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MVT721S - Mine Ventilation 324 - 1st Opp - Nov 2022 |
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nAmlBIA UnlVERSITY
OF SCIEnCE Ano TECHnOLOGY
FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT
DEPARTMENT OF CIVIL MINING AND PROCESS ENGINEERING
QUALIFICATION : BACHELORS OF ENGINEERING IN MINING ENGINEERING
QUALIFICATION CODE: 08BMIN LEVEL: 7
COURSE CODE: MVT721S
COURSE NAME: MINE VENTILATION
SESSION: NOVEMBER 2022
PAPER: THEORY
DURATION: 3 HOURS
MARKS: 100
FIRST OPPORTUNITY QUESTION PAPER
EXAMINER(S) Mallikarjun Rao Pillalamarry
MODERATOR: Mr. Lawrence Madziwa
INSTRUCTIONS
1. Answer all questions.
2. Read all the questions carefully before answering ..
3. Marks for each question are indicated at the end of each question.
4. Please ensure that your writing is legible, neat and presentable.
PERMISSIBLE MATERIALS
I. Examination paper.
2. One Graph Paper
3. Mathematical Instruments
THIS QUESTION PAPER CONSISTS OF 5 PAGES (Including this front page)
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Instructions: Answer Question I and any 4 other questions. Excess questions will not be marked.
Question I is compulsory.
Time allowed: 3 hours
Question I
(Short Answer Questions)
(20)
a) What measure is used to determine the workers' exposure to radon concentration? [I]
b) Which of the axial flow and centrifugal fan requires complex arrangement for fan reversal? [I]
c) What is Kirchhoff's second law with respect to the mine ventilation networks?[!]
d) What is the major difference between whirling hygrometer and aspirated psychometer? [2]
e) What is the source of eddy losses in centrifugal fan? [I]
t) What is the pressure inside a mine using forcing ventilation system compared to atmospheric
pressure? [I]
g) What is lag on ignition with respect to methane? [I]
h) What is homotropal ventilation system and what is its advantage? [2]
i) What are the different ways to determine the resistance of a planned airway? [3]
j) Which of the axial flow and centrifugal fan delivers more airflow at lower pressure head? [I]
k) If airflow through the mine is doubled what would be the increase in the cost of ventilation? [I]
1) What is the importance of psychometry in mine ventilation? [2]
m) What is the major advantage of having main fan in the underground?[!]
n) What is the gauge pressure? [1]
o) What is stall zone? [I]
Question II
a) Briefly describe following ventilation controls
i. Air locks
11. Stoppings
iii. Air crossing
iv. Regulator
b) Briefly describe uni and bidirectional district ventilation with the help of Figures
. (12)
(8)
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Question III
a) Ventilation survey in an inclined drift (1-2) dipping at 30° from horizontal is connected with a level (14)
airway (2-3) as shown in Figure I provided the following measurements.
Location
I
2,.,
.)
Airflow
m3/s
56
Cross-sectional
area (m2)
5x5
4x5
4x4
Barometric pressure
(kPa)
IOI
102
101.5
Detennine the yearly cost of ventilating the airway if cost of electricity is N$2.25/kWh and fan
efficiency is 75%.
:~ •~>---',,
'"-,
->ct,~-,
"1 ', ..._.. ·,,
-,_ '-----
----
~-,-~2· ____________
3.
-.~----------
500 ru
Figure I
b) Give the arrangement of U-tube manometer for measuring static, velocity and total pressures in a (6)
straight airway
Question JV
a) In the ventilation network shown in the Figure 2, the resistances of the branches are given in Ns2/m8• (20)
The inlet air flow rate is 15 m3/s. Solve the given network using Hardy Cross successive approximation
method until two iterations.
0.3 Ns½n 8
0.1 Ns½n 8
15 m3/s
0.8 Ns2/m8
15 m3/ s
--
0.4 Ns2/m8
Figure 2
0.6 Ns2/m8
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Question V
a) The combined characteristics of two identical fans working in a series is given below
1030 950 840 690 490 100
m 3/s
20
30
40
50
60
70
The air quantity flowing through the mine under these conditions is 55 m3/s. However, due to
mechanical reason one of the fans had to be shut-off. What is the pressure and quantity in this situation?
b) Briefly discuss losses in cetrifugal and axial flow fans.
(10)
Question VI
a) The diagram (Figure 3) shows a development end with a force fan and column. The volume flowing (I 0)
through the fan is 5 m3/s. The only leakage from the column takes place at point z which is 3.34 m3/s.
In the development end two fissures giving of methane at X and Y. Fissure X giving off0.01 m3/s which
mixes completely with the air at the point of issue. Fissure Y giving off 0.03 m3/s which mixes
completely with the air at the point of issue.
i. Calculate percentage of methane at A
11. Calculate percentage of methane at B
111. What will be the methane percentage at A if the leakage is stopped and the fan quantity is
reduced to 4 m3/s.
j 5 ru'I•
.
B
0.01 m1/s of Methane
lx
z.
A
Figure 3
b) Briefly discuss about the installation of auxiliary fan in mines
(10)
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ADDITIONAL INFORMATION
The quantity of dilution air required for a steady-state situation is calculated as follows
100
m3
Q = Eg (MAC-B)
s
The time required to dilute the concentration of contaminants to a specific level
Modified Bernoulli's equation for mine ventilation
uf
-2+Z1B
+-P=p1-+Zu22~B
+-P+p2F12
J
kg
Resistance
klo
R=A3
Coefficient of Friction
Resistance of shockloss
t=-2pk
Equivalent length
Shockloss factor sudden expansion
A,
A,
u,-
u, -
IIJ--.,.
rectangular
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