Droplet size distributions in dropwise condensation heat transfer: Consideration of droplet overlapping and multiple re-nucleation

Xu, Wei; Lan, Zhong; Liu, Qiancheng; Du, Bingang; Ma, Xuehu

doi:10.1016/j.ijheatmasstransfer.2018.07.020

Cited by 30 publications

(28 citation statements)

References 34 publications

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“…To enhance the fidelity of the theoretical calculations, and to enable better insights into near field condensation mechanisms, we developed a numerical simulation by incorporating condensation multi-scale physics and simulating the entire process 56,57 . A superhydrophilic top surface was employed to adsorb condensate from the condensing surface once the droplets reached the top surface.…”

Section: Bridging Dynamicsmentioning

confidence: 99%

“…To optimize the design of the near field condensation system, we performed direct numerical simulations of the condensation process starting from nucleation to droplet growth, coalescence, and departure ( Fig. 6C-D) 56,57 . The nucleation sites were randomly assigned to the condensing surface, using a Poisson distribution 73 .…”

Section: Numerical Simulations Of Near Field Condensationmentioning

confidence: 99%

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Near Field Condensation

Yan

Chen

Zhao

et al. 2020

Preprint

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Dropwise condensation represents the upper limit of condensation heat transfer. Promoting dropwise condensation relies on surface chemical functionalization, and is fundamentally limited by the maximum droplet departure size. A century of research has focused on active and passive methods to enable the removal of ever smaller droplets. However, fundamental contact line pinning limitations prevent gravitational and shear-based removal of droplets smaller than 250 µm. Here, we break this limitation through near field condensation. By de-coupling nucleation, droplet growth, and shedding via droplet transfer between parallel surfaces, we enable the control of droplet population density and removal of droplets as small as 20 µm without the need for chemical modification or surface structuring. We identify droplet bridging to develop a regime map, showing that rational wettability contrast propels spontaneous droplet transfer from condensing surfaces ranging from hydrophilic to hydrophobic. To demonstrate efficacy, we perform condensation experiments on surfaces ranging from hydrophilic to superhydrophobic. The results show that near field condensation with optimal gap spacing can limit the maximum droplet sizes and significantly increase the population density of sub-20 µm droplets. Theoretical analysis and direct numerical simulation confirm the breaking of classical condensation heat transfer paradigms through enhanced heat transfer. Our study not only pushes beyond century-old phase change limitations, it demonstrates a promising method to enhance the efficiency of applications where high, tunable, gravity-independent, and durable condensation heat transfer is required.

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Section: Bridging Dynamicsmentioning

confidence: 99%

Section: Numerical Simulations Of Near Field Condensationmentioning

confidence: 99%

Near Field Condensation

Yan

Chen

Zhao

et al. 2020

Preprint

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“…When a droplet grows large enough to contact with adjacent droplets, they merge and speed up droplet growth, stabilizing the surface coverage to a constant value, known as the self-similarity in dropwise condensation [14,15,17,33,34]. On a vertical or inclined hydrophobic surface, condensed droplets are generally removed by the gravity-driven shedding.…”

Section: Basics Of Dropwise Condensationmentioning

confidence: 99%

“…As a result, condensed droplets with a wide range of sizes exist on a surface, forming a unique self-similarity. The transient characteristic of droplet size distribution has been widely studied to understand the heat transfer mechanism of dropwise condensation [14,17,32,34,51,81,82]. In the initial droplet growth stage after nucleation, all the droplet sizes are uniform and droplet size distribution has a peak value, showing the lognormal distribution (Figure 7a).…”

Section: Nucleation and Droplet Size Distributionmentioning

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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“…Droplet growth mainly depends on the direct condensation of steam on the droplet surface at the initial stage of condensation. However, when the droplet size reaches the combined critical size, the combination between adjacent droplet is the main way for droplet growth [11][12].…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of condensation heat transfer characteristics and corrosion resistance on coated tube surfaces

Wang

2021

THERM SCI

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The condensation heat transfer characteristics and corrosion resistance of copper, Ni-P-Cu, polytetrafluoroethylene, Ni-P and Ni coated tube surfaces were investigated. The results indicate that condensation heat transfer coefficient of Ni-P-Cu, PTFE, Ni-P and Ni coated tubes grows by 36.8%?29.3%, 19.6% and 7.5% than that of copper tubes, respectively. The phase structure of Ni, Ni-P, Ni-P-Cu and PTFE coated tube surfaces is mixed crystal structure(nanocrystals-based), mixed crystal structure (amorphous-based), amorphous structure and crystal structure, respectively. Compared with Ni coating and Ni-P coated tube surfaces, the condensation droplets outside Ni-P-Cu and PTFE coated tubes are smaller in size, more densely distributed, and fall off more quickly, which can significantly promote dropwise condensation. Ni-P-Cu coated tube surfaces achieve optimal condensation heat transfer. The corrosion speed of copper, Ni, Ni-P, Ni-P-Cu and PTFE coated tubes are 86.5, 42.6, 18.2, 10.7 and 6.1 mg?dm-2?d-1, respectively. PTFE coating tubes have the optimal corrosion resistance. Ni-P-Cu and PTFE coated tube surfaces have the best condensation heat transfer characteristics and corrosion resistance, and can be well used in the recovery of waste heat from low-temperature flue gas. The multiple linear regression of the experimental data was carried out to obtain the experimental correlation formula for Nusselt number of convective condensation composite heat transfer for different coated tubes. The relative error between the predicted value and the experimental value is within ?15%.

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Droplet size distributions in dropwise condensation heat transfer: Consideration of droplet overlapping and multiple re-nucleation

Cited by 30 publications

References 34 publications

Near Field Condensation

Near Field Condensation

Advances in Dropwise Condensation: Dancing Droplets

Experimental investigation of condensation heat transfer characteristics and corrosion resistance on coated tube surfaces

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