Centrifugal Dredge Pumps

Abstract

Transportation of slurries over a distance has always been one of the main objectives for the dredging industry. To accomplish a transport, centrifugal dredge pumps and mixture pipelines need to be perfectly intertwined. For the centrifugal dredge pump, available information is relatively scattered or confidential. The performance of a centrifugal pump is mainly determined by conducting experiments with actual slurries or estimated on the performance characteristics obtained from water. Besides empirical research in laboratories and field studies, numerical Computational Fluid Dynamics (CFD) simulations have become an interesting asset in creating models for multiphase situations. This mainly due to increasing computational power that is currently available. The goal of this research is to gather and analyse information on particle trajectories near impeller blades and its unsteady head characteristics in a centrifugal dredge pump for visual validation of Cao et al. (2019) CFD model outcomes. In the literature research, information was gathered on empirical models, CFD simulations, an analytical description of particle behaviours along impeller blades, (dimensionless) pump characteristics and impeller/shell designs. On the experimental side, the executed experiments consist out of head and discharge recording by throttling the exit valve for pump characteristics in single phase water conditions and mixture conditions at 564, 846, 1128 and 1410 RPM. The used impeller has a diameter of 155 mm and is a so called "open impeller". At mixture conditions, delivered volumetric concentration (Cvd ) of 5%, 8%, 12%, 15% and 20% are reached with glass bead particles of 1.5mm and 3.0mm with a density of 2500 kg /m3 . High speed image recording are made of the impeller blades at above mentioned situations but with a steady exit valve set to 50% open. The experimental study gives an interesting inside on the behaviour of particles internally. On the particle trajectory side, where PIVlab image analysis are conducted, the result can be used partially on the streamline verification from the CFD model of Cao et al. (2019). This especially applies for the single phase situations and partially less for the mixture situation due to problems with particle distinguishing. Summarised, this means that the conducted experimental study is not able to fully verify the CFD model outcomes of Cao et al. (2019) for the instantaneous streamlines and concentration distribution between the impeller blades. Though, it supplies a steady base for further research. For the unsteady head characteristics that are enhanced during mixture loading at high-concentrations on the other hand, interesting data is collected. The unsteady head characteristics shows an enhancement in noise at the lower side of the spectra with an increase of concentration and engine speed. At low engine speed, the unsteady head amplitude has a wider spread that results in a lot of short quick amplitude changes. For an increase in speed, these quick amplitude changes are reduced and become more stable. The conditions are similar as in single phase water conditions due to a shift towards the lower side of the spectra. This same behaviour is visible in Cao et al. (2019) CFD model outcome.