The entrainment behavior of colloidal particles in a submerged jet

The research reported in this dissertation is aimed at relating the jet entrainment of a sludge to the pH of the suspending fluid and the hydraulic properties of a 3-D offset submerged jet. The research results can be applied to the design and scale-up of the mixing pumps in waste tank retrieval projects at Hanford and other Department of Energy sites or similar experiments and industrial applications.; Computer simulations and/or experiments were conducted to measure and simulate the submerged jet mean velocity field distributions, model sludge yield shear stress, and determine the relationship between sludge erosion rates, the pH values of the fluid and the flow rate of the fluid.; The velocity field distributions of the submerged offset jet were calculated using a realizable k-ϵ model with FLUENT. After the velocity field distributions were verified experimentally with a LDA, the shear stress generated by the jet was predicted using the same model and with the same software package. The average relative error between the experiment and prediction for the mean velocity on the jet axis is around 2%. A sludge average relative error between the experiment and prediction for the mean velocity on the jet axis is around 2%. A sludge yield stress model was developed by adding repulsive interactions to Rumpf's tensile strength model according to the DLVO theory. This model contains only a single unknown parameter, the inter-particle spacing. A typical yield shear stress for the sludge (aluminum hydroxide, ferric hydroxide, and their mixtures) in the research is from 1 to 5 Pa. The model was experimentally verified by measuring the force-separation curve for alumina particles with an Atomic Force Microscope (AFM).; The yield shear stress model and the shear stresses generated by the submerged jet were combined to predict the erosion rate of the sludge. The measurement of the velocity profiles of the submerged 3-D offset is the first documented in this work. The CFD simulation of the velocity profiles and the shear stress of the jet above is the first performed here too. The results show that only when the hydraulic shear stress is greater than the yield shear stress (for example ferric hydroxide, τyield ≈ 2.7 Pa), will erosion occur. The erosion rates predicted with the models developed in this research are in good agreement with experimental data previously obtained in the laboratory. The average relative error for the experimental data and the simulated results for the mixture of aluminum, ferric, and zirconium hydroxides is 9∼58% using a fixed particle spacing obtained from single components.; This research project provides a framework for a better understanding of the relationship of jet properties, sludge rheological properties, and the effect of the pH values of the fluid on the mobilization of sludge which can be used for design and scale-up in engineering applications. Especially, if the results of this research are adopted, the cost of the waste tank retrieval projects could be reduced substantially.