DYNAMIC CAPILLARY-PRESSURE VARIATIONS IN DIPHASIC FLOWS THROUGH GLASS-CAPILLARIES

We present an experimental study of diphase flows in capillary tubes with millimeter size diameters: we measure the capillary pressure variations dynamically during the motion of the interface in such tubes in order to study the effects of the flow velocity and of the nature of the fluids used. The reproducibility of the experiments allows us to perform measurements under very low applied pressures on the order of the capillary pressure. Under strong wetting conditions (kerosene displacing air) the variations of the dynamic capillary pressure pcd with velocity are very small, in agreement with the predictions of the Hoffman-Tanner theory. The variation of the difference between the static capillary pressure and pcd is also compatible with this model. Under weaker wetting conditions (water displacing cyclohexane), we have measured the variations of pcd as a function of the velocity; these variations are one order of magnitude larger than those predicted by Cox and their main features are compatible with the existence of an adsorption-desorption process. A particularly striking effect is a large increase of pcd observed at very low velocities. The influence of a prewetting of the tube by water prior to its filling by cyclohexane is finally measured: the driving effect of the capillary forces is then strongly increased. © 1991.