Flow regimes within horizontal particle-laden pipe flows

This study presents numerical simulations for particle-laden gas–solid flows in horizontal circular pipes to identify the key flow regimes as a function of the main dimensionless parameters. A Euler–Lagrangian approach is employed, using direct numerical simulations (DNS) coupled with a Lagrangian particle tracking (LPT) method, to consider the drag, gravitational and lift forces on particles, as well as the effect of inter-particle collisions. The influence of the Stokes number (Sk), mass loading ratio (Φm) and Froude number (Fr) on critical flow regimes is assessed to identify conditions under which gravity bias becomes either negligible or dominant with regard to fluid characteristics and particle statistics. Three different regimes of the flow behaviour are identified, depending on the combination of these dimensionless parameters. These flow regimes are described and their dependence on these three parameters (Sk, Φm and Fr) is reported, including the significance of gravity in generating a bias on distributions of the flow statistics.