Calculate sedimentation velocity online

Calculation of the sinking velocity / settling velocity in a stagnant body of water or basin

First of all, Stokes' equation is used to calculate the rate of descent, which is based on the following ideal conditions. The sediment particles are smooth spheres that settle in an infinitely extended liquid, in which neither the walls nor neighboring particles affect the settling speed.

vs:	Rate of descent	[ m / s]
d:	Grain diameter	[ mm ]
g:	Acceleration due to gravity	[ 9,81 m / s2 ]
ρp:	Grain density	[ kg / m3 ]
ρf:	Density liquid	[ kg / m3 ]
η:	Dynamic viscosity liquid	[ Pa / s ]
ν:	Kinematic viscosity liquid	[ m2 / s ]
Re:	Reynolds number
CD:	Drag coefficient

The conditions for the application of the Stokes formula are mostly not fulfilled in real sediments:

• the particles are not smooth
• The particles are not spheres, sand particles are mostly ellipsoidal-discus-shaped, clay minerals have a plate-like shape
• according to Stokes, the settling speed depends on the square of the grain size. If the grain size is large, the rate of descent increases to such an extent that turbulence occurs, which reduces the rate of descent. In natural sediments, sands, with a density of 2650 kg / m³, this occurs with a grain size above 0.08 mm.
• It may well be the case, for example when there is a large amount of sediment, that neighboring particles impede the sinking. At concentrations of around 1 g/l and above, there is a reduction in the rate of descent, since the fluid flowing back prevents the subsequent particles from sinking

To correct the deviations caused by the turbulence, the following formula is calculated with the drag coefficient C_D:

The drag coefficient C_D depends on the Reynolds number.
For low sedimentation velocities or Reynolds numbers < 0.5, laminar flow, C_D = 24 / Re applies. In this case, the sedimentation rate can be calculated using Stokes' equation.
If the Reynolds number is in the transition range between 0.5 < Re > 1000 there is no simple formula for C_D, but various empirical formulas, e.g. B. C_D = 18.5 / Re^0.6 .
For high sedimentation velocities or Reynolds numbers Re > 1000, turbulent flow, C_D = 0.44.
Sedimentationsgeschwindigkeit Wikipedia

Oseen provides an improved approach to calculating sink rate.

For particle diameters of up to about 0.1 mm, the approaches according to Stokes and Oseen deliver almost the same sinking speeds. For larger grain diameters, the Stokes range of application ends and the Oseen equation gives better results.

Grain size

Grain size:     [ mm ]

Density of material:

Density of material:     [ kg / m³ ]

Density of fluid:

Density of fluid:     [ kg / m³ ]

Dynamic viscosity η:

Dynamic viscosity of the fluid:     [ Pa /s ]

Error: