Three-dimensional numerical simulations of product changeover: Miscible and immiscible displacements in circular tubes

초록

We perform three-dimensional simulations of miscible and immiscible displacements in a cylindrical pipe. For the miscible case, both laminar and turbulent displacement regimes are considered, and our numerical framework uses direct numerical simulation (DNS) and a Large Eddy Simulation (LES) approach based on a Lilly-Smagorinsky model. The dynamics of the flow are governed by the Navier-Stokes equations, coupled with a convective-diffusion equation for the concentration of the more viscous fluid when considering the miscible cases. For the immiscible laminar cases, we perform two-phase DNS considering both pinned and moving contact lines to capture the full range of immiscible dynamic behaviours. The pinned contact line reflects stationary interfaces constrained by surface heterogeneity, while the moving contact line accounts for dynamic interfacial motion influenced by viscous and capillary forces. This study shows that the viscosity contrasts between the two fluids play a significant role in determining the efficiency of 'cleaning' of a pipe containing an initially highly viscous resident fluid. When the viscosity of the displaced fluid is low, the laminar displacement flow is efficient in cleaning the pipe; however, when the viscosity increases, the laminar displacement becomes inadequate. Our numerical predictions in the turbulent regime showed that more efficient cleaning is achieved when the viscosity contrast between the two fluids is large. Lastly, our results reveal that the dynamics of a moving contact line can impact both the efficiency and the pattern of cleaning within the pipe.

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