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for the proposes of the design of separation equipment that utilize inclined plates, a series of baffles or separation media of any kind, a Reynolds Number of less than 500 is the industry norm (less than 300 preferred).
The Reynolds Number is a non-dimensional parameter defined by the ratio of
The Reynolds Number can be used to determine if flow is laminar, transient or turbulent. The flow is
and can be expressed as
Re = (ρ u2) / (μ u / L)
= ρ u L / μ
= u L / ν (1)
where
Re = Reynolds Number (non-dimensional)
ρ = density (kg/m3, lbm/ft3 )
u = velocity (m/s, ft/s)
μ = dynamic viscosity (Ns/m2, lbm/s ft)
L = characteristic length (m, ft)
ν = kinematic viscosity (m2/s, ft2/s)
For a pipe or duct the characteristic length is the hydraulic diameter. The Reynolds Number for a duct or pipe can be expressed as
Re = ρ u dh / μ
= u dh / ν (2)
where
dh = hydraulic diameter (m, ft)
A Newtonian fluid with a dynamic or absolute viscosity of 0.38 Ns/m2 and a specific gravity of 0.91 flows through a 25 mm diameter pipe with a velocity of 2.6 m/s.
The density can be calculated using the specific gravity like
ρ = 0.91 (1000 kg/m3)
= 910 kg/m3
The Reynolds Number can then be calculated using equation (1) like
Re = (910 kg/m3) (2.6 m/s) (25 mm) (10-3 m/mm) / (0.38 Ns/m2)
= 156 (kg m / s2)/N
= 156 ~ Laminar flow
(1 N = 1 kg m / s2)
Below are two links to online Reynolds Number Calculators.