Determination of dynamic capillary effect on two-phase flow in porous media: A perspective from various methods

The relationship between capillary pressure and saturation plays a critical role in the characterization of two-phase flow and transport in aquifers and oil reservoirs. This relationship is usually determined under the static condition, where capillary pressure is the only function of saturation. However,considerable experiments have suggested that the dependence of capillary pressure on desaturation rate is under the dynamic condition. Thus, a more general description of capillary pressure that includes dynamic capillary effect has been approved widely. A comprehensive understanding of the dynamic capillary effect is needed for the investigation of the two-phase flow in porous media by various methods. In general, dynamic capillary effect in porous media can be studied through the laboratory experiment, pore-to macro-scale modeling, and artificial neural network. Here, main principle and research procedures of each method are reviewed in detail. Then, research progress, disadvantages and advantages are discussed, respectively. In addition, upscaling study from pore-to macro-scale are introduced, which explains the difference between laboratory experiment and pore-scale modeling. At last, several future perspectives and recommendations for optimal solution of dynamic capillary effect are presented.

Capillary effect on the sloshing of a fluid in a rectangular tank submitted to sinusoidal vertical dynamical excitation

Surface tension effects on fluid sloshing in a tank subjected to external excitation has been less studied. This work aims at understanding this phenomenon in order to derive practical solutions to problems faced in several engineering. A tank containing a fluid with a free surface is submitted to gravity and capillary forces and subject to external dynamic excitation. Introduction of vertical sinusoidal dynamical excitation leads to a problem of paramtric oscillations governed by the Mathieu equation. Analysis of the Mathieu equation shows the existence of stable and unstable regions in the stability diagram. Some results induced by harmonic excitations on the fluid sloshing are presented. When the external dynamical excitation amplitude ~ is small, periodic solutions appear in stable regions and when e increases, the fluid behavior is not perfectly periodic and the amplitudes are not regular. Nonlinear effects make the behavior of the fluid complicated and render it almost unpredictable. In stable regions, the solution remains bounded at any time. When changing the perturbation parameter 6, the phase difference increases and also with the increase of the surface tension.

The capillary pressure curves from upscaling interfacial and unsaturated flows in porous layers with vertical heterogeneity

We provide the capillary pressure curves p_(c)(s)as a function of the effective saturation s based on the theoretical framework of upscaling unsaturated flows in vertically heterogeneous porous layers proposed recently(Z.Zheng,Journal of Fluid Mechanics,950,A17,2022).Based on the assumption of vertical gravitational-capillary equilibrium,the saturation distribution and profile shape of the invading fluid can be obtained by solving a nonlinear integral-differential equation.The capillary pressure curves p_(c)(s)can then be constructed by systematically varying the injection rate.Together with the relative permeability curves k_(rn)(s)that are already obtained.One can now provide quick estimates on the overall behaviours of interfacial and unsaturated flows in vertically-heterogeneous porous layers.

Effect of the lenticles on moisture migration in capillary zone of tailings dam

Small-particle interlayers(lenticles)show some characteristic hydraulic properties and can affect the movement of unsaturated water.In this study,we developed a novel online capillary-water-absorption monitoring device and conducted three groups of comparison tests to simulate lenticle positions and thicknesses with respect to the capillary rise.The results show that the characteristic wetting front exhibits a fast rise in the early stage,a slow rise in the middle stage,and stability in the later stage.The motion of the capillary water in the lenticle is mainly transversal,with the upward curve being"flat,"and the longer is"flat,"the longer is the time needed for the water to move.The interlayer can form a capillary stagnation zone with moisture content close to saturation.The high interlayer may form a discontinuous corrugated capillary zone.Thus,when the wetting front reaches the"coarse-grain(lower)-fine-grain(upper)"interface,the"anti-capillary barrier effect"results in more moisture in the upper layer.Thus,when the wetting front of the capillary water reaches the"fine-grain(upper)-coarse-grain(lower)"interface,the"capillary barrier effect"causes the moisture content of the upper tailings to decreases sharply because of the horizontal movement of the water in the fine medium.It is clear that the presence of lenticles can retard the rise of capillary water by storing water.

Deliverability of wells in carbonate gas condensate reservoirs and the capillary number effect

With the development of the Tazhong No. 1 carbonate gas condensate reservoir in China, it has become more and more important to study the characteristics of gas condensate well deliverability. A single-well radial simulator for dual-permeability reservoirs was established to study the influences of fluid properties, permeability, and pressure drawdown on well deliverability with and without the capillary number effect. The simulation shows that well deliverability basically maintains its initial value and is not affected by the capillary number when the formation pressure is higher than dew-point pressure. However, well deliverability drops rapidly when the formation pressure is lower than dew-point pressure. Even if the condensate dropout is very low, well deliverability without the capillary number effect reduces to 50 percent of its initial value when reservoir pressure declines to 95 percent of dew-point pressure, but well deliverability is significantly improved if the capillary number effect exists. The capillary number effect is most significant when reservoir pressure is just lower than dew point pressure, then the effect decreases; the reduction of well deliverability is mainly caused by the reduction of gas relative permeability of the matrix system near the wellbore.

