Controlling flow behavior of micro food powder in the mixer is important for improving the efficiency of premix powder production. Four important factors (particle diameter, particle diameter distribution, particle shape, adhesion force) which could influence the flow behavior in the mixer were examined by several experiments and Distinct Element Method simulations. The experiments and simulations showed that the particle diameter, particle diameter distribution and particle shape had little effect on the flow behavior of the food powder in the rotating drum, while the adhesive force had a very large effect. On the basis of this finding, we proposed a simple adhesion model for representing the behavior of micro food powder in the mixer. It was found that the flow behavior of several kinds of food powder can be represented by the proposed model.
Ball motions in wet ball milling with a tumbling ball mill were simulated using the DEM. Effects of rotation speed and ball size were investigated. Results of DEM simulation were compared with the observed ball motions and the results of real grinding tests in wet ball milling. In DEM simulation, calculated ball motions were adjusted to observed motions using the suitable friction coefficient. Then, energy distributions of ball impact energy and their cumulative values were calculated. As for changing of rotation speed, results of grinding tests of wet ball milling were well related to the impact energy. However, the grinding efficiency of ball impact energy was smaller as the ball size was larger. The energy efficiency of 10 mm balls was estimated 21% of that of 3 mm balls.
A novel particle classification process by utilizing cross-flow microfiltration has been developed. In this process, particles which are smaller than the pores of membranes are collected in the permeate and those larger than the pores are collected in the retentate. This technique has a great potential to classify particles at any cut-off diameter just by choosing an appropriate membrane with a pore size that corresponds to the target classification diameter, even in the sub-micron region. Here we discuss two important issues, how to prevent the deposition of particles onto the membrane surface and the clogging inside the pores, in order to develop this process as a robust and practical one. Some examples of successful particle classification operations are also presented.
When a container filled with granular material is shaken, the solid content is fluidized due to the loss of force balance acting on each solid. This vibration-induced fluidization technique is useful for creating ordered mixtures as well as preventing particles from clogging. In addition, improving powder flowability enables new applications such as surface modification and gas–solid reactions to be developed. However, handling fine powders is generally difficult because of particle adhesion, even when vibration is applied. In this study, new systems to fluidize fine powders are presented and the effect of vibration on the behavior of particles is explained in detail. In particular, the relationship between convection rolls produced by bubbles and pressure distribution is described based on experimental data.