Large variation in the boundary-condition slippage for a rarefied gas flowing between two surfaces

TL;DR

This paper investigates how gas slippage along surfaces varies with pressure in a confined geometry, revealing a transition from no-slip to near-perfect slip as pressure decreases, emphasizing the importance of mean free-path effects.

Contribution

It demonstrates that macroscopic hydrodynamics remains valid in primary vacuum conditions by analyzing boundary-condition variations in rarefied gas flows.

Findings

Slippage varies significantly with pressure.

Transition from no-slip to slip boundary condition.

Hydrodynamics applicable even in vacuum environments.

Abstract

We study the slippage of a gas along mobile rigid walls in the sphere-plane confined geometry and find that it varies considerably with pressure. The classical no-slip boundary condition valid at ambient pressure changes continuously to an almost perfect slip condition in a primary vacuum. Our study emphasizes the key role played by the mean free-path of the gas molecules on the interaction between a confined fluid and solid surfaces and further demonstrates that the macroscopic hydrodynamics approach can be used with confidence even in a primary vacuum environment where it is intuitively expected to fail.