Abstract
Our team is currently running experiments to investigate the phenomenon of 'floc-rollup' through the tube settler which occurs when the drag and buoyant forces acting on a floc particle exceed the force of gravity. We have been working on different ways to model this physical situation (in most cases based on a force balance), and hope to eventually obtain data that agrees with one of our theoretical predictions.
Overview of Methods
To show evidence of floc-rollup occurring in the tube settler, we have been setting up experiments in which the apparatus was subjected to a ramped volumetric rate, (flow through the settler was increased linearly over the duration of the experiment). Once good data has been collected, we hope to be able to graph effluent turbidity against time and identify a "spike" in turbidity that corresponds to the threshold flow rate at which roll-up starts to occur. This observed threshold flow rate will be compared to that determined from all of our different predictions, and thus may help us determine which physical model is most appropriate for our system. We plan to perform these experiments and clearly identify threshold flow rates for all available tube settler diameters.
Theoretical Analysis Based on Force Balance
Calculations have been performed in MathCad to help make predictions that will be useful in analyzing our future experiments. More detailed information can be found here:
Rollup Analysis Based on Force Balance
Theoretical Analysis of the Velocity Gradient