1. 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?
2. 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.
3. In a given stope 350 m2 of ore and 200 m2 of waste rock surface are exposed. The stope also contains 600 tonnes of broken ore. Assuming the ore has a density of 2700 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
4. 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
5. Moist air has a dry bulb temperature of 30 °C and a wet bulb temperature of 27 °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 25 m3/s, calculate the air mass flow rate.
6. Calculate the same properties as in the previous question for a saturated airstream with a temperature of 28 °C at a pressure of 100 kPa using either formulae and/or chart. (NB For saturation the dry and wet bulb temperatures are equal).
7. 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.