微结构梯度能表面冷凝液滴的生长特性
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摘要
利用疏水表面获得滴状冷凝进而提高冷凝器传热系数是目前冷凝器强化传热的重要方法。以聚二甲基硅氧烷(PDMS)为基底,采用光刻技术制备了微方孔结构的梯度能表面,分析了微方孔结构梯度能表面的冷凝液滴生长的动态过程.研究发现:由于微方孔边长的梯度变化,冷凝液滴的填孔速率不同,从而造成表面液滴的不同形态。通过冷凝液滴的表面覆盖率特征分析,进一步研究了冷凝液滴成核能垒、成核半径在表面梯度能作用下的规律.此外,分析了孔外平面液滴合并的速度特征,发现在冷凝初期,f=0.5的表面处,液滴的表面覆盖率增长速度最快,归因于梯度张力和表面结构的共同作用.
It is a very important method to enhance heat transfer for dropwise condensation using hydrophobic surfaces. Microholed gradient surfaces are prepared with the polydimethyl-siloxane(PDMS) substrate using photolithography techniques. The dynamic processes of condensation droplet growth on gradient surfaces are observed. It is found that the fill rates of condensation droplets are different with the gradient variation of microholed surfaces, leading to the regular changes of droplet morphologies. According to the analysis of the surface coverage of condensation droplets, the energy barrier and radius of nucleation are further discussed. In addition, during the early stage of condensation, the maximum surface coverage is found when the area fraction is 0.5 by the speed analysis of droplets merging, due to the common influence of gradient surface tension and surface structure.
It is a very important method to enhance heat transfer for dropwise condensation using hydrophobic surfaces. Microholed gradient surfaces are prepared with the polydimethyl-siloxane(PDMS) substrate using photolithography techniques. The dynamic processes of condensation droplet growth on gradient surfaces are observed. It is found that the fill rates of condensation droplets are different with the gradient variation of microholed surfaces, leading to the regular changes of droplet morphologies. According to the analysis of the surface coverage of condensation droplets, the energy barrier and radius of nucleation are further discussed. In addition, during the early stage of condensation, the maximum surface coverage is found when the area fraction is 0.5 by the speed analysis of droplets merging, due to the common influence of gradient surface tension and surface structure.
引文
[1] Peng B, Lan Z, Xu W, et al. A Numerical Study of Droplet Motion/departure on Condensation of Mixture Vapor Using Lattice Boltzmann Method[J]. International Journal of Heat and Fluid Flow, 2017, 68:53-61
[2] Kajiya T, Schellenberger F, Papadopoulos P, et al. 3D Imaging of Water-Drop Condensation on Hydrophobicand Hydrophilic Lubricant-Impregnated Surfaces[J]. Scientific Reports, 2016, 6:23687
[3]焦龙,陈蓉,何雪丰,等.憎水表面光控液滴蒸发及冷凝液滴的演化特性[J].工程热物理学报,2017, 38(3):575-580JIAO Long, CHEN Rong, HE Xuefeng, et al. IR Laser Evaporation of Sessile Droplet and Dynamic Evolution of Condensed Droplets on Hydrophobic Surface[J]. Journal of Engineering Thermophysics, 2017, 38(3):575-580
[4] Chen X, Yao S, Wang Z. Evaporation of Condensate Droplets on Structured Surfaces with Gradient Roughness[J]. Journal of Heat Transfer, 2015, 137(8):388-392
[5] Deng Z, Zhang C, Shen C, et al. Self-propelled Dropwise Condensation on a Gradient Surface[J]. International Journal of Heat and Mass Transfer, 2017, 114:419-429
[6]张而耕,朱州,张体波.超硬纳微米PVD涂层技术在刀具领域的应用及研究进展[J].表面技术,2015, 44(4):89-96ZHANG Ergeng, ZHU Zhou, ZHANG Tibo. Research Progress and Application of Superhard Nano-Micron PVD Coating Technology in the Cutting Manufacturing Area[J]. Surface Technology, 2015, 44(4):89-96
[7] Lin X, Liu C, Xiao H. Fabrication of Al-Si-Mg Functionally Graded Materials tube Reinforced with in Situ Si/Mg2Si Particles by Centrifugal Casting[J]. Composites Part B:Engineering, 2013, 45(1):8-21
[8] Ta V D, Dunn A, Wasley T J, et al. Laser Textured Surface Gradients[J]. Applied Surface Science, 2016, 371:583-589
