78
3 Flow Rates and Pressure Measurements
that the substances it contains can be expelled by squeezing a flexible bulb (smokecloud generator). These substances react with the humidity in the air, the reaction
generating a cloud of smoke that moves with the airflow, filling the entire section of
the gallery.
The speed of the current can be determined by measuring the time it takes
the smoke to move between any two points. The average cross section is usually
calculated as an arithmetic mean of sections at a separation distance of 2 m.
Exercise 3.4 The air moves in a westerly to easterly direction along a mine gallery.
A smoke tube is broken in section K, and is moved around quadrants, i, ii, iii, iv.
The sections A 1 , A 2 and A 3 were measured as being 9.8, 8.9 and 9.5 m
2 , respectively.
The average time the smoke took to get from each quadrant in K to its counterpart
in S, a distance of 7.5 m away, is given in the table. Determine the best possible
approximation of the ventilation airflow rate in this gallery.
7.5 m
A1
A2
A3
iv
i
iii
ii
E
K
S
Quadrant
Time from K to S in each repetition (s)
1
2
3
4
I
10
9
9
10
II
11
11
10
10
III
9
9
10
9
IV
10
11
11
10
Solution
Quadrant
Time from K to S for each repetition (s)
1
2
3
4
Average
I
10
9
9
10
9.5
II
11
11
10
10
10.5
III
9
9
10
9
9.25
IV
10
11
11
10
10.5
Overall average
9.94