Thermal Engineering Questions and Answers – Reheat Factor and Energy Losses in Steam Turbines

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This set of Thermal Engineering Question Bank focuses on “Reheat Factor and Energy Losses in Steam Turbines”.

1. What is ‘state point’?
a) It is that point on h-s diagram which represents the condition of steam at that instant
b) It is that point on P-v diagram which represents the condition of steam at that instant
c) It is that point on T-s diagram which represents the condition of steam at that instant
d) It is that point on P-s diagram which represents the condition of steam at that instant
View Answer

Answer: a
Explanation: State point is that point on h-s diagram which represents the condition of steam at that instant. Therefore, to know the initial state point, one must have the knowledge of the initial condition of the steam entering the nozzle.
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2. The curve traced by joining all the state points is called _____
a) state point curve
b) state point locus
c) state point diagram
d) state point graph
View Answer

Answer: b
Explanation: State point on a h-s diagram represents the condition of the steam at that particular instant. The curve traced by joining all the state points is called ‘state point locus’. Using state point locus, the condition of steam at any point from initial to final state can be determined.

3. Which of the following is the correct expression for reheat factor?
a) \(\frac{Cumulaive \, heat \, drop}{Isentropic \, enthalpy \, drop} \)
b) \(\frac{Isentropic \, enthalpy \, drop}{Cumulaive \, heat \, drop} \)
c) \(\frac{Adiabatic \, heat \, drop}{Isentropic \, enthalpy \, drop} \)
d) \(\frac{Isentropic \, enthalpy \, drop}{Adiabatic \, heat \, drop} \)
View Answer

Answer: a
Explanation: Reheat factor is the ratio of cumulative heat drop to isentropic enthalpy drop.
Therefore, the correct answer is –
Reheat factor = \(\frac{Cumulaive \, heat \, drop}{Isentropic \, enthalpy \, drop} = \frac{h_{cum}}{h_{adi}} \)
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4. The value of reheat factor doesn’t depend on _____
a) stage efficiency
b) initial condition of steam
c) final pressure
d) atmospheric temperature
View Answer

Answer: d
Explanation: The value of reheat factor depends on stage efficiency, final pressure and initial pressure and condition of steam. It doesn’t depend on the atmospheric temperature. Reheat factor is calculated using the expression \(\frac{Cumulaive \, heat \, drop}{Isentropic \, enthalpy \, drop} \).

5. Which of the following statements regarding reheat factor is TRUE?
a) It is always less than 1
b) It is always greater than 1
c) It is always equal to or less than 1
d) It might be less than one
View Answer

Answer: b
Explanation: Reheat factor is the ratio of cumulative heat drop (hcum) to isentropic (or adiabatic) enthalpy drop (hadi). Isentropic (or adiabatic) enthalpy drop is always less than the cumulative heat drop, hence reheat factor is always greater than 1.
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6. The process of draining steam from the turbine, at specific points during its expansion for heating the feed water is called _____
a) governing
b) reheating
c) bleeding
d) recycling
View Answer

Answer: c
Explanation: Bleeding is the process of draining of steam from the turbine, during its expansion, for heating the feed water supplied to the boiler. The steam temperature drops when it comes in contact with the feed water and thus is condensed. The condensed steam is taken to hot well.

7. Which of the following in an implication of bleeding process?
a) efficiency and power developed both are increased
b) efficiency is decreased and power developed is increased
c) efficiency and power developed both are decreased
d) efficiency is increased and the power developed is decreased
View Answer

Answer: d
Explanation: As a result of bleeding hotter water is supplied to the boiler due to which the efficiency of the boiler is increased. But small amount of steam is withdrawn from the turbine, which results in reduction of turbine work. Hence, power developed is reduced.
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8. Which of the following losses does not come under ‘Internal losses in steam turbines’?
a) Losses due to wetness of steam
b) Losses in regulating valve
c) Leaving velocity losses
d) Mechanical losses
View Answer

Answer: d
Explanation: Mechanical losses doesn’t come under internal losses; it comes under external losses. Losses due to wetness of steam, losses in regulating valve and exit velocity losses are all internal losses. External losses also include losses due to leakage of steam from the labyrinth gland seals.

9. Which of the following statements is TRUE regarding the losses the steam turbines?
a) Impingement losses are a type of internal losses
b) Losses due to shrouding are a type of internal losses
c) Mechanical losses are external losses
d) Losses in exhaust piping are a type of external losses
View Answer

Answer: d
Explanation: Losses in exhaust piping are characterized under internal losses. Internal losses also include impingement losses and losses due to shrouding. Mechanical losses and losses due to leakage come under external losses.
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10. Losses directly connected with the steam conditions while it is flowing through the turbine are called internal losses.
a) True
b) False
View Answer

Answer: a
Explanation: Internal losses are directly connected with the steam conditions while it is flowing throughthe turbine. Internal losses include losses in regulating valves, losses in nozzles, losses in moving blades, exit velovity losses etc.

11. Losses which do not influence steam conditions are called external losses.
a) True
b) False
View Answer

Answer: a
Explanation: External losses are the losses that do not influence the steam conditions. External losses are further classified as mechanical losses and losses due to leakage of steam from the labyrinth gland seals.

Sanfoundry Global Education & Learning Series – Thermal Engineering

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter