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Статті в журналах з теми "Condensation droplet jumping"

Автор: Grafiati

Опубліковано: 11 березня 2023

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1

Gao, Sihang, Fuqiang Chu, Xuan Zhang, and Xiaomin Wu. "Behavior of condensed droplets growth and jumping on superhydrophobic surface." E3S Web of Conferences 128 (2019): 07003. http://dx.doi.org/10.1051/e3sconf/201912807003.

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Droplets on the superhydrophobic surface can fall off the surface spontaneously, which greatly promote dropwise condensation. This study considers a continuous droplet condensation process including droplet growth and droplet jumping. A droplet growth model considered NCG is developed and droplet jumping is simulated using VOF (Volume Of Fluid) model. Al–based superhydrophobic surfaces are prepared using chemical deposition and etching method. The Al-based superhydrophobic surface has a contact angle of 157°±1° and a rolling angle of 2°±1°. An observation experiment is designed to observe droplet jumping on superhydrophobic surface using a high– speed camera system. The result of droplet growth model shows a good match with experimental data in mid-term of droplet growth. Fordroplet jumping, simulation and experiment results show that droplet jumping of different diameter hasa universality in a non–dimensional form. The jumping process can be divided into 3 stages and droplet vibration is observed.

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2

Birbarah, Patrick, Shreyas Chavan, and Nenad Miljkovic. "Numerical Simulation of Jumping Droplet Condensation." Langmuir 35, no. 32 (July 12, 2019): 10309–21. http://dx.doi.org/10.1021/acs.langmuir.9b01253.

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3

Chongyan, Zhao, Chen Feng, Yan Xiao, Yan He, Huang Zhiyong, and Bo Hanliang. "SIMULATION OF DROPLET SIZE DISTRIBUTION DURING JUMPING-DROPLET CONDENSATION." Proceedings of the International Conference on Nuclear Engineering (ICONE) 2019.27 (2019): 1748. http://dx.doi.org/10.1299/jsmeicone.2019.27.1748.

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4

Zhang, Lenan, Zhenyuan Xu, Zhengmao Lu, Jianyi Du, and Evelyn N. Wang. "Size distribution theory for jumping-droplet condensation." Applied Physics Letters 114, no. 16 (April 22, 2019): 163701. http://dx.doi.org/10.1063/1.5081053.

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5

Mukherjee, Ranit, Austin S. Berrier, Kevin R. Murphy, Joshua R. Vieitez, and Jonathan B. Boreyko. "How Surface Orientation Affects Jumping-Droplet Condensation." Joule 3, no. 5 (May 2019): 1360–76. http://dx.doi.org/10.1016/j.joule.2019.03.004.

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6

Birbarah, Patrick, and Nenad Miljkovic. "Internal convective jumping-droplet condensation in tubes." International Journal of Heat and Mass Transfer 114 (November 2017): 1025–36. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2017.06.122.

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7

Nath, Saurabh, S. Farzad Ahmadi, Hope A. Gruszewski, Stuti Budhiraja, Caitlin E. Bisbano, Sunghwan Jung, David G. Schmale, and Jonathan B. Boreyko. "‘Sneezing’ plants: pathogen transport via jumping-droplet condensation." Journal of The Royal Society Interface 16, no. 155 (June 2019): 20190243. http://dx.doi.org/10.1098/rsif.2019.0243.

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We show that condensation growing on wheat leaves infected with the leaf rust fungus, Puccinia triticina , is capable of spontaneously launching urediniospores off the plant. This surprising liberation mechanism is enabled by the superhydrophobicity of wheat leaves, which promotes a jumping-droplet mode of condensation powered by the surface energy released from coalescence events. We found that urediniospores often adhere to the self-propelled condensate, resulting in liberation rates of approximately 10 cm −2 h −1 for leaves infected with rust. Urediniospores were catapulted up to 5 mm from the leaf’s surface, a distance sufficient to clear the laminar boundary layer for subsequent dispersal even in gentle winds.

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8

Mulroe, Megan D., Bernadeta R. Srijanto, S. Farzad Ahmadi, C. Patrick Collier, and Jonathan B. Boreyko. "Tuning Superhydrophobic Nanostructures To Enhance Jumping-Droplet Condensation." ACS Nano 11, no. 8 (July 31, 2017): 8499–510. http://dx.doi.org/10.1021/acsnano.7b04481.

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9

Antao, Dion S., Kyle L. Wilke, Jean H. Sack, Zhenyuan Xu, Daniel J. Preston, and Evelyn N. Wang. "Jumping droplet condensation in internal convective vapor flow." International Journal of Heat and Mass Transfer 163 (December 2020): 120398. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2020.120398.

