Research progress of the restitution coefficients of collision of particles in agricultural and food fields

Abstract: The collision of particles has been widely found in the processing of agricultural and food fields. The restitution coefficient of collision (RCC) of particles is one of the most important parameters to represent the behavior of particles after the collision. The responsive behavior of particles after the collision can also be predicted to obtain an accurate RCC of the particle after measurement. However, the RCC selection of particles still remained unclear, particularly on the limited function of devices and simplification in the application. Three RCC types are divided, including the restitution coefficient of kinematics, the restitution coefficient of kinetics, and the restitution coefficient of energy. The restitution coefficient of kinematics can be generally defined as the ratio of the velocities of particles before and after the collision. Since the variation in the velocity of particle collision can be caused by the forces on the particle, the restitution coefficient of kinetics is defined as the ratio of the momentums of restituted and extruded particles. Furthermore, two stages are divided in the process of particle collision using energy. In one stage, the particle is compressed and the energy of the particle would be absorbed. In another stage, the particle is restituted that the energy of the particle would be released. Subsequently, the RCC of particles needs to be calibrated to combine physical and simulation tests. As such, a physical experiment was performed on three types of RCC particles to verify the equivalence and applicability under different collision conditions. The features of the devices for testing RCC of the particle were illustrated. The Discrete Element Method (DEM) and Finite Element (FE) were also selected to simulate the interaction between agricultural particles and machinery. The influencing factors were summarized to improve the theoretical models, including the velocity and angle of particle collision, surface roughness of particle, temperature, and the material of particle. Thus, enhanced accuracy of predicted motion would be achieved for the particle after the collision. An attempt was also made on the applications of particle RCC in the theoretical model and numerical simulation related to mechanical parameters design. Consequently, it was found the resultant effect of different factors on RCC of particle, in order to enrich RCC of the particle under the real collision for the higher accuracy of the calculated. A promising prospect was also proposed from the multi-point collision of particles. A creative design of the device was also proposed to evaluate the RCC of particles. The finding can provide a strong reference for further investigation on the RCC of agricultural and food particles.