Buoyancy-driven Particle-laden Exchange Flows in Inclined Conduits



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As an extension to the previously investigated buoyancy-driven exchange flow of pure fluids in inclined ducts, we propose an experimental and theoretical approach to practically study the effect of solid particles within the flow. The flow problem starts in a density-unstable lock-exchange configuration with heavy suspension being on top of a light pure fluid in a long narrow pipe or channel. Suspension is a mixture of negatively-buoyant solid particles in a Newtonian pure fluid. The density difference between the heavy and light phases is small enough to neglect the inertia (Boussinesq approximation).

Flow is firstly studied through an experimental framework. Various sedimentary, transitionary, and mixing regimes are observed based on the pipe inclination angle, [Greek small letter beta], and initial volume fraction of particles, [Greek small letter phi][subscript 0] . The results are mapped on dimensionless diagrams suitable for industrial design and environmental planning. Effects of particle size and fluid’s viscosity are further discussed. The sedimentary behavior is diminished by reducing particle size, whereas remains unchanged with fluid’s viscosity. The advancement frontal speed of the heavy suspension layer into the light pure fluid, V[subscript f] , is measured over full range of experiments. It is found that V[subscript f] becomes larger as the pipe is titled away from the horizontal direction. An intermediate range of particle volume fraction, [Greek small letter phi][subscript 0], is interestingly discovered to lead to maximal V[subscript 0] . A non-dimensional scale for frontal velocity is successfully proposed constituting various flow and geometrical parameters.

For strictly vertical duct, a lubrication model is developed to theoretically investigate the flow in this simplified configuration. Novel particle-rich zones inside the suspension are further discovered in the vicinity of the advancing heavy and light fronts. It was further revealed that the geometry confinement plays a significant role in exchange flow dynamics through formation of interfacial patterns and particle-enrichment behavior. The fundamental findings of this thesis help understand the dynamics of important flows observed in nature within oceanographic and geophysical contexts as well as in industry through discharge, transport and dispersion of slurries, mine tailings, pastes, pharmaceuticals, paper pulp, drill cuttings, sludge, effluents and sewage, manufacture of cement clinker in inclined kilns, mineral processing in hydrocyclones, and inclined fluidized beds.



Particle-laden, Buoyancy-driven flow, Flow, Fluid dynamics, Suspensions, Complex Fluid, Multi-phase flow, Buoyant Exchange Flow


Portions of this document appear in: Mirzaeian, N., and K. Alba. "Monodisperse particle-laden exchange flows in a vertical duct." Journal of Fluid Mechanics 847 (2018): 134-160. https://doi.org/10.1017/jfm.2018.325.