VorTek Pro-T, Instruction Manual

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Chapter 1 Introduction Series M22/M23 Instruction Manual
1-6 M-000-00010
The Strouhal number is the other dimensionless number that quantifies the vortex
phenomenon. The Strouhal number is defined as:
St = f d
V
Where
St = Strouhal Number
f =
frequency of vortex shedding
d = shedder bar width
V = fluid velocity
As shown in Figure 1-3, Pro- V™ meters exhibit a constant Strouhal number
across a large range of Reynolds numbers, indicating a consistent linear output
over a wide range of flows and fluid types. Below this linear range, the intelligent
electronics in Pro-V automatically corrects for the variation in the Strouhal num-
ber with the Reynolds number. The meter’s smart electronics corrects for this
non-linearity via its simultaneous measurements of the process fluid temperature
and pressure. This data is then used to calculate the Reynolds number in real
time. Pro-V meters automatically correct down to a Reynolds number of 5,000.
Figure 1-3. Reynolds Number Range for the Pro-V
Pressure Drop
The pressure drop for series M23 insertion meters is negligible. The pressure drop
for series M22/M24 in-line meters is defined as:

P = .00024

V 2 English units (

P in psi,

in lb/ft 3 , V in ft/sec)

P = .000011

V 2 Metric units (

P in bar,

in kg/m 3 , V in m/sec)
Minimum Back Pressure
A minimum back pressure is required to prevent cavitation in the vortex
flow meter when installed in liquid applications. Cavitation is a phenom-
enon wherein a liquid passing through a low pressure zone no longer can
r
emain in the liquid phase and therefore partially flashes (or “boils”) into
0.3
0.2
0.1
0.0
3 4
10
Linear range
Rey nolds Number, Re
St
rouhal
N
um
ber,
St
10
5
10 10
8
10
6
10
7
5000
Corrected range