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.
Question1.
Air passes through a 1.5m-diameter ventilation duct at a velocity of 3.0 m/s. Calculate the volumetric flow rate and the mass flow rate assuming that the air has a density of 1.12 kg/m3.
Question2.
During a ventilation survey the cross-sectional area of a mine airway is measured to be 25 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 231 m of air was registered on the anemometer. In the second traverse 245 m was measured, in the third 238m and in the final traverse 228m. Given that each anemometer traverse was timed over 100 s, determine the average flow velocity of the air and the air quantity flowing.
Question3.
Measurements of gas concentration at a particular site underground indicate that the concentration of methane in the general body of the air is 0.85%. If 33.5 m3/s of air is flowing at the site determine the volume of methane present in the airstream?
Question 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 950 Pa is measured, assuming the air has a density of 1.12 kg/m3 what is the air velocity at that point?
Question5.
Incompressible flow
A tunnel in a mine is 620 m in length and has a cross-sectional area of 24 m2 and a perimeter of 20 m. If the friction factor for the airway is 0.014 kg/m3, determine the resistance of the airway.
Question6.
A 5 x 4.5 m rectangular tunnel is 950m in length and contains a single right angled bend 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 80 m3/s of air with a density of 1.25 kg/m3. Calculate the airway resistance and the frictional pressure drop.
Question7.
Determine the equivalent length for a sudden contraction in a mine airway from a cross-sectional area of 20 m2 to 15m2assuming that the perimeter of the airway remains unchanged at 16m. Assume k = 0.01 kg/m3.
Question8.
Two mine airways with resistances of 0.5 Ns2/m8 and 1.1 Ns2/m8 are connected in series determine the resistance of the series combination. If the airflow through these airways is 37 m3/s, what is the pressure drop in each of the airways and the total pressure drop in the series combination of airways?
Question9.
Three mine airways with resistances of 0.5 Ns2/m8, 0.4 Ns2/m8 and 1.2 Ns2/m8 are connected in series determine the resistance of the series combination. If the airflow through these airways is 54 m3/s, what is the pressure drop in each of the airways and the total pressure drop in the series combination of airways?
Question10.
For the ventilation network shown below, determine the flow and pressure drop in each branch of the network.
Question11.
A section of a mine ventilation system is connected together as shown in the diagram below, if the pressure drop across the system is 3 kPa and the resistances are as indicated determine the flow in each airway.
Question12.
23. A working area of a mine has diesel equipment operating within it. The maximum diesel loading is 450 kW. The same section of the mine also has a methane inflow of 0.65 m3/s flowing into it. If the maximum permissible methane concentration in the general body of the air is 1% and the design diesel air quantity is 6 m3/s per 100 kW of installed diesel power, determine the required ventilation flow rate for the working area.
Determine the characteristic curves for the fan illustrated in figure 1 for the following cases:
- Two fans in series
- Two fans in parallel
Question 13.
A worker in a development drive is working at a rate of 275 W/m2. If the air velocity passing over the worker is 1.5 m/s, the air dry bulb temperature is 33°C, the air wet bulb temperature is 31°C, radiant temperature of the surroundings is 35°C, and it can be assumed that the worker's skin temperature is 34 °C, if the barometric pressure is 100 kPa determine:
- The air cooling power
- The basic effective temperature
Is the environment safe to work in?
Question14.
During a 40h underground working week radiological monitoring indicates that a miner is subjected to the following levels and periods of exposure to radon daughters
20 h at 0.15 WL
10 h at 0.2 WL
10 h at 0.4 WL
Determine the cumulative exposure in WLM for that week.
Question15.
The airflow is 35 m3/s in a 1000m long airway of perimeter 14m and cross sectional area 12 m2. If the initial concentration of radon in the airway is 20 pCi/l, there is an initial radon daughter activity of 0.05 WL at the entry and the rate of emanation J = 265 pCi/m2, determine the following:
- The working level of radon daughters at exit due to the initial radon
- The activity of radon daughters at outlet due to radon emitted from the rock surfaces
- The activity of radon daughters at outlet due to decay of radon daughter products available at entry
- The total working level of radon daughters leaving the airway
Question16.
A moist airstream with a pressure of 100 kPa has an initial dry bulb of 30 °C and a wet bulb of 24 °C. Use the 100 kPa psychrometric chart provided to calculate the end dry/wet bulb to this original airstream when subjected to the following processes:
(a) Heating at constant moisture content, raising the specific enthalpy by 8 kJ/kg. (b) Enthalpy increase of 8 kJ/kg, moisture content increases to 19 g/kg.
(c) Constant dry bulb cooling to a moisture content of 0.01 kg/kg.
(d) Constant dry bulb heating to a relative humidity of 90 %.
(e) Constant wet bulb (and sigma heat) process to a relative humidity of 30 %.
(f) Constant wet bulb process to saturation.
(g) Constant moisture content process to saturation.
Question17.
A mine opening is ventilated by an airflow of 30 m3/s. The exit concentration of radon daughters is 1.0 WL. If this is to be reduced to 0.33 WL, determine the required airflow.
Question18.
The conditions at the entrance to a crosscut are temperatures, 29°C wet bulb and 35°C dry bulb and barometric pressure 110 kPa. At the exit of the crosscut the temperatures are 30°C wet bulb and 32°C dry bulb and the barometric pressure 110 kPa. The volume flow at the entrance is 25 m3/s. Determine;
- the water picked up in litres per day ,
- the heat picked up by the air in kW ,
- the increase in relative humidity