Thermodynamics Questions and Answers – Mean Temperature of Heat Addition and Reheat Cycle

This set of tough Thermodynamics Questions focuses on “Mean Temperature of Heat Addition and Reheat Cycle”.

1. In the Rankine cycle, heat is added reversibly at
a) constant pressure and constant temperature
b) constant pressure and infinite temperature
c) infinite pressure and constant temperature
d) infinite pressure and infinite temperature
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2. The efficiency of Rankine cycle is given by
a) 1 – (Q1/Q2)
b) 1 – (Tmean/T2)
c) 1 – (T2/Tmean)
d) none of the mentioned
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3. Which of the following statement is true?
a) for given Tmean, lower is the T2, higher will be the efficiency of Rankine cycle
b) the lowest possible temperature of heat rejection is the surroundings temperature
c) higher is the mean temperature of heat addition, higher will be the efficiency
d) all of the mentioned
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4. If we ____ the superheat at constant pressure then the cycle efficiency ____
a) decrease, increases
b) increase, decreases
c) increase, increases
d) decrease, decreases
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5. The maximum temperature of steam that can be used is not fixed.
a) true
b) false
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6. To prevent erosion of blades, quality should not fall below
a) 85%
b) 90%
c) 95%
d) 100%
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7. To fix the maximum steam pressure at the inlet of turbine we need to first fix
a) the maximum steam temperature at turbine inlet
b) minimum temperature of heat rejection
c) the minimum quality of steam at turbine exhaust
d) all of the mentioned
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8. Which of the following is true about a reheat cycle?
a) used to limit the quality at turbine exhaust at 0.85 when steam pressure is higher than (p1)max
b) after partial expansion in turbine, steam is brought back to boiler
c) the steam is reheated by combustion gases
d) all of the mentioned
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9. The correct sequence of expansion in a reheat cycle is
a) HP turbine – LP turbine – constant pressure in boiler
b) HP turbine – constant pressure in boiler – LP turbine
c) LP turbine – constant pressure in boiler – HP turbine
d) LP turbine – HP turbine – constant pressure in boiler
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10. Why is steam not allowed to to expand deep into two-phase region before being taken for reheating.
a) to protect the reheater tubes
b) to prevent solid deposits being left behind while evaporating
c) both of the mentioned
d) none of the mentioned
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11. Why should the reheat pressure be optimized?
a) a low reheat pressure brings down the mean temperature of heat addition and hence the cycle efficiency
b) a high reheat pressure increases the moisture content at turbine exhaust
c) both of the mentioned
d) none of the mentioned
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12. The optimum reheat pressure is ____ times that of the initial steam pressure.
a) 0.2
b) 0.23
c) 0.25
d) all of the mentioned
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13. With the use of reheat,
a) the net work output of the plant increases
b) there is only a marginal increase in cycle efficiency
c) the quality of steam at turbine exhaust is kept within a limit
d) all of the mentioned
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14. More than three reheats have not been used so far.
a) true
b) false
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Sanfoundry Global Education & Learning Series – Thermodynamics.
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