Analysis of grinding in a spiral jet mill. Part 2: Semi-batch grinding

Abstract

The breakage and classification of particles in a spiral air jet mill, operated in a semi-batch mode, is studied for varying operating conditions. The particle size distributions of the product leaving the mill and the material inside the mill are measured, along with the mass in the mill. The median particle size of the product is found to be unchanged with inlet jet pressure at about 5 μm but increases with holdup to about 7.5 μm. At low pressures and high holdups, the classification is imperfect and a significant fraction of large particles, in the size range 150–350 μm, exit in the product. The mass flux from the mill increases with both pressure and holdup and an empirical expression is given to calculate it. A population balance model is presented, which predicts size distributions, mean sizes and mass flux from the mill, in agreement with the measurements.