The influence of system scale on impinging jet sediment erosion: Observed using novel and standard measurement techniques

Jet impingement as a method for eroding particulate beds and maintaining sediment in suspension is an important process for a host of industries, particularly in nuclear waste processing, where such systems to disperse and mix particulate beds have a number of advantages over other approaches. Existing work has utilised fairly rudimentary techniques for the measurement of erosion depths and here we demonstrate a new technique for measuring both static and dynamic erosion of cohesionless particulates under an impinging jet, using ultrasonic Doppler velocimetry. This approach is tested on both quartz sands and on a range of Mg(OH)₂ particulates that are key simulants for nuclear waste facilities, such as the Highly Active Storage Tanks at Sellafield, U.K. A critical jet height was found to exist that balanced the impingement velocities and total entrained jet volume to maximise erosion. The effect of system scale was also considered by normalising steady-state crater depths and sizes, with erosion being enhanced in the small scale, possibly due to increased turbulent recirculation. Additionally, velocity profiles and acoustic backscatter were used to determine both steady-state crater profiles and kinetic changes in bed-depths with time, and highlighted important differences between static and dynamic measurements of erosion depth.