Condensation heat transfer on two-tier superhydrophobic surfaces

Cheng, Jiangtao; Vandadi, Aref; Chen, Chung‐Lung

doi:10.1063/1.4756800

Cited by 137 publications

(88 citation statements)

References 17 publications

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“…36,56 How to avoid the ooding of nano-textures is one of the key issues to consider in the design and preparation of novel super-hydrophobic textured surfaces. 1-3 And such drops aer coalescence could jump and shi away from the surfaces 1-3,20,21,27,54,55 so that efficient dropwise condensation may be realized.…”

Section: Wetted States Of Condensed Droplets On Rough Surfaces and Thmentioning

confidence: 99%

Growth modes of condensates on nano-textured surfaces and mechanism of partially wetted droplet formation

Liu

Sun

et al. 2013

Soft Matter

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Condensed droplets on different nano-textured surfaces may appear in three distinct wetting states, the Cassie-Baxter state with composite wetting, Wenzel state with complete wetting, and the partially wetted (PW) state. To maintain the super-hydrophobicity of a textured surface, condensed drops on it are usually expected to be in a Cassie-Baxter or PW state. Therefore, it is of importance to clarify the relation between condensed droplet wetting states and the nano-pillar geometries of surfaces. In view of the fact that all condensed droplets in diverse wetting states originate from the nuclei and/or condensate spots growing along different pathways, we think that the distinct growth modes of a condensate correspond to different energy increasing rates (EIRs), and a condensed drop should grow along the route with the minimum EIR. In this paper, accordingly, the EIRs of a droplet on different textured surfaces were analyzed during its growth along three pathways. The results show that the smallest initial EIR of a condensate spot occurs in the increasing contact angel (CA) mode, so that it will grow with the CA enlarging and the base area initially remaining unchanged. Then the EIR of the increasing CA mode becomes much higher than that of the other two modes. The base area of the drop begins to enlarge while the CA remains unchanged. During this period, the increasing base area can be either in a wetted or composite state, resulting in a Wenzel or PW droplet forming, respectively.The growth mode and the wetting state of a condensed droplet are strongly related to the nanostructure of the surface. Additionally, the calculation results of this model are consistent with experimental observations in the literature for the wetting states of condensed drops on nano-textured surfaces, with an accuracy of 91.9%, which is higher than the accuracy of results calculated with previously reported formulas.

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Section: Wetted States Of Condensed Droplets On Rough Surfaces and Thmentioning

confidence: 99%

Growth modes of condensates on nano-textured surfaces and mechanism of partially wetted droplet formation

Liu

Sun

et al. 2013

Soft Matter

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“…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.…”

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confidence: 99%

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

2017

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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...

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“…Most of researchers have focused on fabrication of a non-wetting surface with high water contact angle (WCA), which is measured by a sessile drop. For a couple of decades, there are various well-known methods such as organic promoters [2][3][4][5], fatty acids [6], noble-metal electroplating (gold, silver, and platinum) [7][8][9][10][11][12], hydrophobic polymer coating (polytetrafluoroethylene (PTFE) [13][14][15]), and micro/nano composite-structured surfaces (cuprous oxide [16][17][18][19][20][21], carbon nanotube (CNT) [22]). …”

Section: Introductionmentioning

confidence: 99%