Transition from dripping mode to jetting mode under passive control with a drainage device

Abstract

Traditional Chinese medicine is a pivotal industry in China, and the technology for manufacturing high-quality pills is of great interest to numerous sectors. Among various methodologies, the liquid drip method has gained significant attention from the pharmaceutical industry due to its advantages such as high drug content uniformity, low cost, ease of operation, high production efficiency, and extensive adjustment range. However, the occurrence of undesirable satellite droplets during the drip production process remains a persistent issue. These satellite droplets are challenging to collect and their prolonged presence can disrupt the normal functioning of the system. Previous studies have identified two primary modes of droplet formation: dripping mode and jetting mode. Given that droplet formation in dripping mode is more stable and satellite droplets can be effectively suppressed, studying the transition between dripping and jetting modes and improving the uniformity of the generated droplets become crucial. Achieving this transition can be accomplished through both active and passive methods. In view of the limitations of the active methods in actual productions, we explored a passive method of adding a drainage device, which can effectively inhibit satellite droplets.In this experimental and numerical simulation investigation, we successfully induced the dripping-to-jetting transition by incorporating a drainage device into the dropper. Additionally, we examined how modifications to the dropper's structure influenced droplet formation. Results indicated that increasing the length and diameter of the drainage device resulted in higher critical Weber numbers required for the dripping-to-jetting transition. Contrarily, the effect of the Kapitza number on the critical Weber numbers exhibited an opposite trend. The critical Kapitza number without complex droplets was also discussed.