重力驱动的水滴在土壤毛孔内非稳态运动研究

重力驱动下的水滴入渗是多孔介质特别是土壤中水分运移的一个基本问题,理论研究中常常用毛细管内的液塞(slug)运动来模拟。考虑前端液面的动态接触角效应,建立包含接触角参数的描述液塞非稳态运动过程的动力学模型,并对该模型进行了试验验证。应用该模型,研究多孔介质物理性质如斥水性、毛细管内径和液塞初始长度等参数对液塞运动过程的影响。结果表明:接触角的增加能显著影响毛管内液塞的下落速度,表明斥水性增加将显著降低土壤等多孔介质的导渗率;液塞在大管径毛管中平均速度较大,但能够到达的最终深度较小;相反地,液塞在小管径毛管中的平均下落速度较小,但能到达的最终深度较大。综合得出,在考虑孔隙结构统计分布的基础上,该模型可用于宏观入渗过程的模拟研究。

Study on Unsteady Motion of Gravity-driven Water Droplets in Soil Pores

Infiltration of liquid droplets into dry porous media has been widely modeled as liquid slug flow in capillaries.In this work, a math-ematical model was developed to model the gravity-driven slug motion in vertically oriented capillary tubes.Experiments on water slugs were conducted in partially wettable capillary tubes.Good agreements between the experimental and theoretical results demonstrated that the present model is capable of describing the unsteady-state dynamics of slugs fall in partially wettable capillaries.Then the developed model was applied to study the effects of contact angle and pore radium on slug dynamics.It showed that the slug falls down a longer distance at a larger average velocity for a smaller contact angle, and in a wide tube the slug had a larger average velocity than that in a narrow one.The model developed in this work could be employed to study how slugs propagate in porous media such as soils and help to explore the liquid droplets infiltration from a new point of view.