Page 41 - Advanced Mine Ventilation

24 Advanced Mine Ventilation

Table 2.3 Friction Factors in British Coal Mines

Friction Factor,
Type of Airway Condition of Airway K (Ave)
Shafts Brick lined 29
Arched Straight to slightly waved 28
Smooth lined circular/semi Concrete-lined 24
circular arch
Steel-arch girdered Timber-lined 62
Unlined airways Uniform to irregular cross section 20e55
Timbered airways Uniform to irregular 48e81

Table 2.4 Values of K for Rectangular Airways (Coal)

Condition of Airway Value of K
Smooth, concrete-lined 20
Steel girders on brick walls 50
Unlined, straight airways 65
Unlined, rough airways 85
Wood beams on timber legs 100

as expected to 200e350. The corresponding values of l for K values of 20 and 200 are
0.0246e0.246, respectively, making the mine airways extremely rough pipes.
A ventilation engineer must use experience as a guide to select proper K values
when planning the total pressure requirement for mines. There is a tendency to gener-
ally underestimate the pressure requirements.
An example:
Two vertical shafts of 1000 ft depth and 20 ft diameter are connected by a 3000 ft
long rectangular tunnel of a cross section of 20 8 ft. Calculate the pressure loss if
200,000 CFM air is flowing from one shaft to the other.
Assume K for shaft as 20 and K for the tunnel as 30.
1. For shaft:
L ¼ 1000 ft
P ¼ PD ¼ 3.14 20 ¼ 62.8 ft
3
Q ¼ 200,000 ft /min
P D 2 2
A ¼ ¼ 314 ft
4
20 10 10 62:8 1000ð200; 000Þ 2
Now calculate H ¼ ¼ 0:312 in.
3
5:2 ð314Þ