Abstract
The compressible and turbulent gas–solid multiphase flow inside a fluidized bed opposed jet mill was systematically investigated through numerical simulations using the Euler–Euler approach along with the kinetic theory of granular flow and frictional models. The solid holdup and nozzle inlet air velocity effects on the gas–solid dynamics were assessed through a detailed analysis of the time-averaged volume fraction, the time-averaged velocity, the time-averaged streamlines, and the time-averaged vector field distributions of both phases. The simulated results were compared with the experimental observations available in the literature. The numerical simulations contributed to a better understanding of the particle–flow dynamics in a fluidized bed opposed gas jet mill which are of fundamental importance for the milling process performance.
Highlights
Comminution is a major size reduction process in solids processing
Comminution by stresses induced by mechanical forces is performed for instance in ball mills, hammer mills, planetary mills, oscillating mills, and fluidized bed jet mills which are in widespread use in various industries such as minerals, foods, pharmaceuticals, and ceramics
A fluidized bed opposed jet mill is commonly comprised of three different regions: the grinding region, where the pressurized air is injected through the nozzles; the transport region, where the particles are pushed upward by the nozzles’ gas jets in the grinding region; and the classifying region, at the top of the equipment which consists of one or more classifier wheels rotating at a certain velocity depending on the desired particle cut size
Summary
Comminution is a major size reduction process in solids processing. To break a particle, critical stress must be provided to the material. A fluidized bed opposed jet mill is commonly comprised of three different regions: the grinding region, where the pressurized air is injected through the nozzles; the transport region, where the particles are pushed upward by the nozzles’ gas jets in the grinding region; and the classifying region, at the top of the equipment which consists of one or more classifier wheels rotating at a certain velocity depending on the desired particle cut size. The coarse fraction is recycled to the grinding region, whereas the fine ones are discharged as product. This equipment, which is used for instance in the production of dry abrasion- and contamination-free pharmaceutical powders, involve complex particle–particle and particle–fluid interactions due to the presence of a highly expanded and turbulent gas jet which are still poorly understood [2]
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