Dynamic behavior of droplets impact on a hot microstructured surface with wetting gradient

doi:10.16085/j.issn.1000-6613.2017-1281

Abstract

Abstract: Using copper plates as substrates,the microholed gradient surface was fabricated by the optical etching,and dynamic behaviors of droplets impact on the high temperature microholed gradient surface were studied by high-speed camera. The results showed that when a droplet impacts on the microholed gradient surface,there are five different impact modes. They are wetting mode,contact boiling mode,transition mode,explosion mode and rebound mode. When surface temperature reached Leidenfrost point,the droplet is in the rebound mode and it appears continues rebound behavior along the direction of the wetting gradient. Due to the energy reducing continues in rebound process,the rebound height gradually reduces to zero. Based on surface physical and chemical theories,the directional bouncing behavior of the droplet was analyzed. In addition,the dynamic characteristics of the droplet rebound were analyzed by using image processing technology. Moreover,the rebound height,the spreading factor and the horizontal acceleration of the droplet were discussed by experiments. It was found that they have same characteristics with the increase of rebound numbers. It experienced the same stages:rapid reducing at acceleration. The spreading factor were highly consistent with the theoretical analysis.

Key words: droplet, impact, wetting gradient, directional rebound, Weber number

摘要： 以铜片为基底制备了微方孔结构浸润梯度表面，利用高速摄像技术对液滴撞击高温梯度表面的动态行为特性进行了研究。结果表明：在不同表面温度和韦伯数（We）下，液滴撞击在梯度表面上会出现5种不同的撞击模式，即润湿模式、接触沸腾模式、过渡模式、碎裂模式和反弹模式；当表面温度达到Leidenfrost温度时，液滴进入反弹模式，反弹液滴会沿着梯度能方向发生多次连续弹跳行为，且由于弹跳过程中能量的不断衰减，反弹高度逐渐减小直至趋于零。基于表面物理化学理论分析了液滴的定向弹跳行为，并利用图像处理技术，分析了弹跳液滴的动态特征。进一步地，通过液滴以相同We数撞击不同表面温度实验，研究了液滴在弹跳运动过程中反弹高度、铺展因子和运动的水平加速度变化特征，发现三者随反弹次数的增加具有相似的变化过程，即呈现先快速减小、后逐渐稳定的特征。水平加速度的与铺展因子的变化趋势具有一致性，从而验证了理论分析的合理性。

关键词: 液滴, 撞击, 浸润梯度, 定向反弹, 韦伯数

CLC Number:

TK121

LUO Liming, JIA Zhihai. Dynamic behavior of droplets impact on a hot microstructured surface with wetting gradient[J]. Chemical Industry and Engineering Progress, 2018, 37(03): 906-912.

罗黎明, 贾志海. 液滴撞击高温梯度表面的动态行为特性[J]. 化工进展, 2018, 37(03): 906-912.

References

[1] 马玺,刘义佳,关松,等. 汽油发动机不同燃油喷射方式下缸内燃烧情况的试验研究[J]. 小型内燃机与摩托车,2015,44(4):36-39. MA X,LIU Y J,GUAN S,et al. Experimental study on combustion in cylinder about gasoline engine under different fuel injection modes[J]. Small Internal Combustion Engine and Motorcycle,2015,44(4):36-39.
[2] 张孟昀,赵增武,张亚竹,等. 不同射流方式对钢板换热的影响研究[J]. 内蒙古科技大学学报,2013,32(3):221-224. ZHANG M Y,ZHAO Z W,ZHANG Y Z,et al. Study on the heat transfer of cooling plate with different ways of spray[J]. Journal of Inner Mongolia University of Science and Technology,2013,32(3):221-224.
[3] LI X,ZHANG L,MA X,et al. Dynamic characteristics of droplet impacting on prepared hydrophobic/superhydrophobic silicon surfaces[J]. Surface & Coatings Technology,2016,307:243-253.
[4] LIANG G,MUDAWAR I. Review of drop impact on heated walls[J]. International Journal of Heat and Mass Transfer,2017,106:103-126.
[5] KHOJASTEH D,KAZEROONI N M,SALARIAN S,et al. Droplet impact on superhydrophobic surfaces:a review of recent developments[J]. Journal of Industrial & Engineering Chemistry,2016,42:1-14.
[6] OKUMURA K,CHEVY F,CLANET C,et al. Water spring:a model for bouncing drops[J]. EPL(Europhysics Letters),2003,62(2):237-243.
[7] 施其明,贾志海,林琪焱. 液滴撞击微结构疏水表面的动态特性[J]. 化工进展,2016,35(12):3818-3824. SHI Q M,JIA Z H,LIN Q Y. Dynamic behavior of droplets impacting on microstructured hydrophobic surfaces[J]. Chemical Industry and Engineering Progress,2016,35(12):3818-3824.
[8] RAMACHANDRAN R,SOBOLEV K,NOSONOVSKY M. Dynamics of droplet impact on hydrophobic/icephobic concrete with the potential for superhydrophobicity[J]. Langmuir,2015,31(4):1437-1444.
[9] CHEN L,BONACCURSO E,SHANAHAN M E. Inertial to viscoelastic transition in early drop spreading on soft surfaces[J]. Langmuir,2013,29(6):1893-1898.
[10] ALIZADEH A,BAHADUR V,ZHONG S,et al. Temperature dependent droplet impact dynamics on flat and textured surfaces[J]. Applied Physics Letters,2012,100(11):111601.
[11] 王宏,廖强,朱恂. 梯度表面能材料上液滴运动机理[J]. 化工学报,2007,58(9):2313-2320. WANG H,LIAO Q,ZHU X. Mechanism of liquid droplet movement on surface with gradient surface energy[J]. CIESC Journal,2007,58(9):2313-2320.
[12] 黄志,王琳玮,刘抗,等. 润湿性梯度表面凝结水量研究[J]. 工程热物理学报,2011,32(11):1937-1940. HUANG Z,WANG L W,LIU K,et al. Moisture condensation on surface with wettability gradients[J]. Journal of Engineering Thermophysics,2011,32(11):1937-1940.
[13] MALOUIN B A,KORATKAR N A,HIRSA A H,et al. Directed rebounding of droplets by microscale surface roughness gradients[J]. Applied Physics Letters,2010,96(23):261.
[14] WU J,MA R,WANG Z,et al. Do droplets always move following the wettability gradient?[J]. Applied Physics Letters,2011,98(20):204104.
[15] LIU Y,WHYMAN G,BORMASHENKO E,et al. Controlling drop bouncing using surfaces with gradient features[J]. Applied Physics Letters,2015,107(5):051604.
[16] LINKE H,ALEMAN B J,MELLING L D,et al. Self-propelled Leidenfrost droplets[J]. Physical Review Letters,2006,96(15):154502.
[17] DUPEUX G,BAIER T,BACOT V,et al. Self-propelling uneven Leidenfrost solids[J]. Physics of Fluids,2013,25(5):051704.
[18] JIA Z H,CHEN M Y,ZHU H T. Reversible self-propelled Leidenfrost droplets on ratchet surfaces[J]. Applied Physics Letters,2017,110(9):091603.
[19] LI J,HOU Y,LIU Y,et al. Directional transport of high-temperature Janus droplets mediated by structural topography[J]. Nature Physics,2016,12(6):606-612.