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10

Ashrafi-Habibabadi, Amir, and Ali Moosavi. "Droplet condensation and jumping on structured superhydrophobic surfaces." International Journal of Heat and Mass Transfer 134 (May 2019): 680–93. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2019.01.026.

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11

Liao, Ming-Jun, and Li-Qiang Duan. "Investigation of Coalescence-Induced Droplet Jumping on Mixed-Wettability Superhydrophobic Surfaces." Processes 9, no. 1 (January 12, 2021): 142. http://dx.doi.org/10.3390/pr9010142.

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Coalescence-induced droplet jumping has received more attention recently, because of its potential applications in condensation heat transfer enhancement, anti-icing and self-cleaning, etc. In this paper, the molecular dynamics simulation method is applied to study the coalescence-induced jumping of two nanodroplets with equal size on the surfaces of periodic strip-like wettability patterns. The results show that the strip width, contact angle and relative position of the center of two droplets are all related to the jumping velocity, and the jumping velocity on the mixed-wettability superhydrophobic surfaces can exceed the one on the perfect surface with a 180° contact angle on appropriately designed surfaces. Moreover, the larger both the strip width and the difference of wettability are, the higher the jumping velocity is, and when the width of the hydrophilic strip is fixed, the jumping velocity becomes larger with the increase of the width of the hydrophobic strip, which is contrary to the trend of fixing the width of the hydrophobic strip and altering the other strip width.

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12

Miljkovic, Nenad, Ryan Enright, Youngsuk Nam, Ken Lopez, Nicholas Dou, Jean Sack, and Evelyn N. Wang. "Jumping-Droplet-Enhanced Condensation on Scalable Superhydrophobic Nanostructured Surfaces." Nano Letters 13, no. 1 (December 17, 2012): 179–87. http://dx.doi.org/10.1021/nl303835d.

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13

Birbarah, Patrick, and Nenad Miljkovic. "External convective jumping-droplet condensation on a flat plate." International Journal of Heat and Mass Transfer 107 (April 2017): 74–88. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2016.11.016.

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14

Mukherjee, Ranit, Hope A. Gruszewski, Landon T. Bilyeu, David G. Schmale, and Jonathan B. Boreyko. "Synergistic dispersal of plant pathogen spores by jumping-droplet condensation and wind." Proceedings of the National Academy of Sciences 118, no. 34 (August 20, 2021): e2106938118. http://dx.doi.org/10.1073/pnas.2106938118.

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Plant pathogens are responsible for the annual yield loss of crops worldwide and pose a significant threat to global food security. A necessary prelude to many plant disease epidemics is the short-range dispersal of spores, which may generate several disease foci within a field. New information is needed on the mechanisms of plant pathogen spread within and among susceptible plants. Here, we show that self-propelled jumping dew droplets, working synergistically with low wind flow, can propel spores of a fungal plant pathogen (wheat leaf rust) beyond the quiescent boundary layer and disperse them onto neighboring leaves downwind. An array of horizontal water-sensitive papers was used to mimic healthy wheat leaves and showed that up to 25 spores/h may be deposited on a single leaf downwind of the infected leaf during a single dew cycle. These findings reveal that a single dew cycle can disperse copious numbers of fungal spores to other wheat plants, even in the absence of rain splash or strong gusts of wind.

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15

Wen, Rongfu, Shanshan Xu, Dongliang Zhao, Yung-Cheng Lee, Xuehu Ma, and Ronggui Yang. "Hierarchical Superhydrophobic Surfaces with Micropatterned Nanowire Arrays for High-Efficiency Jumping Droplet Condensation." ACS Applied Materials & Interfaces 9, no. 51 (December 15, 2017): 44911–21. http://dx.doi.org/10.1021/acsami.7b14960.

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16

Meng, Kaixin, Wenli Fan, and Hao Wang. "Dynamic scenario simulation of dropwise condensation on a superhydrophobic surface with droplet jumping." Applied Thermal Engineering 148 (February 2019): 316–23. http://dx.doi.org/10.1016/j.applthermaleng.2018.11.049.

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17

Birbarah, Patrick, Zhaoer Li, Alexander Pauls, and Nenad Miljkovic. "A Comprehensive Model of Electric-Field-Enhanced Jumping-Droplet Condensation on Superhydrophobic Surfaces." Langmuir 31, no. 28 (July 6, 2015): 7885–96. http://dx.doi.org/10.1021/acs.langmuir.5b01762.

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18

Yuvaraj, R., and Kumar Senthkil. "Study of droplet dynamics and condensation heat transfer on superhydrophobic copper surface." Thermal Science, no. 00 (2020): 89. http://dx.doi.org/10.2298/tsci190126089y.

