Rough Nanochannel Research Articles

Rough Surface Effect on CO2 Displacement at the Nanoscale

CO2 injection has great potential for enhancing shale oil recovery. Understanding the CO2 displacement in nanometer pores of shale is critical for developing effective CO2 injection techniques. In this work, we applied direct numerical simulation to study the effect of the rough surface on CO2 displacement in nanometer pores of shale. By quantifying CO2 displacement in rough nanochannels, we aimed to understand how surface roughness and morphology affect displacement progress. We found that the rough surface results in shrinkage of the CO2 displacement path, slowing overall displacement rate. Additionally, the pinch-point effect in a rough nanochannel impedes the smooth progression of the interface contact line, causing periodic velocity fluctuation that further hinders CO2 displacement. We also simulated the CO2 displacement in rough nanoporous media, finding that the rough surface leads to a substantial decrease in CO2 displacement efficiency, especially under low pressure gradient conditions. Our simulation results indicate that the rough surface of a shale nanometer pore has a nonnegligible effect on CO2 displacement.

Effect of nanostructured surface configuration on the interface properties and heat transfer of condensation process of argon inside nanochannels using molecular dynamics simulation

Present work studies the impact of surface structure on the heat transfer and liquid–vapor interface properties of condensation flow formed inside rough nanochannels compared to the smooth ones, using molecular dynamics simulation. Considering rectangular roughness configuration on the walls of nanochannel, simulations are performed under various saturated temperature conditions to obtain density, velocity, and temperature profiles. Furthermore, the effect of rough elements on the mechanism of liquid film formation and condensation rate as well as the thermal properties of two-phase flow has been investigated. It is observed that the amount of the oscillations in the vicinity of the walls at the end of the simulation time in rough nanochannels, is less than in smooth nanochannels. Results show that the effect of rough structures on the distribution of particles as well as velocity profile is greater at a lower temperature. Also, rough surfaces increase heat transfers at the beginning of the condensation process that leads to higher values of thermal conductivity in the rough nanochannel compared to the smooth nanochannel. Moreover, it is demonstrated that the thermal conductivity of argon condensation in rough nanochannel is approximately equivalent to the value of thermal conductivity in smooth nanochannel by adding one copper nanoparticle to the base fluid of argon.

Study on effect of different surface roughness on nanofluid flow in nanochannel by using molecular dynamics simulation

In this paper, the influence of surface roughness inside the nanochannel on nanofluid flowing properties was studied by using molecular dynamics simulation (MDS). In our simulations, water molecules were employed as the base fluid, and copper atoms were adopted to model the nanochannel walls and nanoparticles. In order to investigate the effect of surface roughness including rectangular, triangular, and hemispherical roughness on the flow properties of nanofluid, parameters such as temperature, total potential energy, velocity, and density profiles of H2O/Cu nanofluid were calculated. From the above simulation results, we find that increasing the roughness height increases the temperature and velocity of nanofluid. In addition, the surface roughness increases the velocity and temperature in the nanochannel by shrinking the cross-section with constant roughness height. And the surface roughness also reduces the range of fluctuations of the density near the walls in the nanochannel, which is because fewer fluid particles reside near the rough nanochannel walls compared to the ideal nanochannel. The other result is that the triangular roughness has the greatest effect on the flow properties of nanofluid, the effect of surface roughness on the flow property of nanofluid cannot be ignored.

Influence of nanostructure morphology on the heat transfer and flow characteristics in nanochannel

Based on the molecular dynamics principle, the convective heat transfer of the fluid through nanochannel with various rough nanostructure morphologies is investigated. The influences of nanostructure free shear ratio, morphology period and nanostructure depth on the flow and heat transfer characteristics are probed. A comprehensive evaluation on the convective heat transfer in rough nanochannel considering the flow resistance is performed. The result shows that the temperature jump and velocity slip dominate the heat and momentum exchange between the channel wall and fluid. Under the weak wall-fluid interaction, the smaller the nanostructure free shear ratio, the better the heat transfer performance as well as drag reduction characteristic. In contrast, the smaller the nanostructure morphology period, the better the heat transfer performance, the greater the flow resistance. Therefore, the wall rough morphology with small free shear ratio and sparse nanostructures is conducive to heat transfer augmentation and drag reduction jointly. The deeper rough nanostructure groove is unfavorable to reduce the flow resistance. The combination of rough nanostructure morphology and weak wall-fluid interaction is crucial, which will bring about a favorable impact on the heat transfer and flow resistance in nanochannel. Specifically, the nanostructure free shear ratio with ϕa=0.1875 is a favorable rough morphology to obtain optimum heat transfer and drag reduction characteristics in nanochannel.

