Institute of Fundamental Technological Research

Reliable experimental data are essential for good research. Also, the interaction of drop and liquid surface is ubiquitous and of practical importance in our lives. However, beginning researchers often face an unavoidable long learning curve due to a lack of systematic collection of failure experiences. These include somewhat trivial but also influential factors, especially in cases of low impact velocities, e.g., the feeding process into a liquid tank, the dropping into a drip chamber, and/or neglecting the initial velocity associated with the dripping drop generation in the experimental preparation processes, etc. Inconsistent experimental comparisons may arise from different methods of thin-film preparation and measurement or from nonunified parameter definition, e.g., the penetration depth of vortex rings induced by low-velocity drop impact, which makes experimental data analysis and comparison even more challenging. Here, we have accumulated some of our experience in preparing drop and liquid surface interactions including a short review of preparing thin (or very thin) target liquid film of well-defined thickness; the method to minimize the commonly neglected current underneath the target liquid; the method of generating the satellite-free drop along with the correct prediction of drop oscillation phase in the free-falling period after pinch-off, and the role of drop initial velocity, etc. These archival data are expected to shorten the learning period and facilitate benchmarking of related experiments for future users in our community.

Liquid wetting on a container wall forms a meniscus that causes the reading uncertainty of interface measurement, which was considered as an “inevitable” interference in experiments. For minimizing the meniscus interference, the dynamic instead of the static contact angle should be focused on and θr ≤ 90° ± ε ≤ θa is the guideline to achieve a meniscus-free interface for a practical experiment, where θr, θa, and ε are the receding and advancing contact angles, and image measuring uncertainty, respectively. A simple and systematic technique to achieve the meniscus-free interface has been proposed and visualized.

Thermal instruments, Liquids, Fluid dynamics, Flow visualization, Capillary flows