Resistance law of a rod penetrating a multilayer granular raft

This paper presents an experimental study on the resistance law of a rod vertically penetrating different kinds of multilayer granular rafts with a constant velocity so as to reveal the mechanical properties of the multilayer granular rafts.The resistance was quasi-static under the chosen velocity.Experiments were conducted with different granular thicknesses,rod diameters and combinations of particles and liquids.The study shows that the resistance–displacement relation of the rod has three smooth stages.In the first stage,the resistance rapidly increased.In the second stage,the resistance curve maintained an almost constant slope.In the third stage,the resistance smoothly changed with its slope continuously increasing.Based on the corresponding physical models for each stage,the study reveals the exponential dependence of the load-bearing capacity of the multilayer granular raft on its thickness,and clarifies the capillary effects on the resistance law.The study extends the knowledge of the granular raft from monolayer to multilayer structure.

Transpiration-inspired Capillary for Synchronous Synthesis and Patterning of Silver Nanoparticles

Traditional synthesis strategy of nanomaterials with complicated process and high cost limits their applications.Here,we propose a facile process for the synchronous synthesis and patterning of silver nanoparticles(Ag NPs)through the self-driven microchannel reactor with the capillary effect inspired by transpiration.The evaporation contributes to capillary and accumulation effects in the microchannels.The silver reactant-containing droplets can be spontaneously divided and distributed in multiple microchannels during the whole fabrication process by the capillary effect.The newly formed Ag NPs at the gas-liquid interface can be assembled on both sides of the microchannels by the accumulation effect.The capillary effect decreases the disturbances,which ensures the uniformity of the patterning.By the combination of microchannels with different widths,various Ag NPs-assembled patterns with stable electrical properties are achieved.This efficient strategy with a simple fabrication procedure is towards the technological engineering of nanoscale architected materials.

Biomimetic Capillary Inspired Heat Pipe Wicks

The possibility of mimicking desirable properties from nature accelerates material improvement and generates commercial interests. For heat pipe development, many attempts have been made in heat pipe wicks to enhance its capillary performance by mimicking biology. Constructing biporous, composite, or nanopillar wicks with aim of achieving hierarchical structure has been found in many studies. Mimicking beetle shell surface to obtain hybrid wettability shows biomimetic potential in heat pipe wicks. This paper firstly reviews some fundamental studies in biomimetics, establishing a general idea of surface wetting and capillary effect. MR/scanning of two live plants （Musa X Paradisiaca and Salix Flamingo） provides the possibility of visualising internal structures in vivo and obtaining rates of water transport in xylem vessels. In addition, by investigating the work inspired directly or indirectly from biomimetics, the role that biomimetics plays in modern heat pipe technology is revealed. Our innovation which syntheses a low level of hierarchical structure and integrates integral wicks for different heat pipe sections including evaporator, adiabatic, and condenser is introduced. Mathematical modelling in terms of capillary pressure and capillary rise rate to characterise such new structure is provided.

Transparent ultrathin SiO_(2) nanowire aerogel displaying novel properties when interacting with water:A promising versatile functional platform

With low density,high porosity,and outstanding physicochemical stability,ceramic nanowire aerogels and sponges exhibit various interesting properties.Herein,an ultrathin silica nanowire aerogel(SiO_(2)NWsA)was achieved via a facile chemical vapor deposition route.In addition to good mechanical and thermal performances,properties resulting from active water-aerogel interactions are revealed,i.e.,outstanding transparency,strong capillary effect,enhanced compressive strength(a reversible strain of∼62%),switchable wettability and robust shape retention ability when filled with water.The physical mechanism related to these interesting properties is demonstrated basically according to its unique features(distinctly reduced nanowire diameter,enriched nanoscopic gap channels,and reinforced network).To demonstrate the superiority,an advantageous solar vapor generation system(hydrophilic NWs-A/reduced graphene oxide(rGO)/hydrophobic NWs-A)was obtained by integrating these favorable characteristics,giving rise to remarkably promoted vapor evaporation rate and energy efficiency compared to the rGO hydrophobic NWs-A device.These results contribute to the structural design and functional exploration of nanowire aerogels.