Transport of Liquids in Unsaturated Bi- and Polydisperse Particle Beds

Wet granular materials show complex flow features and are key for numerous industrial processes such as mixing, granulation and coating. Previous studies on liquid transfer mainly focused on the static bridges, or bridge rupture [1,2] mainly in monodisperse systems. However, few theoretical and experimental studies provide a detailed understanding of the initial bridge formation process, and the subsequent liquid transfer rate in realistic (i.e., polydisperse)particulate systems. In this work, we provide a set of models to predict the distribution of liquid in a polydisperse powder bed by extending our previous work [3, 4, 5].
Specifically, we employ two approaches to study the transfer of liquid: Direct Numerical Simulations (DNS) [3, 4] and the Discrete Element Method (DEM) [5]. The DNS methods allow us to resolve the solid particle motion and the liquid interface, using either (i) the Volume of Fluid (VoF), or (ii) the Immersed Boundary (IBM) method combined with VoF. Based on these simulations, we extract data on the time evolution of the liquid bridge volume between wet particles, and parameterize a recently proposed liquid transfer model [3, 4]. We present DNS results considering a varying film thickness, as well as for the case of differing particle sizes. The DNS results will then be used to calibrate a scale-bridging model for liquid transfer that can be used in DEM-based simulations. Finally, the DEM-based model is used to perform realistic, yet efficient simulations of liquid transfer associated with each particle-particle contact. Our results lay the foundation for the future development of continuum models that can be used to predict process performance of, e.g., granulation devices, in industrial applications with higher confidence.