Fluid transport through heterogeneous pore matrices: Multiscale simulation approaches

Abstract

Fluids confined in nanopores exhibit several unique structural and dynamical characteristics that affect a number of applications in industry as well as natural phenomena. Understanding and predicting the complex fluid behavior under nano-confinement is therefore of key importance, and both experimental and computational approaches have been employed toward this goal. It is now feasible to employ both simulations and theoretical methods, the results of which can be validated by cutting-edge experimental quantification. Nevertheless, predicting fluid transport through heterogeneous pore networks at a scale large enough to be relevant for practical applications remains elusive because one should account for a variety of fluid–rock interactions, a wide range of confined fluid states, as well as pore-edge effects and the existence of preferential pathways, which, together with many other phenomena, affect the results. The aim of this Review is to overview the significance of molecular phenomena on fluid transport in nanoporous media, the capability and shortcomings of both molecular and continuum fluid modeling approaches, and recent progress in multiscale modeling of fluid transport. In our interpretation, a multiscale approach couples a molecular picture for fluid interactions with solid surfaces at the single nanopore level with hierarchical transport analysis through realistic heterogeneous pore networks to balance physical accuracy with computational expense. When possible, comparison against experiments is provided as a guiding roadmap for selecting the appropriate computational methods. The appropriateness of an approach is certainly related to the final application of interest, as different sectors will require different levels of precision in the predictions.

Recycling and rheology of poly(lactic acid) (PLA) to make foams using supercritical fluid

“…The heterogeneity of the composite should not affect the solubility of CO 2 but could affect the CO 2 diffusion. 66 However, we assumed that the talc content does not affect the CO 2 diffusivity, and this assumption is valid based on the foamed structure (see Sec. II I 3).…”

Solute Sorption, Diffusion, and Advection in Macro–Mesoporous Materials: Toward a Realistic Bottom-Up Simulation Strategy

“…These limitations suggest the combination of a molecular-level model for the interfacial dynamics − with geometrical models of the involved pore space morphologies derived from three-dimensional physical reconstructions . Although simulations addressing interfacial dynamics and multiscale transport in porous media have significantly advanced in recent years, − particularly in the context of heterogeneous catalysis, − the coupling of a molecular-detail picture of the solute–surface interactions with advective–diffusive solute transport in physically reconstructed, hierarchical pore space morphologies remains a challenge. Quantum mechanical approaches and molecular simulations provide essential details about elementary reaction steps, adsorption, and diffusion inside a single pore, , but translating the molecular-level information to the mesoscopic and macroscopic scale requires a suitable strategy for linking the information obtained at different length scales …”

“…Quantum mechanical approaches and molecular simulations provide essential details about elementary reaction steps, adsorption, and diffusion inside a single pore, 20,24 but translating the molecular-level information to the mesoscopic and macroscopic scale requires a suitable strategy for linking the information obtained at different length scales. 18 This Perspective focuses on multiscale simulations of solute sorption, diffusion, and advection in hierarchical, macro− mesoporous adsorbents for chemical separations. The latter rely on a wide variety of solute−surface interactions that depend on the actual functionalization of the adsorbent surface (the stationary phase) and the composition of the fluid (mobile phase).…”

Use of Boundary-Driven Nonequilibrium Molecular Dynamics for Determining Transport Diffusivities of Multicomponent Mixtures in Nanoporous Materials

“…This is done by applying an external field only to a small region in the simulation box, positioned far from the pore. This tool has been extensively used in literature for pure components ,− and mixtures. , …”