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Introduction
The current theory about the of plate settlers predicts the failure for a certain specific sedimentation tank and plate settler spacing based on a failure mechanism called floc rolluproll-up. The floc roll-up theory states that a floc hitting the bottom plate will experience both a fluid velocity at its edge and a settling velocity. If the fluid velocity is higher than the settling velocity, then the floc will roll up the plate and will exit the plant without being captured.
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- The velocity profile at the edge of the particle is linearized,.
- Flocs are following straight lines,.
- Flocs are spheres,.
- There are is no floc breakup or collision,.
- The presence of flocs do not affect the velocity profile,.
- The entrance region of a plate settler (where the velocity profile is not fully-developed) is ignored.
The current theory predicts failure by the mean of a dimensionless ∏
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\huge $$\Pi$$ |
Our firsts first experimental results showed that this ratio is able to predict that the effluent turbidity that will be above 0.25 NTU . But but it is unable to predict the magnitude of the failure.
The Therefore, the PSS team therefore concluded that it needed to develop a numerical simulation taking more phenomenon into account is needed in order to be able to better understand the failure mechanisms and maybe be able to assess the effluent turbidity.
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How does the code
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work?
The code works on a Velocity-Verlet algorithm which computes all particles paths based on their experienced local velocities. The code takes particles sizes and , the tube (or plate) geometry as well as , and the up flow velocity as an input. The figure below summarizes the steps taken by the algorithm:
The output of the program is the number of particles that were not captured and their respective paths.
Further Developments
The team plans to adjust some of the parameters in order to be able to compare (at least roughly) the results and predictions of the numerical model with the experiments.
Further steps include implementing more interactions than floc roll up (e.g. floc break-up, floc recombination and how flocs influence the local velocity profile. Hence, the plate settler performance).
Attachments
trajectory9.m ||The main file. Contains the input parameters as well as the velocity-Verlet algorithm
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