Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

Abstract

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 µm/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena. Video LinkThe video component of this article can be found at

Wet granular flow control through liquid induced cohesion

“…Since the contact angle affects the strength of the capillary force, here, differently from e.g. [33,34], the variability of the contact angle is taken into account. The bond number Bo (Equation 2), representing the ration of the capillary force to the gravitational force, is also shown along the y-axis as a function the water-ethanol fraction.…”

Scaling of wet granular flows in a rotating drum

“…The higher the contact angle, the lower the wettability of the glass. To characterize the motion of wet particles, the particle based Weber number is often used [14,15], given by the ratio of kinetic to capillary energy of the particle.…”

“…Here, differently from e.g. [14,15], the variability of the contact angle T is taken into account. We vary We by varying the capillary force F c~γ cosθ, for different particle sizes.…”