Scale effect on flow and thermal boundaries in micro‐/nano‐channel flow using molecular dynamics–continuum hybrid simulation method

Abstract

SUMMARYThe molecular dynamics (MD)-continuum hybrid simulation method has been developed in two aspects in the present work: (1) The energy equation has been combined into the coupling method in order to obtain the hybrid temperature profile and (2) the coupling method has been improved by the local linearization to obtain a smoother parametric profile. The developed method is primarily validated by analytical solutions and full MD results. Then, it is employed to study the scale effect on the flow and thermal boundaries in micro-/nano-channel flow. The hybrid velocity and temperature profiles are obtained with the channel height (H ) ranging from 60 to 2014 and the solid-liquid coupling ( ) ranging from 0.1 to 50. Scale effect has shown strong influence on the boundaries. Obvious slip characteristics can be found in the profiles, i.e. velocity slip and temperature jump, when H is small and is large. However, the results also show that the profiles can be well predicted to converge to the macroscale non-slip/non-jump analytical solutions when H is large enough, where the effect of can be omitted and the slip characteristics disappear. Correlations of relative slip length, relative temperature jump and pressure gradient with H are fitted from the simulation results.

A localized momentum constraint for non-equilibrium molecular dynamics simulations

“…The CV constraint must be applied every timestep, with the total CV surface forces calculated from the intermolecular forces and the positions of molecules i and j using Eq. (44). With a Verlet cell list, this requires a single order M calculation of forces per timestep, performed during the main force calculation.…”

“…(24), is a localization of the equations obtained by Nie et al, 18 which have become widely employed in the fluid coupling literature. [42][43][44][45][46] Equation (24) reduces to the Nie et al 18 constraint when the CV is the whole domain, ϑ i = 1 ∀ i, so that the surface flux term vanishes dS i = 0 ∀ i.…”

Modeling of Micro/Nano Channel Flows

“…The multiscale hybrid models were developed for solving a micro channel flow in which the channel height is relatively large while the fluid-wall interfacial phenomena should be considered (Atkas and Aluru, 2002;Liu et al, 2007;Nie et al, 2004;Sun et al, 2010;Yang and Zheng, 2010;Yen et al, 2007). In this case, close to the wall is implemented an MDS or MCS (Monte Carlo simulation) scheme, while away from the wall is implemented a continuum model.…”

A unified coupling scheme between lattice Boltzmann method and finite volume method for unsteady fluid flow and heat transfer

“…A compression operator (CO) is employed at the macroscopic boundary for the information transfer from the micro/mesoscale to the macroscale and a reconstruction operator (RO) is adopted at the micro/mesoscopic boundary for the inverse information transfer [7]. Based on this strategy, many coupling methods between different numerical models have been proposed for various multiscale problems, such as molecular dynamic (MD)-continuum [8][9][10][11][12][13], direct simulation of Monte Carlo (DSMC)-continuum [14,15], and lattice Boltzmann method (LBM)-finite volume method (FVM) [16][17][18][19][20][21].…”