Centrifugal Settling Time for Wear Particles

Centrifugal settling calculator

Estimate radial separation time for spherical wear particles in a Newtonian fluid, or solve for the required speed or separable diameter.

Operating conditions

Particle-size sensitivity

Diameter (µm)	Time (min)	Reₚ

How to use

Choose whether to solve for settling time, required RPM, or separable diameter.
Enter particle diameter and particle density in the displayed units. The diameter is an equivalent spherical diameter.
Enter fluid density and dynamic viscosity at the actual operating temperature; do not enter kinematic viscosity.
Enter rotor speed and the initial and final radii measured from the rotation axis. Dense particles move outward; particles lighter than the fluid move inward.
For an inverse mode, enter the available centrifugation time.
Select Calculate to update the canonical result, Stokes check, size table, and plot. Select Reset to restore the example.
Interpret the sign/direction, final RCF, radial speed, and Reₚ warning together. Confirm that the required RPM is within the rotor, tube, and centrifuge ratings.
Do not use this model for non-Newtonian fluids, concentrated suspensions, strongly nonspherical particles, significant wall/hindered-settling effects, or Reₚ above 1; use a validated finite-Re or multiparticle model instead.

Equations used

For constant angular speed and Stokes drag:

ω = 2πN/60

v_r = dr/dt = Kr, K = (ρ_p − ρ_f)d²ω²/(18μ)

t = ln(r₂/r₁)/K = 18μ ln(r₂/r₁)/[(ρ_p − ρ_f)d²ω²]

N = (60/2π)√{18μ ln(r₂/r₁)/[(ρ_p − ρ_f)d²t]}

d = √{18μ ln(r₂/r₁)/[(ρ_p − ρ_f)ω²t]}

RCF₂ = ω²r₂/g₀, Re_p = ρ_f|Kr₂|d/μ

Symbols and units: N is rpm; ω is rad/s; d, r₁, and r₂ are converted to metres; ρ_p and ρ_f are kg/m³; μ is Pa·s; t is seconds; g₀ = 9.80665 m/s². Sign convention: outward radial motion is positive. Thus ρ_p > ρ_f requires r₂ > r₁, while buoyant particles require r₂ < r₁.

Assumptions and limits: dilute rigid spheres, Newtonian fluid, constant properties and speed, negligible Brownian motion, acceleration transient, wall effects, and hindered settling. Reₚ < 0.1 is preferred; 0.1–1 requires caution; above 1 is outside the model.

Reference: G. G. Stokes (1851), “On the Effect of the Internal Friction of Fluids on the Motion of Pendulums,” Transactions of the Cambridge Philosophical Society 9, 8–106.