| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 94 === Drop impact is a complex interaction between inertia, surface tension, and viscous forces. The break–off of a drop from a stream of liquid was studied for almost 200 years. In general, there are two possible outcomes of droplet impact onto a solid and dry surface. The droplet may deposit on the surface and form a liquid film or the droplet will splash and produce secondary droplets. How a liquid droplet will behave depends on the internal parameters (mass, local velocity, viscosity) and external parameters (type of surface where droplet will contact).
We can find drop impact phenomenon in our daily lives. The simple example is raindrop. We can see that a falling of liquid droplet can exhibit a variety of behaviors. From this simple example, we design this system in order to observe this phenomenon and try to find out the best method to calculate droplet size and center of mass when drop oscillates in the air.
According to Rein [3], Rioboo [15], and Middleman [35], the liquid show spreading, rebounding, and splashing phenomena if drop impact on dry surface. In this work, we demonstrated those phenomena for water drop impact onto paraffin wax surface at 5, 9, and 13 cm heights from the sequence image in figure III.2, III.4, and III.6, respectively. From our observations, the system we designed is similar to the references.
In order to get volume of drop and center of mass, we use AutoCAD 2007 software and rotates the image in X and Y directions. These two parameters will be use to calculate the conservation among potential, kinetic, and surface energies. The height in potential energy equation is assumed the same with center of mass which is depending on time. To find out the local velocity, we used center of mass and made the linear relation. From the linear equation, we used the slope value and multiply it with 2900 frame / second. We took the results as the local velocities. And we use equation (I.16) to calculate the surface energy. However, the surface energy cannot be calculated for the moment due to there is no maximum diameter data of water drop available.
|
|---|
