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Examination for the Bachelor of Engineering
(Civil, Environmental & Mining Engineering)
Semester 2 , 2010
Course ID:
Mine Ventilation 3068
(Undergraduate)
C&ENVENG
Official Reading Time:
Writing Time:
Total Duration:
10 mins
120 mins
130 mins
Parts
A
B
Questions
Answer all questions
Answer one questions
Time
90 mins (Recommended)
30 mins (Recommended)
Marks
30 marks
10 marks
40 Total
Instructions for Candidates






This is a closed-book examination.
The examination has 2 sections: Candidates must answer ALL three ( 3) questions from Part A .
Candidates must answer ONLY ONE (1) question from Part B .
All questions are of equal value.
Examination materials must not be removed from the examination room.
Show all calculations and assumptions.
If you believe that a parameter or an important piece of information has been inadvertently omitted by
the examiner, assume a suitable value, clearly stating it, and continue with the solution.
Permitted Materials



The use of calculators is permitted, this equipment to be supplied by the candidate. No pre-recorded
material nor calculator instruction book is permitted, and calculators with remote communication links
will be barred from the examination room.
Graph paper will be provided.
Books and notes MAY NOT be used.
DO NOT COMMENCE WRITING UNTIL INSTRUCTED TO DO SO
SECTION A
ANSWER ALL THREE (3) QUESTIONS FROM THIS SECTION
Question 1
Total 10 Marks
A three heading maingate circuit in a coal mine has the layout depicted in the diagram below. The
drawing is not to scale. The longwall blocks (i.e. E to F) are 3km long, and the longwall face (i.e. F to H) is
400m across. Cut throughs, spaced every 100m between mains, and stoppings are not shown.
Goaf
20 m3/s
55 m3/s
(To bleeder
fan)
Tailgates
25 m3/s
To
upcast
shaft
718 Pa
100 m3/s
A survey of the mine gives resistance values as follows:
Travel roads, main return, and tailgate:
Belt road:
Longwall Face:
R100 = 0.005Ns2/m8 (per 100 m)
k = 0.019Ns2/m4
R100 = 0.020Ns2/m8 (per 100 m)
The pressure drop across the maingate overcasts (i.e. E to G) is 718Pa
Page 2 of 14
Required ventilation flow rates are given on the diagram above:
Maingate roads beyond face (into Goaf and then leaking to bleeder fan):
Longwall Face:
Maingate conveyor belt:
20m3/s
55m3/s
25m3/s
For the calculations below, ignore the length of goaf already mined. Ignore any leakage between inlet and
outlet airways. Assume a density of 1.2 kg/m3.
It may help you to sketch a resolved network showing the inlet and outlet airways.
a) Calculate the resistance of a single 3000m travel road
[1 mark]
b) Calculate the resistance of the 3000m conveyor belt road; the road has a 5m x 3 m high profile.
[1 mark]
c) Calculate the resistance of the combined fresh air inlets E to F.
[1 mark]
d) Calculate the combined resistance of the longwall & return airways (F-H-I)
[1 mark]
e) Calculate the frictional pressure drop across the regulator, R.
[1 mark]
f) Calculate the pressure drops throughout the circuit, and fill them in on the table
below. Ignore any flow through the overcasts
[2 marks]
Airway
Flow Rate (m3/s)
E–F
100
F – H (longwall)
55
Pressure drop (Pa)
H – I (tailgates)
E – G (overcasts)
F–G
ignore
ignore
25
Regulator in F - G
G–I
g) Briefly explain any three (3) of the following coal mining items and give their
purpose. Use labeled sketches where helpful.
i.
ii.
iii.
iv.
[3 marks]
Brattice
Overcasts
Coffin Seal
Limiting intake velocitie
Page 3 of 14
Question 2
Total 10 Marks
The temperatures of air at the beginning of a horizontal tunnel are 15C/20C. The AB section
of the tunnel is 500m with a cross section of 5m  3m and k=0.012Ns2/m4. The BC section of
the tunnel is 250m with a cross section of 4.5m  3.5m and k=0.015Ns2/m4. The total heat
added to the air in the AB section is 506kW. Assume 50m3/s air enters the tunnel at point A
and the pressure remains constant throughout the tunnel (P=100kPa). You can use the
attached Psychrometric chart for your entire analysis.
QA=50 m3/s
A
Heat=506 kW
B
WB=15C
DB=20C
a)
Determine the wet bulb temperature at point B?
C
[1 mark]
b) How much is the dry bulb temperature at point B if the moisture exchange throughout
the process from A to B is 63.3ml/s?
[1 mark]
c) Calculate the volumetric flow rate of humid air at point B?
[1 mark]
d) If a 320kW (rated power) loader enters section BC of the tunnel, determine the wet
bulb temperature at point C. Assume 33% diesel efficiency and continuous operation
at 38.18% load.
[1 mark]
e) Calculate the moisture exchange throughout the process from B to C if the dry bulb
temperature does not change from B to C (ie. DBC=DBB)
[1 mark]
f) Calculate the volumetric flow rate of humid air at point C?
[1 mark]
g) How much diesel fuel would the loader consume at this work rate over an 8 hour shift?
[1 mark]
Calorific value of diesel fuel is 45.6MJ/kg
Density of diesel fuel = 845 kg/m3
h) Using the approximation that 50kW of heat raises the temperature of 10m 3/s of air by
1C WB, what would the return side wet bulb temperature be if a second loader was to
work in the same section (ie. BC) with the same work rate, air quantity and intake
temperatures?
[1 mark]
i) Is it acceptable for a second loader to operate in this area using normal standards for
m3/s per kW (rated power) and resultant air temperatures, explain your answer?
[1 mark]
Page 4 of 14
j) Provide values for the following;
[1 mark]

Wet bulb temperature below which heat stress effects are negligible.

