Page 44 - Advanced Mine Ventilation

Air Flow in Mine Airways 27

Airway height ¼ d
Radius ratio ¼ m ¼ r/b
Aspect ratio ¼ a ¼ d/b
McElroy [8] gives an estimate for K L as

2
0:25 q
K L ¼ 2 0.5 (2.15)
m a 90
For a sharp bend, where r ¼ b/2

2
0:60 q
K L ¼ 0.5 (2.16)
ma 90
Appendix A shows other equations for different situations.

2.6.2 Shock Losses by Increasing Friction Factor
McElroy [8] advocates compensating for shock loss by increasing the friction factor
for the airway. Only limited data are available in this area. It is, therefore, not
commonly used.

2.6.3 Equivalent Length For Shock Losses
The most popular method for compensating for shock losses is to increase the length of
an airway by a calculated amount.
K L V 2
Pressure loss due to shock, H S ¼
2g
In mining units:
2 !
WV
H S ¼ K L
2
ð1; 098Þ
Equating H S to an equivalent length of L e we can write:

WV 2 KL e V 2
K L ¼
2
ð1; 098Þ 5:2R H
or

3; 235 R H K L
L e ¼ 10 (2.17)
10 K
Some calculated equivalent lengths are shown in Table 2.6.