Drainage from a Fluid-Handling Component Because of Inclination

The onset of drainage of liquids from fluid-handling components with a single, circular orifice was evaluated. A component was filled with water, ethylene glycol, or ethyl alcohol and then oriented vertically with its orifice facing downward. The lower end of the component was slowly tilted toward the horizon. No flow occurred until a critical angle of inclination was reached. The onset of drainage was successfully modeled as a balance between the hydrostatic pressure in the bulk liquid and the Laplace pressure of the air-liquid interface within the orifice. If the Laplace pressure was greater than the hydrostatic pressure, then the flow from the component was impeded. With further inclination, a critical angle was exceeded that allowed the liquid to flow from the component. The theoretical model gave reasonable estimates of the measured values.