This set of Thermal Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Steam Condensers – Air Pump”.
1. Which of these has a similar working mechanism to a compressor?
a) Boiler
b) Generator
c) Nozzle
d) Air Pump
View Answer
Explanation: A compressor is used in a continuous-flow operation to compress a gas to develop high pressure in a closed system. In the same way, the Pumps are used in a continuous-flow operation to compress a liquid to develop a relatively low pressure in a closed system.
2. The air pump that removes both air as well as condensate is called a Wet Air Pump.
a) True
b) False
View Answer
Explanation: Air pump is used to create vacuum corresponding to the exhaust steam temperature for removing the condensate air from condenser. Among the classification of air pumps, the pump that removes condensate along with air is called a Wet Air Pump. While the pump that removes only moist air is called a Dry Air Pump.
3. The Edward’s pump is design for which class of Air Pumps?
a) Bucket pumps
b) Rotary pumps
c) Steam jet air pumps
d) Water jet pumps
View Answer
Explanation: The Edward’s design is for a Bucket pump. The feature present in the Edward’s pump design is the absence of inaccessible foot and bucket valves. This is a feature suitable for designing the Bucket pumps or Reciprocating piston.
4. Which of the following is not an effect produced in the down stroke of piston in an Edward’s air pump?
a) Covers the ports
b) Production of partial vacuum
c) Assembly of air and water vapor
d) Rise in pressure
View Answer
Explanation: In an Edward’s air pump, a partial vacuum is produced above the piston as the head valves are closed and sealed by water. Also, once the piston undergoes a down stroke, the ports are uncovered for the movement of air and water onto the space above the piston.
5. An Air-sealed relief valve is used in Bucket wet air pump.
a) True
b) False
View Answer
Explanation: While the pumping process is being done in a Bucket wet air pump, if the inside pressure exceeds the atmospheric pressure, there should be a safety valve for releasing the pressure. For this purpose, a Water-sealed relief valve is placed on the base of the cylinder.
6. Which of the following is not a feature of Rotary air pumps?
a) To remove moist air alone
b) The speed of operation is not limited
c) Lighter in weight comparatively
d) Occupy large space
View Answer
Explanation: The development of this Rotary air pumps was to overcome the disadvantages of reciprocating air pumps. The reciprocating compressors had a limited speed of operation, also were bulky in large power generation applications. Also, the Rotary air pumps are dry air pumps (air pump that removes moist air alone).
7. In a condenser, the air pump and the water pump are installed separately. The steam enters the condenser at 42°C and the condensate is removed at 37°C. The quantity of air infiltrating into the condenser through various zones is 6 kg/h. What is the volume of air handled by the air pump?
a) 35.5 m3/h
b) 37.5 m3/h
c) 41.8 m3/h
d) 39.7 m3/h
View Answer
Explanation: Given, pressure of steam at 42°C = 0.08 bar
Condensate removing temperature = 37°C
Pressure corresponding to 37°C -> 0.065 bar
So, the Partial pressure of air (pa) = 0.08 – 0.065 = 0.015 bar
Now, the volume of air (Va):
Va = \(\frac{mRT}{pa} = \frac{6*0.287 * (273+37)*1000}{0.015*100000}\)
= 35.58 m3/h
8. Entraining effect is seen in which of the following air pumps?
a) Rotary dry air pump
b) Steam jet air pumps
c) Water jet pump
d) Bucket pump
View Answer
Explanation: In the steam-operator air ejector, the steam jet flows through air chamber where it entrains the air other gases adjacent to its surface. The entraining operation is done due to the viscous drag between high velocity steam and air.
9. For maintaining a high vacuum pressure in a steam plant, multiple ejectors (steam operated) are connected in series.
a) True
b) False
View Answer
Explanation: In a steam plant where high vacuum pressure is maintained, it is imperative to use two or three ejectors in series to obtain sufficient increase in pressure in the mixture for discharging it into the atmosphere.
10. Which of these is not a type of water circulating pumps?
a) Rotary type water jet pump
b) Plunger type water jet pump
c) Propeller type water jet pump
d) Centrifugal type water jet pump
View Answer
Explanation: In the water jet pump, the water is circulated through a head. The water jet pumps may be classified as reciprocating type, Plunger type, Centrifugal type and Propeller type.
11. The air leakage into the condenser operating in conjunction with a steam turbine is estimate at 0.675 kg per minute. The vacuum near the outlet to the air pump is 720 mm when the barometer reads 770 mm and the temperature at this point is 18°C. What is the mass of the vapour extracted in kg/min?
a) 0.5 kg/min
b) 1.05 kg/min
c) 1 kg/min
d) 0.18 kg/min
View Answer
Explanation: Pressure in the condenser = 770 – 720 = 50mm of Hg
= 50 * 0.001333
= 0.0666 bar
Partial pressure at 18°C = 0.0206
Partial pressure of air (pa) = 0.0666 – 0.0206 = 0.046 bar
Mass of air leakage = 0.675 kg/min
V = \(\frac{mRT}{pa} = \frac{0.675*287 * (273+18)}{0.046*105}\)
= 12.25 m3/min
From Dalton’s Law of Partial Pressures, volume of steam is same as that of air
Mass of Steam condensed / min = \(\frac{Volume \, of \, steam}{specific\, volume\, of\, steam\, at\, 0.0206 \, bar}\)
= 0.18 kg/min
Sanfoundry Global Education & Learning Series – Thermal Engineering
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