Particle Breakage with High Velocity Air Jets

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Author Last Name: 
J A Dodds, P Guigon and A Thomas
Report Type: 
Research Area: 
Size Reduction
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An experimental rig has been built to investigate breakage phenomena similar to that encountered in air jet milling. Particles of alumina hydragillite are accelerated by air in a nozzle and impacted on a target. Energy loss during impact is evaluated by measuring particle velocities before and after impact using two different methods : one based on observation with a high speed shutter video camera, the other based on cross-correlation of signals from an emitter-receptor optical fibre system. The particle size shape and distribution of the particle fragments from the apparatus are determined as a function of : solids loading, air flow rate, orientation and the material used for the target.

More detailed structural analysis of the debris is made by morphological characterisation based on fractal dimension. The basic hypothesis is that the breakage mechanism and kinetics depend on the initial fault network in the original particles. This is used to establish a fragmentation scheme for alumina hydragillite. Initial experiments with particles produced as a function of time in a batch operated air jet mill confirm the possibilities of the method of analysis.