Page 42 - Advanced Mine Ventilation

Air Flow in Mine Airways 25

2. For the tunnel:

30 10 10 56 3000 ð200; 000Þ 2
H ¼ ¼ 0:948 in.
3
5:2 ð160Þ
3. Total pressure loss ¼ 2(0.312) þ 0.948 ¼ 1.572 in.

2.5 Air Flow in Ventilation Duct/Pipes

In the development section of a coal mine, an auxiliary fan with ventilation ducts are
used to improve the air supply to the working face. It dilutes gases better and gets dusty
air out of the working faces. A small fan is used to create the air flow. Table 2.5 shows
typical friction factors for different types of ducts.
The length of tubing in use generally does not exceed 100 feet in the mines, but it
can be longer for tunnels.
An example:
Calculate the pressure loss in a 500-ft-long steel duct of 2 ft. diameter required to
deliver 15,000 CFM air at the working face.
Assume
K ¼ 20 2
Pd 2
Area ¼ ¼ 3:14 ft
4
Perimeter ¼ P d ¼ 3.14 2 ¼ 6.28 ft
Q ¼ 15,000 CFM
L ¼ 500 ft.
Using Eq. (2.5)

20 10 10 6:28 500 ð15; 000Þ 2
HðW.G.Þ¼ ¼ 8:78 inches of water.
3
5:2 ð3:14Þ

2.6 Shock Losses in Mine Airways

As the air current changes direction, it creates a shock loss that increases the total pres-
sure loss for the ventilation network. The following are three ways to determine and
compensate for this loss:
Table 2.5 Typical Friction Factors for Different Types of Ducts

Type of Duct Friction Factor, K (New) (Average for Used Ducts
Steel or fiberglass 15 21
Canvass or plastic 20 25
Spiral canvass 23 28