3.6 Air Speed Measurement
75
v 1
v 2
v 3
v 4
w
H
H/3
H/2
150 mm
150 mm
150 mm
a)
b)
c)
Fig. 3.11 Breaking down of a mine gallery to calculate average air speed. a Breaking down into
squares of approximately the same area. Measurements are taken in the middle point of each square;
b Measurements with a single homothetic curve; c Determination based on local measurements
Determinations that are more precise can be obtained by means of the polar
method of the homothetic curves, as depicted in Fig. 3.12 (Simode 1962).
According to this procedure points A, B, C and D represent a distance to the wall
of:
• A: 1/10 half the width of the gallery,
• B: 1/4 of half the width of the gallery,
• C: 1/2 of half the width of the gallery, and
• D: Centre of the gallery.
To calculate the speed in accordance with the method above Eq. 3.8 is employed:
Fig. 3.12 Determination of
average airflow speed in a
mine gallery by the polar
method of the homothetic
curves