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Superhydrohobic surface for dropwise condensation is prepared using hotplate solution immersion method on copper substrate. The preprocessed bare copper plate is immersed in a solution consist of 0.004 - 0.008M ethanol (CH3?CH2?OH) and tetradecanoic acid (CH3(CH2)12COOH) then heating the plates in the solution at 30 - 50?C for 1 - 6 hours. The contact angle of water droplet on the prepared surface is measured using Low Bond Axisymmetric Drop Shape Analysis (LBADSA), which gives the maximum contact angle of 168? and average value of 166? ? 2?. The maximum contact angle is obtained by adjusting the composition of the solution, temperature of the solution and immersion time to 0.006M, 45? and 4 hours respectively. The various superhydrophobic surfaces are prepared by changing constituents of solution, hotplate temperature and processing time respectively. Further dynamic behavior of water droplet on the prepared surfaces like jumping effect and rolling effect is presented in this work. In addition, experimental work is carried out on the prepared surface for dropwise condensation and the obtained results are compared with condensation on bare copper plate produces higher heat transfer coefficient.

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19

Wang, Xin, Jingyi Chang, Zhenqian Chen, and Bo Xu. "Mesoscopic lattice Boltzmann simulation of droplet jumping condensation heat transfer on the microstructured surface." International Communications in Heat and Mass Transfer 127 (October 2021): 105567. http://dx.doi.org/10.1016/j.icheatmasstransfer.2021.105567.

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20

Yanagisawa, Kosuke, Munetoshi Sakai, Toshihiro Isobe, Sachiko Matsushita, and Akira Nakajima. "Investigation of droplet jumping on superhydrophobic coatings during dew condensation by the observation from two directions." Applied Surface Science 315 (October 2014): 212–21. http://dx.doi.org/10.1016/j.apsusc.2014.07.120.

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21

Cheng, Yongpan, Jinliang Xu, and Yi Sui. "Numerical investigation of coalescence-induced droplet jumping on superhydrophobic surfaces for efficient dropwise condensation heat transfer." International Journal of Heat and Mass Transfer 95 (April 2016): 506–16. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2015.11.074.

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22

Fedorova, Nataliia, Christian Lindner, Lucia Helena Prado, Vojislav Jovicic, Ana Zbogar-Rasic, Sannakaisa Virtanen, and Antonio Delgado. "Effect of Steam Flow Rate and Storage Period of Superhydrophobic-Coated Surfaces on Condensation Heat Flux and Wettability." Processes 9, no. 11 (November 2, 2021): 1958. http://dx.doi.org/10.3390/pr9111958.

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The jumping-droplet phenomenon occurring on superhydrophobic (SHPhob) surfaces under special conditions may be beneficial for numerous systems using condensation, due to the reported increased heat transfer coefficients. One technique to create a SHPhob surface is coating, which can be applied to larger areas of existing elements. However, challenges are associated with coating stability and the realization of continuous dropwise condensation. This research examined the condensation of steam at different flow rates (2, 4 and 6 g/min) and its influence on heat flux and water contact angles on the SHPhob spray-coated aluminum samples. Special emphasis on the impact of time was addressed through a series of one and five-hour condensation experiments on the samples with different storage periods (coated either one year ago or shortly before testing). Over the experimental series at a higher steam flow rate (6 g/min), heat flux decreased by 20% through the old-coated samples and water contact angles transferred from the superhydrophobic (147°) to hydrophobic (125°) region. This can be attributed to the joint effects of the partial coating washout and the adsorption of the condensed water within the porous structures of the coating during steam condensation. The new-coated samples could sustain more than fifty hours of condensation, keeping the same heat fluxes and SHPhob characteristics.

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23

Ma, Jingcheng, Zhuoyuan Zheng, Muhammad Jahidul Hoque, Longnan Li, Kazi Fazle Rabbi, Jin Yao Ho, Paul V. Braun, Pingfeng Wang, and Nenad Miljkovic. "A Lipid-Inspired Highly Adhesive Interface for Durable Superhydrophobicity in Wet Environments and Stable Jumping Droplet Condensation." ACS Nano 16, no. 3 (March 11, 2022): 4251–62. http://dx.doi.org/10.1021/acsnano.1c10250.

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24

Zhang, Hongqiang, Guanlei Zhao, Shuwang Wu, Yousif Alsaid, Wenzheng Zhao, Xiao Yan, Lei Liu, et al. "Solar anti-icing surface with enhanced condensate self-removing at extreme environmental conditions." Proceedings of the National Academy of Sciences 118, no. 18 (April 26, 2021): e2100978118. http://dx.doi.org/10.1073/pnas.2100978118.

