Abstract
Swelling of grains due to water absorption is ubiquitous in many natural materials and industrial products. Hence, a thorough understanding of grain swelling is of great scientific importance. An experimental investigation can only provide limited information, whereas great insight could be gained from numerical modelling, rigorous numerical models for describing particle swelling are essential. Thus, the objective of this study is to develop and validate a discrete element method (DEM) model for swelling of grains. A first order kinetic model was introduced to describe the swelling of a single grain, and subsequently implemented into the DEM code LIGGGHTS. Model validation was performed by comparing the time evolution of the expansion of a packed bed made of super absorbent polymer (SAP) particles obtained numerically and experimentally. It was demonstrated that the developed model can accurately predict the bed expansion. The validated model was then used to investigate the effect of material properties on the swelling behaviour using rice and SAP as the model materials. It is shown that the swelling depends significantly on material properties, as expected; the expansion of the powder bed made of rice is much lower than that of SAP. The developed model could be further advanced to study consequences of swelling phenomena in granular materials, such as segregation and heat generation.
Highlights
The expansion of a solid due to water absorption is commonly known as swelling and is caused by restoration of the equilibrium in chemical potential between the absorbing solid and the absorbed fluid [1]
Rice can increase its volume by about 40% during soaking [2] and a single super absorbent polymer particle can increase its radius by about 600% [3]
Many reseaerchers experimentally investigated water absorption of biological materials during isothermal soaking [4, 5] and a few studies were performed to examine swelling associated with the water uptake [2, 6,7,8,9]
Summary
The expansion of a solid due to water absorption is commonly known as swelling and is caused by restoration of the equilibrium in chemical potential between the absorbing solid and the absorbed fluid [1]. Perez et al [2] investigated hygroscopic swelling in rice kernels and proposed a theoretical model to describe the variation of moisture absorption in the radial direction Their model was successfully validated using the finite element method (FEM), and employed to investigate the effect of soaking temperature on infiltration of water and swelling of a single grain. [3], in which DEM was coupled with a pore finite volume (PFV) method to model the swelling of super absorbent polymers (SAPs) under fully saturated conditions Their theoretical model and simulations well reproduced the expansion of the granular bed observed experimentally, the deformation (i.e. height) of the granular media after swelling for over two minutes was somehow overestimated. Using the validated DEM model, a preliminary analysis of the effect of material properties on the macroscopic swelling of granular materials is performed
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