Basic Ventilation Calculations
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 1m-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 1.2 kg/m3.
2. During a ventilation survey the cross-sectional area of a mine airway is measured to be 14.5 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.
3. Measurements of gas concentration at a particular site underground indicate that the concentration of methane in the general body of the air is 0.85%. If 22.5 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 650 Pa is measured, assuming the air has a density of 1.2 kg/m3 what is the air velocity at that point?
5. Describe the method of undertaking an anemometer traverse for a mine airway
6. Describe the two main methods of undertaking a pressure survey in a mine. What advantages and disadvantages do each method have?
7. Describe a method of undertaking a point measurement traverse for airflow in a circular duct using a pitot static tube
8. What methods are available for measuring the area of a mine airway
9. An explosion occurs when a pre-mixed cloud of gas and air (or other oxidiser) combusts resulting in a rapid increase in pressure. Four conditions must exist underground for an explosion to occur. Name the four conditions and give a brief description thereof.
Incompressible flow
10. A tunnel in a mine is 951 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 0.014 kg/m3, determine the resistance of the airway.
11. A straight 5 x 4.5 m mine tunnel is 453m in length. If this tunnel is shotcrete lined, determine the resistance of the tunnel. If 70 m3/s of air is passed along this tunnel what would be the pressure drop along the tunnel.
12. A straight 5 x 5 m tunnel is 1200m in length and is roughly blasted, determine the airway resistance.
13. Measurements from a ventilation survey indicate that along a particular tunnel a pressure drop of 0.24 kPa for a flow of 35m3/s. If the tunnel is 304m in length and is a 4.5 x 3.7m airway what is the friction factor of the tunnel?
14. A 4 x 3 m rectangular tunnel is 450m in length and contains a single right angled bend with a centre-line radius of curvature of 2.5m. 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.
15. Determine the equivalent length for a sudden contraction in a mine airway from a cross-sectional area of 20 m2 to 15m2 assuming that the perimeter of the airway remains unchanged at 16m. Assume k = 0.01 kg/m3.
16. Two mine airways with resistances of 0.5 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 27 m3/s, what is the pressure drop in each of the airways and the total pressure drop in the series combination of airways?
17. 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 27 m3/s, what is the pressure drop in each of the airways and the total pressure drop in the series combination of airways?
18. Two mine airways with resistances of 17 and 11 Ns2/m8 are connected together in parallel. Determine the resistance of the parallel combination. If 35 m3/s flows into this parallel combination of airways determine the flow in each airway.
19. Two mine airways with resistances of 1.5 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?
20. A section of a mine ventilation system is connected together as shown in the diagram below, if the pressure drop across the system is 1.1 kPa and the resistances are as indicated determine the flow in each airway.
21. Define Kirchoff's first and second laws.
22. A mine has a total airflow requirement of 248 m3/s. If the equivalent resistance of the workings is 0.09 Ns2/m8 determine the pressure to be developed by a single mine fan to ventilate the workings.
23. A working area of a mine has diesel equipment operating within it. The maximum diesel loading is 350 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.
Figure 1: Fan Characteristic curve
24. Determine the characteristic curves for the fan illustrated in figure 1 for the following cases:
• Two fans in series
• Two fans in parallel
25. A worker in a development drive is working at a rate of 250 W/m2. If the air velocity passing over the worker is 1.5 m/s, the air dry bulb temperature is 35°C, the air wet bulb temperature is 33°C, radiant temperature of the surroundings is 35°C, and it can be assumed that the worker's skin temperature is 34 °C, determine:
• The air cooling power
• The basic effective temperature
Is the environment safe to work in?
26. 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
15 h at 0.2 WL
5 h at 0.4 WL
Determine the cumulative exposure in WLM for that week.
