Dynamics and Stability of a Suspended Layer in a Pneumatic Classifier

This article is devoted to the theoretical and experimental study of the conditions for stable motion of the dispersed phase in a rotating suspended layer of a pneumatic classifier. The main goal was to ensure effective separation of bulk material into coarse and fine fractions. It was shown that a rational design for this purpose is a pneumatic rhomb-shaped classifier. A mathematical model was developed as a system of differential equations describing the motion of solid particles in a suspended layer. This model accounts for the oscillatory (floating) motion of particles in the suspended layer induced by gas-flow pulsations. A feature of the proposed model is the consideration of damping factors for particle oscillations in the gas flow, as well as the gravitational displacement of particles and the hydrodynamic resistance of the gas flow. The stability of the solutions was also investigated analytically. This established the conditions for the stable motion of a solid particle in a suspended layer. In particular, the combined influence of vibration damping and gravitational displacement of particles in the gas flow should exceed that of hydrodynamic resistance. Numerical integration of the system of nonlinear differential equations was also performed using the fourth-order Runge–Kutta method. This enabled the identification of different solid-particle motion modes within the suspended layer, one of which corresponds to the layer’s stability. A physical experiment confirmed the existence of different modes of motion. As a result, it was shown that implementing a stable suspended-layer mode ensures effective separation of a polydisperse granular mixture. In this case, the separation efficiency reaches 95–97% at relatively low hydraulic resistance (80–200 Pa), with maximum purity of the obtained fine and coarse fractions (contamination does not exceed 5%) after separating the binary mixture. The specified efficiency is achieved at a gas velocity at the inlet to the working zone in the range of 11–12 m/s (a volume flow rate of 0.020–0.025 m3/s).