Draining of a water tank under inadequate ventilation conditions.

This article investigates the drainage processes of a water tank through a bottom orifice under varying ventilation conditions, identifying three distinct drainage modes: periodic draining with bubble generation at a sealed top (mode I), full-flow draining without bubbles under sufficient ventilation (mode II), and a combined mode with bubbles appearing after the water level falls below a critical depth (mode III). Experimental measurements of water and air pressures, along with visual observations, reveal how ventilation influences bubble formation, drainage efficiency, and pressure fluctuations. A mathematical model is developed and validated for mode II, accurately predicting water depth variation and emptying time based on ventilation slit size and orifice dimensions. Transition criteria between drainage modes are established, providing guidance on critical ventilation requirements to avoid bubble formation during drainage. This study enhances understanding of air–water interactions in tank drainage relevant to engineering applications involving liquid storage and discharge under limited ventilation.