Mapping jet coalescence in fluidized beds using positron emission particle tracking

• Novel PEPT method maps individual jets in multi-orifice fluidised beds. • Clustering approach detects jet paths, merging points, and velocity peaks. • Jets retain constant diameter until merging, unlike isolated conical jets. • Jet coalescence limits effective penetration length in industrial systems. • PEPT reveals particle entrainment occurs mainly near the distributor base. Positron Emission Particle Tracking (PEPT) is used in this study to follow particle motion close to a multi-orifice gas distributor in a 9.4 cm diameter bed of 300 μm sand particles, with particular emphasis on the structure of the multiple jets. Using PEPT, a clustering algorithm has been used to follow the evolution of each of the 12 jets and to show how they deviate from the vertical and eventually merge. Jet dimensions have been determined for each individual jet. Unlike isolated single jets, the multiple jets in this study maintain an almost constant diameter up to the point at which they merge. Particle entry points into the jets were identified, showing that particles are entrained into the jets from all directions but predominantly from the direction of the wall. The time-averaged particle velocity within the jets was measured, with velocities peaking at approximately 1 cm from the origin of each jet.