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The inhibition of condensation freezing under extreme conditions (i.e., ultra-low temperature and high humidity) remains a daunting challenge in the field of anti-icing. As water vapor easily condensates or desublimates and melted water refreezes instantly, these cause significant performance decrease of most anti-icing surfaces at such extreme conditions. Herein, inspired by wheat leaves, an effective condensate self-removing solar anti-icing/frosting surface (CR-SAS) is fabricated using ultrafast pulsed laser deposition technology, which exhibits synergistic effects of enhanced condensate self-removal and efficient solar anti-icing. The superblack CR-SAS displays superior anti-reflection and photothermal conversion performance, benefiting from the light trapping effect in the micro/nano hierarchical structures and the thermoplasmonic effect of the iron oxide nanoparticles. Meanwhile, the CR-SAS displays superhydrophobicity to condensed water, which can be instantly shed off from the surface before freezing through self-propelled droplet jumping, thus leading to a continuously refreshed dry area available for sunlight absorption and photothermal conversion. Under one-sun illumination, the CR-SAS can be maintained ice free even under an ambient environment of −50 °C ultra-low temperature and extremely high humidity (ice supersaturation degree of ∼260). The excellent environmental versatility, mechanical durability, and material adaptability make CR-SAS a promising anti-icing candidate for broad practical applications even in harsh environments.

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25

Lv, Cunjing, Pengfei Hao, Zhaohui Yao, Yu Song, Xiwen Zhang, and Feng He. "Condensation and jumping relay of droplets on lotus leaf." Applied Physics Letters 103, no. 2 (July 8, 2013): 021601. http://dx.doi.org/10.1063/1.4812976.

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26

Preston, Daniel J., and Evelyn N. Wang. "Jumping Droplets Push the Boundaries of Condensation Heat Transfer." Joule 2, no. 2 (February 2018): 205–7. http://dx.doi.org/10.1016/j.joule.2018.01.011.

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27

QUAN, YUN-YUN, PEI-GUO JIANG, and LI-ZHI ZHANG. "DEVELOPMENT OF FRACTAL ULTRA-HYDROPHOBIC COATING FILMS TO PREVENT WATER VAPOR DEWING AND TO DELAY FROSTING." Fractals 22, no. 03 (September 2014): 1440002. http://dx.doi.org/10.1142/s0218348x14400027.

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Superhydrophobic films fabricated on copper and aluminum surfaces have potential applications to solve water condensation and frosting problems on chilled ceiling system. The rough surfaces of copper foils obtained by solution immersion method exhibit the existence of fractal structures. The hydrophobicity of copper surfaces is enhanced with fractal structures. The relationship between contact angles (CAs) and the fractal dimensions (FDs) for surface roughness of Cu samples with different etching time is investigated. Moisture condensation and frosting experiments on the two kinds of surfaces are conducted in natural environment under different chilling temperatures. During condensation, micro water condensate droplets drift down the surface like dust floating in the air. Several larger condensate droplets about 1–2 mm appear on the substrates after 3 h condensation. This continuous jumping motion of the condensate will be beneficial in delaying frosting. The results demonstrate that dense nanostructures on copper surfaces are superior to loose lattice-like microstructures on aluminum surfaces for preventing the formation of large droplets condensate and in delaying the icing. The large water droplets of 2–3 mm in diameter that would form on a common metal foil are sharply decreased to dozens of microns and small droplets are formed on a modified surface, which will then drift down like a fog.

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28

Miljkovic, Nenad, Ryan Enright, and Evelyn N. Wang. "Modeling and Optimization of Superhydrophobic Condensation." Journal of Heat Transfer 135, no. 11 (September 23, 2013). http://dx.doi.org/10.1115/1.4024597.

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Superhydrophobic micro/nanostructured surfaces for dropwise condensation have recently received significant attention due to their potential to enhance heat transfer performance by shedding water droplets via coalescence-induced droplet jumping at length scales below the capillary length. However, achieving optimal surface designs for such behavior requires capturing the details of transport processes that is currently lacking. While comprehensive models have been developed for flat hydrophobic surfaces, they cannot be directly applied for condensation on micro/nanostructured surfaces due to the dynamic droplet-structure interactions. In this work, we developed a unified model for dropwise condensation on superhydrophobic structured surfaces by incorporating individual droplet heat transfer, size distribution, and wetting morphology. Two droplet size distributions were developed, which are valid for droplets undergoing coalescence-induced droplet jumping, and exhibiting either a constant or variable contact angle droplet growth. Distinct emergent droplet wetting morphologies, Cassie jumping, Cassie nonjumping, or Wenzel, were determined by coupling of the structure geometry with the nucleation density and considering local energy barriers to wetting. The model results suggest a specific range of geometries (0.5–2 μm) allowing for the formation of coalescence-induced jumping droplets with a 190% overall surface heat flux enhancement over conventional flat dropwise condensing surfaces. Subsequently, the effects of four typical self-assembled monolayer promoter coatings on overall heat flux were investigated. Surfaces exhibiting coalescence-induced droplet jumping were not sensitive (<5%) to the coating wetting characteristics (contact angle hysteresis), which was in contrast to surfaces relying on gravitational droplet removal. Furthermore, flat surfaces with low promoter coating contact angle hysteresis (<2 deg) outperformed structured superhydrophobic surfaces when the length scale of the structures was above a certain size (>2 μm). This work provides a unified model for dropwise condensation on micro/nanostructured superhydrophobic surfaces and offers guidelines for the design of structured surfaces to maximize heat transfer. Keywords: superhydrophobic condensation, jumping droplets, droplet coalescence, condensation optimization, environmental scanning electron microscopy; micro/nanoscale water condensation, condensation heat transfer.

