Applied for years, vibratory conveyors are well established in many industrial processes. Despite frequent use their design is still mostly based on practical experiences. A prototype apparatus was specially developed to perform the experiments within a large range of adjustable parameters. Detailed investigations of the transport properties of coarse sand layers in the size range of 0.2 < d < 2 mm were carried out for linear, circular and elliptic mode of vibrations. Interesting phenomena were observed such as reverse of the flow, non-monotonous dependence of transport velocity and structure formation [1]. The focus of this work was to characterise the mixing kinetics of a granular flow transported on a surface of an oscillating trough. Particle diameter, mass flow, mode of vibration and the energy fed to the system were considered as the main process parameters. The dispersion was examined using an image processing system recording the growth of the mixing layer thickness δ of two differently coloured but otherwise identical sand streams, along the longitudinal position on the transporting channel. A preliminary report of the first experimental results may be found in [2]. Based on a simple analysis of the diffusion equation for a mixing layer the transversal dispersion coefficient was determined by adapting the measured local concentration profiles to the equation describing the growth of the mixing layer thickness [3]. The mixing process was found to be directly proportional to the vertical acceleration of the conveyor and inversely proportional to the mass flow of transported material. Keeping above mentioned parameters constant the dispersion increases with increasing mean particle diameter. The question arises: is the particle diameter correctly implemented into the equation describing the mixing kinetics as the scaling parameter of the process? We found out that, when performing the experiments with bulks having different mean particle diameter and tuning the mass flow to achieve the same level of dimensionless bed height h* the magnitude of D_y remained constant. In other words, the points representing the growth of the mixing layer thickness collapsed on the same curve. The mixing was found to be distinctly depending on h*, increasing h*>1 (i.e. the trough fully covered by particles) strongly reduces the dispersion phenomenon.

[1] R. Grochowski, P. Walzel, M. Rouijaa, C. A. Krülle, I. Rehberg, Reversing granular flow on a vibratory conveyor, Appl. Phys. Lett. 84 (2004) 1019

[2] R. Grochowski, P. Walzel, Dispersion of Granular Material on a Vibrating Conveyor, Chem.-Ing.-Tech. 77 (2005) 1020

[3] S.S Hsiau and M.L Hunt, Shear-induced particle diffusion and longitudinal velocity fluctuations in a granular-flow mixing layer, J. Fluid Mech. 251 (1993) pp. 299-313

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