Chapter 10 - Positron emission particle tracking: Particle velocities in gas fluidised beds, mixers and other applications

Abstract

This chapter discusses the positron emission particle tracking (PEPT). PEPT is a technique for tracking a single radioactive tracer particle by detecting the distribution of emitted γ-rays. Like other radioactive particle tracking techniques, it allows non-invasive observation of the motion of a single particle within a dense optically-opaque system, which may contain many other similar particles. It differs from other tracking techniques in that it uses positron emitting radioisotopes, which have the unique attribute that their decay leads to simultaneous emission of a pair of back-to-back γ-rays. The PEPT technique employs an iterative algorithm to discard the corrupt annihilation vectors. Starting with a set of vectors, it finds the point in space that minimises the total perpendicular distance from all the vectors to the point. Those vectors with a perpendicular distance greater than some multiple of the mean distance are rejected, and the process is repeated using just the remaining vectors; this continues till a specified fraction of the original set remains. The chapter discusses various applications of PEPT and the examples presented here—fluidization, mixing in rotating drums and in rotating shaft devices and gravity flow—each demonstrate different advantages of the PEPT technique. In each case, particle tracking reveals details of the physical basis for the phenomena under observation. This more detailed observation will enable more physically realistic models for particulate processes to be derived,