Where required the following can be assumed, acceleration due to gravity g = 9.81 m/s2, density of water = 1000 kg/m3, standard density of air = 1.2 kg/m3, Specific gravity of mercury = 13.6.
1. Air passes through a 1.5m-diameter ventilation duct using a forcing ventilation system. If it is required to deliver 22 m3/s at the end of the duct what is the air velocity in the duct. If the duct has a 20% leakage rate what is the airflow that needs to be developed by the fan supplying the system?
2. During a ventilation survey the cross-sectional area of a mine airway is measured to be 30 m2. Anemometer traverses of the airway have been undertaken and the results from four such traverses at the area measuring site indicated that on the first pass a total of 440 m of air was registered on the anemometer. In the second traverse 427 m was measured, in the third 444m and in the final traverse 428m. Given that each anemometer traverse was timed over 100 s, determine the average flow velocity of the air and the air quantity flowing.
3. Measurements of gas concentration at a particular site underground indicate that the concentration of methane in the general body of the air is 0.5%. If 25 m3/s of air is flowing at the site determine the volume of methane present in the airstream?
4. A Pitot-static tube is used to measure air velocity as part of a ventilation survey. At a particular measuring site a velocity pressure of 250 Pa is measured, assuming the air has a density of 1.02 kg/m3 what is the air velocity at that point?
5. The instantaneous liberation rate of methane in a room being advanced by a continuous miner varies from 0.05 m3/s to 0.18 m3/s. Calculate the quantity of fresh air containing no methane that must be delivered to the working place to maintain continuously the methane concentration at the face at less than 0.5%.
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:
|
Time (h)
|
Activity
|
Respirable Dust Exposure (mg/m3)
|
|
0.5
|
Travel to longwall
|
0.2
|
|
1.0
|
Prepare to mine
|
0.5
|
|
3.0
|
Advance shields
|
3.5
|
|
0.5
|
Lunch
|
0.4
|
|
2.5
|
Run shearer
|
1.2
|
|
0.5
|
Travel to portal
|
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. A tunnel in a mine is 2000m m in length and has a cross-sectional area of 25 m2 and a perimeter of 20 m. If the friction factor for the airway is 0.013 kg/m3, determine the resistance of the airway.
8. A straight 5.5 x 5.5 m mine tunnel is 1950m in length. If this tunnel is smooth blasted, determine the resistance of the tunnel. If 200 m3/s of air is passed along this tunnel what would be the pressure drop along the tunnel.
9. Measurements from a ventilation survey indicate that along a particular tunnel a pressure drop of 0.05 kPa for a flow of 55m3/s. If the tunnel is 600m in length and is a 5.5 x 6 m airway what is the friction factor of the tunnel?
10. A 6 x 6 m rectangular tunnel is 1550m in length and contains four right angled bends with a centre-line radius of curvature of 3.5m. The tunnel is unlined but is in good condition with the major irregularities having been trimmed away. The tunnel is required to pass 50 m3/s of air with a density of 1.25 kg/m3. Calculate the airway resistance and the frictional pressure drop.
11.Two mine airways with resistances of 0.15 Ns2/m8 and 0.7 Ns2/m8 are connected in series determine the resistance of the series combination. If the airflow through these airways is 30 m3/s, what is the pressure drop in each of the airways and the total pressure drop in the series combination of airways?
12.Two mine airways with resistances of 1.1 and 0.5 Ns2/m8 are connected together in parallel. Determine the resistance of the parallel combination. If 75 m3/s flows into this parallel combination of airways determine the flow in each