# Mesoscale investigations of fluid-solid interaction: Liquid slip flow in a parallel-plate microchannel

## TL;DR

This study develops a mesoscopic lattice Boltzmann model with continuous fluid-solid interaction forces to analytically and numerically investigate liquid slip flow in microchannels, revealing key parameters influencing slip behavior.

## Contribution

It introduces a novel mesoscopic F-S interaction force model with analytical solutions, validated by LBM simulations and experiments, advancing understanding of slip flow in microchannels.

## Key findings

- Analytical solutions match LBM results for slip flow.
- Permeability ratios depend on F-S interaction parameters.
- Calibrated force functions describe hydrophobic surface slip behavior.

## Abstract

Liquid slip flow with a Knudsen number Kn = 0.001-0.1 plays a dominant role in confined flow channels. Its physical origin can be attributed to the intermolecular fluid-solid (F-S) interaction force. To this end, we propose herein continuous force functions (decaying either exponentially or by a power law) between fluid particles and two confined flat walls in the framework of the mesoscopic lattice Boltzmann model (LBM). The analytical solutions for density profile, velocity profile, slip length, and permeability ratio are derived and related to the mesoscale F-S interaction parameters and the size of the gap of the flow channel. Through nondimensionalization of the analytical solutions, we obtain the dimensionless numbers that indicate the key feature of slip-flow systems for each of the proposed force functions. The analytical solutions are strictly consistent with the LBM solutions. We suggest reasonable ranges for the F-S interaction parameters based on the observed range of density ratio (film fluid to bulk fluid) and the increasing permeability ratios with narrowing gap size. Within the given range of interaction parameters, simple relationships between permeability ratios and dimensionless numbers are provided by fitting. The curves for continuous F-S interaction force with two free parameters are calibrated for a hydrophobic surface by using LBM simulations, which were validated a priori by comparison with the slip velocity profile measured in a benchmark flow experiment. The mesoscopic LBM model based on the proposed F-S interaction force functions provides a robust framework to elucidate the physical process of liquid slip flow.

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Source: https://tomesphere.com/paper/1906.06664