Dynamics of particle-laden plumes and jets.
The work presented in this dissertation represents a novel theoretical and experimental study of the sedimentation from particle-laden, axisymmetric, turbulent plumes and jets.
In the first part of the work, we present a theoretical model for the motion of the particles in the plume and in the surrounding environment, and calculate the deposition pattern on the ground. We consider flows with low particle concentration and particles of uniform size. Our theoretical predictions for the deposition patterns on the ground and for the evolution of concentration of particles in the environment are successfully compared with data from our laboratory experiments. We apply our model to estimate the patterns of sedimentation from both a gas turbine plant and a boiler.
In the subsequent work, we consider flows with particles of different sizes and/or densities. We show theoretically and experimentally that the effect of the polydispersivity of settling velocities of the particles on the deposition patterns is significant, particularly at large radial positions. Our theoretical model is applied to estimate the deposition patterns of chromium particles exhausted from a stack at a chromium plating plant.
We then consider plumes with large particle concentrations at the source. We find that the environment surrounding the plume may become unstable, leading to the formation of finger-like convective instabilities. We use a simple scaling analysis to derive a criterion for the onset of the instability in the environment. A simple theoretical model is developed for the dynamics of the plume and the mechanism of deposition on the floor in the presence of strong settling convection. We show that the deposition patterns differ significantly from those observed during settling in a stable environment.
Finally, in the last part of the work, we consider the dynamics and deposition patterns from surface currents generated by particle-laden jets. We consider surface currents generated by the impingement of the jet on both a free surface and on a solid surface. We find that for these momentum-dominated flows, there is an enhanced entrainment of environmental fluid into the current near the impingement region. We investigate theoretically and experimentally the effect of this enhanced entrainment on the motion of the particles and the deposition pattern.