Particle tracking in opaque mixing systems: An overview of the capabilities of PET and PEPT

The mixing of opaque multiphase systems presents a wide range of challenges that have not been addressed/resloved because of a lack of adequate visualization and measurement techniques. The present understanding of mixing in such systems is not likely to be significantly improved either at a fundamental or practical level without new experimental techniques being utilized. Positron emission tomography (PET) and positron emission particle tracking (PEPT) are unique in flow visualization terms, being capable of probing such opaque systems and examining flow phenomena in three dimensions that could not be observed as effectively by using other techniques. They are particularly suited to the study of solid-liquid flows, to map the flow of fluids and the flow of particles, where one component can be labelled and its behaviour observed. This paper reviews the highlights of recent work in single phase and solid-liquid systems, and discusses the capabilities of the techniques and their potential to help solve some of the outstanding problems in opaque systems.