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29

Hoque, Muhammad Jahidul, Shreyas Chavan, Ross Lundy, Longnan Li, Jingcheng Ma, Xiao Yan, Shenghui Lei, Nenad Miljkovic, and Ryan Enright. "Biphilic jumping-droplet condensation." Cell Reports Physical Science, March 2022, 100823. http://dx.doi.org/10.1016/j.xcrp.2022.100823.

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30

Hoque, Muhammad Jahidul, Shreyas Chavan, Ross Lundy, Longnan Li, Jingcheng Ma, Xiao Yan, Shenghui Lei, Nenad Miljkovic, and Ryan Enright. "Biphilic Jumping-Droplet Condensation." SSRN Electronic Journal, 2021. http://dx.doi.org/10.2139/ssrn.3956661.

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31

Ma, Chen, Li Chen, Lin Wang, Wei Tong, Chenlei Chu, Zhiping Yuan, Cunjing Lv, and Quanshui Zheng. "Condensation droplet sieve." Nature Communications 13, no. 1 (September 14, 2022). http://dx.doi.org/10.1038/s41467-022-32873-1.

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AbstractLarge droplets emerging during dropwise condensation impair surface properties such as anti-fogging/frosting ability and heat transfer efficiency. How to spontaneously detach massive randomly distributed droplets with controlled sizes has remained a challenge. Herein, we present a solution called condensation droplet sieve, through fabricating microscale thin-walled lattice structures coated with a superhydrophobic layer. Growing droplets were observed to jump off this surface once becoming slightly larger than the lattices. The maximum radius and residual volume of droplets were strictly confined to 16 μm and 3.2 nl/mm2 respectively. We reveal that this droplet radius cut off is attributed to the large tolerance of coalescence mismatch for jumping and effective isolation of droplets between neighboring lattices. Our work brings forth a strategy for the design and fabrication of high-performance anti-dew materials.

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32

Wang, Hai, Quang Nguyen, Jae W. Kwon, Jing Wang, and Hongbin Ma. "Droplets Jumping from a Hybrid Superhydrophilic and Superhydrophobic Surface." Journal of Heat Transfer 139, no. 2 (January 6, 2017). http://dx.doi.org/10.1115/1.4035578.

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The wetting condition effect of the condensation process on a hybrid superhydrophobic and superhydrophilic copper surface as shown in Fig. 1a was experimentally investigated. The superhydrophilic surface (Fig. 1b) consists of micro-flowers (CuO) and nanorods (Cu(OH)2) obtained by immersing the copper substrate into alkaline solution of 2.5 M sodium hydroxide and 0.1 M ammonium persulphate, and the superhydrophobic nanostructured surface (Fig. 1c) was formed by spin coating the Cytop on the hierarchically structured CuO / Cu(OH)2 surface. Experimental results show that the film condensation started on the superhydrophilic region while the dropwise condensation of tiny droplets with an average contact angle of 160° were formed on the superhydrophobic region. Because the film condensation was confined within the superhydrophilic region of 1 mm x 1 mm, the contact angle of this droplet became larger and larger. When a tiny droplet developed on the superhydrophobic area joins with the big droplet formed on the superhydrophilic surface (square region), the coalesced droplet obtains additional energy and jumps off from the condensing surface.

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33

刘小娟, 李占琪, 金志刚, 黄智, 魏加争, 赵存陆, and 王战涛. "Energy Conversion During Eletrowetting-Induced Jumping of Droplets." Acta Physica Sinica, 2022, 0. http://dx.doi.org/10.7498/aps.71.20212133.

