Analysis of Asymmetric Drop Shape on Horizontal, Inclined and Curved Surfaces by Using Image Process

Contact angle measurement of a drop on surface is known as a common method for determining the surfaces wettability. Although the drop contact angle measurement on horizontal surface is fully-described, but contact angle measurement for the asymmetric drop on inclined and specially curved surfaces, mainly is analyzed by tangent line method, suffers from inadequate accuracy and speed. The main objective of this study is to introduce an effective algorithm for determining the contact angle of drops on inclined and curved surfaces without using fluid parameters such as density and drop volume. For this purpose, real and artificial image of drops are used. The developed method uses side view image of drops and creates the binary matrix of the image by using the Otsu method. Then, the solid-fluid-fluid interface is detected and the contact angle is calculated by means of determining the derivative at the three phases contact point. One problem which contact angle measurement faces with is determination of the location of  three-phase contact point, instead of calculating the derivative based on just one pixel, averaging of several pixels are used to reduce effect of this problem. In order to validate the proposed method, real images of the drops of four different fluids on the calcite surface, as well as artificial images created with the aid of graphic software with a specific contact angle, are used. The results show the accuracy of the proposed method for contact angle measurement of the symmetric and asymmetric drop on horizontal, inclined and curved surfaces.