Residual film dynamics in glass capillaries

We report measurements of the residual film thickness profiles resulting from the displacement of a fluid by an immiscible fluid in a 50-cm-long and 1.1-mm i.d. capillary tube. A radioactive tracer technique is used to measure the variations of the local thickness along the tube, Spatial variations of the film thickness are observed experimentally increasing with the viscosity ratio M=mu(2)/mu(1) between the displacing and displaced fluids (10(-3)<M<30), with the capillary number Ca (5x10(-6)<Ca<3) and with the distance from the meniscus tip (up to 70 cm). The thickness along the tube is constant only for low M values and/or low Ca values. The film thickness averaged over the tube length increases with the capillary number as Ca-0.6: this variation is independent of the relative viscosity of the fluids and very similar to the observations of other authors using different sets of fluids. Differential equations verified by the film thickness variations with time and distance far from the meniscus tip are established and their relations with the observed results are discussed. (C) 1996 Academic Press, Inc.