This set of Thermodynamics assessment questions focuses on “Characteristics of an Ideal Working Fluid in Vapor Power Cycles”.
1. Which of the following statement is true about steam?
a) the maximum temperature that can be used in steam cycles is 600 degree Celsius
b) the critical temperature of steam is around 375 degree Celsius
c) large superheating is required
d) all of the mentioned
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Explanation: These are certain drawbacks with steam as working fluid.
2. With steam as working fluid, as pressure increases
a) metal stresses increases
b) thickness of walls of tubes, boiler drums, etc increases
c) both of the mentioned
d) none of the mentioned
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Explanation: These changes take place very rapidly because of prevalence of high temperature.
3. At the heat rejection temperature of 40 degree Celsius, the saturation pressure of steam is 0.075 bar.
a) true
b) false
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Explanation: This pressure is considerably lower than the atmospheric pressure.
4. The working fluid should have ____ critical temperature.
a) low
b) high
c) it does not matter
d) none of the mentioned
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Explanation: This is to have a low saturation pressure at the maximum allowed temperature.
5. The saturation pressure at heat rejection temperature should be ____ atmospheric pressure.
a) equal to
b) below
c) above
d) none of the mentioned
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Explanation: This is done to avoid the necessity of vacuum in the condenser.
6. The specific heat of the working fluid should be ____
a) small
b) large
c) very large
d) none of the mentioned
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Explanation: This is done so that little heat transfer is required to raise the liquid to its boiling point.
7. The freezing point of fluid should be ____ room temperature.
a) equal to
b) below
c) above
d) none of the mentioned
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Explanation: So that the fluid does not get solidified when it flows through pipelines.
8. The fluid should be chemically ____ and ____ contaminate the material of construction.
a) unstable, should
b) unstable, should not
c) stable, should
d) stable, should not
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Explanation: The working fluid used should be stable and should not contaminate at any temperature.
9. The fluid should not be toxic, corrosive or excessively viscous.
a) true
b) false
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Explanation: Also the working fluid should be low in cost.
10. Why is superheat desired?
a) to reduce piping losses
b) to improve efficiency
c) both of the mentioned
d) none of the mentioned
View Answer
Explanation: The thermal efficiency of the cycle is close to Carnot efficiency.
Sanfoundry Global Education & Learning Series – Thermodynamics.
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