(206f) DEM Study of a Vibrational Powder Transport System

Vibrational transport systems are used in various industries to aid the transport of the granular material between unit operations. The system tipically consists of one or several parts that oscillate with the help of a vibration source, which is controlled remotely. The parameters that control the vibration are the amplitude and the frequency of the vibration, and the length of the vibration period, which can be adjusted.

The horizontally vibrating system used in this work is shown in Fig. 1. It is essentially a hopper attached to an elbow-shaped tube, with a diameter size reduction in the horizontal part. Powder is introduced from the top in the filling hopper and transported downstream to the next unit operation. The vibration source is fixed to the horizontal transport tube, and the whole system oscillates as one part.

The challenges, in this case, come from the particle agglomeration, system clogging, and flow blockage in the hopper and transport tube, especially because the transported material has poor flowability and is highly cohesive. Experimental trials using three powders with different cohesivity showed that the operating frequency affects the flowability of the powder.

To better understand why the operating vibrational frequency affects the particle flow behavior, the Discrete Element Method (DEM) was used to simulate the process [1], [2]. With the DEM approach, it is possible to investigate various process conditions and equipment designs in a short period, gaining process insight that is difficult or even impossible to get experimentally.

The vibrational transport trials were closely replicated in the DEM model, with the same operating conditions and equipment design. The three powders were calibrated prior to the investigation (DEM reproduction of the FT4 shear cell and compression tests [3]), in order to closely replicate the behavior of the real powders. The particle size was distributed with a normal distribution function and scaled in comparison to the original one in order to speed up the simulations.

The DEM results revealed an interesting mechanism, i.e., the segregation of the particles with small diameter in several locations in the system, including the fill hopper and the horizontal tube. The investigation of the particle stress distribution in the system showed a peak of the normal and shear stress at the position of the segregated particles. The fact that these positions overlap led to the conclusion that the system clogging is caused by the agglomeration of the small particles.

The DEM investigation showed that the frequency change affects the position and trajectories of the small particles. The small particles are dispersed more in the system when the operating frequency is lower, which reduces the segregation and helps to improve the powder flowability. Our finds were confirmed by the experiments as well.

[1] D. Jajcevic, E. Siegmann, C. Radeke, and J. G. Khinast, “Large-scale CFD-DEM simulations of fluidized granular systems,” Chem. Eng. Sci., vol. 98, pp. 298–310, 2013, doi: 10.1016/j.ces.2013.05.014.

[2] E. Siegmann, D. Jajcevic, C. Radeke, D. Strube, K. Friedrich, and J. G. Khinast, “Efficient Discrete Element Method Simulation Strategy for Analyzing Large-Scale Agitated Powder Mixers,” Chemie-Ingenieur-Technik, vol. 89, no. 8, pp. 995–1005, 2017, doi: 10.1002/cite.201700004.

[3] P. Toson et al., “Continuous mixing technology: Validation of a DEM model,” Int. J. Pharm., vol. 608, no. September, p. 121065, 2021, doi: 10.1016/j.ijpharm.2021.121065.