Page 108 - Advanced Mine Ventilation

Mechanical and Natural Ventilation 89

6.7 Natural Mine Ventilation

An underground coal mine can have a natural circulation of air in it without any fans.
This happens because the air in the mine extracts heat from the mine workings and gets
lower in density, creating a natural flow of air. This is called “natural ventilation.”
Usually, it is not strong enough to allay the use of mechanical mine fans, but it
does assist and hence it is worth our study.
Consider a mine ventilated naturally without fans, and assume that the downcast
and upcast shafts are of equal depth and the shaft tops are at the same level on surface
as shown in Fig. 6.6.
The points 1, 2, 3, and 4 are the top and bottom of downcast shaft (intake air) and the
bottom and top of the upcast shaft (return air), respectively. The temperature, pressure,
2
3
and density of air are denoted by t in degree Fahrenheit, p, in lb/ft , and w in lb/ft .
From Eq. (1.5),
1:3258 ðB 0:378 'e'Þ
W ¼
460 þ t

Figure 6.6 Natural ventilation.