Drop spreading dynamics with liquid needle deposition technique
This paper represents a theoretical and an experimental study of the spreading dynamics of a liquid droplet, generated by a needle free deposition system called the liquid needle droplet deposition technique. This technique utilizes a continuous liquid jet generated from a pressurized dosing system which generates a liquid drop on a substrate to be characterized by optical contact angle measurements. Although many studies have explored the theoretical modelling of the droplet spreading scenario, a theoretical model representing the spreading dynamics of a droplet, generated by the jet impact and continuous addition of liquid mass, is yet to be addressed. In this study, we developed a theoretical model based on the overall energy balance approach which enables us to study on the physics of variation of droplet spreading under surrounding medium of various viscosities. The numerical solution of the non-linear ordinary differential equation has provided us the opportunity to comment on the variation of droplet spreading, as a function of Weber number (We), Reynolds number (Re) and Bond number (Bo) ranging from 0.5-3, 75-150, and 0.001-0.3, respectively. We have also presented a liquid jet impact model in order to predict the initial droplet diameter as an initial condition for the proposed governing equation. The model has been verified further with the experimental measurements and reasonable agreement has been observed. Experimental observations and theoretical investigations also highlight the precision, repeatability and wide range of the applicability of liquid needle drop deposition technique.
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We have an image processing capability to investigate different droplet dynamics; spreading, coalescence, drop-impact, etc. "Engineering Beyond, a collaborator of iSSELab, had developed this customized commercial image processing algorithm that is being used for numerous applications in industries.
The role of medium viscosity on a non-deformable rolling body has long been understood while its deformable counterpart still awaits clarification. In this article, we present a scaling analysis with experimental evidences to demonstrate that in creeping flow, medium viscosity significantly alters how the descent speed of a drop responds to an increase in drop size. While descending down an incline in a viscous medium, a rolling drop may travel with either increasing or decreasing velocities as its size increases. The boundary between these two motion behaviors can be maneuvered by altering the viscosity of the surrounding medium.
Droplet Deposition Techniques
Droplet Spreading - Liquid-Fluid Interface
We studied the early time dynamics of viscous drop spreading on a liquid–fluid interface. Unlike spreading on solid substrate, a drop deforms at the base as it spreads on a liquid–fluid interface. Hence the dynamics are seen to deviate from the classical power law of spreading. Experimental observations allowed us to establish a simple empirical expression to predict the temporal growth of the contact radius. Further, inertial oscillations were observed for spreading of less viscous liquid drop that can be described by the inertial capillarity model.