27. In a given stope 250 m2 of ore and 200 m2 of waste rock surface are exposed. The stope also contains 300 tonnes of broken ore. Assuming the ore has a density of 2000 kg/m3, determine the rate of emanation into the stope given the following:
J (ore) = 550 pCi/m2s
B (ore) = 600 pCi/m3s
J (waste) = 85 pCi/m2s
28. The airflow is 25 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
29. Moist air has a dry bulb temperature of 30 °C and a wet bulb temperature of 25 °C, if the pressure is 100 kPa, calculate the following using either formula or a 100 kPa psychrometric chart.
• moisture content
• specific enthalpy
• relative humidity
• sigma heat
• specific volume
• density If the airflow is 30 m3/s, calculate the air mass flow rate.
30. Calculate the same properties as in the previous question for a saturated airstream with a temperature of 26 °C at a pressure of 100 kPa using either formulae and/or chart. (NB For saturation the dry and wet bulb temperatures are equal).
31. 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.
32. The following two airstreams mix at the junctions of two roadways. The first airstream has a mass flow of 10 kg/s and a dry/wet bulb of 20/10 °C, the second airstream has a mass flow of 20 kg/s and a dry /wet bulb of 30/19 °C. The pressure is 100 kPa. Determine the dry/wet bulb temperatures of the mixed airstream.
If the mass flows were 20 kg/s for the first airstream and 10 kg/s for the second airstream, what would be the dry/wet bulb of the new mixed airstream?
33. For the following psychrometric combinations, calculate the dry/wet bulb temperature assuming a pressure of 100 kPa:
• 100 % relative humidity, 0.02 kg/kg dry air moisture content.
• Enthalpy of 70 kJ/kg, relative humidity of 20 %
• Sigma heat of 60 kJ/kg, moisture content of 0.0125 kg/kg dry air.
34. The radon daughter concentration leaving a mine section is 0.2 WL when the airflow is 20 m3/s. A temporary obstruction caused by stocked materials reduces the airflow to 5 m3/s. Determine the effect on the radon daughter concentration.
35. A mine opening is ventilated by an airflow of 15 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.
36. An airflow of 25 m3/s and radon daughter concentrations of 0.2 WL passes a seal from which issues a leakage flow of 0.4 m3/s at 150 WL. Determine the radon daughter concentration in the downstream airflow.
37. Describe the various methods of methane drainage available to drain gas for longwall mining operations.
38. In the case of cross measures methane drainage of longwall operations what factors influence the spacing of drainage boreholes?
39. On retreating longwall coalfaces active ventilation of the goaf is undertaken, why is this. Detail three methods of ventilating the goaf in such conditions.
40. Briefly describe the methods used to control radiation in uranium mines.
41. List the main sources of heat and humidity in mines.
42. Briefly describe the methods that can be used to control heat and humidity in an underground mining situation.
43. The conditions at the entrance to a crosscut are temperatures, 28°C wet bulb and 35°C dry bulb and barometric pressure 110 kPa. At the exit of the crosscut the temperatures are 31°C wet bulb and 32°C dry bulb and the barometric pressure 110 kPa. The volume flow at the entrance is 55 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 .
44. What are the primary sources of dust in underground mining operations? Detail the methods of dust control available.
45. What is methane layering and how can it be controlled in a mine ventilation system.
46. Describe the construction of an explosion proof seal.
47. What indicators can be used to determine if an underground fire is developing and how do these indicators change as the fire develops.
48. Define the following:
• Antitropal Ventilation
• Homotropal Ventilation
• Ascentional Ventilation
• Descentional Ventilation
What are the objectives of a mine ventilation system?
49. List the main ventilation contaminants.
What systems are available for the ventilation of dead end drivages? For each system, sketch the system and detail particular advantages and disadvantages of the system.
What are the advantages of siting main mine fans on surface?
50. Detail the main parameters involved in the metabolic heat balance of a human being and define the main factors, which influence a human's ability to work in a hot environment. Briefly describe the following heat stress indices, comment on any short comings and give limiting good practice values for each which can be employed for heat stress management and design purposes;
• Wet bulb temperature
• Effective temperature
• Air Cooling Power.