Here is a recent example of a PEPT application: a bi-disperse mixture of 3 mm and 5 mm diameter glass ballotini moving in a rotating cylinder as prepared by the undergraduate third year class at UCT Physics. Students typically invest in theoretical modelling and simulation of the system under study, undertake a measurement campaign at PEPT Cape Town, and undergo detailed data analysis to investigate the phenomena of interest.
Tracer occupancy (as frequency scatter plot of XY position) with 1 mm2 bins for (a) 5 mm and (b) 3 mm particles in a rotating cylinder, with red indicating highest occupancy. Using such data it is possible to determine residence time distributions, a dynamic density profile, and investigate mixing, segregation, and transport effects such as convection.
As PEPT is a dynamic technique it is possible to measure the time differential of the tracer particle trajectory to gain access to the underlying velocity fields. Here we show an overlay of multiple measurements of a rotating system in the steady state, each data point is coloured by the absolute speed of the particle at that instant.
Average velocity field of (a) 3 mm and (b) 5 mm tracer particles in a rotating cylinder. The vectors are colour coded by magnitude, with red indicating highest velocity.
With a detailed experimental campaign multiple experimental parameters can be investigated and the operational phase diagram for such a system can be observed. Here we show how changing the ratio of large to small glass beads, and how changing the rotational speed of the drum, affects both the angle of repose and the degree of particle species segregation. This data was produced and analysed by UCT Physics third year students in 2019.