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The document contains a test with multiple questions on topics related to mine ventilation including: calculating properties of air at different temperatures and pressures using psychrometric charts, estimating air density given wet and dry bulb temperatures and pressure, calculating pressure loss in an airway, determining velocity required for turbulent flow, and listing heat sources and illnesses caused by excessive heat in mines.

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26 views5 pages

From Gongo

The document contains a test with multiple questions on topics related to mine ventilation including: calculating properties of air at different temperatures and pressures using psychrometric charts, estimating air density given wet and dry bulb temperatures and pressure, calculating pressure loss in an airway, determining velocity required for turbulent flow, and listing heat sources and illnesses caused by excessive heat in mines.

Uploaded by

juliusambrosi03
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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UNIVERSITY OF DAR ES SALAAM

DEPARTMENT OF CHEMICAL AND MINING ENGINEERING


MN 323: MINE VENTILATION TEST 1
Instruction
1. Time: 1:30 hours
2. psychometric charts are provided
3. Answer all questions Date: 20/12/2013
Question 1:

a) Consult the given psychometric chart (at barometric pressureof 101.325 kPa) and find the mixing
ratio, enthalpy, and vapour pressure of air at 319d.b.t/294w.b.t.

Answer:

i. The mixing ratio, =5kg/kg of dry air


ii. Enthalpy, - 59 kJ/kg
iii. Vapour pressure= 0.8KPa
b) If the air in (a) above is evaporatively cooled to its saturation find
its dry bulb temperature, mixing ratio and enthalpy

Answer:

iv. The Dbt, =294 k


v. Enthalpy, -=61 kJ/kg
vi. Mixing ratio=15.5

c) What will be its dry bulb temperature if 6KJ of heat is removed per kg of dry air in (b) above?

Answer:

vii. The Dbt, =292.5 k

d) Define the following terms:


i) Dew point temperature, ii) mixing ratio, iii) mine ventilation iv) specific volume v) Heat index
vi) air conditioning.

Question 2:

a) Estimate the density of the air in a drive where the wet and dry bulb temperatures are 29°C
and33°C respectively and the barometric pressure is 101.3kPa

Answer:

The relationship used is PV=RTfor one kg of air

V=RT/P and density = Density -1/V= P/RT=101.3/(0.2871*303K)=1.164484 m3/kg

1
b) Calculate:the pressure loss in a mine airway 100m long, and 3.5x 4 m in cross section for a
flow of 30 m3/s given that the coefficient of friction is 0.01 N s2m-4 mine air density is 1.1
kg/m3, the viscosity of the air =18 x 10 -16 kg/ms

Answer:

c) Given
Length of airway =100 m
Area of airway = 3.5x 4 m
Flow quantity 30 m3/s
Coefficient of friction is 0.01 N s2m-4
Mine air density is 1.1 kg/m3 ,
Viscosity of the air =18 x 10 -16 kg/ms

Using Atkinson ventilation (quantity) equation

Given
Length of airway =100 m L 4C/A
Size of airway/Area =
3.5x 4 m 4*3.5 4 14
Flow quantity 30 m3/s 30
2 -4
Coefficient of friction is 0.01 N s m 0.01
3
Mine air density is 1.1 kg/m , 1.1
18*10-
Viscosity of the air =18 x 10 -16 kg/ms
16
Circumference C= 14

4.5983 kPa
Neglecting
- visicsity

2
d) In the airway in question 2 (b) above, calculate the velocity of air required to create turbulent
flow

Answer:

Re=ρLV/ц Therefore V=цRe/ρL=18 x 10 -16 kg/msx4000/1.1x4C/A=1.75 x10-11m/s

e) List the heat sources in underground mines and the illnesses caused by excessive heat to mine
workers

Question 3

P2=101061Pa, densitρ2=1.187788 kg/m3, V2=60.61 m3

B c D

Answer

Mine static head Hs= HfAB+HfBC+HfCD+HxA+HxB+HxC+HxD

=2.5 +2+1.5+1+1+1+0= 9 in

Mine velocity head= HVCD=0.5 in

Mine Total Head= MneHs+MineHv=9.5 in

3
10
5
8

-2

Total head gradient

Static head gradient

4
5

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