Transport Phenomena of Water in Molecular Fluidic Channels

Abstract

In molecular-level fluidic transport, where the discrete characteristics of a molecular system are not negligible (in contrast to a continuum description), the response of the molecular water system might still be similar to the continuum description if the time and ensemble averages satisfy the ergodic hypothesis and the scale of the average is enough to recover the classical thermodynamic properties. However, even in such cases, the continuum description breaks down on the material interfaces. In short, molecular-level liquid flows exhibit substantially different physics from classical fluid transport theories because of (i) the interface/surface force field, (ii) thermal/velocity slip, (iii) the discreteness of fluid molecules at the interface and (iv) local viscosity. Therefore, in this study, we present the result of our investigations using molecular dynamics (MD) simulations with continuum-based energy equations and check the validity and limitations of the continuum hypothesis. Our study shows that when the continuum description is subjected to the proper treatment of the interface effects via modified boundary conditions, the so-called continuum-based modified-analytical solutions, they can adequately predict nanoscale fluid transport phenomena. The findings in this work have broad effects in overcoming current limitations in modeling/predicting the fluid behaviors of molecular fluidic devices.

Modeling of Ion and Water Transport in the Biological Nanopore ClyA

“…In an attempt to improve upon the quantitative accuracy of the PNP-NS equations for nanopore simulations, we developed an extended version of these equations (ePNP-NS) and implemented it in the commercial finite element solver COMSOL Multiphysics (v5.4, www.comsol.com). Our ePNP-NS equations self-consistently take into account 1) the finite size of the ions, 76,78 2) the reduction of ion and water motility close to the nanopore walls, 54,58,79,80,83 and 3) the concentration dependency of ion diffusion coefficients and electrophoretic mobilities, as well as electrolyte viscosity, density and relative permittivity. 87,92,93 Most of these corrections make use of using empirical functions that were fitted to experimental data (Tabs.…”

Effects of Anisotropic Thermal Conductivity and Lorentz Force on the Flow and Heat Transfer of a Ferro-Nanofluid in a Magnetic Field

“…For the velocity at the walls, a no-slip boundary condition is used; for the nanoparticles concentration a no-flux boundary condition ensures that no particle is capable of penetrating the wall. It is worth pointing out that in nanofluidics the hydrodynamic slippage of the fluid is also possible due to the effect of the properties of the interface, such as wettability and roughness [29,35,37,84,85]. Table 1.…”

“…Usually the thermal conductivity and viscosity of nanofluids is considered to be a function which may depend on the nanoparticles concentration and the properties of the base fluids [13,14,[28][29][30]. According to the review articles [31,32], the thermal conductivity and viscosity usually increase non-linearly in the function of nanoparticle volume concentration.…”

“…For revealing the mechanism of the thermal and momentum diffusivity of nanofluids and the thermal/dynamic performance at the interface between the fluid and nanoparticles, many works based on experiments [33], theoretical analysis/modelling [6,33] and molecular dynamics simulations [34][35][36][37] have been performed. For example, some works indicated that the viscosity of the nanofluids is dependent on the nanoparticles concentration due to the apparently enhanced-viscosity of the base fluid near the solid surface caused by the surface force effects at small scales [29,35,36]. For getting empirical correlations for engineering simulations, many efforts have been made on experimentally measuring the physical properties of nanofluids as well [17,38,39].…”

Effect of Thermal-Electric Cross Coupling on Heat Transport in Nanofluids

“…Although some studies supported the importance of Brownian motion for the enhanced thermal conductivity of nanofluids [35,36], there are other researchers against it [37,38]. As for the liquid layer at the liquid/particle interface, molecular dynamic simulations [39][40][41][42] discovered water density fluctuation near the solid surface representing the liquid layer and could explain the thermal behavior such as temperature jump on the surface, while some studies [43][44][45] indicated that the liquid layer might not influence the thermal behavior of nanofluids. In addition, Keblinski et al [44] found that ballistic heat transport still could not explain the anomalous thermal conductivity enhancements either.…”