Dynamic Characteristic Study Of A Droplet Impact On Horizontal Surface

It is a common phenomenon in life that droplet impacts on flat, such as pesticide spraying, paint spraying, fuel injection and so on. The process involve in basic theoretical knowledge of heat and mass transfer, surface material science, fluid mechanics, so studying the process of droplet impacting on flat is has important significance to production and life. It could change a variety of forms after droplet impacted on flat, so the paper studied the morphological characteristics of static droplet and oscillating droplet on flat by analyzing the forces acting on droplet.Firstly, the paper studied the static droplet on flat. The paper hypothesized that the static droplet was similar in form to spherical segment, built a theoretical model of spherical segment droplet, analyzed surface tension and internal pressure forces acting on the droplet on flat, and deduced a theoretical equation about droplet property parameters, and then compared the theoretical solution by dichotomy to experimental data in order to verify the accuracy of the model. The model provided a theoretical method to predict the effects of droplet physical parameters on static spreading radius quantitatively.Secondly, the paper studied the oscillating droplet on flat. The paper analyzed surface tension, internal pressure, inertia force and viscosity force of spherical segment droplet model, deduced the theoretical relationship expression of oscillating radius with time, and gave the correlation between the static spreading radius, height, droplet volume, density, contact angle and surface tension coefficient, and then using the Fortran program with fourth order Runge-Kutta method to solve the equation. The paper also simulated the droplet oscillating process by ANSYS with verify the accuracy of oscillating model, and then analyzed the viscosity force that caused bigger error.Finally, the paper studied the drop dynamic contact angle (DCA) in the oscillating process. The theoretical derivation above was based on the hypothesis of constant contact angle in oscillating process, however, the contact angle was changing actually because of many factors. And so need to study further dynamic contact angle. The paper measured and analyzed the parameters of contact angle and drop diameter changing with drop volume by sessile drop method in the experiments. In addition, the paper simulated the process of droplet impacting on flat in different contact angle setting, and compared simulated result with experimental data. And then got the influence rules of contact angle on oscillating process.