Engineering context

Settling slurries carry coarse, heterogeneous solids that drop out of suspension if velocity falls too low, so they need dedicated treatment rather than being modelled as a plain liquid. The first decision is classification — settling versus non-settling — because that choice determines how the slurry is modelled.

The classification comes first: with slurry test data, scale-up testing confirms settling behaviour; without it, a slurry made up mostly of solids 75 microns and smaller is treated as a non-settling slurry having non-Newtonian characteristics (which belongs on the non-Newtonian workflow), while coarser or mixed solids are treated as settling. For a settling slurry, the solids are stored in the fluid database and the settling correlations are configured — one method per category, by engineering judgement, for deposition velocity, inclined-pipe adjusted deposition velocity, and horizontal and vertical friction loss — with FluidFlow detecting pipe orientation and applying them automatically. Boundaries are then added with the inlet boundary fluid type set to heterogeneous settling so the solids data is defined there, the network is built and connected, and the system is modelled as a liquid system with centrifugal pump solids derating. After solving, it is analysed as a typical liquid system (velocity, capacity, NPSH margin) and then for slurry-specific results: deposition issues, pressure losses, specific energy consumption, slope impact, and the drop in pump performance from derating.

Settling slurries don’t behave like conventional liquids — friction loss does not rise monotonically with velocity, and as velocity falls through the moving-bed regime it can increase with decreasing velocity, producing an inverse relationship over part of the operating range, which makes settling slurries complex to model.

Engineering workflow

1. Classify the slurry as settling. If slurry test data is available, use it — scale-up testing confirms settling behaviour. Without test data, apply the particle-size rule: a slurry made up mostly of solids 75 microns and smaller is treated as a non-settling slurry having non-Newtonian characteristics, while coarser or mixed solids are treated as settling. (Non-settling/non-Newtonian slurries belong on the non-Newtonian workflow.)
2. Define the solids in the fluid database. Store the solids’ properties in FluidFlow’s fluid database as required.
3. Configure the settling correlations. Choose one method per category using engineering judgement: deposition velocity, inclined-pipe adjusted deposition velocity, horizontal friction-loss correlation, and vertical friction-loss correlation. FluidFlow detects pipe orientation and applies the methods automatically.
4. Define the boundary conditions. Add the boundaries and set the inlet boundary fluid type to heterogeneous settling so the solids data is defined there; set the operating conditions (inlet pressure and flow, outlet pressure or flow), choosing the pressure model correctly — stagnation for vessels, static for pipes or wall measurements.
5. Build and connect the network. Add pipes, fittings, elevations, and equipment, and connect them to establish topology, including any centrifugal pumps.
6. Model the system as a liquid system with centrifugal pump solids derating. Enable the option to derate centrifugal pump performance for the additional friction loss that coarse solids impose on the pump internals.
7. Solve, then analyse as a typical liquid system. Review pipe velocity, capacity, and NPSH margin as you would for any liquid network.
8. Analyse the slurry-specific results. Check pipes for deposition issues (velocity against deposition velocity), pressure losses, specific energy consumption, and the impact of slope; and check pumps for the drop in performance due to derating.

How FluidFlow helps

FluidFlow handles them within its steady-state pipe network solver, detecting pipe orientation, applying the chosen correlations automatically, derating centrifugal pumps for solids friction, and reporting velocity, deposition margin, pressure drop, specific energy consumption, and NPSH. It is not CFD and does not perform transient or particle-tracking simulation.

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