Granular Flow and Pattern Formation on a Vibratory Conveyor

Summary Vibratory conveyors are well established in routine industrial production for controlled transport of bulk solids. Because of the complicated interactions between the vibrating trough and the particles both glide and throw movements frequently appear within one oscillation cycle. Apart from the amplitude and frequency, the form of the trajectory of the conveyor’s motion also exerts an influence. The goal of our project is a systematic investigation of the dependence of the transport behavior on the three principle oscillation forms: linear, circular and elliptic. For circular oscillations of the shaking trough a non-monotonous dependence of the transport velocity on the normalized acceleration is observed. Two maxima are separated by a regime, where the granular flow is much slower and, in a certain driving range, even reverses its direction. In addition, standing waves oscillating at half the forcing frequency are observed within a certain range of the driving acceleration. The dominant wavelength of the pattern is measured for various forcing frequencies at constant amplitude. These waves are not stationary, but drift with a velocity equal to the transport velocity of the granular material, determined by means of a tracer particle. Finally, the fluidization of a monolayer of glass beads is studied. At peak forcing accelerations between 1.1 g and 1.5 g a solid-like and a gas-like domain coexist. It is found that the number density in the solid phase is several times that in the gas, while its granular temperature is orders of magnitude lower.