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Series 220/221 Instruction Manual Chapter 1 Introduction
IM-22 1-5
Re =
ρ V D
µ
St =
f d
V
Flow Velocity Range
To ensure trouble-free operation, vortex flow meters must be correctly
sized so that the flow velocity range through the meter lies within the
measurable velocity range (with acceptable pressure drop) and the linear
range.
The measurable range is defined by the minimum and maximum velocity
using the following table.
Gas Liquid
Vmin
25
ρ
ft/s
1 ft/s
English
ρ
(lb/ft
3
)
Vmax 300 ft/s 30 ft/s
Vmin
37
ρ
m/s
0.3 m/s
Metric
ρ
(kg/m
3
)
Vmax 91 m/s 9.1 m/s
The pressure drop for series 221 insertion meters is negligible. The pres-
sure drop for series 220 in-line meters is defined as:
∆P = .00024 ρ V
2
English units (∆P in psi, ρ in lb/ft
3
, V in ft/sec)
∆P = .000011 ρ V
2
Metric units (∆P in bar, ρ in kg/m
3
, V in m/sec)
The linear range is defined by the Reynolds number. The Reynolds num-
ber is the ratio of the inertial forces to the viscous forces in a flowing
fluid and is defined as:
Where
Re = Reynolds Number
ρ = mass density of the fluid being measured
V = velocity of the fluid being measured
D = internal diameter of the flow channel
µ = viscosity of the fluid being measured
The Strouhal number is the other dimensionless number that quantifies the
vortex phenomenon. The Strouhal number is defined as:
Where
St = Strouhal Number
f = frequency of vortex shedding
d = shedder bar width
V = fluid velocity