Flow regimes

Flow regimes

Flow regimes

Slurry flows are typically split into two categories for the purpose of predicting pipeline friction losses: non-settling (or homogeneous) and settling (or heterogeneous).

Non-settling / homogeneous

The diameters of particles in non-settling/homogeneous flows are very fine, and settling in the quiescent stat is very slow. A non-Newtonian fluid model is usually applicable for these slurries, and stationary deposits do not form at low velocities. Pipelines flows may be either laminar or turbulent, and the solid particles are distributed uniformly within the slurry at all velocities.  The particles may be flocculated and the suspension mechanism for these particles may be fluid turbulence or interaction between the flocs.

Settling / heterogeneous

The particles are typically larger.  The flows are usually turbulent, and stationary deposits form at low velocities. The concentration distribution is less uniform for these slurries, and the velocity distribution is asymmetric. Homogeneous fluid models are not appropriate for predicting pressure gradients for these slurries.

Flow regimes of a heterogeneous mixture

Assuming that particles have a specific gravity in the order of 2.65, Durand and Condolios originally proposed to classify the flows of non-settling slurries in horizontal pipes into four categories based on the average particle size:

• Homogeneous suspensions for particles <40 μm (325 mesh)
• Suspensions maintained by turbulence for particle sizes from 40 μm to 150 μm (325 mesh to 100 mesh)
• Suspension with saltation for particle sizes between 150 μm to 1500 μm (100 mesh to 11 mesh)
• Saltation for particles >1500 μm