A semi-analytical model research of liquid collar shape and coalescence in pore throat during snap-off

Abstract

When a wetting fluid is being displaced by a non-wetting gas in a capillary tube, a thin film of the wetting fluid is often left on the tube walls. To snap off the non-wetting gas, sufficient wetting fluid has to be collected in the pore throat, which will form a liquid lens that across the throat like a bridge, and a smaller gas bubble can be generated by snap-off. A number of researches have been conducted to study the phenomenon of snap-off both theoretically and experimentally. However, some dynamic characteristics of snap-off still remain unclear. In this work, a geometric model of pore throat and liquid collar formed in it was established, and multiple data sets of liquid collar shape were calculated. Following the principle that an interface system has a tendency of reducing its surface area, an evolvement path of liquid collar shape was concluded from the contour maps of calculation outcomes. Then a model of liquid flowing in film was derived, and the flow rate of liquid flowing from film into collar was calculated. Finally, the coalescence time of liquid collar calculated by model is almost the same with the measured time by experiment, and the film thickness utilized in model calculation is within a reasonable range of the experiment result, which proves a considerable reasonability and precision of the model. The liquid collar model in this work provides a new idea and reference for studying the morphological and dynamic characteristics of liquid collar in pore throat during snap-off.