5.3 Natural Ventilation
169
ΔPA
ΔP B
ΔP c
ΔP D
ΔP E
ΔP F
Answer
As can be seen, the NVP is the pressure difference at the bottom of the downcast and
upcast shafts. In this case, both come together at the same depth, thus:
P n = A + B + C + D − ( E + F )
As indicated in the previous question, air can circulate in different directions
depending on the difference in temperature between inside and outside the mine,
thus changing the sign of NVP.
Exercise 5.2 The ventilation of a mine takes place through two vertical shafts of
600 and 400 m. The conditions in them are monitored automatically, recording
average temperatures of 2 °C in the mouth and 9 °C at the bottom for the long shaft,
and 17 °C at the mouth and 12 °C at the bottom for the short shaft. It is also known
that the pressure at the average depth of both shafts is 108.475 kPa. You are asked to:
(a) Estimate the NVP of the system.
(b) Comment on the direction of the airflow and the temperature measurements
provided in the problem statement.
Solution
(a) Firstly, average pressure must be estimated for the midpoint of the air columns
in the shafts. This value could be slightly higher than the atmospheric pressure.
As this value is supplied, 108.475 kPa is used directly.
Secondly, the average temperatures of the downcast and upcast shaft are
calculated:
T md = (5.5 + 273) K = 278.5 K
169
ΔPA
ΔP B
ΔP c
ΔP D
ΔP E
ΔP F
Answer
As can be seen, the NVP is the pressure difference at the bottom of the downcast and
upcast shafts. In this case, both come together at the same depth, thus:
P n = A + B + C + D − ( E + F )
As indicated in the previous question, air can circulate in different directions
depending on the difference in temperature between inside and outside the mine,
thus changing the sign of NVP.
Exercise 5.2 The ventilation of a mine takes place through two vertical shafts of
600 and 400 m. The conditions in them are monitored automatically, recording
average temperatures of 2 °C in the mouth and 9 °C at the bottom for the long shaft,
and 17 °C at the mouth and 12 °C at the bottom for the short shaft. It is also known
that the pressure at the average depth of both shafts is 108.475 kPa. You are asked to:
(a) Estimate the NVP of the system.
(b) Comment on the direction of the airflow and the temperature measurements
provided in the problem statement.
Solution
(a) Firstly, average pressure must be estimated for the midpoint of the air columns
in the shafts. This value could be slightly higher than the atmospheric pressure.
As this value is supplied, 108.475 kPa is used directly.
Secondly, the average temperatures of the downcast and upcast shaft are
calculated:
T md = (5.5 + 273) K = 278.5 K