Thermophoresis and its effect on particle impaction on a cylinder for low and moderate Reynolds numbers

TL;DR

This study investigates how thermophoresis influences particle impaction on a cylinder at low to moderate Reynolds numbers, revealing that particle conductivity and temperature gradients significantly affect small particle deposition.

Contribution

The paper introduces an algebraic model based on fundamental principles that accurately predicts thermophoretic effects on particle impaction, validated by DNS results.

Findings

Thermophoresis mainly affects small particles' impaction efficiency.

Higher Reynolds numbers increase impaction for middle-sized particles.

The developed model accurately predicts thermophoretic particle deposition.

Abstract

The effect of thermophoresis on the impaction of particles on a cylinder is investigated for different particle sizes, particle conductivities, temperature gradients and for Reynolds numbers between 100 and 1600. Simulations are performed using the Pencil Code, a high-order finite difference code. An overset-grid method is used to precisely simulate the flow around the cylinder. The ratio of particles impacting the cylinder and the number of particles inserted upstream of the cylinder is used to calculate an impaction efficiency. It is found that both the particle conductivity and the temperature gradient have a close to linear influence on the particle impaction efficiency for small particles. Higher Reynolds numbers result in higher impaction efficiency for middle-sized particles, while the impaction efficiency is smaller for smaller particles. In general, it is found that thermophoresis only has an effect on the small particles, while for larger particles the impaction efficiency is controlled by inertial impaction. Finally, an algebraic model, developed based on fundamental principles, which describes the effect of thermophoresis is presented. The model is found to accurately predict the DNS results. As such, this model can be used to understand the mechanisms behind particle deposition due to the thermophoretic force, and, more importantly, to identify means by which the deposition rate can be reduced.