Mechanochemical reactions can be induced in a solution by the collision of balls to produce high-temperature and high-pressure zones, with the reactions occurring through a dissolution–precipitation mechanism due to a change in solubility. However, only a fraction of the impact energy contributes to the mechanochemical reactions, while the rest is mainly consumed by the wear of balls and the heat generation. To clarify whether the normal or tangential component of collisions makes a larger contribution on the reaction, herein we studied the effect of collision direction on a wet mechanochemical reaction through combined analysis of the experimental reaction rates and simulated ball motion. Collisions of balls in the normal direction were found to contribute strongly to the wet mechanochemical reaction. These results could be used to improve the synthesis efficiency, predict the reaction, and lower the wear in the wet mechanochemical reactions.

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A new simpler coarse-grain model (SCG) for analyzing particle behaviors under fluid flow in a dilute system, by using a discrete element method (DEM), was developed to reduce calculation load. In the SCG model, coarse-grained (CG) particles were enlarged from original particles in the same way as the existing coarse-grain model; however, the modeling concept differed from the other models. The SCG model focused on the acceleration by the fluid drag force, and the CG particles’ acceleration coincided with that of the original particles. Consequently, the model imposed only the following simple rule: the product of particle density and squared particle diameter is constant. Thus, the model had features that can be easily implemented in the DEM simulation to comprehend the modeled physical phenomenon. The model was validated by comparing the behaviors of the CG particles with the original particles in the uniform and the vortex flow fields. Moreover, the usability of the SCG model on simulating real dilute systems was confirmed by representing the particle behavior in a classifier. Therefore, the particle behavior in dilute particle-concentration systems would be analyzed more simply with the SCG model.

A new method to determine both the coefficients of particle and rolling friction in distinct element method (DEM) was proposed. The coefficients are two of the most important parameters which have great effect on particle behavior in DEM. However, it is difficult to determine the values of the coefficients, which is applicable to multiple behaviors, from an experiment. We proposed the method to determine the two coefficients uniquely so that two indicators correspond to experimental results. As the indicators of static and dynamic behaviors, the angle of repose and the discharge flow rate were adopted, respectively. The values of the coefficients which can represent both static and dynamic behaviors of particles were determined by means of the method. The particle behavior in a rotating drum at three different rotational speed was simulated by using the determined coefficients in order to verify the applicability of them to dynamic behavior of particles under various conditions. The simulated behaviors for spherical particles corresponded to the experimental ones. The determined coefficients by means of the proposed method could be applied to the behavior of spherical particles at all of the rotational speeds. On the other hand, the simulated behaviors for irregularly shaped particles did not correspond to the experimental ones, in particular at higher rotational speed. It would be because the rolling friction of irregularly shaped particles depends on the particle velocity in a rotating drum.

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