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Many industrial processes such as condensation cooling and fuel cells demand solid-liquid separation. Electrowetting is a very efficient approach for detaching droplets from hydrophobic surface, and it is easy to control. In this study the EW-actuated droplet jumping motion on superhydrophobic surface was captured using high-speed camera. The threshold voltage driving droplet detachment was estimated based on the deformation and contact angle change of the droplet. The varying forms of energy during droplet detachment and repeated bouncing was analyzed and calculated using Matlab program. Our result indicates that AC pulse is more efficient in promoting droplet jumping, because AC-driven dynamic oscillation endows the droplet with more interfacial energy. By revealing the mechanism of energy conversion and dissipation during electrowetting-induced droplet jumping, this study offers valuable insights to related industrial applications such as solid-liquid separation and three dimensional digital microfluidics.

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34

Chakraborty, Soumik, Uttam Kumar Kar, Sayantan Sengupta, and Shantanu Pramanik. "Influence of jumping-droplet condensation on the properties of separated flow in an air-cooled condenser tube: An Euler-Lagrange approach." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, November 18, 2022, 095765092211386. http://dx.doi.org/10.1177/09576509221138623.

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An Air-cooled condenser (ACC), which finds popularity in a steam power plant in arid areas, is usually less efficient as film condensation occurs inside the condenser tube. Recent research is directed towards eliminating the thermally insulating liquid film with the application of novel superhydrophobic surfaces. The self-cleaning property of such surfaces facilitates easy condensate drainage in the form of jumping droplets exposing favourable nucleation sites, thereby significantly promoting dropwise condensation. The present study explores the characteristics of jumping droplet condensation in finite condenser tubes using computational fluid dynamics (CFD). The wall-heat-flux for condensation is modelled here by a uniform suction boundary condition. The strength of suction is quantified by a suction Reynolds number Re s. We mainly focus on the zone corresponding to 2.3 < Re s < 10, where no previous solution exists. In a long horizontal tube, the progressive realization of a self-similar region starting from the developing regions is demonstrated. We examine the characteristics of the developing region based on the sign of the pressure gradient. The results of three-dimensional CFD simulations illustrate the variations of droplet trajectories with the inception size and coordinates of jumping droplets determined locally by the relative contributions of various force components, viz. gravity, axial drag in the vapour core, suction induced radial drag and Saffman lift. The present study also predicts the effect of pipeline inclination on condensate drainage. Ultimately, considering multiple jumps, we found that the maximum condensate emission can be obtained for small droplets (5−15 μm), while medium-sized droplets (20−50 μm) are most advantageous for isolated jumps.

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35

Aili, Abulimiti, QiaoYu Ge, and TieJun Zhang. "How Nanostructures Affect Water Droplet Nucleation on Superhydrophobic Surfaces." Journal of Heat Transfer 139, no. 11 (June 21, 2017). http://dx.doi.org/10.1115/1.4036763.

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Nucleation is the first stage of phase change phenomena, including condensation on nanostructured superhydrophobic surfaces. Despite plenty of theoretical studies on the effect of nanostructure density and shape on water droplet nucleation, not many experimental investigations have been reported. Here, we show both experimentally and theoretically that a moderate increase in the nanostructure density can lead to an increase in the nucleation density of water droplets because of the decreased energy barrier of nucleation in cavities formed between the nanostructures. Specifically, we observed droplets aligned in regions with denser nanostructures. The number and average volume of the aligned droplets in these regions were larger than that of the droplets in the surrounding areas. However, nucleation in cavities subsequently caused initial pinning of the droplet base within the nanostructures, forming a balloonlike, slightly elongated droplet shape. The dewetting transition of the pinned droplets from the Wenzel state to the unpinned Cassie state was predicted by quantifying the aspect ratio of droplets ranging from 3 to 30 μm. Moreover, the coalescence-jumping of droplets was followed by a new cycle of droplet condensation in an aligned pattern in an emptied area. These findings offer guidelines for designing enhanced superhydrophobic surfaces for water and energy applications.

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36

Xie, Fang-Fang, Dan-Qi Wang, Yi-Bo Wang, Yan-Ru Yang, and Xiao-Dong Wang. "Coalescence-induced jumping of nanodroplets on mixed-wettability superhydrophobic surfaces." Canadian Journal of Physics, June 1, 2020. http://dx.doi.org/10.1139/cjp-2020-0060.

