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MVT721S - Mine Ventilation 324 - 2nd Opp - Nov 2022 |
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nAmlBIA unlVERSITY
OF SCIEnCE TECHnOLOGY
FACULTY OF ENGINEERING AND THE BUILT ENVffiONl ENT
DEPARTMENT OF CIVIL MINING AND PROCESS ENGINEERING
QUALIFICATION : BACHELORS OF ENGINEERING IN MINING ENGINEERING
QUALIFICATION CODE: BEMIN LEVEL: 7
COURSE CODE: MVT721S
COURSE NAME: MINE VENTILATION
SESSION: NOVEMBER 2022
PAPER: THEORY
DURATION: 3 HOURS
MARKS: 100
SECOND OPPORTUNITY QUESTION PAPER
EXAMINER(S) Mallikarjun Rao Pillalamarry
MODERATOR: Mr. Lawrence Madziwa
INSTRUCTIONS
I. Answer all questions.
-:-:,:::-:-:-::-_:-:_:-.:.-:-:;-~.,~::.-.-'_=;.;::-2-:°.-::-Rtehaed:qaullestions -carefuIly 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. Examinationpaper.
-~~=== _ _ _ _
2. O_neGraphPaper
_
=-:~---=-:---:-:-_::.~?.:--~~h~m_atif~I:n~tn_unen-t-s-- ·------ ·----··:--_--- ------- --
THIS QUESTION PAPER CONSISTS OF 05 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
(20)
(Short Answer Questions)
a) What is recoil distance and how it influences the radon emission in mines? [3]
b) What is black damp? [I]
c) Why a fan vibrates when it is operating at stall point? [I]
d) In a coal mine three openings with same cross-sectional area having a shape of circle, rectangle
and square were made. Which of these openings have highest resistance for the airflow? [I]
e) What is the equivalent length with respect to shock losses? [I]
f) In which situation reversal of airflow in a mine may be necessary? [I]
g) Which of axial flow and centrifugal fan produces more noise when operating? [I]
h) What is psychometry? [I]
i) What happens when a person subjected to a hot environment with I 00% humidity? [I]
j) In a mine wet and dry bulb thermometer on a Whirling hygrometer are recoded the same
temperature. What does it mean with respect to moisture content [I]?
k) What properties of CO makes it more dangerous gas than any other gases usually found in
mines? [3]
I) What is volumetric efficiency? [I]
m) What is Short Term Exposure Limit? [I]
n) Why use of booster is fan restricted in underground coal mines? [I]
o) What are the different ways to solve mine ventilation networks? [2]
Question II
a) A copper mine is ventilated with an exhaust ventilation system to ventilate two working levels (20)
as shown in Figure 1. Mine is fitted with a main exhaust fan whose characteristics are given
in the table. Determine
a) Airflow through the level 1 and Level 2
b) What options are available to increase the airflow through level 2
Total Pressure Pa
Quanti m 3/s
1240 I 180 1080 920 740 540 200
5
10
15 20
25
30
35
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A
i"'-=
M
0
- l"-:::::
0
l.6Ns:1ms
B
E
Level I
"-:::::
"::
;:i-
zN<I>
'0
0
-z<I>
C!
0.2Nsi/w 8
C
Level 2
D
Figure I
Question III
a) A mine has three splits A, B, and C each of resistance 0.1 Ns2/m8• The trunk roadways have a (20)
total resistance of 0.2 Ns 2/m8• The surface fan pressure is 700 Pa. What is the flow in each
split A, B and C. The quantity in splits A and B is desired to be fixed at 30 m3/s, and IO m3/s
respectively. What is the resultant unrestricted flow in flow in split C? What are the
specifications of the flow control devices needed in splits A and B to achieve the desired flow
conditions?
Question IV
a) Describe how to solve complex ventilation networks using Hardy Cross method
(I 0)
b) A segment of ventilation network of an underground mine is shown in Figure I. Pressure drops (IO)
are indicated in tenns of inches of water (I inch= 2.54 cm) and airflow in m3/min. By using
Kirchhoffs second law determine the location of regulators and the pressure drop there are
causing.
H•O.45"
o 283.2m'/m 1418.Sm'/m
G
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:n
ci
849.Sm'/m
:l:
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H•l.Z-
H•O.65"
H•O.4"
...;:-EE
,-, d
2 :c
& ___._.. 1li1B.8m1/m
N
p
L H•O.3" M H•o.1s·
H•O.6" o H•o.ss·
H•o.e·
0
849.Sm'/m
H•l.05"
3
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Question V
a) Methane is explosion took several lives in the history of coal mining. Briefly discuss about (I 0)
methane gas in coal mines.
b) An inflow of0.034 m3/min of strata gas occurs whenever cutting and loading operations are
conducted in a stope. The following data are provided for the stope:
Stope volume 2832 m3
Intake-air volume 56.7 m3/min
Concentration of the strata gas in intake air 50 ppm
Concentration of the strata gas in stope prior to start of work 75 ppm
1. The cycle times are normally distributed with a mean of 34 min and a standard
deviation of3.5 min. Calculate the probability of being gassed out during a particular
cycle given that the maximum allowable concentration for the strata gas is 400 ppm.
ii. A remotely operated cutting and loading machine is being considered. Assume that no
miners will be in the stope return where the concentration may be higher than the
MAC, calculate the steady-state concentration in the stope. Calculate the time at which
95% of this concentration will be reached
Question VI
a) What are the methods used to measure humidity in the air and explain the significance heat - ( I0)
humidity of air in an underground mine?
b) A rectangular tunnel of cross section 5 x 3 m2 and 500 m in length changes of direction by (IO)
means of a 90° arch of 3 m radius as shown in the figure. The tunnel is in good condition but
shows significant wall irregularities, so its Atkinson friction factor is estimated to be 0.012 N
s2 m-4• In addition, the shock loss factor in the arch union is assumed 0.86. If 80 m3 s- 1 of air
whose density is I. 15 kg m-3, is expected to flow through it. Calculate, omitting inlet and
outlet shock losses:
a. Resistance due to friction
b. Resistance of the arch union (shockloss)
c. Equivalent length of the elbow
d. Total pressure drop in the tunnel
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ADDITIONAL INFORMATION
The quantity of dilution air required for a steady-state situation is calculated as follows
Q--E---9
100
(MAC-B)
m3
s
The time required to dilute the concentration of contaminants to a specific level
Modified Bernoulli's equation for mine ventilation
u-+2~Z1g +-=Pp1-+Z2ug2~
P2
+-+pF12
J
kg
Resistance
Coefficient of Friction
Resistance of shockloss
t=-2pk
Equivalent length
Shockloss factor sudden expansion
ll1~
rectangular
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