Determination of erosion rate characteristic for particles with size distributions in the low Stokes number range

Abstract

This work presents an approach to producing erosion rate equations that takes into account both the effect of particle size and Stokes number on particle trajectories. Erosion is measured on the surface of a cylinder in cross flow, while computational fluid dynamics is used to determine the impact characteristics of particles between 0.5μm and 212μm. Results are combined to produce a predictive equation for erosion rate for a wide variety of particle sizes. The experiments use silica flour suspended in air and impacting samples of stainless steel grade 316 and 304, at nominal flow velocities of 60 and 80m/s.Analysis indicates that the impact velocity magnitude and angle is affected by local carrier gas velocity for particles below 32.5μm in size, even though Stokes number is greater than ten. In the case examined, over 82% of erosion is caused by particles larger than 32.5μm. However, filtered sand erosion is necessarily caused by the finer material where Stokes number effects come into play, and the approach outlined here should be employed. The analysis presented in this paper is equally valid for slurry flows where Stokes number effects will apply to all particle sizes.