Capillary filling with wall corrugations] Capillary filling in microchannels with wall corrugations: A comparative study of the Concus-Finn criterion by continuum, kinetic and atomistic approaches

TL;DR

This study compares continuum, kinetic, and atomistic methods to analyze how wall corrugations affect capillary filling in microchannels, revealing molecular fluctuations can enable flow beyond classical pinning predictions.

Contribution

It provides a comparative analysis of CFD, LBE, and MD approaches to test the Concus-Finn criterion in microchannel capillary filling, highlighting the role of molecular fluctuations.

Findings

CFD and LBE agree with the CF criterion at certain contact angles.

MD simulations show fluctuations allow flow beyond the CF prediction.

Molecular fluctuations influence pinning and flow in microchannels.

Abstract

We study the impact of wall corrugations in microchannels on the process of capillary filling by means of three broadly used methods - Computational Fluid Dynamics (CFD), Lattice-Boltzmann Equations (LBE) and Molecular Dynamics (MD). The numerical results of these approaches are compared and tested against the Concus-Finn (CF) criterion, which predicts pinning of the contact line at rectangular ridges perpendicular to flow for contact angles theta > 45. While for theta = 30, theta = 40 (no flow) and theta = 60 (flow) all methods are found to produce data consistent with the CF criterion, at theta = 50 the numerical experiments provide different results. Whilst pinning of the liquid front is observed both in the LB and CFD simulations, MD simulations show that molecular fluctuations allow front propagation even above the critical value predicted by the deterministic CF criterion, thereby introducing a sensitivity to the obstacle heigth.