| Summary: | 碩士 === 國立臺灣科技大學 === 材料科學與工程系 === 101 === In this work, the wetting phenomenon, drop morphology and bubble-entrapment behavior were studied for water drop impinging on PVC polymer surface. These phenomena during the drop impact are dependent upon the liquid properties (density, viscosity and surface tension), impact velocity, drop size, and solid properties (roughness and surface hydrophobicity). A high speed video camera was utilized for this study and both the images of the side view and 45 degree topic view were recorded continuously.
Water drops of different sizes were used on the impact study onto the PVC planar surface. The relaxations of drop wetting diameter, drop high and contact angle were recorded for studying the wetting phenomenon from the side view images. The bubble entrapment behavior was investigated from the 45 degree topic view images. Three drop sizes (D0 =2.38, 3.14, and 3.87 mm) were used in this work.
We observed the following phenomena from this study: (i) , (ii), (iii) and (iv).
(i)A half closed region on the Vi-D0 plot was identified for the formation of entrapped bubble. The upper and lower boundaries of Vi showed a tendency of decreasing as D0 increases. The entrapped bubble generally resulted in a hemispherical bubble after settling down on PVC surface.
(ii)The Re-We curve increase depend on the drop size increase.
(iii) With the analyze of needle 28, diameter of maximum bubble inverse with speed of impact. And impact speed also inverse with drop height.
(iv) The lowest height of drop with bubble is higher than the normal one. What’s more is drop size affect drop behave directly.
|
|---|
