Transport and deposition behaviour of model slurries in closed pipe flow

Suspensions of solid particles are ubiquitous in nature and industry. From subaqueous
and aeolian dunes and ripples to plug flow in the minerals engineering industry, the complexity of the fluid dynamics and interparticle interactions in multiphase flow is such that specific applications require specific solutions.
The behaviour of suspensions of solid particles in a water carrier fluid in closed pipe flow is investigated over a range of flow regimes, from fully suspended, homogeneous flows to settled beds, using four particle species. The suspensions are intended to be simple analogues of more complex slurries that are encountered in the nuclear industry, the disposal and transport of which represent an ongoing challenge.
An off-the-shelf ultrasonic signal processing unit, with two ultrasonic transducers operating at 2 and 4 MHz, is used as both a Doppler velocimeter and an acoustic
backscatter system. The results of a range of distinct measurements are presented. The effect of suspended particles of several types at several volume fractions on
the first- and second-order flow statistics is described. The dependence of two critical velocities that delineate the homogeneous, heterogeneous and moving-bed
flow regimes on the flow and particle properties is described, and the results are compared to two correlations of critical transport velocity in the literature. A
model was developed to measure the scattering and attenuation properties of arbitrary solid particles in suspensions, and the measured values are incorporated
into an inversion method in order to construct particle concentration profiles in pipe flow. Lastly, the behaviour of stable and time-dependent bedforms, which have been studied in natural and rectangular channels extensively, is investigated in closed pipe flow, and phase diagrams of bedform types are presented and compared with a similar diagram in the literature. A full set of particle characterisation results is also presented in terms of size,
density, shape and packing fraction, and the effect of the particle properties on the results is discussed in detail.