A weakly-compressible DEM–CFD framework for dense gas–solid multiphase flows: Foundations consistent with reactive coupling

The design of large-scale multiphase reactors, such as fluidized beds for methanation, requires numerical methods that are both computationally efficient and physically accurate. This study addresses the limitations of existing approaches, where traditional DEM–CFD solvers are often computationally expensive and computationally less expensive methods typically fail to capture crucial physical phenomena such as finite-speed acoustic waves. We present a novel DEM–CFD framework for low-Mach number flows that couples the Discrete Element Method (DEM) with a non-iterative, weakly-compressible fractional-step method for the gas phase. This approach combines the particle-scale accuracy of DEM with a gas solver that efficiently handles both density variations and acoustic wave propagation. As a fundamental step before simulating reactive flows, this paper validates the framework’s hydrodynamic and acoustic capabilities using non-reactive test cases. First, simulations of pressure drop across a fixed bed show excellent agreement with the Ergun equation, validating the momentum exchange model. Second, the complex dynamics of a spout-fluidized bed are shown to reproduce experimental trends, while also highlighting the simulation’s sensitivity to particle contact parameters like restitution and friction coefficients. Finally, speed of sound measurements in various gases (Dry Air, CO 2 , H 2 ) within a particle bed confirm the framework’s ability to accurately capture finite sound speed and species-dependent properties, with results aligning well with pure-gas theory. The framework’s flexibility was further demonstrated by successfully reproducing an alternative ”frozen” two-phase sound speed. These comprehensive validations demonstrate the framework’s capability as a robust and efficient tool for investigating complex reactive multiphase flows. • A new DEM–CFD framework for low-Mach number flows is developed based on weakly-compressible formulation. • The proposed framework efficiently captures both particle-scale physics and acoustic phenomena. • Gas–particle momentum exchange is validated via pressure drop tests against the Ergun equation. • Fluidized bed simulations reproduce experimental dynamics and high sensitivity to DEM parameters. • The framework accurately predicts the speed of sound in various gases within a particle bed.