1.

Literature Review

This literature review focuses on researching the available knowledge of the

underground thermal environment and reviewing the challenges being experienced to
develop a solution to reduce heat in the mine.

1.1 Ventilation theory

Ventilation theory refers to the principles and concepts used to determine the
movement of air in the underground mine to provide fresh air, dilution of toxic fumes,
gas, and reduce heat in the mine. It discusses the various factors that affect the
movement of air in the mine, which are differences in air pressure and opposition of
flow due to friction and shock losses, among other factors.

1.2 Principles of ventilation theory

Atkinson’s resistance is used to determine the frictional losses of air as it travels

through the underground passageways of irregular shapes and sizes. The resistance of
the passageways plays an important role in determining the amount of energy needed
to overcome that resistance. Resistance of the mine is a major factor used to
determine the ventilation efficiency of the mine. Proper calculations of this resistance
ensure adequate air flows to needed areas.

The Atkinson equation was further improved by Chezy and Darcy to produce the
equation

per u2
P=fL P 1
A 2

Were
P = pressure drop Pa
F= frictional coefficient of the surrounding pipe
L= length of pipe
Per is the perimeter of pipe
A= cross sectional area of pipe
p= density of fluid
u= velocity of fluid

In turbulent flows Atkinson assumes a constant frictional factor k by assuming the air
density remains constant to give

fp
k= 2
2
By substituting 2 in 1 we get

per 2
P=KL u 3
A

The equation can be expressed in terms of airflow

Where Q =UA 4

per 2
Thus P=KL 3
Q 5
A

In an airway where the cross-sectional area A is known and the length is also known,
the friction only depends on the conditions of the airway surface without taking into
account the effects of density. When all these factors are known, R can be calculated
as a constant by

per
R=KL 3 6
A
By substituting 6 in 5

We get P=R Q2
Were
P = pressure drop
R = Atkinson resistance
Q = air quantity or flow rate

1.3Shock losses
In a mine ventilation network, energy is lost due to frictional pressure drop and shock
losses.
Shock losses are due to the change in direction of the flow of air. High shock losses
are experienced when air moves from the shaft to the mine passageway, at branches,
junctions, obstructions, and while entering and leaving the mine
The pressure loss due to shock is given by

Xp
Pshock = Rs 2
2A

P
But P=R Q2 hence R = 2
Q
And Q = u A2

Xp
Thus Rshock=Rs 2
2A

Mine head loses

Air is a fluid flowing in the underground mine and hence it encounters head loses
Hl = Hf + H x
H l is the total head
H f is the frictional loss
H x is the shock losses

Frictional loss calculations

The Darcy Weisbach equation is used to calculate frictional head loses

2
H f = fL v
2 gD
Where H f = frictional head loss (m)
f is frictional factor (dimensionless)
L is the length of air pathway (m)
v is fluid velocity (m/s)
g is acceleration due to gravity (m/s2)
D is the hydraulic diameter(m)

Determination of frictional factor values

Charts for friction values

1.2.1 Shock losses calculation

2
Hx = k v
2g
Where k is shock loss coefficient (dimensionless)
v is the fluid velocity (m/s)
g is acceleration due to gravity (m/s2)

Determination of shock losses directly

(McElroy,1935) calculate the shock loss measured in inches/mm , where Pa is
calculated from head( H)
H x = XH v
Where X is a dimensionless shock loss factor
The underground thermal environment

Major heat sources and continuous monitoring

Strata heat
This heat comes from the surrounding rock surface in the underground mine as the
rock interacts with the ventilation air. The heat from the strata is greatly influenced by
the geothermal gradient as temperatures of rock strata increase with depth. Air
temperature along the main airway turns to fluctuate due to surface climatic
conditions, while the temperature at development faces turns to remain constant as the
mine establishes thermal equilibrium between heat from strata and the ventilation air.

Auto compression
This is a result of the air temperature increase as the air travels at certain depths into
the mine. The heat increase is due to some of the potential energy in the air being
converted to enthalpy, and thus increases air pressure, the enthalpy of the air, and
consequently, the air temperature increases. As the depth of the mine increases, auto
compression increases, and thus there is a higher increase in air temperature

Mining equipment

Heat due to mine equipment is associated with highly mechanized mines. Heat from
machinery is due to the machine's low efficiency and incomplete combustion of
diesel-powered machinery. The increase in heat due to mine machinery can be
measured by calculating the machine energy losses using the machine's rated
efficiency. Sometimes continuous monitoring tools are used to compare the increase
in temperature during the working hours of the machine against when that machine is
off in a particular area of the mine.

The monitoring plan.

