46
2 Environmental Conditions in the Mine
being. The temperature of a saturated atmosphere without air movement is what
causes the sensation of heat in most people. This temperature cannot be measured
directly. Instead, it must be obtained through graphs or mathematical equations. The
equations that are most commonly used in mining are Eqs. 2.1 and 2.2:
T e = 0.9 T w + 0.1 T d
(2.1)
or
T e = 0.7 T w + 0.3 T d − v
(2.2)
where
• T e : Equivalent temperature (°C),
• T w : Wet-bulb temperature (°C),
• T d : Dry-bulb temperature (°C), and
• v: Air velocity (m s
−1 ).
Absolute Humidity (AH)
Humidity is the mass of water vapour per air mass or volumen unit. If the air is
humid, then we speak about absolute humidity (kg of water vapour/m
3 of humid
air) or specific humidity (kg of water vapour/kg of humid air) depending on whether
mass or volume units are used for humid air. If the data refer to dry air (kg of water
vapour/kg of dry air), it is termed mixing ratio or humidity ratio.
9
Maximum Humidity (Saturation Humidity) (SH)
Saturation humidity is the maximum amount of water vapour that a volume of air
can contain at a given temperature. It is usually measured in g m
−3 .
Relative Humidity (RH)
Relative humidity is the ratio between the mass of water vapour in the air and the
maximum possible mass of water vapour in the air at that temperature. In other
words, it is the relationship between the water vapour pressure in the air (P v ) and the
saturation pressure (maximum water vapour pressure) at the same temperature and
pressure (P s ) (Eq. 2.3):
RH(%) =
P v
P s
100
(2.3)
It can also be expressed in terms of mole fractions as the ratio between the mole
fraction of water vapour in the air with certain humidity and the mole fraction of
water vapour that saturates the sample at the same pressure and temperature.
9 There is a lot of confusion regarding specific humidity and mixing ratio because they offer similar
results, which has often encouraged people to use them interchangeably for many purpuses.
2 Environmental Conditions in the Mine
being. The temperature of a saturated atmosphere without air movement is what
causes the sensation of heat in most people. This temperature cannot be measured
directly. Instead, it must be obtained through graphs or mathematical equations. The
equations that are most commonly used in mining are Eqs. 2.1 and 2.2:
T e = 0.9 T w + 0.1 T d
(2.1)
or
T e = 0.7 T w + 0.3 T d − v
(2.2)
where
• T e : Equivalent temperature (°C),
• T w : Wet-bulb temperature (°C),
• T d : Dry-bulb temperature (°C), and
• v: Air velocity (m s
−1 ).
Absolute Humidity (AH)
Humidity is the mass of water vapour per air mass or volumen unit. If the air is
humid, then we speak about absolute humidity (kg of water vapour/m
3 of humid
air) or specific humidity (kg of water vapour/kg of humid air) depending on whether
mass or volume units are used for humid air. If the data refer to dry air (kg of water
vapour/kg of dry air), it is termed mixing ratio or humidity ratio.
9
Maximum Humidity (Saturation Humidity) (SH)
Saturation humidity is the maximum amount of water vapour that a volume of air
can contain at a given temperature. It is usually measured in g m
−3 .
Relative Humidity (RH)
Relative humidity is the ratio between the mass of water vapour in the air and the
maximum possible mass of water vapour in the air at that temperature. In other
words, it is the relationship between the water vapour pressure in the air (P v ) and the
saturation pressure (maximum water vapour pressure) at the same temperature and
pressure (P s ) (Eq. 2.3):
RH(%) =
P v
P s
100
(2.3)
It can also be expressed in terms of mole fractions as the ratio between the mole
fraction of water vapour in the air with certain humidity and the mole fraction of
water vapour that saturates the sample at the same pressure and temperature.
9 There is a lot of confusion regarding specific humidity and mixing ratio because they offer similar
results, which has often encouraged people to use them interchangeably for many purpuses.