Pressure-driven supercritical CO₂transport through a silica nanochannel

Abstract

A thorough understanding of supercritical CO 2 (scCO 2 ) transport through nanochannels is of prime significance for the effective exploitation of shale resources and the mitigation of greenhouse gas emission. In this work, we employed the non-equilibrium molecular dynamics simulations method to investigate the pressure-driven scCO 2 transport behavior through silica nanochannels with different external forces and pore sizes. The simulations reveal that the capability of scCO 2 diffusion enhances both in the bulk region and the surface adsorbed layer with the increasing of pressure gradient or nanochannel size, in addition, the slip length increases nonlinearly with the external acceleration or nanochannel width increases and finally reaches a maximum value. The negative slippage occurs at lower pressure gradient or within the narrower nanochannel. Overall, it is the combined effect of strong adsorption, surface diffusion and slippage that causes the nonlinear relation between flow rate and pressure gradient or nanochannel size. The present work would provide theoretical guidance for the scCO 2 enhanced shale oil/gas recovery, CO 2 storage, and mass transport in nanoporous materials.

Nanoscale Two-Phase Flow of Methane and Water in Shale Inorganic Matrix

“…The dependence between flow rate and acceleration is first studied to explore the applicability of Darcy’s equation for methane flow in two-phase flow of water and methane and in single-phase flow of methane, as shown in Figure . It shows a nonlinear relationship between methane flow rate in single-phase flow and the acceleration, demonstrating the breakdown of Darcy’s equation for methane flow. , This arises from the strong influence of the surfaces on methane and gas slip at the surface. − However, methane flow rate in two-phase flow is linearly proportional to the acceleration, indicating that Darcy’s equation holds for methane flow. This is attributed to the shielding effect of water film on the interaction between the surface and methane.…”

Flow of long chain hydrocarbons through carbon nanotubes (CNTs)

“…However, this method affects the dynamics of the molecules and the resulting interference with the fluid wall interactions may lead to inaccurate results. In this study, we chose to use an approach that does not interfere with the fluid wall interactions and requires relatively low computational resources 52 , which is a modified method used by Wu and Firoozabadi 53 . The CNT length was divided into three regions, force, buffer, and calculation (see Fig.…”

“…The length of force and buffer region is equal to the tube’s diameter, and the length of the calculation region is five times the diameter. Then a constant force ( ) was applied to all the carbon atoms present in the force region to simulate a pressure drop of 1 atm/Angstrom ( across the tube length inside the CNT 39 , 47 – 52 . Since applying an external force interrupts the natural dynamics of molecules, applying an external force on a small region along with the buffer region allows the dynamics to be restored so that the calculations are performed on the molecules without the influence of the external force.…”

Molecular dynamics study of convective heat transfer mechanism in a nano heat exchanger

“…Therefore, research on the ow and heat transfer characteristics at the micro/nanoscale emerge in an endless stream. [5][6][7][8][9][10] At microscale level, the explorations of the convective heat transfer are conducted by experiments and simulations. In 1981, Tuckerman et al rstly experimentally studied the convective heat transfer in microchannels and they veried that employing the cooling uid ow in microchannels could effectively dissipate the heat.…”