Product Description
FLOWSIC100 Flare · Operating Instructions · 8013344/11L2/V 2-5/2018-10 · © SICK Engineering GmbH 25
Subject to change without notice
Determination of gas velocity
Measuring path L is equivalent to the active measuring path, i.e. the free flow path. For
measuring path L, sound velocity c and path angle α between sound and flow directions,
the following is valid for the transit time of the sound for sound propagation in direction of
the gas flow (forward direction):
i.e. a relation in which, except for the two transit times measured, only the active measuring
path and the path angle exist as constants.
Determination of sound velocity
The sound velocity can be determined by resolving formulas 2.1 and 2.2 for c.
Based on the dependencies according to formula 2.5, the sound velocity can be used for
the determination of the gas temperature, of the molecular weight and for diagnostic
purposes.
Volume flow determination
The volume flow in operating mode is calculated from the gas velocity and the geometric
dimensions of the pipeline.
→
pg. 70, § 2.3.2 describes the calculations for volume flow in standard state, mass flow and
molecular weight.
(2.1)
Valid against the flow is:
(2.2)
Resolving for v results in:
(2.3)
v =
· ()
L 1 1
2 · cos α t
AB
t
BA
t
BA
=
L
c - v · cos α
t
AB
=
L
c + v · cos α
c = · ()
Lt
AB
+ t
BA
2t
AB
·
t
BA
(2.4)
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