The behavior of liquid bridges between two relatively moving particles

Abstract

The strength and rupture point of a liquid phase between two moving spherical particles in air were studied experimentally and theoretically. The liquid forms an axisymmetrical bridge when the particles are in close proximity which subsequently elongates and finally ruptures as the spheres are moved away from each other in an axial direction. The resistance of the liquid to the movement of the spheres (bridge strength) was measured using a strain gauge and high-speed photography. It was found that dynamic bridges are much stronger than geometrically identical static bridges where the attraction force is due to surface tension only. The force required to separate two moving particles is sometimes orders of magnitude higher than that required in static systems because the viscosity of the fluid resists the motion in the dynamic case. These findings explain why in fluidized beds, for example, where either high temperatures create sticky granules by surface softening (melting) or an added liquid creates a viscous surface coating, quenching or collapsing of the bed is such a catastrophic phenomenon. It also explains why in other systems such as coating and drying devices and wet powder processing, small amounts of fluid drastically change the properties and the behavior of the system.