Investigation of the relationship between nanochannel width and mass transfer characteristics for dense methane nanofluidics

In this paper, we analytically investigate the influence of the nanochannel width on mass transfer characteristics through the rough nanochannel by using non–equilibrium multiscale molecular dynamics simulation. The mass transfer characteristics are analyzed by fitting the curve correlation between the diffusion coefficient and nanochannel width. The diffusion coefficient is calculated using the revised Green–Kubo relation in different nanochannels. The numerical results demonstrate that the relationship between diffusion coefficient and the inverse of nanochannel width is parabolic. Moreover, the diffusion coefficients show significant variations in the small rough nanochannel, and gradually approach the values of bulk system with increasing the width of nanochannel. In addition, to explore its mechanism, the local atom number density, velocity profile, velocity autocorrelation function, the escape rate of molecule, local diffusion coefficient and projection radial distribution function are given in different widths of nanochannel under given boundary condition. Simulation results show that the local structure and number density of fluid influence the transfer mass characteristics. These results of this work may be conducive to further understand the mass transfer behaviors of nanofluidics, and guide the optimal design of nano–devices.

The effects of surface topography and non-uniform wettability on fluid flow and interface slip in rough nanochannel

The flow of argon liquid in an asymmetric nanochannel with smooth and rough wall is investigated by molecular dynamics method. Considering the relationships of related factors which include characteristic dimensions, the number and the dense arrangement pattern of nanostructure, the effects of surface topography on fluid flow and interface slip are probed. The results show that the variation of the surface topography height has a significant influence on the fluid flow and interface slip. However, the effect of the variation of topography width is greatly related to the number and dense arrangement pattern of nanostructure. Surface topography causes an increase in interfacial resistance and more reduction in velocity slip at the rough wall, which even results in the forming of sticky boundary condition. The effect of non-uniform interface wettability of rough wall on the flow behavior and slip at the solid–liquid interface is investigated as well. The results show that the influence of non-uniform interface wettability on the flow in the hydrophobic channel is more obvious than that in the hydrophilic channel. Hydrophobic substrate with hydrophobic nanostructures has a smaller interfacial hydrodynamic resistance than that with hydrophilic nanostructures, which makes the average velocity and velocity slip become greater. Obviously, non-uniform interfacial wettability strengthens the effect of surface topography on the fluid flow and interface slip. It is possible to achieve effective velocity slip and obtain drag reduction by applying the non-uniform wettability of nanostructures under the same surface topography.

Direct investigation of methane nanofluidic microstructure and system dynamics in rough silicon nanochannel

The microstructure and system dynamics of methane nanofluidic are important to determine the flow properties. In this study, we use non-equilibrium multiscale molecular dynamics simulation (NEMSMD) to investigate the microstructure and system dynamics of methane nanofluidic confined by rough silicon atomic walls. To capture the detailed atomic microstructure of methane moving in rough nanochannel accurately, the modification of OPLS methane fully atomic model is employed. The average number density distributions of C (H) atom, average velocity profile, velocity autocorrelation function and projection radial distribution function (XOY-, XOZ- and YOZ planes) plots give a clear observation of the impacts of different conditions (roughness, body driving force, fluid–wall interaction strength and cutoff radius) on the methane Poiseuille flow in nanochannel. The projection radial distribution functions and diffusivity appear anisotropic, and seem to be affected more significantly by roughness, fluid–wall interaction strength and cutoff radius than body driving force in the whole channel region. Moreover, the body driving force and cutoff radius also play an important role in methane nanofluidic simulation using NEMSMD. The present simulation results are very meaningful for the design of energy-saving emission reduction nanofluidic devices.

