3.6 Air Speed Measurement
79
v =
s
t
=
7.5 m
9.94 s
= 0.754
m
s
A m = 9.4 m
2
Q = A m v = 0.754
m
s
· 9.4 m
2
= 7.1
m
3
s
Note that the speed measurements obtained by this method are frequently
increased by 10%, so 0.9v should be considered as the approximate speed value.
3.6.6 Tracers
The use of tracers is a procedure similar to the preceding method. Sulphur hexafluoride (SF 6 ) is used as the tracer gas because of its low toxicity and because it is easy
to detect at low concentrations. The steady release method is as follows: a constant
flow rate of tracer (q) is injected into an airflow (Q), and at a given distance from the
emission point (L m ) and at a given time (t m ) the measurement
4 of the concentration
(c) is made, as shown in Fig. 3.14 (Higgins and Shuttleworth 1958; Thimons and
Kissell 1974).
q
v, Q
L m
Measurement point
c
Fig. 3.14 System of measuring flow rate in a mine gallery by the dilution method
4 This conditions aim for thorough mixing and equilibrium.
79
v =
s
t
=
7.5 m
9.94 s
= 0.754
m
s
A m = 9.4 m
2
Q = A m v = 0.754
m
s
· 9.4 m
2
= 7.1
m
3
s
Note that the speed measurements obtained by this method are frequently
increased by 10%, so 0.9v should be considered as the approximate speed value.
3.6.6 Tracers
The use of tracers is a procedure similar to the preceding method. Sulphur hexafluoride (SF 6 ) is used as the tracer gas because of its low toxicity and because it is easy
to detect at low concentrations. The steady release method is as follows: a constant
flow rate of tracer (q) is injected into an airflow (Q), and at a given distance from the
emission point (L m ) and at a given time (t m ) the measurement
4 of the concentration
(c) is made, as shown in Fig. 3.14 (Higgins and Shuttleworth 1958; Thimons and
Kissell 1974).
q
v, Q
L m
Measurement point
c
Fig. 3.14 System of measuring flow rate in a mine gallery by the dilution method
4 This conditions aim for thorough mixing and equilibrium.