Continuous monitoring of humidity and air temperature in the mine.
To assess the underground thermal environment, various continuous monitoring tools
were installed along the mine shaft from the surface to the bottom and along airway
passages. The focus of the monitoring plan was mainly the development ends where
high temperatures are being experienced. The purpose of continuous monitoring was
to gather adequate data for developing an accurate ventilation model, determine the
heat load and temperature changes due to geothermal gradient and auto compression.

Climatic data collection

The continuous monitoring tools were set to record data at regular intervals to
determine the changes in these parameters with time. To verify the accuracy of the
continuous monitoring tools hand handheld spot measuring tools were used to
monitor the data in the same area, and the obtained data were compared.

Table 1. Climatic data collection plan for the primary ventilation system
Locations, Purpose, Monitoring plan
Zone 1: At the top and bottom of the intake and exhaust shaft Zone 2: From the
bottom of the intake shaft to the lowest production area Zone 3: From the lowest
production area to the bottom of the exhaust shaft
1. To quantify the heat load from auto compression, strata heat, groundwater and
geothermal gradient 2. Develop and calibrate a dynamic ventilation-thermal-humidity
model 3. To identify and quantify the thermal damping effect 4. To understand the
transient heat exchange between fresh air and the surrounding environment
Twelve ACR units throughout the primary systems in the direction air flow to record
climatic data every minute for two weeks Spot measurements of climatic parameters
and surface rock temperature to validate the continuous measurements Ventilation
surveys to measure the airflow and pressure at the locations of ACRs
The underground thermal environment

Introduction
Thermal hazard can affect the health and safety of underground workers and at the
same time reduce productivity due to heat-related disease and reduced working
efficiency. When a worker is exposed to high temperatures for a short period of time,
the core body temperature of the worker urns to increase and this results in heat-
related illnesses. Heat exposure can cause heat accumulation in the body, which can
result in fatal injuries over time. Heat stroke and heat exhaustion are the most
common hazards experienced by workers in a hot environment. Heat stroke can be a
fatal incident, which can cause permanent problems to the heat-regulating mechanism,
and in some instances, death can occur

There are many methods of accessing the underground thermal environment and
determining the thermal comfort for the mine workers. To access the underground
thermal environment, a heat index must be used to determine the combination of
parameters that can provide a comfortable working environment. With the large
number of heat stress index, it is difficult to find an appropriate heat stress index as
there is no one heat stress index that takes into account all the variables that provide
thermal comfort. Furthermore, heat stress index that take into account most of the
environmental parameters into account are complex and time-consuming to use in real
time at any particular mine.
An environment can be said to achieve thermal comfort when 80% or more of the
workers experience thermal comfort. For hot and humid environment comfort indices,
which are used, include wet and dry bulb temperatures, WGBT, air humidity, body
temperature, and effective temperature. The purpose of measuring the underground
thermal environment is to determine the optimal working conditions for the
underground workers. To achieve this, a trial-and-error method must be used to
identify how the human body responds to certain parameters when doing work. The
problem, however, is to measure each individual's body temperature and work rate,
which can be very costly and tiresome. And the thermal comfort of individuals is very
different due to psychological and physiological factors. For a worker to work in a hot
environment, depending on the degree of heat, the workers' exposure time must be
limited. The exposure time is directly proportional to the maximum dehydration
tolerance of the human body in such environments.

The underground worker

The human body is capable of regulating body temperature to the environment to

keep the internal body temperature relatively constant. When the heat is too much, the
body loses its ability to reject heat to the environment. Excess heat in the human body
increases the chances of heat stress and related illnesses. Considering steady states,
the heat storage (S) is often considered as zero to assure comfort for a worker. The
thermal interaction of the human body with the
environment can be written as follows (ISO 7933, 2005):

S = M - (C + R + B + E + K + W) (W/m2)

The body can transfer heat to the surrounding environment to achieve thermal
equilibrium through convection, radiation, evaporation cooling, and respiratory heat
exchange. The recommended working temperature (Donoghue, 2004) when doing
work at high metabolic rates is 29 degrees Celsius. Beyond this temperature, there is a
high risk of heat exhaustion and heat stress. Thermal comfort can be achieved at
higher temperatures provided the humidity is very low and the wind speed is high.

Methods of controlling heat

There are many methods that can be used to control heat, depending on the size of the
mine and the associated heat therein. Ventilation amounts to about 60% of the
underground cost of operating the mine. To reduce the heat in the mine, it is of
paramount importance to identify the sources of heat to come up with a suitable
method of reducing heat.

Modelling of the underground thermal environment

Continuous monitoring data is used to create a suitable model for the underground
thermal environment. Underground thermal models help to understand the current
underground thermal conditions and can be used to predict future ventilation needs as
the mine is always expanding. Modelling also provides an interface for trial mine
ventilation designs and offers trial and error methods of ventilation without the need
to purchase ventilation equipment, which is very costly.