A computational study of particle deposition patterns from a circular laminar jet

TL;DR

This study numerically investigates how nozzle taper angle and jet-to-plate distance influence particle deposition patterns in a circular laminar jet impactor, revealing effects on particle distribution and efficiency at different Reynolds numbers.

Contribution

It provides new insights into how nozzle geometry and flow conditions affect particle deposition patterns and efficiency in inertial impactors, using a Lagrangian CFD approach.

Findings

Tapered nozzles produce a high-density ring at the deposition edge at high Re.

Reducing Re or increasing jet-to-plate distance diminishes the edge density peak.

Small particles with low Stokes number tend to impact the center, affecting impactor accuracy.

Abstract

Particle deposition patterns on the plate of inertial impactor with circular laminar jet are investigated numerically with a Lagrangian solver implemented within the framework of the OpenFOAM$^{\circledR}$ CFD package. Effects of taper angle of the nozzle channel and jet-to-plate distance are evaluated. The results show that tapered nozzle tends to deposit more particles toward the circular spot edge than straight nozzle. At jet Reynolds number $Re = 1132$, a tapered nozzle deposits particles to form a pattern with a high density ring toward the deposition spot edge, especially for particle Stokes number $St > St_{50}$, which is absent with a straight nozzle. Increasing the jet-to-plate distance tends to reduce the value of particle density peak near deposition spot edge. Reducing $Re$ to $283$ (e.g., for $300$ ccm flow through a $1.5$ mm diameter jet nozzle) yields particle deposition patterns without the high density ring at the deposition spot edge when the same tapered nozzle is used. The particle deposition patterns with the straight nozzle at $Re = 283$ exhibit further reduced particle density around the spot edge such that the particle density profile appears more or less like a Gaussian function. In general, the effect of reducing $Re$ on particle deposition pattern seems to be similar to increasing the jet-to-plate distance. The computed particle deposition efficiency $\eta$ shows the fact that very fine particles with extremely small values of $St$ near the jet axis always impact the center of plate, indicating that the value of $\eta$ does not approach zero with a substantial reduction of $St$. Such a "small particle contamination" typically amounts to $\sim 10\%$ of small particles (with $\sqrt{St} < 0.1$) at $Re \sim 1000$ and $\sim 5\%$ at $Re \sim 300$, which may not be negligible in data analysis with inertial impactor measurement.