Confined Liquid Flow in Nanotube: A Numerical Study and Implications for Energy Absorption

Abstract

Understanding nanofluidic behavior is of fundamental value to the development of many potential nano-technology applications, including high-performance energy absorption. We carry out non-equilibrium molecular dynamics (NEMD) simulations to study the transport characteristics of liquids in a confined nano-environment. It is shown that the distributed electric field arising from either an electrolyte water solution (due to the dissolved ions) or a polar solid surface, could lead to nanofluidic properties that are significantly different to those associated with pure water or a neutral nanotube. In addition, the nanopore size and the transport rate are shown to be important factors that strongly influence the flow process. The nominal viscosity and the shearing stress between the nanofluid and tube wall, which characterize the ease for nanofluid transport under an external driving force, are found to be dependent on the liquid phase and solid phase properties, as well as liquid flow rate and nanotube size. By varying properties of liquid phase and solid phase, liquid flow rate and nanotube size, the energy absorption characteristics of nanofluidic devices might be adjusted.

Electrolyte solution transport in electropolar nanotubes

“…Under a given transport rate (∼200 m s −1 ) and medium polar nanotube diameter (2.51 nm), figure 3 presents the decreasing trend of the effective shear stress with increasing concentration of electrolyte inside the model SiO 2 nanotube, which is again similar to that in a neutral CNT [34]. Taking the KCl-water solution for example, the shear stress decreases by around 17% as the molar concentration increases from 1.0 to 4.0 M. Comparing with the neutral CNT [34], the shear stress in the polar model SiO 2 nanotube is almost one order of magnitude higher.…”

“…Under a given transport rate (∼200 m s −1 ) and medium polar nanotube diameter (2.51 nm), figure 3 presents the decreasing trend of the effective shear stress with increasing concentration of electrolyte inside the model SiO 2 nanotube, which is again similar to that in a neutral CNT [34]. Taking the KCl-water solution for example, the shear stress decreases by around 17% as the molar concentration increases from 1.0 to 4.0 M. Comparing with the neutral CNT [34], the shear stress in the polar model SiO 2 nanotube is almost one order of magnitude higher. The ion size effect is also apparent: when the molar concentration is fixed at 2.0 M, the shear stresses for the three electrolyte solutions are τ LiCl ≈ 22.6 MPa, τ NaCl ≈ 24.4 MPa and τ KCl ≈ 25.7 MPa, respectively, which echo the fact that the larger ionic size leads to a stronger transport shear stress, since the ionic size ϕ of these three ions follows the order of…”

“…Compared with the neutral CNT, the larger shear stress and effective shear viscosity in the SiO 2 model nanotube are caused by the extra electrostatic interaction between the polar nanotube wall and the charge-enhanced liquid. The MD simulations show that such an interaction draws the first solvation shell closer to the wall and thus greatly increases the transport resistant force in comparison to that in the neutral channel [34].…”

“…With different pore radii, the distinct confinements from the solid wall strongly affect the distribution of liquid molecules: a single water molecule chain is formed in the small SiO 2 model nanotube (D = 0.81 nm), instead of a 'layered' structure observed in the medium size nanotube (D = 2.51 nm). This distribution significantly influences the repulsive force imposed by the solid wall during the nanofluidic transport and thus dominates the shear transport stress [18,34].…”

Effect of Degassing on the Stability and Reversibility of Glycerol/ZSM-5 Zeolite System

“…When nonwetting liquid is forced into hydrophobic nanopores by applying external pressure, a large amount of mechanical energy can be converted to solid-liquid interfacial energy [1][2][3][4][5][6]. Due to the ultra-large solid-liquid interface, the pressure-induced intrusion of liquid into nanopores can contribute to a highly efficient energy absorption system [7,8].…”