Blowers - Waste Water Engineering Questions and Answers

This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Blowers”.

1. Aeration energy consumes _______ of all electrical usage.
a) 30%
b) 40%
c) 60%
d) 80%
View Answer

Answer: c
Explanation: There are two important considerations for the wastewater treatment plant. They are proper aeration and blower selection. Aeration energy consumes 60% of all the electrical usage.

2. Which of the following is created by blowers?
a) Air flow
b) Water flow
c) Wastewater flow
d) Vacuum flow
View Answer

Answer: a
Explanation: Blowers create air low. The blower system creates pressure through resistance to air flow. By combining the flow rate and back pressure, the actual operating air flow can be identified.

3. Proper air flow can help the bacteria remain suspended.
a) True
b) False
View Answer

Answer: a
Explanation: The essential function of the aeration system is to fulfil the oxygen demands and maintain the treatment process at the lowest possible costs. Proper air flow can help the bacteria remain suspended.

4. What is the purpose of the blower?
a) Decrease air flow
b) Increase air flow
c) Create vacuum
d) Maintain air flow
View Answer

Answer: b
Explanation: The purpose of the blower is to increase the air flow or create additional air flow, the purpose of blower controls is to provide the correct air flow at any time, which in time provides the enhanced aeration efficiency.

5. The presence of DO is necessary for wastewater.
a) True
b) False
View Answer

Answer: a
Explanation: The presence of some amount of dissolved oxygen is necessary in wastewater otherwise the system becomes anaerobic and insufficient. DO help in satisfactory biological wastewater decomposition.

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6. Air is used to ________ the filter bed.
a) Compact
b) Expand
c) Aerate
d) Fluidize
View Answer

Answer: b
Explanation: Air is used to expand the filter bed, breaking up compacted material. When the clean water is pumped in for backwash, it suspends and loosens the material and the particles are lifted through and carried away.

7. Which technology’s principle is used in screw blowers?
a) Air expander
b) Air compressor
c) Ventilators
d) Vacuum creators
View Answer

Answer: b
Explanation: The technology employed with the screw blowers is essentially a scaled version of the principles used in an air compressor. The rotors trap and then squeeze air between them. Air is progressively compressed during each rotation.

8. Which blower among the following has the highest nominal efficiency?
a) Positive displacement
b) Single stage centrifugal
c) Multi stage centrifugal (inlet throttled)
d) Multi stage centrifugal (variable speed)
View Answer

Answer: b
Explanation: The nominal efficiency for single stage centrifugal blower is 70-80%. The nominal efficiency for positive displacement blower is 45-65%. The nominal efficiency for multi stage centrifugal (inlet throttled) is 50-70%. The nominal efficiency for Multi stage centrifugal (variable speed) is 60-70%.

9. When is high pressure required, which type of blower is preferred?
a) Positive displacement blower
b) Centrifugal blower
c) Helical screw blower
d) Regenerative blower
View Answer

Answer: a
Explanation: A blower is selected based on the system’s pressure requirements. When high pressure is required a positive displacement blower is preferred. Performance curve of the blower helps us to identify the suitable blower required for that application.

10. Which type of blower is preferred for fluid bed reactor?
a) Centrifugal blower
b) Positive displacement blower
c) Regenerative blower
d) Helical screw blower
View Answer

Answer: a
Explanation: Centrifugal blowers are used for fluid bed reactors. These are used for dust controlling systems also. These are used for aeration systems in water or waste water treatment plant.

11. What is the specific ratio for a blower?
a) <1.1
b) 1.11-1.2
c) >1.2
d) 1.11
View Answer

Answer: b
Explanation: The ratio of discharge pressure to that of suction pressure is known as the specific ratio. This is 1.1-1.2 for blowers. It is is>1.2 for compressors and <1.1 for fans.

12. Normally what is the pressure under which centrifugal blowers operate?
a) 0.35-0.7 kg/cm²
b) 0.5 -0.7 kg/cm²
c) 0.35 kg/cm²
d) 0.35-0.5kg/cm²
View Answer

Answer: a
Explanation: The centrifugal blower usually works under the pressure 0.35-0.7 kg/cm².In some cases it is used to produce negative pressure. This is achieved under vacuum conditions.

13. Which blower is used when the system is prone to clogging?
a) Centrifugal blower
b) Positive displacement blower
c) Regenerative blower
d) Helical screw blower
View Answer

Answer: b
Explanation: Positive displacement blowers are used when the system is prone to clogging. This is because they provide constant air even when the system pressure changes. These are usually belt driven.

14. Centrifugal pumps have a greater speed of rotation when compared to that of positive displacement blower.
a) True
b) False
View Answer

Answer: a
Explanation: Centrifugal blowers they rotate at a speed up to 15000 rpm. Whereas positive displacement blowers, they rotate at a speed of around <3600 rpm. Also, these are belt driven to facilitate changes in the speed.

15. Dimensionless pressure rise is not dependent on which of the following?
a) Density of the fluid
b) Speed of the blower
c) Diameter of the blower
d) Power of the blower
View Answer

Answer: d
Explanation: Dimensionless pressure rise is not dependent on the power of the blower. It is equal to pressure rise/ {(Diameter of blower)² x (speed of the blower)² x density of the fluid}. It is independent of the flow rate of interest liquid that is handled.

16. What is the maximum discharge pressure of a twin lobe blower?
a) 0.5 kg/cm²
b) 1 kg/cm²
c) 1.5 kg/cm²
d) 0.75 kg/cm²
View Answer

Answer: b
Explanation: The maximum pressure discharged from a twin lobe blower is 1 kg/cm². The capacity of these blowers range from 100-8000 cubic meter/hr. These blowers fall under the positive displacement blowers.

17. How is the static pressure drop in the water column related to the air flow rate?
a) Linearly
b) Inversely
c) There is no relation between them
d) A parabolic curve is obtained
View Answer

Answer: a
Explanation: The static pressure drop in the water column is related linearly to the air pressure. It increases with an increase in air pressure. The air pressure is calculated in terms of ACFM.

18. Which of these is not a characteristic of variable speed drive?
a) Improved speed control of the blower
b) Speed adjustments over a continuous range
c) High cost
d) Can be retrofitted into an existing motor
View Answer

Answer: d
Explanation: Variable speed drives cannot be retrofitted into an existing motor. Variable frequency drive can be retrofitted into an existing motor. Variable frequency drives are less expensive than variable speed drives.

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