Flownex Slurry and Non-Newtonian Flow
Flownex models Non-Newtonian fluids such as slow/non-settling slurries and settling slurries. Slow/non-settling slurries are usually well described by non-Newtonian fluid models. However, settling slurries require additional calculation methods which are accounted for in Flownex. This section will give a brief overview of the various slurry types and flow models used by Flownex.
Slurry Applications in Industry
The demand for industries to predict/simulate the behavior of slurry pipelines in plant building and maintenance is ever increasing. Slurry flow simulation allows engineers to design and maintain:
- Ash handling systems in coal-fired power plants.
- Lime handling systems in flue gas desulphurization plants.
- Ore transport systems.
- Tailings transport systems.
- Backfill transport in deep mines.
- Hydraulic materials transport.
- Hydraulic transport of fine ore.
- Transport of processed ore to tailings dams.
What is a Slurry/Non-Newtonian Fluid?
- Broadly defined as a solid-liquid mixture.
- First important distinction is whether the slurry is a settling or non-settling solid-liquid mixture.
- For non-settling slurry – solid particles remain suspended or settle out at very low rates (< 1 mm/s).
- For settling slurries – solid particles settle out with settling velocity > 1.5 mm/s.
- Example: Paint vs. coarse sand particles in water (fish bowl).
Slurry Types Modeled in Flownex:
In terms of modeling, slow and non-settling slurries are usually well described by non-Newtonian fluid models, while settling slurries require totally different calculation methods. Mixed regime slurries are calculated by combining elements from both settling slurries and non-Newtonian fluids in a specific way. The two main parameters determining slurry characteristics:
- Slurry particle settling velocity.
- Solids concentration.
Slurries are broadly categorized in three categories, all of which are modeled in Flownex:
- Non-settling slurries.
- Slow settling slurries.
- Settling slurries.
Flownex SE will allow simulation of horizontal flows, inclined flows and vertical flows. Flownex can model: Non-Settling Slurries; Slow Settling Slurries; Settling Slurries and Mixed Regime Slurries.
Settling vs. Non-Settling Slurries
Slow / Non-settling slurry:
- Usually small particles, thumb ruled particle < 75 µm.
- Can be treated as homogenous liquid – solid mixture.
- Concentration does not vary over cross-section.
- Typically results in Non-Newtonian type flow.
- Usually larger particles, thumb ruled particle > 75 µm.
- Solid particles settle out unless supported by turbulent mixing.
- Results in varying solid concentration over cross-section.
- Moving bed of higher solid concentration at the bottom of horizontal pipe.
What is implemented in Flownex?
The Flownex slurry flow module deals with the following three aspects:
- Predicting pressure losses in systems operating with non-settling slurries, especially Non-Newtonian mixtures such as mine backfill in pipes.
- Predicting pressure losses in systems operating with settling slurries in horizontal, inclined and vertical pipe segments such as ash removal systems on power stations or dredging systems on mines.
- Predicting centrifugal pump derating factors for pumps operating with either Non-Newtonian fluids or Settling slurries.
- For flow and pressure drop calculations, the slurry mixtures are assumed to be homogeneous.
- Mixing is assumed to be instantaneous.
- Settling is not calculated explicitly by way of a mass conservation equation for solids. Rather, the user is warned whenever physically undesirable situations occur, such as settling. Any change in the local concentration is assumed to occur instantaneously.