170
5 Main Ventilation
T mu = (14.5 + 273) K = 287.5 K
These values can be substituted in Eq. 5.4:
P n = P 2 − P 3 = 0.03415
N K
J
h P m
1
T md
−
1
T mu
An airflow direction can easily be assigned considering that the air outside
is colder than inside the shafts. In such a case, the air enters the system
through the short shaft, then it is more appropriate to assume a height of 600 m
corresponding to the depth of the long shaft. However, it is a common practice
to use the mean values, therefore:
P n = 0.03415
N K
J
400 + 600
2
m · 108,475 Pa ·
1
278.5 K
−
1
287.5 K
P n = 208.2 Pa
Checking by the approximated formula:
P n = 0.044
Pa
C m
(T mu − T md )
h d + h u
2
We have:
P n = 0.044
Pa
K m
(287.5 − 278.5) K
600 + 400
2
m = 198 Pa
(b) As a conclusion, it can be deduced that the NVP in this mine is low. This is due
to the rapid increase in temperature throughout the long shaft, the low increase
in temperature towards the outlet in the short shaft as well as the short effective
height of the latter. This first approach points to an unstable equilibrium which
makes inversions frequent.
5
As the direction of the airflow is given by the increase of temperatures in the circuit
(from colder to hotter), there would be no discussion about its direction. However,
there are grounds for suspecting that some measurements could be incorrect. Thus,
temperatures at the bottom of the long shaft and at the mouth of the short shaft could
be lower and higher respectively than those supplied by the problem statement.
5 In cold and shallow mines (<400 m), natural ventilation is unreliable. In other words, it does not
guarantee that there is an adequate NVP, nor that it takes place in the required direction.
5 Main Ventilation
T mu = (14.5 + 273) K = 287.5 K
These values can be substituted in Eq. 5.4:
P n = P 2 − P 3 = 0.03415
N K
J
h P m
1
T md
−
1
T mu
An airflow direction can easily be assigned considering that the air outside
is colder than inside the shafts. In such a case, the air enters the system
through the short shaft, then it is more appropriate to assume a height of 600 m
corresponding to the depth of the long shaft. However, it is a common practice
to use the mean values, therefore:
P n = 0.03415
N K
J
400 + 600
2
m · 108,475 Pa ·
1
278.5 K
−
1
287.5 K
P n = 208.2 Pa
Checking by the approximated formula:
P n = 0.044
Pa
C m
(T mu − T md )
h d + h u
2
We have:
P n = 0.044
Pa
K m
(287.5 − 278.5) K
600 + 400
2
m = 198 Pa
(b) As a conclusion, it can be deduced that the NVP in this mine is low. This is due
to the rapid increase in temperature throughout the long shaft, the low increase
in temperature towards the outlet in the short shaft as well as the short effective
height of the latter. This first approach points to an unstable equilibrium which
makes inversions frequent.
5
As the direction of the airflow is given by the increase of temperatures in the circuit
(from colder to hotter), there would be no discussion about its direction. However,
there are grounds for suspecting that some measurements could be incorrect. Thus,
temperatures at the bottom of the long shaft and at the mouth of the short shaft could
be lower and higher respectively than those supplied by the problem statement.
5 In cold and shallow mines (<400 m), natural ventilation is unreliable. In other words, it does not
guarantee that there is an adequate NVP, nor that it takes place in the required direction.