Experiments were conducted to study the inertial flow transitions of a non-Brownian neutrally buoyant particle-fluid suspension in the Taylor-Couette apparatus. The apparatus consists of a stationary outer cylinder and a concentric rotating inner cylinder. The suspension is made of non-Brownian rigid particles suspended in a Newtonian fluid. The densities of the particles and the fluid are matched. The inertia of the flow is given by Reynolds number, Re = riOdeltarho/mu s, where O is the rate of angular rotation of the inner cylinder and rho and mus are the density and the effective viscosity of the suspension. With the increase in Re from rest in a quasi-steady manner, the flow of a Newtonian fluid with no particles transitions from circular Couette flow to Taylor vortex flow at Re = 120 and from TVF to wavy vortex flow at Re = 151. The primary objective of this work is to study the effect of particle size and concentration on the flow transitions.

To study the effect of particle concentration on the flow transitions, the Re was reduced in a quasi-steady manner from that corresponding to WVF to that corresponding to CCF. Here the particles with size ratio alpha = 30 were used and the particle volume fraction was varied in the range 0 ≤ &phis; ≤ 0.3. The influence of the particles manifested in the reduction of Re corresponding to the flow transition to CCF and appearance of new region on the Re versus &phis; phase map with non-axisymmetric flow states not seen for the pure fluid with only inner cylinder rotating. For &phis; < 0.05, the suspension underwent flow transitions similar to that of the pure fluid but the transition Re was observed to reduce with increase in &phis;. For 0.05 ≤ &phis; ≤ 0.15, the suspension flow transitions were observed to deviate significantly from that of the pure fluid. With the reduction of Re, additional non-axisymmetric flow states, namely spiral vortex flow and ribbons were observed between TVF and CCF. At &phis; = 0.3, only non-axisymmetric flow states, namely wavy spirals and SVF, were observed before transitioning in to CCF. The transition Re corresponding to various flow transitions were observed to reduce with the increase in &phis; for 0 ≤ &phis; ≤ 0.3, for example, the Re for transition into CCF reduced from Re = 120 for the pure fluid to Re ≈ 75 for the &phis; = 0.3 suspension. For the &phis; = 0.1 suspension, when the particle size was reduced to yield alpha = 100, the region of non-axisymmetric region between TVF and CCF reduced and only RIB flow state survived.

Governing equations to perform linear stability analysis of CCF for a fluid with radially varying viscosity across the annular width were formulated. Comparison of the the pure fluid SVF and RIB structures obtained from the analysis with those observed in the suspension experiments revealed that the suspension exhibits same non-axisymmetric flow structures as pure fluid in terms of their wave lengths and wave speeds. LSA of CCF was performed for three radially varying viscosity profiles. Two center peaked profiles were considered to account for the equilibrium concentration profiles due to inertial migration corresponding to the average particle concentrations of &phis; avg = 0.025 and 0.1. And the third profile at &phis;avg = 0.1 was considered to simulate the uniform concentration in the annular core and depleted particle regions near the walls. For all the three profiles, the CCF was predicted to go unstable to a perturbation with an azimuthal wavenumber ktheta = 0 and, interestingly, with a non-zero time modulation (kti ≠ 0). The time modulation was found to increase with increase in &phis;avg for the center peaked profiles and reduce with increase in uniformity of the profile across the annular gap for &phis;avg = 0.1.

In addition, experiments were performed to study the mixing characteristics of CCF, SVF, TVF and WVF of &phis; = 0.15 suspension. A known amount of tracer was injected at the top of the flow structure and the temporal evolution of the axial concentration profile of the tracer was used to characterize the mixing. CCF with no axial velocities exhibit slowest axial transport while WVF with azimuthal waviness of the vortices produced fastest mixing. Between TVF and SVF, the later structure produced faster axial transport due to the time modulation of the spiral wave. Since SVF is sustained at Re smaller than that of TVF and WTV, it has lower stress fields making it suitable for applications such as bioreactors to culture cells, for example. (Abstract shortened by ProQuest.).