CAPILLARY RISE OF LIQUID BETWEEN PARALLEL PLATES UNDER MICROGRAVITY

The liquid flow between parallel plates under microgravity due to capillary forces is studied. Experiments were performed during the free fall in a drop tower to investigate the transient rise of the meniscus (free surface). A linear momentum balance around the fluid in the capillary gap leads to a second-order nonlinear differential equation for the height of the meniscus. Good agreement was found between the numerical solution and the experimental data. The meniscus runs through three time domains. In the beginning the inertia force due to the acceleration of fluid in the reservoir acts against the capillary force, which is always the driving force. After that the convective force due to the fluid flow at the entrance becomes dominant, leading to a linear meniscus rise h(t). Subsequently, the frictional force in the gap dominates other resisting forces and the increase of h(t) becomes proportional to the square root of time. Approximate solutions for the three time domains have been found. © 1994 by Academic Press, Inc.