Separation behaviour of polypropylene mixed particles under the coupling of vibration and airflow

Abstract

Granular matter is a disordered system composed of a large number of particles, which appears as a complex physical phenomenon under external excitation. To study the separation behaviour of polypropylene particles, the separation of particles under various excitation methods was simulated based on the DEM-CFD coupling method. The results showed that polypropylene particles did not show Reverse Brazil Nut Separation under the single excitation of either vertical vibration or pulsed airflow, while under the double excitation of vertical vibration and constant airflow, the large particles located in the upper layer of small particles started to sink and formed Reverse Brazil Nut Separation. By analysing the change of voidage in particle bed, the explanation of the change of particle separation state by filling theory is verified. The airflow velocity increased from 15 m·s−1 to 21 m·s−1, and the volume concentration of large particles at the bottom increased by 27.615%, which promoted the formation of Reverse Brazil Nut Separation. The frequency and amplitude increased to 15 Hz, 20 mm or decreased to 5 Hz, 5 mm, respectively, and the volume concentration of large particles at the bottom decreased by 22.025%, 23.807% and 46.712%, 59.003%, indicating that too large or too small vibration acceleration would inhibit the formation of Reverse Brazil Nut Separation. In addition, changing the shape of the container or increasing the filling rate of particles in the container can eliminate the phenomenon of small particles accumulating in the corner.