For simulations involving a large number of particles, it is necessary to employ an unresolved CFD-DEM model where the flow-related quantities, e.g., fluid and particle velocities, pressure and interaction forces, are “volume-averaged”. The above example illustrates the complex flow in a three-phase fluidised bed where the air introduced from the bottom orifice creates bubbles and generates the movements of both the liquid and particles.

When a gas-liquid interface interacts with a group of particles, the wettability of particles can induce Laplace pressure that can significantly affect the movements of both fluids and particles. This phenomenon is relevant to processes in various industries including food, chemical and pharmaceutical. In our research group, we have developed a novel wettability model suitable for unresolved CFD-DEM simulations. The example simulation above demonstrates the sinking and floating behaviour of hydrophilic and hydrophobic particles, respectively, as they fall onto water surface.

In many industrial processes, fluid and particle flows are mechanically driven by using dynamic wall boundaries with complex shapes. Process efficiency, which is crucial for energy and cost savings, is significantly influenced by tool design and operating conditions. The example above shows a simulation of a stirred tank where particles are effectively dispersed within the liquid flow generated by the impeller blade.