Schmidt SS 20.700, Инструкция по эксплуатации

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Instructions for Use
– SCHMIDT
®
Flow Sensor SS 20.700 Page 12
Thus, it is possible to calculate the standard volume flow of the medium
using the measured standard flow velocity in a pipe with known inner di-
ameter:
A w V
w PF w
D A
N N
N N
 
 
 

2
4

D
Inner diameter of pipe [m]
A
Cross-section area of pipe [m
2
]
N
w
Flow velocity in the middle of the pipe [m/s]
N
w
Average flow velocity in the pipe [m/s]
PF
Profile factor (for pipes with a circular cross-section)
N
V

Standard volume flow [m
3
/s]
SCHMIDT Technology provides a "flow calculator" on its homepage for
the calculation of flow velocity or volume flow in (circular) pipes or (rectan-
gular) ducts for the different sensor types:
www.schmidt-sensors.com
or
www.schmidttechnology.de
Installation in systems with square cross-section
For most applications, two limit cases can be distinguished with regard to
flow conditions:

Quasi-uniform flow field
The lateral dimensions of the flow-guiding system are approximately as
large as its length in the flow direction and the flow velocity is small so
that a stable trapezoidal
8
speed profile of the flow is formed. The width
of the flow gradient zone at the wall is negligible in relation to the cham-
ber width so that a constant flow velocity can be expected over the
whole chamber cross-section (in this case the profile factor is 1). The
sensor must be mounted here so that its sensor head, located at a suf-
ficient distance from the wall, measures in the area with the constant
flow field.
Typical applications are:
o
Exhaust ventilation ducts for drying processes
o
Chimneys
o
Open spaces

Quasi-parabolic flow profile
The system length is large compared to the cross-section surface and
the flow velocity is so high that the ratios correspond to that of the cir-
cular pipe. This means that the same requirements apply here to the
installation conditions.
8
A uniform flow field prevails in the largest part of the space cross-section.