摘要
超疏水表面上的液滴合并诱导弹跳现象在冷凝传热、除霜防冰、自清洁等领域具有广阔应用前景.先前研究表明,液滴弹跳速度遵循毛细-惯性标度定律,无量纲弹跳速度vj*≤0.23,自弹跳过程效率低下,能量转化率η≤4%.为研究微尺度表面结构对液滴弹跳的影响,突破跳跃速度限制并诱导液滴扫掠,提高液滴清除效率,设计制备了棱角β=135°和β=90°的V型槽超疏水表面.利用高速显微技术记录了两种V型槽表面上液滴聚合过程中的形态演化.实验结果表明,两种V型槽表面都突破了平壁表面的毛细-惯性标度定律,无量纲最大弹跳速度分别为vj*=0.51和vj*=0.61,跳跃方向与表面法线最大夹角分别为36°和60°.与β=135°相比,β=90°的V型槽具有更高的面内速度,有利于提高液滴扫掠效率,清除更多凝结液滴.使用格子玻耳兹曼方法数值模拟合并液滴动力学,包括合并期间液滴速度和基底驱动力的演变,以及液滴内部压力分布和瞬时速度矢量.此外,利用仿真数据计算液滴合并过程中的不同方向液体动量,以及液滴总动能、弹跳动能和振荡动能.仿真结果表明,V型槽的β=90°槽角诱导液滴在收缩过程中的两侧液体回流方向,从几乎相向改变为趋近合并液滴弹跳的同一方向.β=90°槽角抑制了水平方向的液滴振荡,降低了黏性耗散,使更多过剩表面能转化为弹跳动能.
The phenomenon of coalescence-induced droplet jumping on superhydrophobic surfaces has promising applications in condensation heat transfer,anti-icing and defrosting,self-cleaning.Previous studies demonstrated that the droplet jumping speed follows the inertial-capillary scaling law with a dimensionless jumping velocity vj*≤0.23.The self-jumping process is inefficient,with an energy conversion efficiencyη≤4%.To study the effect of microscale surface structure on droplet bounce,break through the jumping speed limit,and induce droplet sweeping to improve the droplet removal efficiency,superhydrophobic surfaces of V-groove with edge angleβ=135°andβ=90°were designed and prepared.High-speed microscopy was used to record the morphological evolution of droplets on two V-grooves surfaces during the merger process.The experimental result shows that both V-groove surfaces break through the capillary-inertial scaling law of flat surface.The maximum dimensionless jumping velocity is vj*=0.51 and vj*=0.61,and the maximum angle between the jumping direction and the surface normal is 36°and 60°,respectively.Compared with theβ=135°,the surface of V-groove withβ=90°has higher in-plane velocity,which is beneficial to improve droplet sweeping efficiency and remove condensed droplets.The lattice Boltzmann method was used to numerically simulate coalescence droplet dynamics,including the evolution of the droplet velocity and substrate driving force during coalescence and the internal pressure distribution instantaneous velocity vector of the droplet.We also used simulation data to calcu-late liquid momentum in different directions during coalescence,as well as total kinetic energy,jumping kinetic energy,and oscillation kinetic energy.The simulation results show that the edge angleβ=90°of the V-groove induces the liquid backflow direction on both sides of the droplet during the contraction process,changing from almost opposite to approach the same direction of the merged droplet jump.The edge angleβ=90°suppresses th
作者
路敦强
张涵莅
杨永
赵美蓉
郑叶龙
Lu Dunqiang;Zhang Hanli;Yang Yong;Zhao Meirong;Zheng Yelong(School of Precision Instruments and Opto-Electronics Engineering,Tianjin University,Tianjin 300072,China;School of Electronics and Communication Engineering,Tianjin Normal University,Tianjin 300387,China)
出处
《天津大学学报（自然科学与工程技术版）》
EI
CAS
CSCD
北大核心
2021年第9期907-916,共10页
Journal of Tianjin University：Science and Technology
基金
国家自然科学基金资助项目(51425502)
天津市自然科学基金资助项目(18JCQNJC04800,18JCZDJC31800,18JCYBJC16100).
关键词
V型槽棱角
液滴合并
液滴弹跳强化
超疏水表面
V-groove edge angle
droplet coalescence
droplet jumping enhancement
superhydrophobic surface
