Pipe flow of highly concentrated sludge

Abstract

Industries that pump sludges experience pressure to operate at higher concentrations with sludges that have high mechanical strength properties. The viscous character of the sludge becomes increasingly non-Newtonian and yield stress in nature. The two principal problems are regime determination and laminar flow settling, which ultimately results in pipe blockage. In facing the diversities that sludge management currently presents, it is important to resolve these issues and develop solutions for engineering practice. The approaches developed at the Flow Process Research Centre to deal with these problems are introduced. The objectives of this paper are to introduce experimental data of the phenomena associated with the pipe flow of highly concentrated sludge, and use these to develop and evaluate predictive modeling approaches suitable for engineering design purposes. For the prediction of transitional flow, a new general approach for visco-plastic fluids in industrially relevant pipe sizes is presented, based on dimensional analysis of the flow problem. Settled bed behavior is modeled using an adapted two-layer model approach, in all flow regimes. The modeling approaches are evaluated using the experimental results obtained. The analysis shows that the present work provides a workable solution for the prediction of the pipe flow of highly concentrated sludges, for engineering design purposes.

Keywords:

• High concentration
• laminar flow settling
• laminar/turbulent transition
• non-Newtonian
• yield stress