Mesoscopic model framework for liquid slip in a confined parallel-plate flow channel

What is it about?

Liquid slip significantly affects confined fluid flow. The physical origin of slip flow with the Knudsen number ranging from 0.001 to 0.1 can be attributed to the long-range intermolecular fluid-solid interaction (FSI) force. To this end, in the framework of the mesoscopic lattice Boltzmann model (LBM), an exponentially decaying force function between fluid particles and two confined flat walls is proposed herein. For the parallel walls of symmetric FSI forces, we explicitly link density profile, velocity profile, apparent slip length, and permeability-enhancement ratio with the mesoscale FSI parameters (strength and decay length); by nondimensionalization of the exact solutions, we also acquire two dimensionless numbers that indicate the role of complex FSI strength and gap size of the flow channel in the slip-flow system. For the walls with asymmetric FSI properties, the numerical profiles of density and velocity as well as the amount of slip can be provided by the LBM simulations. The curve for continuous FSI force with two free parameters is calibrated for the hydrophobic surfaces in two benchmark flow experiments. Results show that the proposed FSI force function provides a robust model framework to mesoscopically elucidate the physical process of liquid slip flow.

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Why is it important?

Liquid slip significantly affects confined fluid flow. The physical origin of slip flow with the Knudsen number ranging from 0.001 to 0.1 can be attributed to the long-range intermolecular fluid-solid interaction (FSI) force. To this end, in the framework of the mesoscopic lattice Boltzmann model (LBM), an exponentially decaying force function between fluid particles and two confined flat walls is proposed herein. For the parallel walls of symmetric FSI forces, we explicitly link density profile, velocity profile, apparent slip length, and permeability-enhancement ratio with the mesoscale FSI parameters (strength and decay length); by nondimensionalization of the exact solutions, we also acquire two dimensionless numbers that indicate the role of complex FSI strength and gap size of the flow channel in the slip-flow system. For the walls with asymmetric FSI properties, the numerical profiles of density and velocity as well as the amount of slip can be provided by the LBM simulations. The curve for continuous FSI force with two free parameters is calibrated for the hydrophobic surfaces in two benchmark flow experiments. Results show that the proposed FSI force function provides a robust model framework to mesoscopically elucidate the physical process of liquid slip flow.

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