Power Plant Engineering Multiple Choice Questions on “Feedwater Heaters – 2”.
1. Feed water heaters are of how many types?
a) One
b) Two
c) Three
d) Four
Answer: b
Clarification: There are two types of feed water heaters-
1) Open Heater
2) Closed Heater.
2. What is the other name of the open heater?
a) shell & tube heat exchangers
b) contact type heaters
c) regenerative heat exchangers
d) closed heaters
Answer: b
Clarification: Open heaters are also known as contact type heaters where the extracted steam is allowed to mix with feedwater & both leave the heater at a common temperature.
3. What is the condition of the fluids in closed heaters?
a) they are separate
b) they are mixed
c) they are partially mixed
d) none of the mentioned
Answer: a
Clarification: The fluids in a closed heater are un-mixed or separated. Closed heaters are heat exchangers.
4. Closed heaters are ______________ heat exchangers.
a) parallel flow
b) shell-and-tube
c) counter flow
d) cross- flow
Answer: b
Clarification: Closed heaters are shell-and-tube heat exchangers where the feedwater flows through the tubes & the extracted steam condenses outside the walls in the shell. The heat released by condensation is transferred through the walls of the tubes.
5. What is the other name of the condensate obtained after condensation in a shell-and-tube heat exchanger type closed heaters?
a) Heater rise
b) Heater fall
c) Heater drip
d) None of the mentioned
Answer: c
Clarification: Closed heaters are shell-and-tube heat exchangers where the feedwater flows through the tubes & the extracted steam condenses outside the walls in the shell. The heat released by condensation is transferred through the walls of the tubes. The condensate sometimes called the heater drip then passes to the next lower level.
6. What is the function of the trap applied to the condensate?
a) the trap stops the condensate fully
b) the trap stops only vapour & allows liquid to pass through it
c) the trap stops only liquid & allows vapour to pass through it
d) none of the mentioned
Answer: b
Clarification: The main function of the trap applied to the flow of condensate is to stop vapour & allow liquid to flow through it.
7. Which of these is the correct expression for terminal temperature difference(TTD)?
a) TTD = saturation temperature of ‘bled’ steam – exit water temperature
b) TTD = saturation temperature of ‘bled’ steam + exit water temperature
c) TTD = saturation temperature of ‘bled’ steam x exit water temperature
d) TTD = saturation temperature of ‘bled’ steam / exit water temperature
Answer: a
Clarification: The expression for terminal temperature difference for a closed heater is given as,
TTD = saturation temperature of ‘bled’ steam – exit water temperature.
8. If terminal temperature difference (TTD) is too small, what will be its impact on plant efficiency?
a) it increases
b) it decreases
c) it remains same
d) none of the mentioned
Answer: a
Clarification: The formula for TTD is given as,
TTD = saturation temperature of ‘bled’ steam – exit water temperature.
9. If plant efficiency is high, what will be its effect on heater size?
a) it remains same
b) it increases
c) it decreases
d) none of the mentioned
Answer: b
Clarification: Too small a value of TTD, it is good for plant efficiency & consequently, this would require a larger heater.
10. When is a drain-cooler used?
a) when the extracted steam upon condensation gets subcooled
b) when the extracted steam upon subcooling gets condensed
c) the extracted stream has no dependence on drain-cooler
d) none of the mentioned
Answer: a
Clarification: When extracted steam gets subcooled upon condensation, a drain cooler may be used.
11. Which of these is a disadvantage of open heater?
a) simplicity
b) lower cost
c) high heat transfer capacity
d) none of the mentioned
Answer: d
Clarification: The disadvantage is the necessity of a pump at each heater to handle the large feedwater stream.
12. Which of the following is not an advantage of an open heater?
a) simplicity
b) lower cost
c) high heat transfer capacity
d) necessity of a pump at each heater to handle the large feedwater stream
Answer: d
Clarification: The disadvantage is the necessity of a pump at each heater to handle the large feedwater stream.
13. The number of pumps required by a closed heater for pumping the main feedwater stream is?
a) 1
b) 2
c) 3
d) 4
Answer: a
Clarification: A closed heater requires only a single pump for the main feedwater stream regardless of the number of heaters.
14. What is the purpose of using open heaters in steam power plants?
a) feedwater purification
b) feedwater esterification
c) feedwater deaeration
d) feedwater carbonisation
Answer: c
Clarification: In most steam power plants, closed heaters are more favored than open heaters & so are used primarily for the purpose of feedwater deaeration.
15. Why are closed heaters sometimes made vertical?
a) to reduce weight of heaters
b) to reduce floor areas for installations
c) to minimize losses due to weight
d) none of the mentioned
Answer: b
Clarification: Closed heaters are mostly horizontal. Sometimes, they are made vertical to reduce the floor areas needed for their installations.