Random walk discrete element lattice boltzmann model for scalar transport in fluid and particle flows with strict scalar mass conservation

•A hybrid model is introduced to simulate scalar transport in fluid and particle flows.•Strict scalar mass conservation is achieved by using Random Walk Method.•A moving boundary condition is introduced for Random Walk Method.•Numerical dispersion is totally removed from the proposed model. Scalar transport in fluid-particle systems can be found in many natural processes and engineering applications. Modeling these systems can be challenging due to complex moving boundaries involved, such as fluid-particle, solute-particle interfaces. One often overlooked issue is: the scalar mass within the fluid domain is not strictly conserved even the no-flux boundary condition is applied in many grid-based methods. Here we introduce a hybrid model for simulating scalar transport in particulate flows with strict scalar mass conservation. It is achieved by adapting the Random Walk Method (RWM) to simulate the scalar transport and coupled with the Discrete Element Lattice Boltzmann Method (DE-LBM) for fluid-particle interactions. A moving boundary condition is proposed to prevent the scalar from penetrating solid boundaries and special treatments are presented in detail. The proposed model is validated by a series of benchmarks and experiments, then the mass conservation for both RWM and grid-based methods are checked. Finally, the model is applied to simulate scalar (solute) dispersion with particles in an oscillator which demonstrate its capability on simulating fluid-particle-solute systems. Furthermore, it is straightforward to extend the proposed model for non-spherical particles and reactive boundary conditions.