ONICON F-2600 - Manual (Page 15)

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F-2600 & F-2700 Vortex Flow Meter Manual 02/15 - 0808-7 / 19204 Page 15
1.2.4 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
Vmax
25 ft/s
√ ρ
300 ft/s
1 ft/s
30 ft/s
English ρ (lb/ft 3 )
Vmin
Vmax
37 ft/s
√ ρ
91 m/s
0.3 m/s
9.1 m/s
Metric ρ (kg/m 3 )
The pressure drop for F-2700 insertion meters is negligible. The pressure drop for F-2600
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 number 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
ρ V D
Re =
μ
f d
St =
V