2.6 Heat Inside Mines
57
Navarro and Singh (2011) propose an increase of 0.98 °C per 100 m of descent,
a figure that also takes into account the possible inclination of the shaft by means of
Eq. 2.15:
t a = T 2 − T 1 = 0.0098 L sen(α)
(2.15)
where
• t a : Temperature increase with depth (°C),
• α: Angle between the shaft and the horizontal (sexagesimal degrees),
• L: Shaft depth (m),
• T 1 : Surface temperature (°C), and
• T 2 : Temperature at the bottom of the shaft (°C).
2.6.4 Electromechanical Equipment
Several electromechanical machines are commonly used in mining—for example,
conveyor belts, armoured conveyors, pumps, locomotives and fans. These machines
only convert some of the energy that they receive into useful work; most of it is
dissipated as heat.
In the case of diesel equipment, heat losses cluster around the exhaust gas system
(about 1/3), the engine’s cooling system (about 1/3), and friction losses (5–10%).
The rest (<1/3) is useful work (Mollenhauer and Tschöke 2010). Some authors—
e.g., Ganesan (2012)—give a figure of 80% for heat losses meaning that only 20%
of energy is available for useful work.
However, this useful work will ultimately degrade to heat unless it is used to
increase the potential energy of a body. Therefore, if a machine’s activity does not
transform some of its input energy into mass elevation, all of it ends up being dissipated as heat (e.g. horizontal drilling). Thus, lifting machinery such as pumps or
conveyor belts do not dissipate all their input energy in the form of heat, as a part
of it will be stored as potential energy. In addition, combustion not only generates
gases but also water vapour, meaning that only part of the heat generated will be felt
as a temperature change in the air (sensible heat), while another part will be stored
as latent heat. This latent heat is recovered when the water vapor condenses in the
cooling towers of the mine.
15
Heat release can be estimated based on fuel consumption and its calorific value
(Eq. 2.16) (Calizaya and Marks 2011):
q = C PC E
(2.16)
15 The Lower Calorific Value (LCV ) of a fuel does not include the latent heat used in water
vaporization. This heat is considered in the calculation of Higher Calorific Value.
57
Navarro and Singh (2011) propose an increase of 0.98 °C per 100 m of descent,
a figure that also takes into account the possible inclination of the shaft by means of
Eq. 2.15:
t a = T 2 − T 1 = 0.0098 L sen(α)
(2.15)
where
• t a : Temperature increase with depth (°C),
• α: Angle between the shaft and the horizontal (sexagesimal degrees),
• L: Shaft depth (m),
• T 1 : Surface temperature (°C), and
• T 2 : Temperature at the bottom of the shaft (°C).
2.6.4 Electromechanical Equipment
Several electromechanical machines are commonly used in mining—for example,
conveyor belts, armoured conveyors, pumps, locomotives and fans. These machines
only convert some of the energy that they receive into useful work; most of it is
dissipated as heat.
In the case of diesel equipment, heat losses cluster around the exhaust gas system
(about 1/3), the engine’s cooling system (about 1/3), and friction losses (5–10%).
The rest (<1/3) is useful work (Mollenhauer and Tschöke 2010). Some authors—
e.g., Ganesan (2012)—give a figure of 80% for heat losses meaning that only 20%
of energy is available for useful work.
However, this useful work will ultimately degrade to heat unless it is used to
increase the potential energy of a body. Therefore, if a machine’s activity does not
transform some of its input energy into mass elevation, all of it ends up being dissipated as heat (e.g. horizontal drilling). Thus, lifting machinery such as pumps or
conveyor belts do not dissipate all their input energy in the form of heat, as a part
of it will be stored as potential energy. In addition, combustion not only generates
gases but also water vapour, meaning that only part of the heat generated will be felt
as a temperature change in the air (sensible heat), while another part will be stored
as latent heat. This latent heat is recovered when the water vapor condenses in the
cooling towers of the mine.
15
Heat release can be estimated based on fuel consumption and its calorific value
(Eq. 2.16) (Calizaya and Marks 2011):
q = C PC E
(2.16)
15 The Lower Calorific Value (LCV ) of a fuel does not include the latent heat used in water
vaporization. This heat is considered in the calculation of Higher Calorific Value.