No abstract

Different pore shapes correspond to different interaction strengths between pore surface and molecules, which will result in discrepancy of nanoconfined water transport capacity. In this article, complex nanoscale pore shapes are represented by ellipses, which possess an excellent shape-variation physical property, that is, ellipses can gradually transition from circles to slit-like cross-sections by manipulating aspect ratio from 1 to maxima. Moreover, capturing water slip phenomenon and spatially variation of water viscosity, an analytical model for water transport capacity through elliptical nanopores is developed. Results show that (a) water slip effect plays a limited positive role at hydrophilic environment and a strong positive role at hydrophobic environment;(b) nanopores with more flat geometry feature will possess smaller enhance factor at hydrophilic environment; (c) spatially viscosity distribution is a negative factor when contact angle is lower than about 130 and turns to a positive factor when contact angle is higher than about 130 . K E Y W O R D Snanoconfined water flow, various pore shapes, water slip phenomenon, water viscosity

The pursuit, toward transport efficiency, is significantly necessary for energy conversion, water filtration. However, structure design, aiming at further enhancing nanoconfined water flow, is still lacking. With the motivation to bridge the knowledge gap, a simple yet practical model regarding the nanocone structure design is established. This research demonstrates that nanocone, with desirable opening angle and length, possesses the capacity to achieve the optimal flow behavior. Flow resistance occurring inside nanocones, and that at cone entrance, exit, are considered. Optimal nanocone geometry can be determined based on the minimization of total resistance. Results show that (a) suitable opening angle spans from 10 to 30 over a wide range of nanocone geometry; (b) evident decline tendency of the suitable opening angle toward the increasing surface wettability is captured; and (c) water transport capacity inside optimal nanocone is 4-50 times that within cylindrical nanopores. This article forms a theoretical framework for nanocone design.

No abstract

No abstract

Rocks are natural materials with a heterogeneous microstructure, and the heterogeneity of the microstructure plays a crucial role in the evolution of microcracks during the compression process. A numerical model of a rock with a heterogeneous structure under compression is developed by digital image processing techniques and the discrete element method. On the grain scale, the damage mechanism and microcrack characteristics of a heterogeneous Biotite granite under compression fracture are investigated. First, the process of constructing a digital image-based heterogeneous grain model is described. The microscopic characteristics of geometric heterogeneity, elastic heterogeneity, and contact heterogeneity are all considered in the numerical model. Then, the model is calibrated according to the macroscopic properties of biotite granite obtained in the laboratory, and the numerically simulated microcrack cracking processes and damage modes are obtained with a high degree of agreement compared to the experiments. Numerical simulations have shown the following: (1) Microcracking occurs first at the weak side of the grain boundaries, and the appearance of intragranular shear cracks indicates that the rock has reached its peak strength. (2) The stress concentration caused by the heterogeneity of the microstructure is an essential factor that causes rock cracks and induces rupture. Intragranular cracks occur successively in quartz, feldspar (plagioclase), and biotite, with far more intragranular cracks in quartz and feldspar (plagioclase) than in biotite. (3) Microcracking in quartz occurs as clusters, fork and fracture features, and in feldspar (plagioclase) it tends to cause penetration microcracking, which usually surrounds or terminates at the biotite. (4) As the confining pressure increases, the tensile break between the grains is suppressed and the number of shear cracks increases. At the macro level, the rock failure mode of the numerical model changes from split damage to shear destruction, which is consistent with the law shown in laboratory experiments.

The nanoconfinement effect, induced by strong surface−molecule interactions at the nanoscale, is correlated only to the pore size from a traditional perspective. However, when the pore size is comparable to the molecular diameter, the impact of surface wettability on the surface−molecule interaction strength cannot be overlooked. In order to bridge the knowledge gap, in this article, the nanoconfinement effect is described as a function of not only pore size shrinkage but also surface wettability. The Peng− Robinson equation of state is modified by adding a fluid−surface attraction term, incorporating the shift of critical properties induced by surface affinity. Particularly, the wettability effect is described as a function of contact angle, an easily accessed macroscopic parameter, facilitating the model application. Reliability of this research is verified against shifted fluid critical properties, collected from existing reports, focusing on fluid behavior in graphite or mica nanopores. The results show that (a) reduction of methane critical temperature takes place when methane molecules are confined in hydrocarbon-wet nanopores; (b) both the enhancement of surface affinity and decline of pore size will result in the shrinkage of the methane liquid−vapor coexistence curve; and (c) the phase diagram of nanoconfined methane suggests an upward trend, attributed to the shifted critical properties. In this article, the wettability effect on nanoconfined methane behavior is revealed, expecting to enrich the theoretical background about methane behavior inside nanopores.

No abstract