Visualization experiments and pore network models on evaporation of capillary porous media are presented in this work. We show that in a simple model porous medium the pores occupied by gas can be refilled with liquid, snapping off a gas bubble, which then moves to a stable configuration. This phenomenon, referred to as capillary instability, is induced due to heterogeneity in wettability of the pore surfaces and has a much smaller time scale compared to the evaporation process. The capillary instability is exploited based on the optical images obtained from visualization experiments. The residual liquid in pores can suppress the capillary valve effect, which is induced by the sudden geometrical expansion and can hinder the movement of the gas-liquid interface. For better understanding of the capillary instability induced gas-liquid displacement, a pore network model that accounts for capillary and viscous forces as well as the inertial effect is developed. The pore network simulation results agree well with experimental data. The ratio of the square of the average meniscus moving speed predicted by the pore network model with the inertial effect to the average meniscus moving speed obtained from the model without the inertial effect is a linear function of the Weber number. When the Weber number exceeds a critical value, more pores are invaded by the gas-liquid interface in the pore network model with the inertial effect than in the model neglecting the inertial effect. The pore network model developed here opens up a new route to better understand the role of inertial effects in two-phase transport in porous media. {I.

中文翻译：

---

毛细管不稳定引起的气液在多孔介质中的驱替：实验观察和孔网模型

这项工作提出了可视化实验和毛细孔多孔介质蒸发的孔网模型。我们表明，在一个简单的多孔介质模型中，被气体占据的孔可以被液体重新填充，剥去一个气泡，然后气泡变成稳定的构造。这种现象称为毛细管不稳定性，是由于孔隙表面的润湿性不均匀而引起的，与蒸发过程相比，时间尺度要小得多。基于从可视化实验获得的光学图像来利用毛细管的不稳定性。孔中的残留液体可抑制毛细管阀效应，该效应是由突然的几何膨胀引起的，并可能阻碍气液界面的运动。为了更好地了解毛细管不稳定引起的气液位移，建立了考虑毛细力和粘性力以及惯性效应的孔隙网络模型。孔隙网络模拟结果与实验数据吻合良好。由具有惯性效应的孔网络模型预测的平均弯月形运动速度的平方与从没有惯性效应的模型中获得的平均弯月形运动速度的比值是韦伯数的线性函数。当韦伯数超过临界值时，在具有惯性效应的孔隙网络模型中，气-液界面侵入的孔隙比在忽略惯性效应的模型中更多。此处开发的孔隙网络模型开辟了一条新途径，以更好地理解惯性效应在多孔介质中两相传输中的作用。{一世。