Slurry Deposition Velocity
Deposition velocity (limit deposit velocity) is the line speed below which solid particles settle out and form a stationary bed on the pipe invert. It is a bed-formation threshold — not a full-suspension velocity. Above the limit deposit velocity a slurry may still carry a moving (sliding) bed and continue to convey solids; below it the bed becomes stationary, increasing pressure drop, accelerating wear, and ultimately blocking the line. Because the limit deposit velocity varies with solids concentration, FluidFlow takes the maximum limit deposit velocity across the concentration range as the conservative design value. Slurry pipelines are designed to operate above this velocity with a defined margin.
Definition
Deposition velocity depends on particle size and size distribution, solids concentration, particle and carrier-fluid densities, and pipe diameter. Several correlations model it, all valid only for a Newtonian carrier fluid, divided by flow regime: stratified and heterogeneous flow for coarse slurries (d50 > 150 microns) and pseudo-homogeneous flow for fine slurries (d50 < 150 microns). FluidFlow provides three configurable methods: the Wilson-Addie-Sellgren-Clift (WASC) Generalized Relationship (based on Wilson 1992), a particle-size function (from Wilson 1997), and GIW VSCALC, a composite approach that auto-selects among Wilson 1992, Wilson-GIW, Thomas 1979, and Thomas 2015 by particle size.
Engineering context
Slurry line design is a two-sided constraint: too slow and solids deposit; too fast and wear and energy cost climb steeply (wear rises faster than velocity itself). Practical designs run a margin above deposition velocity — commonly on the order of 30% depending on the consequence of a blocked line and how variable the feed is. FluidFlow calculates deposition velocity for defined slurries as part of the network solution and reports the operating-to-deposition velocity ratio per pipe, so the margin is visible across the whole line, not just at one design section. Non-settling slurries are handled separately through non-Newtonian rheology models such as Bingham plastic and power law.
Related definitions
Bingham plastic · Power law fluid · Darcy-Weisbach equation · Pump curve · System curve
See it in FluidFlow
See where your slurry line sits relative to deposition velocity. FluidFlow reports the operating-to-deposition velocity margin pipe-by-pipe across the network.
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Related content
Reviewed by the FluidFlow Engineering Team · Last reviewed: June 2026 · Applies to FluidFlow v3.54 (steady-state analysis)
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