Validation study on a toroidal approximation-based capillary force model in the discrete element method simulation

Abstract

Comprehension of wet particle behavior is of great importance in science and engineering. In the past two decades, modeling and simulation for wet particles have been extensively studied because of their various industrial applications. The discrete element method (DEM) is extensively employed to simulate the wet particle behavior. To calculate the wet particle behavior, several capillary force models have been developed so far. Roughly speaking, the capillary force models are classified into two types, namely, the analytical model and the geometrical approximation model. The analytical model is most frequently employed because of its simplicity, though only a small amount of the liquid volume is applicable. The geometrical approximation model has significant advantages because of no theoretical limitation of the liquid volume as well as its high accuracy. Incidentally, the geometrical approximation model usually expresses the liquid bridge shape by the toroidal approximation. However, validation tests for the geometrical approximation model have hardly been performed due to difficulty in incorporating the complex algorithm into the DEM. From the background, this paper aims to prove the superiority and adequacy of the geometrical approximation model in the DEM simulation for wet particles. First, the superiority of the geometrical approximation model to the analytical model is examined in a two-body system. Afterward, the following two types of validation tests are performed: granular collapse and wet powder mixing in a twin-screw kneader. In the granular collapse, the liquid content is set to be less than 4 vol. %. In the twin-screw kneader system, the liquid content is more than 5 vol. %. Through the validation tests, the adequacy of the geometrical approximation model in the DEM is proved because of the agreement between the computational and experimental results in the above systems. Consequently, this study will significantly contribute to a better understanding of wet particle behavior in science and engineering.