Lesson test: Superheat, reheat and regeneration

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Superheat, reheat and regeneration

1.[2p]
What do superheat, reheat and regeneration all have in common?

Each raises the mean temperature at which the cycle takes heat in

Correct

Each lowers the condenser pressure

The answer is: Each raises the mean temperature at which the cycle takes heat in

Each reduces the back work ratio

The answer is: Each raises the mean temperature at which the cycle takes heat in

Each raises the peak metal temperature in the boiler

The answer is: Each raises the mean temperature at which the cycle takes heat in

2.[3p]
Raising the boiler from $3$ MPa and $350$ degrees Celsius to $3$ MPa and $600$ takes $q_{i n}$ to $3488.0$ kJ/kg and the entropy rise to $6.8593$ kJ/(kg K). What is the mean temperature of heat addition, in kelvin?

CorrectNot quite: 508

3.[2p]
With that mean temperature and heat rejection at $319$ K, what thermal efficiency results?

CorrectNot quite: 0.373

4.[3p]
At $15$ MPa and $600$ degrees Celsius, $s_{3} = 6.6796$ kJ/(kg K). Expanding to $10$ kPa where $s_{f} = 0.6492$ and $s_{f g} = 7.4996$ , what exit quality results?

CorrectNot quite: 0.804

5.[3p]
Raising the boiler pressure improves efficiency and makes the exhaust wetter. Why?

Higher pressure at the same temperature means lower entropy at turbine inlet, so the expansion lands further into the dome

Correct

Higher pressure raises the condenser temperature, which condenses more of the steam

The answer is: Higher pressure at the same temperature means lower entropy at turbine inlet, so the expansion lands further into the dome

The pump work rises, and that energy appears as moisture

The answer is: Higher pressure at the same temperature means lower entropy at turbine inlet, so the expansion lands further into the dome

Higher pressure lowers the latent heat, so less of the steam can stay vapour

The answer is: Higher pressure at the same temperature means lower entropy at turbine inlet, so the expansion lands further into the dome

6.[2p]
Reheat is fitted mainly for the efficiency it adds rather than for the moisture it removes.

True

The answer is: False

False

Correct

7.[3p]
An open feedwater heater at $1.2$ MPa delivers saturated liquid at $798.33$ kJ/kg. It is fed with bled steam at $2860.2$ kJ/kg and pumped condensate at $193.01$ kJ/kg. What fraction of the flow must be extracted?

CorrectNot quite: 0.227

8.[2p]
That regenerative cycle supplies $2769.1$ kJ/kg of heat and rejects $1486.9$ kJ/kg. What is its thermal efficiency?

CorrectNot quite: 0.463

9.[3p]
Match each feature of a real plant to why it is there.

Closed feedwater heaters
One open heater, the deaerator
Double reheat
Supercritical pressure

strips dissolved oxygen
no extra pump per heater
raises the mean temperature further
keeps the exhaust dry at high pressure

Show the answer

Closed feedwater heaters: no extra pump per heater One open heater, the deaerator: strips dissolved oxygen Double reheat: keeps the exhaust dry at high pressure Supercritical pressure: raises the mean temperature further

1.[2p] What do superheat, reheat and regeneration all have in common?

2.[3p] Raising the boiler from 3 MPa and 350 degrees Celsius to 3 MPa and 600 takes qin to 3488.0 kJ/kg and the entropy rise to 6.8593 kJ/(kg K). What is the mean temperature of heat addition, in kelvin?

3.[2p] With that mean temperature and heat rejection at 319 K, what thermal efficiency results?

4.[3p] At 15 MPa and 600 degrees Celsius, s3=6.6796 kJ/(kg K). Expanding to 10 kPa where sf=0.6492 and sfg=7.4996, what exit quality results?

5.[3p] Raising the boiler pressure improves efficiency and makes the exhaust wetter. Why?

6.[2p] Reheat is fitted mainly for the efficiency it adds rather than for the moisture it removes.

7.[3p] An open feedwater heater at 1.2 MPa delivers saturated liquid at 798.33 kJ/kg. It is fed with bled steam at 2860.2 kJ/kg and pumped condensate at 193.01 kJ/kg. What fraction of the flow must be extracted?

8.[2p] That regenerative cycle supplies 2769.1 kJ/kg of heat and rejects 1486.9 kJ/kg. What is its thermal efficiency?

9.[3p] Match each feature of a real plant to why it is there.

1.[2p]
What do superheat, reheat and regeneration all have in common?

2.[3p]
Raising the boiler from $3$ MPa and $350$ degrees Celsius to $3$ MPa and $600$ takes $q_{i n}$ to $3488.0$ kJ/kg and the entropy rise to $6.8593$ kJ/(kg K). What is the mean temperature of heat addition, in kelvin?

3.[2p]
With that mean temperature and heat rejection at $319$ K, what thermal efficiency results?

4.[3p]
At $15$ MPa and $600$ degrees Celsius, $s_{3} = 6.6796$ kJ/(kg K). Expanding to $10$ kPa where $s_{f} = 0.6492$ and $s_{f g} = 7.4996$ , what exit quality results?

5.[3p]
Raising the boiler pressure improves efficiency and makes the exhaust wetter. Why?

6.[2p]
Reheat is fitted mainly for the efficiency it adds rather than for the moisture it removes.

7.[3p]
An open feedwater heater at $1.2$ MPa delivers saturated liquid at $798.33$ kJ/kg. It is fed with bled steam at $2860.2$ kJ/kg and pumped condensate at $193.01$ kJ/kg. What fraction of the flow must be extracted?

8.[2p]
That regenerative cycle supplies $2769.1$ kJ/kg of heat and rejects $1486.9$ kJ/kg. What is its thermal efficiency?

9.[3p]
Match each feature of a real plant to why it is there.