Grafted Nanofilms Promote Dropwise Condensation of Low-Surface-Tension Fluids for High-Performance Heat Exchangers

Khalil, Karim S.; Soto, Dan; Farnham, Taylor A.; Paxson, Adam; Katmis, Asli Ugur; Gleason, Karen K.; Varanasi, Kripa K.

doi:10.1016/j.joule.2019.04.009

Cited by 52 publications

(48 citation statements)

References 39 publications

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“…Prompt removal of discrete highly wetting droplets has the potential to prevent surface flooding in the condensation process. [4,8,13,14,25]…”

Section: Continual Removal Of Tiny Highly Wetting Droplets On Horizontal Gqlsmentioning

confidence: 99%

“…Grafted nanofilms have improved the durability of condensation surfaces, but the contact angle hysteresis (CAH) of low surface tension liquids is very large (>15 o ). [ 8 ] As a result, existing surfaces for the condensation of low surface tension liquids have two inevitable weaknesses. i) They cannot repel ultralow surface tension liquids with fluorine compounds, such as R134a, FC72, and FC40.…”

Section: Introductionmentioning

confidence: 99%

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Gradient Quasi‐Liquid Surface Enabled Self‐Propulsion of Highly Wetting Liquids

Zhang

Guo

Sarma

et al. 2021

Adv Funct Materials

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Self‐propulsion of highly wetting liquids is important in heat exchanger, air conditioning, and refrigeration systems. However, it is challenging to achieve such a spontaneous motion as these liquids tend to wet all the surfaces due to their ultralow surface tensions. Despite that extensive asymmetric surface structures and gradient chemical coatings are developed for directional droplet transport, they will be flooded and covered by these liquids. Here, this challenge is addressed by creating a gradient quasi‐liquid surface to achieve the self‐propulsion of droplets with surface tensions down to 10.0 mN m−1. Such a surface engineered by tethering flexible polymers with gradient grafting density shows ultralow contact angle hysteresis (<1o) to highly wetting liquids. Thus, the surface can simultaneously provide sufficient driving forces through the gradient wettability and negligible retention forces through the slippery boundary lubrication for spontaneous droplet movement. Moreover, continual self‐propulsion of tiny droplets is achieved by spraying highly wetting liquids in simulated condensation conditions and demonstrates that adding temperature gradient can further accelerate the self‐propulsion. The study provides a new paradigm to promote passive removal of highly wetting droplets, leading to potential impacts in enhancing condensation heat transfer regardless of surface orientations.

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“…Prompt removal of discrete highly wetting droplets has the potential to prevent surface flooding in the condensation process. [4,8,13,14,25]…”

Section: Continual Removal Of Tiny Highly Wetting Droplets On Horizontal Gqlsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Gradient Quasi‐Liquid Surface Enabled Self‐Propulsion of Highly Wetting Liquids

Zhang

Guo

Sarma

et al. 2021

Adv Funct Materials

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“…In most thermal systems, liquid condensate typically forms a liquid film on the heat transfer surface because of the high surface energy of common industrial components such as clean metals. To achieve dropwise condensation for highefficient heat transfer, various hydrophobic coatings such as long-chain fatty acid, polymer materials, rare-earth oxide ceramics, and self-assembled monolayers [14,37,[52][53][54][55][56][57][58], are usually applied to increase hydrophobicity for high water repellency. Monolayer coatings, typically a few nanometers in thickness, for example, long-chain fluorocarbons and fatty acids, can increase water repellency of the surface with a negligible additional thermal resistance (Figure 4a).…”

Section: Surface Fabrication For Dropwise Condensationmentioning

confidence: 99%

“…In addition, the initiated chemical vapor deposition (iCVD) and plasma-enhanced CVD techniques have been used to grow ultrathin conformal polymer coatings to achieve hydrophobicity (Figure 4d). However, further study is necessary to evaluate the durability of these ultrathin coatings for condensation heat transfer enhancement [55,58]. Recently, ultrathin graphene ( Figure 4e) with low thermal Hydrophobic coatings for achieving dropwise condensation.…”

Section: Surface Fabrication For Dropwise Condensationmentioning

confidence: 99%

Advances in Dropwise Condensation: Dancing Droplets

Wen¹,

Ma²

2020

21st Century Surface Science - A Handbook

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Vapor condensation is a ubiquitous phase change phenomenon in nature, as well as widely exploited in various industrial applications such as power generation, water treatment and harvesting, heating and cooling, environmental control, and thermal management of electronics. Condensation performance is highly dependent on the interfacial transport and its enhancement promises considerable savings in energy and resources. Recent advances in micro/nano-fabrication and surface chemistry modification techniques have not only enabled exciting interfacial phenomenon and condensation enhancement but also furthered the fundamental understanding of interfacial wetting and transport. In this chapter, we present an overview of dropwise condensation heat transfer with a focus on improving droplet behaviors through surface design and modification. We briefly summarize the basics of interfacial wetting and droplet dynamics in condensation process, discuss the underlying mechanisms of droplet manipulation for condensation enhancement, and introduce some emerging works to illustrate the power of surface modification. Finally, we conclude this chapter by providing the perspectives for future surface design in the field of condensation enhancement.

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“…However, the most recent literature has focused on promoting dropwise condensation by surface modification, e.g. , low surface energy non-wetting coatings and low-friction lubricant-infused surfaces ( Boreyko and Chen, 2009 ; Cho et al., 2016 ; Dai et al., 2018 ; Gong et al., 2017 ; Hou et al., 2015 ; Khalil et al., 2019 ; Lo et al., 2019 ; Ma et al., 2020 ; Miljkovic et al., 2013 ; Park et al., 2016 ; Preston et al., 2015 ; Rose, 2020 ; Sett et al., 2019 ; Wen et al., 2016 , 2017b , 2017c , 2018a , 2018d ). During “conventional” dropwise condensation, droplets fall off from the surface due to gravity when the droplet diameter grows up to a critical diameter comparable to the capillary length, e.g.…”

Section: Introductionmentioning

confidence: 99%

Coupling droplets/bubbles with a liquid film for enhancing phase-change heat transfer

Wen

Liu

et al. 2021

iScience

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Summary Evaporation, boiling, and condensation are fundamental liquid-vapor phase-change heat transfer processes and have been utilized in many conventional and emerging energy systems. Recent advances in the manipulation of interface wetting and heterogeneous nucleation using micro/nano-structured surfaces have enabled exciting two-phase flow dynamics and heat transfer enhancement. However, independently manipulating droplets, bubbles, or liquid films through surface modification has encountered bottlenecks. In this Perspective, we discuss an emerging strategy where droplets/bubbles are coupled with a liquid film to control fluid dynamics for minimizing the thermal resistance between the liquid-vapor interface and solid substrate, thus significantly enhancing the heat transfer performance beyond the state of the art.

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Grafted Nanofilms Promote Dropwise Condensation of Low-Surface-Tension Fluids for High-Performance Heat Exchangers

Cited by 52 publications

References 39 publications

Gradient Quasi‐Liquid Surface Enabled Self‐Propulsion of Highly Wetting Liquids

Gradient Quasi‐Liquid Surface Enabled Self‐Propulsion of Highly Wetting Liquids

Advances in Dropwise Condensation: Dancing Droplets

Coupling droplets/bubbles with a liquid film for enhancing phase-change heat transfer

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