Flow Regimes > Regime 7: Sliding Flow

7: Sliding Flow.

At relatively low concentrations and relatively small particle diameters, the sliding bed regime will have a transition to the heterogeneous regime at the intersection of the two regimes. This is the result of lift forces strong enough to lift the particles and turbulent dispersion to mix them into a heterogeneous mixture. However when the weight of the bed is bigger than the total lift forces, this will not occur and the particles stay in the bed in a sort of sheet flow. A second reason may be that at high concentrations the space above the bed is not big enough to fully develop turbulence. When the line speed increases, the lift forces by turbulence will also increase and the sliding bed will finally vaporize into heterogeneous transport. The pressure losses in this regime are much higher than the pressure losses with heterogeneous transport at lower concentrations. The pressure losses can be determined according to Miedema et al. (2013). The term Sliding Flow is chosen, because there is flow but the flow resistance has the character of sliding friction.

The Shields parameter is far above the Shields curve, so erosion occurs.

The total pressure loss is thus determined by sliding friction between the bed and the pipe wall.





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