11. In a coal mine district, air flows at a rate of 30 m3/s at a pressure of 1200 Pa. The density of air is 1.2 kg/m3. The mine management decided to reduce the flow rate of air to 20 m3/s using a regulator without changing the ventilation pressure. The area of regulator expressed in m2 will be
12. After blasting which gas come out.
13. A Roadheader district produces 20 mg/m3 of airborne dust with the following size distribution:
Size up to
Cumulative wt%
1 μm
1
5 μm
5
10 μm
10
20μm
20
50μm
50
>50μm
100
The concentration of respirable fraction of dust in mg/m3 is
| Size up to | Cumulative wt% |
| 1 μm | 1 |
| 5 μm | 5 |
| 10 μm | 10 |
| 20μm | 20 |
| 50μm | 50 |
| >50μm | 100 |
The concentration of respirable fraction of dust in mg/m3 is
14. The wet bulb temperature of air at a particular place in a mine is 31°C, then the velocity of air in that place should be
15. Intake air containing 0.2% methane enters a section of an underground mine where emission of methane is 0.05m3/s. Assuming that the threshold limit value of methane is 1.25%, the minimum quantity of fresh air required in m3/s is
16. The figure shows PV (pressure-volume) diagram of a mine ventilated by both natural means and an exhaust fan. The total ventilation energy is represented by
17. The black damp accumulates . . . . . . . . to the floor
18. The inflammable gas should be below . . . . . . . . % in the general body of the retunr air way of any ventilating district and below . . . . . . . . % at any place in the mine.
19. A centrifugal fan rotating at 500 rpm. delivers 70 m3/s of air. If the speed is reduced to 200 rpm. the quantity of air delivered in m3/s will be
20. A fan running at a speed of 280 rpm circulates 105 m3/s of air in a mine. If the power input to the motor for driving the fan is recorded to be 75 kW, with the combined efficiency of fan and motor at 70%. If the fan pressure is to be increased by 200 Pa by changing the fan speed. the fan speed in rpm will become
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