Questions:
1. The intake volume to a fan developing a pressure of 5kPa is 236 m3/s. At the entry to the fan the psychrometric condition of the air are:
- Wet bulb temperature = 24°C
- Dry bulb temperature = 31.3°C
- Barometric pressure = 95 kPa
The total power input is 1775kW, the motor efficiency is 95% and the motor is situated in the airstream. Determine:
a) The psychrometric conditions at the fan outlet
b) The efficiency of the fan without the motor
2. In an underground pump station there are 10 pumps, each with a motor output of 1000kW. The motor efficiency is 95% and the pumps are 70% efficient. It can be assumed that the heat input into the pumps is fully dissipated into the pumped water.
Determine the volume of air that must be circulated through the pump chamber if the intake temperature and barometric pressure are 26°C saturated and 95 kPa respectively and when:
a) Through ventilation is employed and when the maximum dry bulb temperature is not to exceed 34°C. it may be assumed that there is no increase in the moisture content of the air. And
b) The air passing through the motors is directly exhausted, allowing a rise in the dry bulb temperature through the motors of 25°C
3. A steel pipe has an internal diameter of 250mm and an outside diameter of 260mm. The pipe carries water at a temperature of 5°C flowing at a velocity of 0.5 m/s. The air surrounding the pipe has a dry bulb temperature of 33°C. The air flow's over the pipe with a velocity of 2.5 m/s. If the pipe is covered by insulation of 20mm thickness with a thermal conductivity of 0.035 W/m°, determine:
(a) The UA factor for 1m length of insulated pipe,
(b) The rate of heat gain by the water per m of pipe
(c) The temperature of the inner and outer surfaces of the pipe and the temperature of the outer surface of the insulation
(Note ksteel = 45 W/m°C, hc inside pipe = 1400 W/m2°C, hc outside insulation = 18 W/m2°C and radiative heat transfer coefficient outside insulation hr = 6.1 W/m2°C)
4. It is required to cool 236 m3/s of downcast air at 18°C wet bulb and 27°C dry bulb and at a barometric pressure oh 85 kPa to 3°C saturated in a two-stage cooling plant in such a manner that the temperature after the first stage is 10°C saturated. The coefficient of performance is 4.
(a) How much heat is removed at each stage?
(b) What is the total refrigeration capacity required?
(c) How much water is removed in each stage?
(d) How much heat must be removed from the condenser?
(e) How much cooling water must be circulated through the condenser if the permissible temperature rise of the cooling water is 8°C, assuming that the condensed water is removed at the lowest possible wet bulb temoerature prevailing in each stage?
5. 3.5 m3/s of air at a barometric pressure of 110 kPa are to be cooled in a cooling coil from 32°C saturated to 26°C. The water inlet temperature 15°C and water outlet temperature is 23°C. The flow is counter flow. Determine.
a. How much heat must be removed?
b. How much water is condensed?
c. How much chilled water must be circulated?
d. What is the water and air cooling efficiency?
6. A coal mine worker on a longwall is studied using an aerosol monitor for an entire shift and is found to have the following exposures:
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Time (h)
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Activity
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Respirable Dust
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|
|
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Exposure (mg/m3)
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|
0.5
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Travel to longwall
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0.2
|
|
1.0
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Prepare to mine
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0.5
|
|
3.0
|
Advance shields
|
3.5
|
|
0.5
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Lunch
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0.4
|
|
2.5
|
Run shearer
|
1.2
|
|
0.5
|
Travel to portal
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0.3
|
Assuming the aerosol monitor is equipped with a 10mm nylon cyclone and is calibrated for coal. Determine:
a) The dose of respirable dust the miner receives
b) The TWA exposure of the respirable dust
7. Diesel exhaust emissions are becoming a concern to the underground mining industry. Provide a brief report on techniques that can be applied to reduce and control diesel exhaust emissions in underground mines. The report should be suitably typed and referenced.
8. Students are to develop a spreadsheet based application to determine the optimum diameter for a ventilation shaft for a range of ventilation quantities ranging from 50 m3/s to 400 m3/s. It may be assumed that the cost of power is Au$ 0.45 kWhr.
Ventilation Design Project: (Ventsim)
The ventilation model SLC design project base network provided in Moodle in the assignments section as a Ventsim model forms the basis of this model. In this mine two sub level caving levels will be active at any one time. In the model provided these are levels 1 and 2. The odd number levels subsequently are mirror images of level 1 and the even numbered ones mirror images of level 2. Ore from the sublevel drives is mucked out to an orepass and passed down to the loading level where it passes through a crusher and then onto a conveyor system located in a straight decline up to surface. In addition there is an intake and return shaft as well as an access decline to surface, see figure 1.
Figure 1
The objective of this exercise is to develop a ventilation strategy to ensure safe working in the mine. It may be assumed that the infrastructure given in the model has been developed, the only development required is for levels 3 through to 10.
The mine runs the following fleet of diesel equipment:
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|
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Required
|
|
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Equipment
|
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Volume per
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|
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Engine
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unit @
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Number
|
|
|
|
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Power (kW)
|
6m3/s/100kW
|
of units
|
|
Atlas MT 5020 truck
|
485
|
24
|
1
|
|
Cat AD45B Truck
|
438
|
22
|
5
|
|
Cat R2900G Bogger
|
321
|
16
|
1
|
|
Cat R1700G Bogger
|
263
|
13
|
3
|
|
Volvo L120F IT
|
180
|
9
|
3
|
|
Cat Grader
|
138
|
7
|
1
|
|
Normet Charge Unit
|
120
|
6
|
2
|
In addition if diesel equipment is not in use a minimum air velocity of 0.5 m3/s is required in airways.
Students are to design and model in Ventsim the following:
1. Fan and duct ventilation for the dead end drives on levels 1 and 2, use 1.2 m diameter flexible ducting a forced ventilation system and the fans shown in Figure 2
2. Determine the main mine fan requirements to ventilate the mine using the fan as shown in figure 3, this will involve determining the fan site, number of fans , are parallel fans needed etc.
3. The maximum air velocity allowed in the access decline is 5m/s and in the conveyor decline 4 m/s (due to dust issues)
Students should submit a report on their findings, detailing any assumptions made, details of the modelling including Ventsim files and other calculations and a summary of their findings.
Figure 2 Auxiliary Fan curve
Figure 3 Main fan curve