Microscopic force for aerosol transport

TL;DR

This paper introduces a new microscopic force model for aerosol transport that improves simulation accuracy across a wide temperature range, especially at cryogenic temperatures, by using Epstein's formulation instead of traditional Stokes' drag.

Contribution

It proposes a direct computation of aerosol forces based on Epstein's formulation, enhancing the accuracy of aerosol transport simulations at various temperatures.

Findings

The new force reproduces Stokes' drag under known conditions.

It shows excellent agreement with experiments at 4 K.

The model is effective across a wide temperature range.

Abstract

A key ingredient for single particle diffractive imaging experiments is the successful and efficient delivery of sample. Current sample-delivery methods are based on aerosol injectors in which the samples are driven by fluid-dynamic forces. These are typically simulated using Stokes' drag forces and for micrometer-size or smaller particles, the Cunningham correction factor is applied. This is not only unsatisfactory, but even using a temperature dependent formulation it fails at cryogenic temperatures. Here we propose the use of a direct computation of the force, based on Epstein's formulation, that allows for high relative velocities of the particles to the gas and also for internal particle temperatures that differ from the gas temperature. The new force reproduces Stokes' drag force for conditions known to be well described by Stokes' drag. Furthermore, it shows excellent agreement to experiments at 4 K, confirming the improved descriptive power of simulations over a wide temperature range.