Resonant acoustic mixing (RAM) is a relatively novel mixing technique that has shown promise for improved powder-powder mixing [1]. The effects of vessel material on the mixing and heating dynamics of RAM systems, both of considerable importance to variety of industrial applications from Defence to Pharmaceuticals, are still to be understood. In order to gain insight into these effects, this study investigates the influence of particle-wall friction on the mixing inside an archetypal RAM vessel. Limited literature exists focusing on the flow dynamics and mixing performance of RAM. Experimental studies by Sezer et al. [2] used PEPT to experimentally visualise the velocity vector fields in RAM. However, their exploration of fill height was limited by vessel heating at the long run times required by PEPT – a limitation DEM is not subject to. This research utilizes DEM to quantify, through full factorial analysis, the mixing performance of a calibrated MCC powder in a RAM mixer operated with differing fill heights, accelerations and particle-wall sliding frictions. The study aims to understand the effect each of these parameters has on the mixing performance. The radial and vertical mixing in RAM was very efficient, as expected from the existing literature. However, transverse mixing was poor. Lower fill heights yielded increased mixing performance with acceleration increasing mixing rate in all dimensions at fill heights up to 70% fill. Lower particle-wall frictions improved mixing in the horizontal axes but hindered vertical and radial mixing. Very high fill heights (90% fill) displayed reduced mixing performance. For studies at 90% fill height and high particle-wall sliding friction, horizontal mixing was at its best for an acceleration of 80g with reduced mixing performance for both 60g and 100g accelerations. The study’s findings suggest to industry that the mixing vessel frictional properties alter the mixing efficiency of RAM differently in different axis of mixing pointing to the particle-wall friction having a role on the flow dynamics in the RAM. Reduced mixing performance with fill height highlights the trade-off between mixing time and fill height to optimise throughput. At high fill heights there is also a need to optimise vibration for mixing with the results suggesting that increased acceleration does not simply result in increased mixing efficiency.
[1] Juan G. Osorio and Fernando J. Muzzio, Evaluation of resonant acoustic mixing performance, Powder Technology, Volume 278, 2015, Pages 46-56, ISSN 0032-5910
[1] H. Sezer, D. Werner, J.A. Sykes, N. Bazin, P. Bolton, C.R.K. Windows-Yule,
Exploring the internal dynamics of resonant acoustic mixing using positron emission particle tracking, Chemical Engineering Science, Volume 306, 2025, 121166, ISSN 0009-2509
