Water movement in glass bead porous media: 1. Experiments of capillary rise and hysteresis
Water movement in glass bead porous media: 1. Experiments of capillary rise and hysteresis
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玻璃珠多孔介质中水的运动：1.毛细管上升和滞后实验
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
D. R. Nielsen
中科院分区：
文献类型：
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作者：
T. Lu;J. Biggar;D. R. Nielsen
对水或乙醇在玻璃微珠中的毛细上升和滞后现象进行了实验观察，以加深我们对多孔介质中这些物理过程的理解。这些结果提供了毛细上升进入多孔介质的证据，不能完全用圆柱体模型来解释。他们进一步证明，“墨水瓶”模型不能很好地解释滞后现象。作为理想土壤模型的玻璃珠被封闭在一个矩形的玻璃室模型中。用电视摄像机结合显微镜记录毛细血管上升和引流的过程。在毛细上升过程中清楚地表明，在初始干燥的剖面中，流体在毛孔的颈部或在初始潮湿的剖面中的水膜底部表现出“跳跃”行为。在初始干燥的条件下，跳跃从直径最小的颗粒开始。跳跃过程持续到更高的海拔，直到达到平衡时，表面张力被流体静力所平衡。当时的湿润锋很容易被观察到是平坦的和饱和的。在初始湿条件下，毛细上升是与跳跃过程相关的水膜增厚过程。湿润锋后面的滞留空气使湿润锋变得不规则和不饱和。进入初始湿多孔介质的毛细上升可能高于进入初始干燥剖面的毛细上升。在干燥过程中，与气液界面相关的大表面积形成，使多孔介质比在相同压力下的润湿过程中保留更多的水。与现在流行的其他机制相比，该机制更好地解释了多孔介质中的滞后现象。
Experimental observations of capillary rise and hysteresis of water or ethanol in glass beads are presented to improve our understanding of those physical processes in porous media. The results provide evidence that capillary rise into porous media cannot be fully explained by a model of cylinders. They further demonstrate that the “Ink bottle” model does not provide an adequate explanation of hysteresis. Glass beads serving as a model for ideal soil are enclosed in a rectangular glass chamber model. A TV camera associated with a microscope was used to record the processes of capillary rise and drainage. It is clearly shown during capillary rise that the fluid exhibits a “jump” behavior at the neck of the pores in an initially dry profile or at the bottom of the water film in an initially wet profile. Under an initially dry condition, the jump initiates at the particle with smallest diameter. The jump process continues to higher elevations until at equilibrium the surface tensile force is balanced by the hydrostatic force. The wetting front at that time is readily observed as flat and saturated. Under an initially wet condition, capillary rise occurs as a water film thickening process associated with the jump process. Trapped air behind the wetting front renders the wetting front irregular and unsaturated. The capillary rise into an initially wet porous medium can be higher than that into an initially dry profile. During the drying process, large surface areas associated with the gas-liquid interface develop, allowing the porous medium to retain more water than during the wetting process at the same pressure. That mechanism explains better the hysteresis phenomenon in porous media in contrast to other mechanisms that now prevail.