5.3 Natural Ventilation
173
Ve (m
3 kg
-1 )
P (N m
-2 )
A
B
C
D
NVE
B
A
D
C
Downcast
shaft
Upcast
shaft
Stopes
Pn (NVP)
Fig. 5.4 Pressure vs. specific volumen (P–V e ) diagram applied to the simplified schematic of a
mine
with the walls of the shafts, the adiabatics AB and CD are formed. In the same way,
the isobar corresponding to the external pressure DA is observed. The highest heat
incorporation to the air mass (BC curve) takes place in mining stopes. However, in
well developed mines it is possible to assume that the heat flow to the air mass is
zero, giving rise to an adiabatic process, which is also isothermal (T B = T C ).
The Natural Ventilation Pressure (NVP, P n ), from a static point of view, is the
PB-PC difference. The ABCD area corresponds to the NVE (Fig. 5.4, right). If the
NVE is multiplied by the density of the air (ρ), the work per unit volume is obtained,
or in other words, the NVP (Eq. 5.9):
P n = NVE ρ
(5.9)
where
• NVE: Natural Ventilation Energy (J kg
−1 ), and
• ρ: Air Density (kg m
−3 ).
The determination of the pressure at each point can be made by means of an
aneroid barometer, while the specific volume can be approximated by the expression
(Eq. 5.10):
V e =
287.1 T
1000(P − P v )
(5.10)
where
• T: Dry-bulb temperature (K),
• P: Barometric pressure (kPa), and
• P v : Vapour pressure of water (kPa).
173
Ve (m
3 kg
-1 )
P (N m
-2 )
A
B
C
D
NVE
B
A
D
C
Downcast
shaft
Upcast
shaft
Stopes
Pn (NVP)
Fig. 5.4 Pressure vs. specific volumen (P–V e ) diagram applied to the simplified schematic of a
mine
with the walls of the shafts, the adiabatics AB and CD are formed. In the same way,
the isobar corresponding to the external pressure DA is observed. The highest heat
incorporation to the air mass (BC curve) takes place in mining stopes. However, in
well developed mines it is possible to assume that the heat flow to the air mass is
zero, giving rise to an adiabatic process, which is also isothermal (T B = T C ).
The Natural Ventilation Pressure (NVP, P n ), from a static point of view, is the
PB-PC difference. The ABCD area corresponds to the NVE (Fig. 5.4, right). If the
NVE is multiplied by the density of the air (ρ), the work per unit volume is obtained,
or in other words, the NVP (Eq. 5.9):
P n = NVE ρ
(5.9)
where
• NVE: Natural Ventilation Energy (J kg
−1 ), and
• ρ: Air Density (kg m
−3 ).
The determination of the pressure at each point can be made by means of an
aneroid barometer, while the specific volume can be approximated by the expression
(Eq. 5.10):
V e =
287.1 T
1000(P − P v )
(5.10)
where
• T: Dry-bulb temperature (K),
• P: Barometric pressure (kPa), and
• P v : Vapour pressure of water (kPa).