Investigation the atomic arrangement and stability of the fluid inside a rough nanochannel in both presence and absence of different roughness by using of accurate nano scale simulation

The present study used molecular dynamics (MD) simulation to study the effects of external forces on the fluid flow passing through a nanochannel with different shapes of the interior wall. To this end, molecular dynamics simulation was employed to investigate the atomic arrangement and stability of the fluid inside a nanochannel in both presence and absence of rectangular and square cuboid, ellipsoid, and hemispheroid roughness. Moreover, the number density, velocity and temperature of argon flowing inside a Platinum nanochannel were investigated for a time step of 1,000,000 at external forces of 0.002, 0.0018, 0.0017, and 0.0014 eV/Å. The results obtained for each of the aforementioned models were compared with respect to the different thrust forces. Our results show that as the driving force increases from 0.0014 to 0.002 eV/Å, the velocity at the center of the nanochannel is increased approximately from 1.7 to 3.6 Å/ps while the velocity near the wall increases approximately from 0.5 to 1.4 Å/ps. Also, the temperature at the center of the nanochannel increases approximately from 355.2 to 536 K while the temperature near the wall increases approximately from 206.5 to 237.6 K.

Role of Solid Wall Properties in the Interface Slip of Liquid in Nanochannels.

A two-dimensional molecular dynamics model of the liquid flow inside rough nanochannels is developed to investigate the effect of a solid wall on the interface slip of liquid in nanochannels with a surface roughness constructed by rectangular protrusions. The liquid structure, velocity profile, and confined scale on the boundary slip in a rough nanochannel are investigated, and the comparison of those with a smooth nanochannel are presented. The influence of solid wall properties, including the solid wall density, wall-fluid coupling strength, roughness height and spacing, on the interfacial velocity slip are all analyzed and discussed. It is indicated that the rough surface induces a smaller magnitude of the density oscillations and extra energy losses compared with the smooth solid surface, which reduce the interfacial slip of liquid in a nanochannel. In addition, once the roughness spacing is very small, the near-surface liquid flow dominates the momentum transfer at the interface between liquid and solid wall, causing the role of both the corrugation of wall potential and wall-fluid coupling strength to be less obvious. In particular, the slip length increases with increasing confined scales and shows no dependence on the confined scale once the confined scale reaches a critical value. The critical confined scale for the rough channel is larger than that of the smooth scale.

Modeling different structures in perturbed Poiseuille flow in a nanochannel by using of molecular dynamics simulation: Study the equilibrium

In this study modeling different structures in perturbed Poiseuille flow in a nanochannel by using of molecular dynamics simulation was performed. Nanochannel limited by parallel Platinum plates containing an Argon fluid. We found that the wall roughness increases the velocity in the nanochannel by shrinking the cross-section. Also, the rectangular roughness and hemispherical roughness have the maximum and minimum effects on the flow properties, respectively. The other result is that the nanochannel roughness reduces the range of fluctuations near the walls. This is due to the fact that less fluid particles reside in the vicinity of the rough nanochannel walls compared the ideal nanochannel. Finally, changing the configuration of the nanochannel roughness from ellipsoid to hemi-spherical increases the number of Pt atoms in the structure and the simulated system; therefore, the total energy is also expected to increase.

Electroosmotic Flow in a Rough Nanochannel with Surface Roughness Characterized by Fractal Cantor

Molecular dynamics simulation is applied to study the electroosmotic flow in rough nanochannels, with particular attention given to the fluid–solid interactions. In the simulation, the surface roughness is characterized by a fractal Cantor. The roles of roughness height and fractal dimension on nanoscale electroosmotic flow are examined and analyzed. The concentration distributions, zeta potential and electroosmotic velocity are presented and investigated. The results indicate that surface roughness plays a significant role in the fluid–solid interaction and nanoscale electroosmotic flow. The distribution of dipole angle for water molecules in both the near-wall region and middle region is almost unaffected by surface roughness; however, a significant difference of dipole angle distribution is observed in the fluid region away from the wall. Interestingly, the concentration distributions, electroosmotic velocity and zeta potential are highly affected by the surface fractal dimension, even with the same roughness height.

