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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 ow meters must be correctly sized so that the

ow velocity range through the meter lies within the measurable velocity range (with

acceptable pressure drop) and the linear range.

The measurable range is dened 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

)

Vmin

Vmax

37 ft/s

√ ρ

91 m/s

0.3 m/s

9.1 m/s

Metric ρ (kg/m

)

The pressure drop for F-2700 insertion meters is negligible. The pressure drop for F-2600

in-line meters is dened as:

∆P = .00024 ρ V

English units (∆P in psi, ρ in lb/ft

, V in ft/sec)

∆P = .000011 ρ V

Metric units (∆P in bar, ρ in kg/m

, V in m/sec)

The linear range is dened by the Reynolds number. The Reynolds number is the ratio of

the inertial forces to the viscous forces in a owing uid and is dened as:

Where

Re = Reynolds Number

ρ = mass density of the uid being measured

V = velocity of the uid being measured

D = internal diameter of the ow channel

 = viscosity of the uid being measured

The Strouhal number is the other dimensionless number that quanties the vortex

phenomenon. The Strouhal number is dened as:

Where

St = Strouhal Number

f = frequency of vortex shedding

d = shedder bar width

V = uid velocity

ρVD

Re =



f d

St =

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 130 131

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