Dynamic Contact Angles And Wetting Front Instability In Soils

Abstract

Dynamic contact could provide a mechanism for initiating the instability of wetting fronts and the formation of gravity fingers/columns in porous media. To study those dynamic contact angles when gravity effects are present, rectangular capillary tubes are used to facilitate the observation of the complete interface without geometric distortion. Results show that if the dynamic contact angle minus the static contact angle is used, we obtain good agreement with previous observations. In addition, we show that in our experiments, unlike previous observations, contact angles are independent of capillary size. It also points out a way to calculate the capillary pressure at the wetting front as a function of the flux in the finger and grain size diameter.