Flow Regimes > Regime 8: Stationary or Sliding Bed, Cvt

8: Fixed bed with suspension, constant Cvt.

Under real life conditions, there will be a “constant” volumetric transport concentration with decreasing line speed. There will be equilibrium between erosion and deposition, resulting in a certain bed height. Gibert (1960) has proposed that the Froude number will be equal to the Froude number at the limit deposit velocity. In this case, the limit deposit velocity is defined as the velocity where the sliding bed has vaporized due to erosion. With decreasing line speed, the bed height increases and so do the pressure losses. Once the bed height is known, the pressure losses can be determined according to the Newitt et al. (1955) model. This regime occurs if the excess pressure gradient is high enough to result in a sliding bed and so this will occur much more with small pipe diameters then with large pipe diameter.

The Shields parameter is 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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