Breakage of a Single Particle in an Air Jet Mill

An experimental study of the impact breakage of a single tapioca grain using an air jet mill is carried out. High-velocity jets at the circumference of the cylindrical grinding chamber propel the grain tangentially, resulting in numerous collisions with the cylinder walls prior to breakage. Videography and image analysis are used to obtain the trajectory of the particle and the sizes of the fragments. Each experiment is repeated 25 times at three different grinding jet pressures (1, 1.5, and 2 bar). The average collision rate and the average breakage times are nearly constant for the higher pressures at 1000 1/s and 0.18 s, respectively. The size distribution at the end of the experiment, obtained using a laser particle size analyzer, is trimodal. The probability of first breakage versus the cumulative specific kinetic energy of impacts is shown to follow the Vogel–Peukert equation (Powder Technology 2003, 129, 101–110).