PME 461
Mine Ventilation and Environmental Engineering
Lecture#06 & 07
Chapter #08
Natural VeNtilatioN
Conducted by:
Mohammad Mamun Ur Rashid
Assistant Professor
Department of Petroleum and Mining Engineering (PME)
Chittagong University of Engineering and Technology (CUET)
mamunpme@cuet.ac.bd
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Quantification of Natural Ventilation
There are two approaches to quantify natural ventilation effects.
1. A simple and, in most cases, a satisfactory approach is to view the cause of natural
ventilation as the density difference between two columns of air of equal height, the
heavier intake air column sinking and the lighter air column rising, as explained before,
and then to calculate the natural ventilation pressure (NVP).
2. The thermodynamic approach, on the other hand, explicitly considers the heat energy
exchange in the mine, and applies the equations developed in Section 5.8 to calculate the
natural ventilation energy (NVE). In all cases, it is necessary to conduct a pressure,
quantity, or temperature survey around the mine circuit to obtain the data for estimating
natural ventilation (NVP or NVE).
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Analysis by Density-Difference-Based Methods
There are several methods to calculate the natural ventilation pressure that are based on the
difference in air specific weight between two air columns of equal height. Using available data,
the specific weight of air can be calculated using Fig. 2.3 or the procedures outlined in Section
6.3.
Method 1:
Consider a column of dry air having a unit cross-sectional area A and a height L, and
assume an incremental height dL.
Let the pressure on the base of this increment be dp. Then the incremental force exerted is
A dp, which is equal to the weight (wA dL) of the incremental volume A dL, where w is
specific weight of the air.
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Analysis by Density-Difference-Based Methods (Cont’d)
Method 1 (Cont’d):
Noting that specific weight for dry air is (p/RT), from Eq. 1.6, the following relationship is
evident:
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Analysis by Density-Difference-Based Methods (Cont’d)
Method 1 (Cont’d):
in which p1 and p2are absolute pressures at the top and bottom of the column, respectively,
and 𝑇 is the average absolute temperature between the top and bottom of the column. To
calculate the natural ventilation pressure, Eq. 8.1 is solved for each column of air. The
pressure difference at the bottom of the two columns is the natural ventilation head Hn in
in. water:
where p2 and p3 are the absolute pressures at the bottom of the two columns expressed here
in in. of mercury (Pa). Omission of the effect of water vapor introduces some error in this
method.
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Analysis by Density-Difference-Based Methods (Cont’d)
Method 2:
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Analysis by Density-Difference-Based Methods (Cont’d)
Method 3: On the basis of the difference in dry-bulb temperatures, the natural pressure in in.
water can also be calculated approximately as (Rees, 1950)
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Analysis by Density-Difference-Based Methods (Cont’d)
Method 4:
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Analysis by Density-Difference-Based Methods (Cont’d)
Method 5:
A rough rule of thumb can be used to estimate the natural pressure (McElroy, 1935). At sea
level, the head is 0.03 in. water per 10°F difference in average temperature of the two
columns per 100 ft difference in elevation of the surface and the mine workings (7.5 Pa per
5.5°C difference per 30.5 m difference), or
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Analysis by Density-Difference-Based Methods (Cont’d)
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Analysis by Density-Difference-Based Methods (Cont’d)
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Analysis by Density-Difference-Based Methods (Cont’d)
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Analysis by Density-Difference-Based Methods (Cont’d)
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Analysis by Density-Difference-Based Methods (Cont’d)
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