Flow Reduction in Pore Networks of Packed Silica Nanoparticles: Insights from Mesoscopic Fluid Models

Abstract

A modified many-body dissipative particle dynamics (mDPD) model is rigorously calibrated to achieve realistic fluid−fluid/solid interphase properties and applied for mesoscale flow simulations to elucidate the transport mechanisms of heptane liquid and water, respectively, through pore networks formed by packed silica nanoparticles with a uniform diameter of 30 nm. Two million CPU core hours were used to complete the simulation studies. Results show reduction of permeability by 54−64% in heptane flow and by 88−91% in water flow, respectively, compared to the Kozeny− Carman equation. In these nanopores, a large portion of the fluids are in the near-wall regions and thus not mobile due to the confinement effect, resulting in reduced hydraulic conductivity. Moreover, intense oscillations in the calculated flow velocities also indicate the confinement effect that contests the external driven force to flow. The generic form of Darcy's law is considered valid for flow through homogeneous nanopore networks, while permeability depends collectively on pore size and surface wettability. This fluid-permeability dependency is unique to flow in nanopores. In addition, potential dependence of permeability on pore connectivity is observed when the porosity remains the same in different core specimens.

Insights into the 3D permeable pore structure within novel monodisperse mesoporous silica nanoparticles by cryogenic electron tomography

“…Figure 4b shows the radius of connected pores inside the reconstructed MSNs varies in 1-10 nm with a mean of 4.6 ± 1.5 nm, which is larger than the rough estimates in Figure 1a but within the 2-30 nm mesopore size range of original surfactant micelles 29 . Simulations of pressure sintering of idealized 30 nm-diameter solid spheres based on the discrete element method [61][62][63] show the mean interparticle pore radius of 4.3 ± 0.7 nm 30 . It is close to the mean of the present MSN intraparticle pore radius (4.6 ± 1.5 mm), indicating that the permeable pathways within these MSNs should not be ignored when estimating the flow and transport properties of fluids in sintered agglomerate of these MSNs.…”

“…Figure 1 shows the transmission electron microscope (TEM) images of those MSNs with diameters measured in 31 ± 4 nm. However, the existing mesoscopic flow models assumed idealized or simplified particle surfaces of these MSNs for pore-flow simulations 30,31 , since 3D imaging approaches based on nano-CT 31 or FIB-SEM 10,11 cannot provide sufficient resolution. This work reports the 3D morphology of those monodisperse MSNs using an individual particle cryogenic electron tomography (IPET) technique [32][33][34] with missing-wedge correction 35 .…”

Insights into Waterflooding in Hydrocarbon-Bearing Nanochannels of Varying Cross Sections from Mesoscopic Multiphase Flow Simulations

“…To simulate a porous domain bearing multicomponent fluids, calibration is required to determine the parameters of the modified mDPD model. We adopt the parameters from our recent work, 82 which used MD simulations as a reference (except the bulk fluid properties of heptane liquid and water, for which experimental data was used for better accuracy in the relevant range of confinement pressure 58 ) to calibrate A, B, γ, r C , r d , and r D for interactions between every particle pair and allow for simulations of coexisting water and heptane confined in amorphous silica at a constant ambient temperature of 303 K. The study used the EOS, free surface tensions of both fluids, and water−heptane interfacial tension to determine the conservative force coefficients, A and B, between each fluid particle pair. The fluid contact angles were used to determine A and B between each fluid−silica pair.…”

“…The channel was initially filled with heptane as a hydrocarbon source fluid used in previous numerical studies. 57,58,82 Water was used as a working fluid to drive the source fluid out of the channel, a choice motivated by waterflooding techniques used in source recovery. 42,63 The solid channel wall was constructed with amorphous silica, 57 which is chosen for its tunable structure, allowing the effects of pore surface geometry on flow properties such as permeability and recovery to be quantitatively characterized.…”

“…The existence of threshold pressure was also confirmed regardless of the wettability of the silica surface by the fluid. 82 In each flooding simulation, sufficient time steps were run to complete the channel flush, which is defined as the period from the time that water starts to enter the channel to the time that water starts to enter the outlet reservoir. A time step size of 0.002, equivalent to 29 fs in the physical units, was used in all of the flooding simulations without observing numerical instability.…”