Panametrics PanaFlow MV80, Руководство пользователя, Страница: 16 / 184

Chapter 1. Introduction
4 PanaFlow™ MV80, MV82 & MV84 User’s Manual
1.3.3 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 Table 1 below.
Table 1: Measurable Ranges
Parameter Gas Liquid Units for

V
min
25ft/s

---------------
1 ft/s
English

(lb/ft
3
)
V
max
0.5 in.
0.75 in.
1 in.
1.5 in. and
greater
175 ft/s
250 ft/s
250 ft/s
300 ft/s
30 ft/s
30 ft/s
30 ft/s
30 ft/s
V
min
37m/s

----------------
0.3 m/s
Metric

(kg/m
3
)
V
max
DN15
DN20
DN25
DN40 and
greater
53 m/s
76 m/s
76 m/s
91 m/s
9.1 m/s
9.1 m/s
9.1 m/s
9.1 m/s
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:
Re
 VD

----------
=
Where,
Re
= Reynolds Number


= mass density of the fluid being measured

V = v
elocity of the fluid being measured

D = i
nternal diameter of the flow channel


= 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:
St
fd
V
----- =
Where,
St
= Strouhal Number

f
= frequency of vortex shedding

d = s
hedder bar width

V = f
luid velocity