Wet bulb temperature above which work should not be undertaken.
Question 3
Total 10 Marks
A mine is using two fans in parallel to exhaust 429 m3/s at 2650 Pa from an upcast shaft. The
Natural Ventilation Pressure in the mine is 100 Pa. The combined characteristic curve (plotted
on the graph) for these two fans in parallel and at a speed of 700 rpm is as follows:
Quantity (m3/s)
275
380
475
600
Pressure (Pa)
3215
2880
2100
0
a) Calculate the mine resistance (Ns2/m8) from the observed operating point?
[1 mark]
b) Plot the mine resistance curve on the attached curve and identify the operating point.
[1 mark]
c) If the fan efficiency is 80% and the cost of power is $0.15 per kwh, what is the annual cost of
power for this operating duty.
[1 mark]
During maintenance one of the fans is turned off and the other one’s speed is increased
to 900rpm.
d) Calculate the characteristic curve for a single fan at 700rpm and plot on the graph?
[3 marks]
e) Calculate the characteristic curve for a single fan at 900rpm and plot on the graph?
[3 marks]
f) Identify the operating point (m3/s and Pa) when the single unit is operating at 900rpm
assuming the mine resistance remains the same.
[1 mark]
Page 5 of 14
Page 6 of 14
SECTION B
ANSWER ONLY ONE (1) QUESTION FROM THIS SECTION
Question 4
Total 10 Marks
a) 70 m3/s of air containing 15ppm CO and 0.75% CH4 mixes with 40m3/s of air containing 10ppm CO
and 1.1% CH4.
Find the concentration of CO and CH4 in the mixture
[1 mark]
At what rate is CH4 leaving the mixing point in l/s?
[1 mark]
b) A section of a mine makes methane gas at a rate of 900l/s and is ventilated by a total of 75m 3/s
intake air containing 0.2% of the gas by volume.
What is the concentration of the gas leaving the section?
[2 marks]
Is this an acceptable level in a coal mine in NSW? Give reason.
[1 mark]
c) The density of a gas mixture found in an underground mine is 1.153kg/m3, the pressure is 90kPa
(abs) and the temperature 20°C. 2m3/s of the gas mixture is reticulated through underground pipes
and reaches the surface pump inlet at 60kPa (abs) and 26°C.
Using gas laws determine the volumetric flow rate in the pipe at surface.
[1 mark]
Find the density at surface.
[1 mark]
d) Identify five (5) fire ignition sources in underground mines.
Identify five (5) potential sources of fuel for mine fires.
[1 mark]
[1 mark]
List the five (5) different categories of fire.
Question 5
[1 mark]
Total 10 Marks
a) Define any four (4) properties used to describe or characterise dust.
[2 marks]
b) Describe any two (2) Heat Stress Indices commonly used in underground mines.
[4 marks]
c) Name any four (4) properties of coal affecting the propensity for spontaneous combustion.
[2 marks]
d) Describe four (4) important aspects/contents of a mine’s heat stress management plan required to
protect the workforce from adverse effects of hot working conditions?
[2 marks]
Page 7 of 14
Exam Data
Pf = R .Q2
Square law.
Q= air quantity, m3/s
Pf = frictional pressure, Pa
R = resistance, Ns2/m8
Atkinson’s equation.
R=K.C.L. 
A3
1.2
 = density, kg/m3
C = circumference, m
K = Atkinson’s friction factor,Ns2/m8
A = cross sectional area, m2
Shock Losses.
Ps = X. 0.5. .V2
L = length, m
OR Ps = X. 0.5. .Q2
A2
Ps = shock loss, Pa
V = velocity, m/s
Series Airways.
Rtot = R1 + R2 +….Rn
Parallel Airways.
1 = 1 + 1 + ….. 1 .
Rtot R1 R2
Rn
Resistance for n identical airways
Rtot = R/n
X = shock loss factor
Qtot
RnQn
2
To calculate quantity in each path, pressure common to all airways.
Qn = Rtot.Q2tot
Rn
Pressure Relationships
Ptotal = Pstatic + Pvelocity
P1 + V12 + gh1 + Pfan = P2 + V22 + g h2 + Pfric
2
2
OR
P2
=
P1 +  (V12 – V22) + g (h1 – h2) - Pfric + Pfan
Page 8 of 14
Exam Data
Pf  RQ2
Square law.
Q= air quantity, m3/s
Pf = frictional pressure, Pa
R = resistance, Ns2/m8

R
Atkinson’s equation.
 = density, kg/m3
C = circumference, m
k.C.L 
A 3 1.2
K = Atkinson’s friction factor,Ns2/m4
A = cross sectional area, m2
L = length, m

Ps  0.5XV 2
Shock Losses.
OR

Q2
Ps  0.5X 2
A
Ps = shock loss, Pa
Series Airways. 
V = velocity, m/s
X = shock loss factor
Rtot  R1 R2 .....Rn

Qtot
1
1
1
1


 ....
Rtot
R1
R2
Rn
Parallel Airways.
RnQn
Resistance for n identical
airways

Rtot 
R
n2
To calculate quantity in each path, pressure common to all airways.

