement in performance using these surfaces are limited. In addition, many studies have used well-defined structures to facilitate the understanding of the condensation process (carbon nanotubes 53 , nanowires 54 , and nanoparticle self-assembly 91 , micropillars 55,58 ), however, it is also important to pursue scalable methods of fabricating superhydrophobic surfaces for the implementation in large scale thermal applications.…”

Section: Fabrication Of Scalable Nanostructuresmentioning

confidence: 99%

“…Extending the work of Boreyko, many researchers have modeled 76,[82][83][84] and fabricated 50,52,[85][86][87][88][89] surfaces that show stable droplet jumping. However, if the supersaturation is too large (high nucleation density), flooding occurs and droplets strongly adhered to the surface are formed 47,55 .…”

Section: Droplet Departurementioning

confidence: 99%

Condensation heat transfer on superhydrophobic surfaces

2013

View full text Add to dashboard Cite

(150 words max)Condensation is a phase change phenomenon often encountered in nature and industry for applications including power generation, thermal management, desalination, and environmental control. For the past eight decades, researchers have focused on creating surfaces allowing condensed droplets to be easily removed by gravity for enhanced heat transfer performance.Recent advancements in nanofabrication have enabled increased control of surface structuring for the development of superhydrophobic surfaces with even higher droplet mobility, and in some cases, coalescence-induced droplet jumping. Here, we provide a review of new insights gained to tailor superhydrophobic surfaces for enhanced condensation heat transfer considering the role of surface structure, nucleation density, droplet morphology, and droplet dynamics.Furthermore, we identify challenges and new opportunities to advance these surfaces for broad implementation into thermo-fluidic systems.

show abstract

“…When the drop radii are significantly different, these scaling laws are no longer appropriate. As a matter of fact, coalescence of drops of disparate radii does not always result in jumping from the superhydrophobic surface (21), likely due to the small yet finite adhesion between the superhydrophobic surface and the drops (especially the larger drop). However, cascading coalescence processes will ensure that the larger condensate drops merge with sufficiently large drops sooner or later.…”

Section: Fig 2 Floating Removal Processmentioning

confidence: 99%

Self-cleaning of superhydrophobic surfaces by self-propelled jumping condensate

Wisdom

Watson

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

550

436

View full text Add to dashboard Cite

The self-cleaning function of superhydrophobic surfaces is conventionally attributed to the removal of contaminating particles by impacting or rolling water droplets, which implies the action of external forces such as gravity. Here, we demonstrate a unique self-cleaning mechanism whereby the contaminated superhydrophobic surface is exposed to condensing water vapor, and the contaminants are autonomously removed by the self-propelled jumping motion of the resulting liquid condensate, which partially covers or fully encloses the contaminating particles. The jumping motion off the superhydrophobic surface is powered by the surface energy released upon coalescence of the condensed water phase around the contaminants. The jumping-condensate mechanism is shown to spontaneously clean superhydrophobic cicada wings, where the contaminating particles cannot be removed by gravity, wing vibration, or wind flow. Our findings offer insights for the development of self-cleaning materials.particle adhesion and removal | water-repellant insect wings | nanostructured interfaces | capillary forces B oth natural and synthetic superhydrophobic surfaces are believed to achieve self-cleaning by the so-called "lotus effect" (1, 2). The lotus effect typically refers to the removal of the contaminating particles by impacting and/or rolling water droplets (1, 3). The superhydrophobicity is important because of the associated large contact angle and small hysteresis (4), which promotes the rolling motion carrying away contaminants. According to the conventional wisdom of the lotus effect, the self-cleaning function will cease without incoming droplets or favorable external forces, posing severe restrictions for practical applications of superhydrophobic materials.Here, we demonstrate an autonomous mechanism to achieve self-cleaning on superhydrophobic surfaces, where the contaminants are removed by self-propelled jumping condensate powered by surface energy. When exposed to condensing water vapor, the contaminating particles are either fully enclosed or partially covered with the resulting liquid condensate. Building upon our previous publications showing self-propelled jumping upon drop coalescence (5, 6), we show particle removal by the merged condensate drop with a size comparable to or larger than that of the contaminating particle(s). Further, we report a distinct jumping mechanism upon particle aggregation, without a condensate drop of comparable size to that of the particles, where a group of particles exposed to water condensate clusters together by capillarity and self-propels away from the superhydrophobic surface.The jumping-condensate mechanism reported here offers a unique route toward self-cleaning, with potential applications ranging from microelectronic wafer cleaning to heat exchanger maintenance (7). Particle removal is often accomplished in a gas flow or a liquid stream by hydrodynamic shear stresses, which are parallel to the surface. The parallel hydrodynamic forces are not ideal in competing against the adhesive mech...

show abstract

Three dimensional aspects of droplet coalescence during dropwise condensation on superhydrophobic surfaces

Cited by 94 publications

References 43 publications

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

Condensation heat transfer on superhydrophobic surfaces

Self-cleaning of superhydrophobic surfaces by self-propelled jumping condensate

Contact Info

Product

Resources

About