An-Bang Wang

Liquid films with thicknesses on the order of 1 mm were commonly used for the study of drop impingement onto a wetted surface. This is because films thinner than 1 mm are difficult to generate and measure due to capillary meniscus. In this work a novel method to produce thin films of well-defined thickness has been developed. Also a reliable process with minimum uncertainty to determine film thickness was proposed. New splashing phenomena were observed for drop impact onto thin films. It is found that the critical splash level (the threshold Weber number) is insensitive to film thickness for a given solid surface if the film is sufficiently thin. It is also shown that the critical splash level increases with liquid viscosity.

With the increasing demand for green energy due to environmental issues, developing batteries with high energy density is of great importance. Li-S batteries, since their big breakthrough in 2009, have attracted much attention in both academia and industry. In academia, significant progress has been made in improving the specific capacity, rate capacity and cycle performance using various novel strategies. However, the performance is hugely different when these strategies are extended to mass production, indicating a significant difference between academic research and industrial production. In this brief review, we discussed the gap between the academic research and commercialization in detail based on literature reports and to our more than ten years’ experience on Li-S pouch cells, which including cathodes, anodes, separators, interlayers, electrolytes, and additives. The problems, which existing in pouch cells by using the materials and technologies developed by academic research using coin cells, was analyzed. We expected that this review could be helpful to both academic research and industrial commercialization of Li-S batteries.

The impact of a drop on liquid surfaces is studied experimentally and theoretically in the region of the fully developed splashing. In order to reveal the influence of viscosity and target liquid depth on the resulting flow patterns, the experiments were carried out with water and 70% glycerol–water solution, and for different target liquid depths. Based on the experimental observations, a dynamic model of the central jet formation at the cavity collapse is developed. This model predicts an emergence of a liquid flow up into the central jet and simultaneously a small flow velocity downward and allows us to evaluate the velocities of these two flows. A theoretical model for the cavity submergence is presented. This model gives the constant velocity of the cavity submergence which is half the initial drop impact velocity. Analytical solution for the gravity–capillary cavity collapse has been derived and provides a good fit to the experimental results. Theoretical analysis and experiments have shown that the maximum cavity radius and the cavity collapse time depend on both the Froude number and the dimensionless capillary length.