Qn 
Rtot .Qtot 2
Rn

Page 9 of 14
Pressure Relationships: Ptotal  Pstatic Pvelocity
V12
V22
P1  
 gh1  Pfan  P2  
 gh2  Pfric
2
2


P2  P1  
(V12  V22 )
 g(h1  h2 )  Pfan  Pfric
2
End Pstatic = Start Pstatic plus change Pvelocity plus Phead - Pfric + Pfan

P  gh
Column Pressure
h = height of column, m
g = gravity, m/s2

Approximate equation for Regulator Areas
A2  1.2Q

P
Friction Factor Values for Mining Applications

Lim it of square law
Friction Factor K Ns2/m4
0.016
0.014
Mining
applications
Turbulent
0.012
0.010
e/D
0.05
Transitional
0.008
0.025
0.006
0.01
0.004
0.001
0.0001
0.004
0.002
Lam inar
0.000
1.0E+03
Smooth
1.0E+04
1.0E+05
1.0E+06
1.0E+07
Reynolds Number
Fan laws
Page 10 of 14
Speed change

Q1 S1

Q2 S2
Air quantity directly proportional.
2
P1 S1 
  
P2 S2 
Pressure proportional to square of speed.
3
kW1 S1 
  
kW2 S2 

Density change 
Power proportional to cube of speed.
P1 1

P2 2
Q1  Q2
Pressure proportional to density.
 Note Fan Total pressure = Fan static pressure + Velocity pressure at discharge

area.
Fan Efficiency =
Air Power
PQ

 100%
Absorbed Power 1000.E
Q = quantity, m3/s
P = pressure Pa


E

E = electrical power, kW
3V .I.cos 
kw AC
1000
Gases And Gas Laws
E av 
E
V .I
kw DC
1000

C1t1  C2 t 2 ...... Cn t n
T
Eav = Average Exposure
Ci = Concentration for period i
ti = Duration of exposure period, hours
T = Total exposure time, hours

E eq  E av .
Eeq = Equivalent exposure
T
8
Approximate Net Gas Make:

Page 11 of 14
G  Q  (Cout  Cin )  0.01 m3/s
G  Q  (Cout  Cin ) 10 l/s
G = Gas flow rate, m3/s or l/s
quantity, m3/s
C = Concentration, %
Q = Total
Heat Relationships
m
Mass flow rate of air
Q
ASV
m = mass flow, kg/s Q = quantity, m3/s
ASV = apparent specific volume, m3/kg
Heat Exchange 
q  m(S2  S1)kW
Moisture Exchange
R  m(r1  r2 )g/s

q = heat, kW S = sigma
heat, kJ/kg
r = moisture content (apparent specific humidity) g/kg

Approximately 50 kW heat raises the temperature of 10 m3/s by 1.0˚C wet bulb in warm
conditions.
WB Increase per 1000 m


6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
0
5
10
15
20
25
Surface Wet Bulb C
Work against gravity
Page 12 of 14
(Z 2  Z1 )
1000
qgrav = diesel heat load, kWm = mass, kg/s or l/s for water
g = gravity (9.8 m/s2)
Z2, Z1 = start and end elevation, m
qgrav  mg
Work to raise a mass

Diesel Unit Heat
Average heat from diesel units
qdiesel 
RP

.Pt av .Pt ut
qdiesel = diesel heat load, kW Ptzv = percent time available, %
RP = rated power of unit, kW Ptu = percent utilization, %

Average heat from fuel consumed
qdiesel 
η = diesel efficiency
Q f .D f .C f
t op
qdiesel = diesel heat load, kW Cf = calorific value of diesel fuel, (typical = 45.6 x 103 kJ/kg)
Qf = quantity of fuel used, litres
top = total operating time during which fuel is consumed, s
Df = fuel density, typical 845 kg/m3 (use 0.845 kg/l)

Psychrometric Equations
287.045  (tdb  273.15) 3
m /kg air
(P  e)
287.045  (t db  273.15) 3
m /kg v air
True specific volume: TSV 
(P  0.378e)
1
kg/m 3 vair
True density: true
TSV
1
ASH
(1 +
) kg/m 3 vair
True density:true 
ASV
1000
Apparent specific volume: ASV 

where,
P = Barometric Pressure

e = Actual
vapour pressure
tdb = Dry bulb temperature
Page 13 of 14
Periodic Table of elements