Experimental investigation into deposition/splashing behavior of droplets impacting vibrating surface

Abstract

An experimental investigation is performed into the behavior of ethanol droplets impacting on a vibrating stainless steel surface. In characterizing the impact behavior, the dimensionless kinetic energy of the droplet prior to its impact on the surface is represented by the original Weber number (We). Meanwhile, the dimensionless relative impact kinetic energy of the droplet as it impacts the vibrating surface, and thus undergoes a change in its relative impact speed, is represented by the relative Weber number (Wer). Impact experiments are performed for various values of the original Weber number We and vibration frequency f. The impact behavior in each case is classified as either post-spreading deposition or crown splashing. It is shown that for a static (non-vibrating) surface, the critical Weber number for the generation of splashing is Wec = 400. Furthermore, for a given impact speed and vibration frequency, if no splashing occurs without vibration but splashing takes place after vibration, the difference between the original Weber number (We) and the critical Weber number (Wec) is proportional to the additional impact Weber number provided by the vibrating surface, that is, (Wer − Wec). For a given relative impact speed, a higher vibration frequency ƒ results in a greater relative impact distance during splashing and a larger effective impact energy. Overall, the experimental results show that the relation between We and Wer for the generation of splashing is given as We=(−cf/(1−cf))Wer+(1/(1−cf))Wec, where c=3.45×10−4.