Dynamics of Drop Formation in the Presence of Interfacial Mass Transfer

Abstract

The dynamics of drop formation have been investigated in the presence of interfacial mass transfer through controlled flow visualization experiments. The mixtures of n-hexane (solvent) and acetone (solute) were used as a dispersed phase, having different initial compositions varying over a broad range. Drops were formed at the submerged position in the continuous phase (water) at the same operating flow conditions. The unsteady force balance model is developed to analyze the implications of the simultaneously occurring interfacial transfer of the solute on the formation dynamics in real time, and predictions are validated with experimental results. Based on initial compositions, the analysis of the transient drop shape shows a sharp transition in the drop formation regime. At lower initial solute concentrations, i.e., ϕ 0 < 0.2, axisymmetric drop formation occurs and the interfacial solute transfer has negligible effects on the formation dynamics. Over an intermediate range of solute concentrations, i.e., 0.2 < ϕ 0 < 0.5, Marangoni instability is triggered along the evolving interface, and therefore, the interface deformations and contractions occur during the drop formation. At ϕ 0 = 0.5, the drop takes highly nonaxisymmetric shapes and remains away from equilibrium until its detachment from an orifice. For ϕ 0 > 0.5, the spontaneous ejection of plumes of the solute results in the rapid generation of multiple droplets of smaller size. This work shows that higher solute concentration gradients not only lead to faster solute transport but also induce strong interfacial instability simultaneously. Thus, the coupled effects of transient change in composition and fluid properties govern the drop size and its formation time in such systems under non-equilibrium.

Understanding the Effects of Physical Properties of Composite Drop on its Formation Dynamics in Presence of Interfacial Mass Transfer

“…However, Oh , Bo ≪ 1 suggests the dominant effects of surface tension over gravity and viscous effects, and at these experimental conditions, the drop formation mode can be expected. , In some cases, We > 1 implies dominant inertial effects, which mainly contribute to the jetting. It is important to note that these dimensionless parameters govern drop formation in the absence of solute transfer, and one can expect the different modes of drop formation in the presence of solute transfer, due to simultaneously occurring solute diffusion from drop to continuous phase . However, the analysis of dimensionless parameters can help to plan the controlled experiments, even in the presence of interfacial mass transfer.…”

“…To quantitatively analyze the process of interface evolution in real time during the drop formation, the dimensions of the drop in each frame captured via high-speed imaging were calculated using the in-house developed MATLAB routines. The image analysis method is similar to our previous work . General steps are as follows: (i) importing the files of images into MATLAB, (ii) transformation of the RGB images to gray-scale images followed by binarization based on color intensity to get the binary image, and (iii) identification of the pixels at the boundary of the binary images using Canny’s method of edge detection …”