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Coalescence-induced droplet jumping on superhydrophobic surfaces has been observed at microscale and even nanoscale. The enhancement in jumping velocity of coalescing droplets is crucial for condensation heat transfer enhancement, anti-icing, self-cleaning, and so forth. However, the research on how to acquire a higher jumping velocity is really very limited. In this paper, we use molecular dynamics simulations to study the coalescence-induced jumping of two equally-sized nanodroplets on chemically heterogeneous surfaces composed of alternating stripes with different hydrophobicity. We show that the jumping velocity is closely related to the stripe width and wettability contrast, and it can even exceed that on an ideal superhydrophobic surface with 180° contact angle when the striped surfaces are properly designed. We also demonstrate that there is always an optimal stripe width yielding the maximum jumping velocity, whereas its value is independent of the wettability contrast. We reveal that the dominant factor to determine the jumping velocity is the apparent contact angle of equilibrated droplets over heterogeneous surfaces for small stripe widths, it changes to the time of liquid bridges impacting surfaces for moderate stripe widths and to the contact area between equilibrated droplets and relatively hydrophobic stripes for large stripe widths. We believe the present simulations can provide useful guidance to design self-jumping superhydrophobic surfaces.

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37

Wang, Hai, Quang Nguyen, Jae W. Kwon, and Hongbin Ma. "Condensation and Wetting Behavior on Hybrid Superhydrophobic and Superhydrophilic Copper Surfaces." Journal of Heat Transfer 142, no. 4 (February 20, 2020). http://dx.doi.org/10.1115/1.4046209.

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Abstract A novel hybrid superhydrophobic and superhydrophilic copper surface was fabricated using a lift-off process to integrate the benefits of dropwise and filmwise condensation together. The superhydrophilic surface was comprised of microflower like CuO and nanorod Cu(OH)2 with a diameter in the range of 200–600 nm and the superhydrophobic surface was fabricated by chemical modification with Cytop on the hierarchically structured surface of CuO/Cu(OH)2. Wetting condition effect on the hybrid surface was investigated experimentally with a high-speed camera attached to a microscope and an environmental scanning electrical microscope (ESEM). Out-of-plane droplet jumping motion on superhydrophilic region and gravity effect on the droplet motion were examined. Experiment results showed that effective heat transfer coefficients of hybrid superhydrophobic and superhydrophilic surfaces were improved as compared with those of pure superhydrophobic surface. Comparison results between two hybrid surfaces with 2 and 4 mm pattern pitches indicated that the distance reduction between two neighboring superhydrophilic areas can enhance the condensation performance because short distance can promote the microcondensate coalescence and droplets removal.

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38

Oh, Junho, Sabrina Yin, Catherine E. Dana, Sungmin Hong, Jessica K. Roman, Kyoo Dong Jo, Shreyas Chavan, Don Cropek, Marianne Alleyne, and Nenad Miljkovic. "Cicada-inspired self-cleaning superhydrophobic surfaces." Journal of Heat Transfer 141, no. 10 (September 13, 2019). http://dx.doi.org/10.1115/1.4044677.

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Abstract Water-based heat transfer surfaces in HVAC&R (Heating, Ventilation, Air Conditioning and Refrigeration) systems have biofouling or microbial growth which might not only impose adverse effects to public health but also deteriorate the heat transfer performance of surfaces. In nature, a living creature is surviving while being exposed to formidable condition such as bacteria and fungi. Cicada wing has known to have multi-functional wings exhibiting nonwetting, and anti-microbial due to nanoscale pillars and biochemicals to achieve non-wetting characteristics. We conducted experiments on cicada wings and cicada-inspired engineered superhydrophobic samples to show that droplets jumping from superhydrophobic wings could carry away individual particles (~100 µm) or cluster of particles. This study was investigated on self-cleaning mechanism using jumping droplet condensation and elucidate further antifouling characteristics of non-wetting heat transfer surfaces.

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39

Ölçeroğlu, Emre. "Spatial Control of Condensate Droplets on Superhydrophobic Surfaces." Journal of Heat Transfer 137, no. 8 (August 1, 2015). http://dx.doi.org/10.1115/1.4030452.

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Super-bi-philic surfaces have been fabricated and characterized using environmental scanning electron microscopy (ESEM) to demonstrate spatial control of microscale droplets during condensation. The surfaces are composed of biotemplated nickel nanostructures based on the self assembly and metalization of the Tobacco mosaic virus. They are then functionalized using vapor-phase deposition of trichlorosilane, and lithographically patterned to create engineered nucleation sites. The resulting surfaces are primarily superhydrophobic (θ ≈ 170°) with arrays of superhydrophilic islands (θ ≈ 0°) with diameters of 3 μm and center-to-center pitches varying from 10 – 50 μm. During condensation the superhydrophilic islands promote nucleation resulting in spatial control of the condensate, which forms into ordered rectangular arrays (a,b). This spatial control has been shown to produce efficient jumping-mode condensation for pitches greater than 15 μm, as well as promote multi-droplet events (c). Additionally, super-bi-philic surfaces have been shown to delay the transition to a flooded state at high supersaturations, as compared to superhydrophobic designs.

