Questions
1. The diagram above represents a ventilation network, determine the following:
a. The equivalent resistance of the entire circuit.
b. If 200 m3/s flows into the network, the pressure drop across the entire network.
c. The flow in each of the branches of the network.
2. A working area of a mine has diesel equipment operating within it. The maximum diesel loading is 750 kW determine the required ventilation flow rate for the working area using the Western Australian standard
3. Determine the static and total pressure/volume characteristic curves for the fan illustrated in figure 1 for the following cases:
- Two fans in series
- Three fans in parallel
- Four fans in a 2 x 2 series/parallel combination
4. 21.A worker in a development drive is working at a rate of 350 W/m2. If the air velocity passing over the worker is 0.6 m/s, the air dry bulb temperature is 35°C, the air wet bulb temperature is 31°C, radiant temperature of the surroundings is 37°C, and it can be assumed that the worker's skin temperature is 34 °C, if the barometric pressure is 110 kPa determine:
- The air cooling power
- The basic effective temperature
Is the environment safe to work in?
5. 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
10 h at 0.15 WL
10 h at 0.2 WL
10 h at 0.4 WL
5 h at 0.6 WL
5 h at 0.05 WL
Determine the cumulative exposure in WLM for that week.
6. In a given stope 550 m2 of ore and 270 m2 of waste rock surface are exposed., determine the rate of emanation into the stope given the following:
J (ore) = 550 pCi/m2s
J (waste) = 185 pCi/m2s
7. The airflow is 40 m3/s in a 1000m long airway of perimeter 20m and cross sectional area 25 m2. If the initial concentration of radon in the airway is 25 pCi/l, there is an initial radon daughter activity of 0.06 WL at the entry and the rate of emanation J = 600 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
8.Air enters an airway at the rate of 60 kg/s with a dry bulb temperature of 22 °C and a wet bulb temperature of 17 °C at a pressure of 100 kPa. This air flows along the airway initially picking up 500 kW of heat and 170 g/s of moisture from the surrounding strata. The air subsequently flows over a number of items of machinery where it is heated at constant moisture content to a dry bulb temperature of 33°C.
Following the machinery the air is split into two distinct flows. Now 20 kg/s of the total flow passes through an air cooler in which the air-dry bulb temperature is cooled to 22°C with the wet bulb temperature reduced to 15 °C. The remainder of the flow is heated at a constant dry bulb temperature to an enthalpy of 80 kJ/kg. The two airflows are then recombined prior to the airflow being passed to another airway.
Using the psychrometric chart provided, calculate the following;
(a) The dry and wet bulb temperatures of the airstream immediately upstream of the machinery.
(b) The heat input from the machinery.
(c) The heat removed and the rate of condensation of water from the airstream passing through the air cooler.
(d) The wet bulb temperature of the airflow, which does not pass through the air cooler.
(e) The dry and wet bulb temperature of the recombined airstream at the exit of the airway.
9. The following two airstreams mix at the junctions of two roadways. The first airstream has a mass flow of 25 kg/s and a dry/wet bulb of 34/25 °C, the second airstream has a mass flow of 15 kg/s and a dry /wet bulb of 30/27 °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 25 kg/s for the second airstream, what would be the dry/wet bulb of the new mixed airstream?