[9] Macner A M, Daniel S, Steen P H. Condensation on Surface Energy Gradient Shifts Drop Size Distribution Toward Small Drops[J]. Langmuir, 2014, 30(7):1788-1798
[10] Pismen L M, Thiele U. Asymptotic Theory for a Moving Droplet Driven by a Wettability Gradient[J]. Physics of Fluids, 2006, 18(4):042104
[11] Fletcher N H J. Size Effect in Heterogeneous Nucleation[J]. The Journal of Chemical Physics, 1958, 29(3):572-576
[12] Aili A, Ge Q Y, Zhang T J. How Nanostructures Affect Water Droplet Nucleation on Superhydrophobic Surfaces[J].Journal of Heat Transfer, 2017, 139(11):112401
[13] Wang F C, Yang F, Zhao Y P. Size Effect on the Coalescence-induced Self-propelled Droplet[J]. Applied Physics Letters, 2011, 98(5):053112
[14] Boreyko J B, Chen C H. Self-propelled Dropwise Condensate on Superhydrophobic Surfaces[J]. Physical Review Letters, 2009, 103(18):184501
[15] Biance A L, Chevy F, Clanet C, et al. On the Elasticity of an Inertial Liquid Shock[J]. Journal of Fluid Mechanics,2006, 554:47-66
[16] Eggers J, Lister J R, Stone H A. Coalescence of Liquid Drops[J]. Journal of Fluid Mechanics, 1999, 401:293-310
[2] Kajiya T, Schellenberger F, Papadopoulos P, et al. 3D Imaging of Water-Drop Condensation on Hydrophobicand Hydrophilic Lubricant-Impregnated Surfaces[J]. Scientific Reports, 2016, 6:23687
[3]焦龙,陈蓉,何雪丰,等.憎水表面光控液滴蒸发及冷凝液滴的演化特性[J].工程热物理学报,2017, 38(3):575-580JIAO Long, CHEN Rong, HE Xuefeng, et al. IR Laser Evaporation of Sessile Droplet and Dynamic Evolution of Condensed Droplets on Hydrophobic Surface[J]. Journal of Engineering Thermophysics, 2017, 38(3):575-580
[4] Chen X, Yao S, Wang Z. Evaporation of Condensate Droplets on Structured Surfaces with Gradient Roughness[J]. Journal of Heat Transfer, 2015, 137(8):388-392
[5] Deng Z, Zhang C, Shen C, et al. Self-propelled Dropwise Condensation on a Gradient Surface[J]. International Journal of Heat and Mass Transfer, 2017, 114:419-429
[6]张而耕,朱州,张体波.超硬纳微米PVD涂层技术在刀具领域的应用及研究进展[J].表面技术,2015, 44(4):89-96ZHANG Ergeng, ZHU Zhou, ZHANG Tibo. Research Progress and Application of Superhard Nano-Micron PVD Coating Technology in the Cutting Manufacturing Area[J]. Surface Technology, 2015, 44(4):89-96
[7] Lin X, Liu C, Xiao H. Fabrication of Al-Si-Mg Functionally Graded Materials tube Reinforced with in Situ Si/Mg2Si Particles by Centrifugal Casting[J]. Composites Part B:Engineering, 2013, 45(1):8-21
[8] Ta V D, Dunn A, Wasley T J, et al. Laser Textured Surface Gradients[J]. Applied Surface Science, 2016, 371:583-589
[9] Macner A M, Daniel S, Steen P H. Condensation on Surface Energy Gradient Shifts Drop Size Distribution Toward Small Drops[J]. Langmuir, 2014, 30(7):1788-1798
[10] Pismen L M, Thiele U. Asymptotic Theory for a Moving Droplet Driven by a Wettability Gradient[J]. Physics of Fluids, 2006, 18(4):042104
[11] Fletcher N H J. Size Effect in Heterogeneous Nucleation[J]. The Journal of Chemical Physics, 1958, 29(3):572-576
[12] Aili A, Ge Q Y, Zhang T J. How Nanostructures Affect Water Droplet Nucleation on Superhydrophobic Surfaces[J].Journal of Heat Transfer, 2017, 139(11):112401
[13] Wang F C, Yang F, Zhao Y P. Size Effect on the Coalescence-induced Self-propelled Droplet[J]. Applied Physics Letters, 2011, 98(5):053112
[14] Boreyko J B, Chen C H. Self-propelled Dropwise Condensate on Superhydrophobic Surfaces[J]. Physical Review Letters, 2009, 103(18):184501
[15] Biance A L, Chevy F, Clanet C, et al. On the Elasticity of an Inertial Liquid Shock[J]. Journal of Fluid Mechanics,2006, 554:47-66
[16] Eggers J, Lister J R, Stone H A. Coalescence of Liquid Drops[J]. Journal of Fluid Mechanics, 1999, 401:293-310