# Knudsen pump inspired by Crookes radiometer with a specular wall

## TL;DR

This paper investigates a novel Knudsen pump design inspired by Crookes radiometers, utilizing asymmetric boundary conditions and specular walls to generate gas flow driven by temperature differences, analyzed through numerical and analytical methods.

## Contribution

It introduces a new gas pumping mechanism based on asymmetric temperature profiles and specular wall effects, with detailed numerical and analytical analysis.

## Key findings

- Net gas flow is generated by temperature-induced asymmetry.
- Specular walls influence the magnitude of the flow.
- The mechanism mimics Crookes radiometer operation.

## Abstract

A rarefied gas is considered in a channel consisting of two infinite parallel plates between which an evenly spaced array of smaller plates is arranged normal to the channel direction. Each of these smaller plates is assumed to possess one ideally specularly reflective and one ideally diffusively reflective side. When the temperature of the small plates differs from the temperature of the sidewalls of the channel, these boundary conditions result in a temperature profile around the edges of each small plate which breaks the reflection symmetry along the channel direction. This in turn results in a force on each plate and a net gas flow along the channel. The situation is analysed numerically using the direct simulation Monte Carlo (DSMC) method and compared with analytical results where available. The influence of the ideally specularly reflective wall is assessed by comparing with simulations using a finite accommodation coefficient at the corresponding wall. The configuration bears some similarity with a Crookes radiometer, where a non-symmetric temperature profile at the radiometer vanes is generated by different temperatures on each side of the vane, resulting in a motion of the rotor. The described principle may find applications in pumping gas on small scales driven by temperature gradients.