Breakage of a Single Particle in an Air Jet Mill

An experimental studyof the impact breakage of a singletapiocagrain using an air jet mill is carried out. High-velocity jets atthe circumference of the cylindrical grinding chamber propel the graintangentially, resulting in numerous collisions with the cylinder wallsprior to breakage. Videography and image analysis are used to obtainthe trajectory of the particle and the sizes of the fragments. Eachexperiment is repeated 25 times at three different grinding jet pressures(1, 1.5, and 2 bar). The average collision rate and the average breakagetimes are nearly constant for the higher pressures at 1000 1/s and0.18 s, respectively. The size distribution at the end of the experiment,obtained using a laser particle size analyzer, is trimodal. The probabilityof first breakage versus the cumulative specific kinetic energy ofimpacts is shown to follow the Vogel-Peukert equation (Powder Technology 2003, 129, 101-110).