Molecular dynamics simulation of fluid flow and heat transfer in an asymmetric nanochannel

Fluid flow and heat transfer in a nanochannel may depart from the traditional behavior due to the scale effect, and the velocity slip and temperature jump at the fluid-solid interface must be taken into account. A lot of papers about fluid flows in nanochannels with the same wettability at two surfaces have been published. It is necessary to investigate fluid flow and heat transfer in nanochannels with the asymmetric wettability by the molecular dynamics method. The fluid velocity and temperature distributions, interfacial velocity slip and temperature jump in a rough nanochannel are evaluated. The effects of asymmetric wettability on the velocity slip, temperature jump and internal fluid heat transfer are analyzed. The results indicate that the velocity of the fluid flow under an external force in a nanochannel in a bulk region is of a parabolic distribution, but the parabolic distribution is not centrosymmetric because of the centrosymmetric density profile. The difference in density distribution can affect the fluid flow. Viscous dissipation due to shear flow will increase the fluid temperature. The range that is affected by the interaction between solid and liquid is small. So the wettability of the cold wall hardly affects the velocity of the fluid near the hot wall, and the slip velocity is almost constant. At this time, the negative slip will take place at the fluid-solid interface near the hot wall. But the velocity of the fluid near the cold wall comes up with the increasing hydrophobicity of the cold wall, and the slip velocity increases. The temperature jump on both sides of interface increases with the increasing hydrophobicity of the cold wall, but the degree of temperature jump at a liquid-cold solid interface is higher than that at a liquid-hot solid interface. Then the fluid temperature near the cold wall gradually exceeds the fluid temperature near the hot wall. The internal heat flow of the fluid will be reversed. The inverted temperature profile of the fluid will appear. The inverted temperature profile becomes more obvious when the degree of asymmetric wettability increases.

Molecular dynamics simulation on fluid flow and heat transfer in rough nanochannels

Fluid flow and heat transfer in a microstructure may depart from the traditional behavior due to the scale effect, and its velocity slip and temperature jump will occur at the fluid-solid interface. A molecular dynamics model of coupled fluid flow and heat transfer in rough nanochannels is developed to investigate the effect of surface roughness on nanoscale fluid flow and heat transfer, as well as velocity slip and temperature jump at the fluid-solid interface. The fluid microscopic structure, velocity and temperature distributions, interfacial velocity slip and temperature jump in a rough nanochannel are evaluated and compared with the corresponding smooth nanochannel. Effects of solid-liquid interaction and wall stiffness on the velocity slip and temperature jump are analyzed. Results indicate that the velocity of the fluid flow under an external force in a nanochannel in a bulk region is of a parabolic distribution, and the viscous dissipation due to shear flow induces the fourth-order temperature profile in the nanochannel. And the velocity slip and temperature jump will occur at the fluid-solid interface. The presence of roughness may introduce an extra viscous dissipation in shear flow, leading to a reduction of overall velocity and an increase in temperature in the nanochannel when compared with the smooth nanochannel. In addition, the degree of velocity slip and temperature jump at a rough liquid-solid interface is smaller than that at a smooth interface. In particular, the increase in fluid-solid interaction strength and reduction in wall stiffness will lead to a small velocity slip and temperature jump.

Molecular dynamics simulation of Poiseuille flow in a rough nano channel with checker surface roughnesses geometry

Molecular dynamics simulation is applied to investigate the effects of checker surface roughness geometry on the flow of liquid argon through nanochannels that the roughness is implemented on the lower channel wall. The Lennard-Jones potential is used to model the interactions between particles and periodic boundary condition is applied in the flow direction. Density and velocity profiles across the channel are investigated for channel that the lower surface is decorated with the checker surface roughness elements. Result show that as the surface attraction energy or the roughness height increase the density layering in the near the wall is enhanced by higher values or secondary layering phenomena.

The effects of surface roughness geometry of flow undergoing Poiseuille flow by molecular dynamics simulation

Numerical simulation of Poiseuille flow of liquid Argon in a rough nano-channel using the non-equilibrium molecular dynamics simulation is performed. Density and velocity profiles across the channel are investigated in which roughness is implemented only on the lower wall. The Lennard–Jones potential is used to model the interactions between all particles. The effects of surface roughness geometry, gap between roughness elements (or roughness periodicity), surface roughness height and surface attraction energy on the behavior of the flow undergoing Poiseuille flow are presented. Results show that surface shape and roughness height have a decisive role on the flow behaviors. In fact, by increasing the roughness ratio (height to base ratio), the slip velocity and the maximum velocity in the channel cross section are reduced, and the density fluctuations near the wall increases. Results also show that the maximum density near the wall for a rough surface is less than a smooth wall. Moreover, the simulation results show that the effect of triangle roughness surface on the flow behavior is more than the cylindrical ones.