1. 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 25/15 °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?
2. 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.
3. The radon daughter concentration leaving a mine section is 0.2 WL when the airflow is 25 m3/s. A temporary obstruction caused by stocked materials reduces the airflow to 10 m3/s. Determine the effect on the radon daughter concentration.
4. 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.
5. 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 125 WL. Determine the radon daughter concentration in the downstream airflow.
6. Describe the various methods of methane drainage available to drain gas for longwall mining operations.
7. Detail the main elements of a methane drainage system?
8. What methods are available to control radioactive dust in mines?
9. Briefly describe the methods used to control radiation in uranium mines.
10. List the main sources of heat and humidity in mines.
11. Briefly describe the methods that can be used to control heat and humidity in an underground mining situation.
12. 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 .
13. What are the primary sources of dust in underground mining operations? Detail the methods of dust control available.
14. What is methane layering and how can it be controlled in a mine ventilation system.
15. Describe the construction of an explosion proof seal.
16. What indicators can be used to determine if an underground fire is developing and how do these indicators change as the fire develops.
17. What is the difference between an oxygen rich and a fuel rich fire?
18. 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?
19. 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.