Power Plant Engineering Multiple Choice Questions on “Flaws of Steam as a Working Fluid and Vapor Cycle Characteristics”.
1. Addition of an infinitesimal amount of heat at the highest temperature is because ___________
a) to initiate reheating
b) to initiate regeneration
c) to initiate superheating
d) none of the mentioned
Answer: c
Clarification: The maximum temperature gained in steam cycles using the best available material is about 600 degree Celsius while the critical temperature of steam is about 375 degree Celsius, which necessitates large superheating and permits addition of an infinitesimal amount of heat at the highest temperature.
2. High moisture content is involved during expansion of steam because ___________
a) to ensure uniform heating
b) to ensure uniform cooling
c) to obtain a higher temperature of heat addition
d) to obtain a lower temperature of heat addition
Answer: c
Clarification: In order to obtain a higher temperature of heat addition, heat moisture content is involved during expansion of steam.
3. What is the relation of the mean temperature of heat addition and cycle efficiency?
a) both are inversely proportional
b) both are directly proportional
c) both are independent of each other
d) none of the mentioned
Answer: b
Clarification: The cycle efficiency is a function of mean temperature of heat addition. Hence, both are directly proportional to each other. The need for high pressure is only forced due to weak characteristics of steam.
4. Temperature of heat rejection in a condenser can be lowered by using?
a) lubricant
b) oil
c) refrigerant
d) diesel
Answer: c
Clarification: A refrigerant in the form of coolant is used to lower the temperature of heat rejection.
5. The use of which of the following becomes necessary during expansion of steam?
a) reheat
b) regeneration
c) refrigeration
d) superheat
Answer: a
Clarification: In order to obtain a higher temperature of heat addition, heat moisture content is involved during expansion of steam. The use of reheat thus becomes necessary.
6. Which is the drawback of the steam as a working substance in a power cycle?
a) in a vapour power cycle, maximum temperature which can be obtained with best available material is more than the critical temperature of water and requires large superheating
b) it allows only small amount of heat addition at the highest temperature
c) it requires reheat and reheater tubes are costly
d) all of the mentioned
Answer: d
Clarification: All the drawbacks mentioned are correct.
7. For maximum efficiency of vapour power cycle, what should be the critical temperature of working fluid?
a) the working fluid should have critical temperature as low as possible
b) the working fluid should have critical temperature as high as possible
c) the critical temperature does not affect the efficiency of the vapour power cycle
d) none of the mentioned
Answer: b
Clarification: More the critical temperature, more efficient will be the working.
8. What is the specific heat of the ideal working fluid used in vapour power cycle?
a) should be constant
b) should be large
c) should be small
d) none of the mentioned