ABSTRACT:

Multiphase displacement in fractured porous media is critical for various subsurface processes. Recent studies have demonstrated the significant role of contact angle in determining displacement regimes in homogenous porous media, yet the understanding of its impacts on flow in fractured porous media remains insufficient. We conduct microfluidics experiments to study the combined impacts of contact angle, fracture aperture, and capillary number on displacement patterns in fractured micromodels. Results show transitions from matrix-preferential flow to fracture-preferential flow and finally to fracture flow even when contact angles are much smaller than 90. Aperture-dependent phase diagrams are proposed to predict the displacement patterns at varying capillary numbers and contact angles. Pore-scale observations suggest that the transition of flow regimes is controlled by pore-scale mechanisms which constrain the crossflow from the fracture to the matrix. This study provides physical insights on incorporating contact angle into the prediction of flow in complex fractured porous media.

ABSTRACT:

This study investigates the effect of system softness on Haines jumps and drainage in porous media using microfluidics. A gas bubble with controlled volume is introduced into the liquid phase to create a soft system. A pore-scale analytical model incorporating softness is developed, and a dimensionless number is proposed to characterize it. Experiments in single pore throats, pores-in-series, and pore networks show that increased softness leads to longer jump distances and waiting times. In series pores, system softness determines the number of pores filled during a jump, while in networks, softness alters invasion dynamics but not the final saturation pattern.

ABSTRACT:

Snow density is a fundamental property that determines the thermal and mechanical behavior of snowpack. It is an important variable for snow water equivalent (SWE) estimation, snow management, slope stability analysis, etc. Artificial snow has become essential for most snow slopes due to climate change and influences regional snow hydrological processes. Snow density of artificial snow differs from that of natural snow due to particle-shape effects and distinct solidification processes. This study presents a particle-scale investigation of snow density variation and proposes a conceptual model considering the effect of critical droplet diameter for artificial snow. An outdoor snowmaking experiment and snow particle characterization are conducted to verify this theory. A theoretical method is proposed to predict critical droplet diameter for snowmaking. Results demonstrate that critical droplet diameter determines the percentage of frozen and unfrozen droplets and therefore, influences the snow density. Frozen droplets form the structure of the snow packing. Unfrozen droplets fill the voids of snow packing and increase snow density. Snowmaking experiments confirm that the snow density increases with SMD at constant environmental conditions. The snow density increases as environmental temperature increases when the atomization performance is constant. Snow particle characterization shows larger frozen particles associated with low-density snow. The calculation results suggest that decreasing air temperature, humidity, and solar radiation and increasing ground clearance of the snowmaker increase the critical droplet diameter and lower the snow density. The effect of humidity, solar radiation, and ground clearance on snow density is more remarkable at higher temperatures.