Noise produced by cooling fans (employed in air cooled heat exchangers or cooling tower) is mainly caused due to the turbulence created by blade passage through air. It can be reduced by use of a slower fan_________________?

Related Mcqs:

1. High noise levels produced during operation of fans and compressors can be reduced by using__________________?

   A. Mufflers (silencers)
   B. Acoustic absorbent
   C. Lagging of noisy duct
   D. None of these

2. Aerodynamic noise resulting from turbulent gas flow is the most prevalent source of valve noise in fluid flow control. It is caused due to_________________?

   A. Reynold stresses
   B. Shear forces
   C. Both A. & B.
   D. Neither A. nor B.

3. Major sources of noise in furnace operation arises from air inspirators, combustion, side wall vibrations and fluctuation in the process heat load. A 50% increase in fuel firing rate may increase the furnace noise level by about ____________ decibels?

   A. 3
   B. 30
   C. 7
   D. 70

4. The major reason of hydrodynamic noise (i.e., noise resulting from liquid flow) is_________________?

   A. Pipe vibrations
   B. Cavitation
   C. Boundary layer separation
   D. Fluctuation in liquid flow

5. Lung cancer & DNA breakage are the major ill effects of excessive ozone exposure to human beings. Ozone layer depletion in the atmosphere is mainly caused by the presence of________________?

   A. CO2
   B. SO2
   C. Hydrocarbons
   D. CFC (chloro fluoro carbon)

6. The resistance of water to the passage of light through it is a measure of the___________________?

   A. Turbidity
   B. Color
   C. Hardness
   D. Dissolved gases

7. The progressive warming up of the earth’s surface is mainly due to the___________________?

   A. Automobile exhaust
   B. Blanketing effect of CO2 in the atmosphere
   C. De-forestation
   D. Thickening of ozone layer

8. Noise pollution level in a chemical plant is expressed in __________________?

   A. Roentgen
   B. Decibel
   C. Hertz
   D. None of these

9. Maximum allowable noise exposure limits for a man working for 8 hours a day in a noisy chemical plant is about ______________ decibels?

   A. 20
   B. 60
   C. 90
   D. 120

10. Noise emitted by a ventilation fan at a distance of 3 metres is about _____________ decibels?

    A. 85
    B. 105
    C. 125
    D. 145