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40

Du, Bingang, Yaqi Cheng, Siyan Yang, Yuanbo Liu, zhong lan, Rongfu Wen, and Xuehu Ma. "Highly Efficient Pure Steam Jumping-Droplet Condensation on Hierarchical Tapered Nanowire-Bunch Arrays." SSRN Electronic Journal, 2021. http://dx.doi.org/10.2139/ssrn.3985182.

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41

Gao, Shan, Jian Qu, Zhichun Liu, and Weigang Ma. "Sequential Self-Propelled Morphology Transitions of Nanoscale Condensates Diversify the Jumping-Droplet Condensation." SSRN Electronic Journal, 2022. http://dx.doi.org/10.2139/ssrn.4279520.

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42

Hou, Youmin, Miao Yu, Xuemei Chen, and Zuankai Wang. "Filmwise-to-Dropwise Condensation Transition Enabled by Patterned High Wetting Contrast." Journal of Heat Transfer 137, no. 8 (August 1, 2015). http://dx.doi.org/10.1115/1.4030454.

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Recent advances in condensing surfaces with hybrid architectures of superhydrophobic/hydrophilic patterns allow us to decrease the nucleation energy barrier and spatially control the water condensation. However, the condensed water is susceptible to the large pinning force of the hydrophilic area, leading to an ultimate flooding. Here, we demonstrate a hierarchical nanostructured surface with patterned high wetting contrast to achieve a natural transition from filmwise-to-dropwise condensation, which reconciles the existing problems. The energy-dispersive X-ray spectroscopy (EDX) indicates that the fluorinated hydrophobic coating conformably covers the nanostructures except for the tops of micropillars, which are covered by hydrophilic silicon dioxide (FIG 1), resulting in an extreme wetting contrast. Condensation on the hybrid surface was observed in the environmental scanning electron microscope (ESEM) and ambient conditions with controlled humidity. Water preferentially nucleates on the top of micropillars and exhibits a rapid droplet growth (FIG 2). The enhancement is attributed to the filmwise-to-dropwise transition induced by the unique architectures and wetting features of the hybrid surface (FIG 3). The water embryos initially nucleate on the hydrophilic tops and quickly grow to a liquid film covering the whole top area. Since the superhydrophobic surrounding confines the spreading of condensed water, the localized liquid film gradually transits to an isolated spherical droplet as it grows. Remarkably, the condensate morphology transition activates an unusual droplet self-propelling despite the presence of abundant hydrophilic patches. It is important to note that such coalescence-induced jumping is dependent on the size of hydrophilic patches, that is, for larger hydrophilic patches, the energy released by coalescence may not overcome the increased droplet pinning, resulting in an immobile coalescence (FIG 4). The droplet departure ensures the recurrence of filmwise-to-dropwise transition, thus prevents the water accumulation in continuous condensation. These visualizations reveal the undiscovered impact of heterogeneous wettability and architectures on the morphology transition of the condensed water, and provide important insights into the surface design and optimization for enhanced condensation.

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Chang, Xiangting, Haibo Huang, Xi-Yun Lu, and Jian Hou. "Width effect on contact angle hysteresis in a patterned heterogeneous microchannel." Journal of Fluid Mechanics 949 (September 23, 2022). http://dx.doi.org/10.1017/jfm.2022.763.

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The width effect on contact angle hysteresis in a microchannel with patterned heterogeneous surfaces is systematically investigated. In the model, identical defects periodically appear on the background surface. To this end, a droplet's evaporation and condensation processes inside the microchannel are studied by theoretical analysis and numerical simulation based on a diffuse-interface lattice Boltzmann method. The microchannel width effect on the system's equilibrium properties is studied. The results demonstrate that the number of equilibrium configurations increases linearly with the microchannel width ( $b$ ), and has a quadratic relationship with the cosine of the reference contact angle and the heterogeneity strength ( $\varepsilon$ ). The average most stable contact angle is independent of $b$ and is always equal to the contact angle predicted by the Cassie–Baxter equation. For contact angle hysteresis ( $H$ ), when the microchannels are narrow and wide, there are individual-effect-dominated hysteresis (IDH) and collective-effect-dominated hysteresis (CDH), respectively. The IDH and CDH are hysteresis modes corresponding to the jumping behaviour of contact lines affected by individual defects and two neighbouring defects, respectively. Based on the graphical force balance approach, we establish a scaling law to quantify the connection between $H$ , $b$ and $\varepsilon$ . Specifically, in the IDH mode, $H\sim b \varepsilon ^2$ , while in the CDH mode, $H$ increases linearly with $\varepsilon$ but nonlinearly with $b$ .

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