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A fan running at a speed of 280 rpm circulates 105 m<sup>3</sup>/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
A
768
B
549
C
392
D
332
Correct Answer:
332
A fan running at a speed of 280 rpm circulates 105 m
3
/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%. the fan pressure in Pa is
A
50
B
350
C
500
D
650
A mine ventilation system consists of two splits A and B with resistances of 0.8 Ns
2
m
-8
and 3.2 Ns
2
m
-8
, respectively as shown in figure. Trunk airways have resistance of 0.2 Ns
2
m
-8
. The main mine fan is generating pressure of 500 Pa.
The flows in the two splits are equalized by placing a booster fan in split B. Assume that the fan pressure does not change after installation of the booster fan. The size of the booster fan in Pa is
A
749.05
B
850.08
C
950.02
D
1000.5
A main fan of a mine circulates 40 m
3
/s of air at a pressure of 500 Pa. the mine has two splits of equal resistance. The trunk airways have a total resistance of 0.2 Ns
2
/m
8
. When a booster fan is installed in one split, the flow of air in the other splits stops. Assuming that the pressure remains unchanged, the new air quantity flowing through the mine in m
3
/s is
A
20
B
30
C
40
D
50
A mine fan produces 30 m
3
/s of air at 240 Pa pressure running at 1400 rpm. If the fan speed is increased to 2100 rpm, the pressure in Pa and the quantity in m
3
/s generated by the fan will be
A
540 and 67.5
B
540 and 45.0
C
360 and 45.0
D
540 and 30.0
Pressure characteristic of a mine fan is given by. P = -0.06Q
2
+ 400. where P is the pressure in Pa and Q is the quantity in m
3
/s. The resistance of the mine is 0.19 Ns
2
/m
8
. An identical fan is installed in the mine to operate in series with the existing fan. The new mine quantity in m
3
/s is
A
75.6
B
56.7
C
50.8
D
30.2
An exhaust fan attached to an evasee of 18 m
2
cross-sectional area at the outlet circulates 150 m
3
/s of air at the pressure of 1000 Pa in a mine ventilation system. The ratio of the inlet to outlet area of the evasee is 1 : 4 and the density of air is 1.2 kg/m
3
. The quantity of air circulated in the mine in absence of evasee is 120 m
3
/s. The eva see efficiency in % is
A
57.6
B
43.2
C
39.06
D
37.7
A mine ventilation system consists of two splits A and B with resistances of 0.8 Ns
2
m
-8
and 3.2 Ns
2
m
-8
, respectively as shown in figure. Trunk airways have resistance of 0.2 Ns
2
m
-8
. The main mine fan is generating pressure of 500 Pa.
The air quantities in m
3
/s circulated in the splits A and B respectively are
A
20 and 30
B
30 and 20
C
20 and 10
D
40 and 10
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
A
Area ABF + Area CDEF
B
Area ABRS + Area CDEF
C
Area ABRS + Area QDCR
D
Area ABF + Area QDCR
The fan drift pressure readings and fan quantities are measured to be 500 Pa and 65 m
3
/s respectively at the time when NVP aids fan pressure. On reversal, the fan delivers a quantity of 50 m
3
/s while acting against NVP with fan drift pressure of 600 Pa. Assuming that the NVP remains constant in both cases the total resistance of the mine in Ns
2
/m
8
will be
A
0.9487
B
0.2750
C
0.4105
D
0.1635
A fan ventilating a heading through a duct of 750mm diameter circulates 5m
3
s
-1
of air at the face. Calculate the heat added to the air by the fan, if the input power of the fan is equal to 3kW.
A
1667 J
B
2617 J
C
2917 J
D
3317 J
