Molecular-dynamics study of Poiseuille flow in a nanochannel and calculation of energy and momentum accommodation coefficients

Abstract

We report a molecular-dynamics study of flow of Lennard-Jones fluid through a nanochannel where size effects predominate. The momentum and energy accommodation coefficients, which determine the amount of slip and temperature jumps, are calculated for a three-dimensional Poiseuille flow through a nano-sized channel. Accommodation coefficients are calculated by considering a " gravity"- (acceleration field) driven Poiseuille flow between two infinite parallel walls that are maintained at a fixed temperature. The Knudsen number (Kn) dependency of the accommodation coefficients, slip length, and velocity profiles is investigated. The system is also studied by varying the strength of gravity. The accommodation coefficients are found to approach a limiting value with an increase in gravity and Kn. For low values of Kn (<0.15), the slip length obtained from the velocity profiles is found to match closely the results obtained from the linear slip model. Using the calculated values of accommodation coefficients, the first- and second-order slip models are validated in the early transition regime. The study demonstrates the applicability of the Navier-Stokes equation with the second-order slip model in the early transition regime.

Real gas transport through nanopores of varying cross-section type and shape in shale gas reservoirs

“…Nanopores type and shape affect gas transport mechanism and capacity, which can be explained from the microscopic point of view: (1) the interaction force between wall solid molecules and gas molecules is different from the gas intermolecular force, which causes the difference of gas molecules number density between the wall vicinity and away from the wall [34,35]; (2) gas molecules near wall prematurely collide with wall, which drastically reduces the mean free path [33]; (3) nanopores with different type and shape have different specific surface, which causes different ratios of the gas moleculeswall collision frequency to the total collision frequency [31]. In addition, this phenomenon can also be explained from a macro point of view.…”

“…For the slip region and transition region, the strong collision between the gas molecules and the nanopore wall affect the gas transport behavior [31], and nanopores with different cross-section types and shapes have different specific surface. Therefore, the cross-section type and shape also affect gas transport behavior in slip and transition regions [32][33][34][35]. Due to the diversity of nanopores in SGRs, finding analytical solutions for gas transport in nanopores with all cross-section types and shapes is complex and/or impossible [12,30,32].…”

An analytical model for shale gas permeability

“…In this study, a fully diffusive boundary condition (χ = 1), which is often assumed for rough surfaces (Prabha and Sathian, 2012), is applied that leads to, For the reminder of the paper, we use Eqn. 21 for apparent permeability calculations.…”

The effect of system boundaries on the mean free path for confined gases

“…1 Generally, the flow properties are calculated by approximating the MFP using the theoretical models. 2,3 The theoretical models that dictate MFP calculate the bulk value and do not give any information regarding the variation with linear dimension, if any. 4,5 However there have been attempts to portray the variation of confined fluid with reflective wall boundary.…”