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標題: 撞擊在乾表面上的液滴特性之實驗探討
Experimental investigations of the impinging droplet onto dry surface
作者: 王耀增
Wang, Yao-Zeng
關鍵字: impinging droplet;撞擊液滴;dry surface;dynamic contact angle;wetting phenomena;乾表面;動態接觸角;濕潤
出版社: 機械工程學系所
引用: [1] Bussmann, M. , Chandra, S. and Mostaghimi, J., “Modeling the Splash of a Droplet Impacting a Solid Surface,” Phys. Fluids, Vol. 12, pp. 3121-3132, 2000. [2] Clanet, C., Beguin, C., Richard, D. and Quere, D.,“Maximal deformation of an impacting drop,”J. Fluid Mech, Vol. 517, pp. 199-208, 2004. [3] Fukai, J. and Zhao, Z. and Poulikakos, D. and Megaridis, C. M. and Miyatake, O., “Modeling of the Deformation of a Liquid Droplet Impinging Upon a Flat Surface,” Phys. Fluids A, Vol. 5 (11), pp. 2588-2599, 1993. [4] Gu, Y. and Li, D., “Liquid drop spreading on solid surfaces at low impact speeds,” Colloids and Surfaces A : Physicochemical and Engineering Aspects, Vol. 163, pp. 239-245, 2000. [5] Manzello, S. L. and Yang, JC.,“An experimental study of a water droplet impinging on a liquid surface,”Exp. Fluids 32, pp. 580-589, 2008. [6] Pasandideh-Fard, M. and Qiao, Y. M. and Chandra, S. and Mostaghimi, J., “Capillary Effects during Droplet Impact on a Solid Surface,” Phys. Fluids, Vol. 8, pp. 650-659, 1996. [7] Park, H. and Wallace, W.,“Single drop impacting on a solid surface,”AIChE J., Vol. 49, no. 10, 2003. [8] Rioboo, R., Marengo, M. and Tropea, C.,“Time evolution of liquid drop onto solid surface,”Exp. Fluids, Vol. 33, pp. 112-124, 2002. [9] Stow, C. D. and Hadfield, M. G.,“An Experimental Investigation of Fluid Flow Resulting From the Impact of a Water Drop with an Unyielding Dry Surface,”Proc. R. Soc. London A, Vol. 373, pp. 419-441, 1981. [10] Sikalo, S., Marengo, M. and Tropea, C.,“Analysis of Impact of Droplets on Horizontal Surfaces,”Exp. Fluids, Vol. 25, pp. 503-510, 2002. [11] Sikalo, S., Wilhelm, H., Roisman, I., Jakirlic, S. and Tropea, C.,“Dynamic contact angle of spreading droplets:Experiments and simulations,”Phys Fluids 17, 062103, 2005. [12] Son, Y., Kim, C., Yang, D. H. and Ahn, D. J.,“Spreading of an inkjet droplet on a solid surface with a controlled contact angle at low Weber and Reynolds numbers ,”Langmuir 24, pp. 2900-2907, 2008. [13] Worthington, A. M., “On the Forms assumed by Drops of Liquids Falling Vertically on a Horizontal Plate,” Proc. R. Soc. London A, Vol. 25, pp. 261-271, 1867. [14] Worthington, A. M., “On Impact with a Liquid Surface,” Proc. R. Soc. London A, Vol. 34, pp. 217-230, 1883. [15] Zhang, X. and Basaran, O. A., “Dynamic Surface Tension Effects in Impact of a Drop with a Solid Surface,” J. Colloid Interface Sci., Vol. 187, pp. 166-178, 1997. [16]楊鴻進, “液滴撞擊之實驗研究及現象分析” 國立台灣大學機械工程研究所碩士論文, 2003.
實驗結果發現:(a)在運動階段( <1):表面材質、不同成分的液滴不會影響撞擊後的擴散外徑以及中心高度的變化;但是撞擊初期的動態接觸角會因薄水層形成狀態的不同而有三種變化;(b)在擴展階段時,雷諾數越小(黏滯係數越大)者,撞擊後的擴散速率會越慢,且撞擊液滴的最大擴散外徑( )會越大,但中心的回縮高度( )較小。當達到最大擴散外徑的過程中,其動態接觸角先呈現鈍角並小幅減少後再增加;但若以純水為液滴,其動態接觸角會呈現銳角,而後,快速增加至鈍角,隨後小幅減少後再增加。(c) 在回縮階段時,若靜態接觸角越大者(斥水性平板),回縮的中心高度( )較大,且回縮速率較快,反之亦然;而在回縮階段中,動態接觸角會因中心液柱的隆起劇烈增大,並以遞減振幅的震盪方式持續趨近於靜態接觸角。(d)溼潤階段:雷諾數越小(黏滯係數越大)者以及靜態接觸角越小(親水性平板)者,其濕潤速率會越快。反之,其濕潤速率會越慢。在此過程中,其動態接觸角仍持續減少並趨近其靜態接觸角。

This study investigates the temporal characteristics of an impinging droplet onto dry surface of various properties via a high speed camera. The dynamic contact angle, the spreading diameter and the central height of the deformed droplet are the subjects of primary interest. Two impinging velocities, three different surface properties and droplets of seven different ingredients are employed to realize the transient behavior of the impinging droplet onto dry surface.

Experimental results show that: (a) during the kinematics stage, all the spreading diameters and the central heights of the deformed droplet are independent of the surface properties, the droplet material and the impinging velocity. However, the variations of the dynamic contact angle depend strongly on these properties. During this stage, three different variations of dynamic contact angles are found relating to the formation of lamella. (b) During the spreading stage, the more viscous of the droplet, the slower is the spreading speed and the thinner is the deformed droplet. The contact angle decreases from an obtuse angle and fluctuates slightly until the maximum spreading diameter is reached. For the less viscous droplet (water), the contact angle starts from an acute angle, increases abruptly and fluctuates slightly until the maximum spreading diameter is reached. (c) Within the receding stage, the more hydrophobic surfaces, the faster is the receding speed, the thicker is the deformed droplet, and vice versa. The contact angle increases drastically due to the eruption of the central liquid column and then decreases significantly and monotonously in an oscillatory manner. (d) During the wetting stage, the more viscous droplet and the more hydrophilic surface, the faster is the wetting speed, and vice versa. During the wetting stage, the contact angle continues to decrease to asymptotically approach the value of static contact angle.
其他識別: U0005-2706200813031200
Appears in Collections:機械工程學系所

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