Gas-induced friction and diffusion of rigid rotors

TL;DR

This paper derives a comprehensive kinetic theory for the motion of convex rigid bodies in a rarefied gas, capturing friction, diffusion, and nonconservative forces, applicable to various shapes and phenomena.

Contribution

It introduces a unified framework deriving the Boltzmann and Fokker-Planck equations for rigid body dynamics in gases, including explicit friction and diffusion tensors for multiple shapes.

Findings

The theory describes thermalization and photophoresis.

It accounts for the inverse Magnus effect.

Provides explicit tensors for different shapes.

Abstract

We derive the Boltzmann equation for the rotranslational dynamics of an arbitrary convex rigid body in a rarefied gas. It yields as a limiting case the Fokker-Planck equation accounting for friction, diffusion, and nonconservative drift forces and torques. We provide the rotranslational friction and diffusion tensors for specular and diffuse reflection off particles with spherical, cylindrical, and cuboidal shape, and show that the theory describes thermalization, photophoresis, and the inverse Magnus effect in the free molecular regime.