This set of Power Plant Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Optimum Degree of Regeneration”.

1. What is the value of “beta” if h represents the local enthalpy on the given expansion line at a given pressure & h_{f} is the enthalpy of saturated water at that pressure?

a) h + h_{f}

b) h x h_{f}

c) h – h_{f}

d) none of the mentioned

View Answer

Explanation: The expression for the value of “beta” if h represents the local enthalpy on the given expansion line at a given pressure & hf is the enthalpy of saturated water at that pressure is given as,

Beta = h – h

_{f}.

2. The expression for temperature rise t in feedwater heater when a & b are the temperatures of boiler saturation & condenser respectively, is given by which of the following expression?

a) t = 0.5 (a x b)

b) t = 0.5 (a / b)

c) t = 0.5 (a + b)

d) t = 0.5 (a – b)

View Answer

Explanation: The expression for temperature rise t in feedwater heater when a & b are the temperatures of boiler saturation & condenser respectively, is given by,

t = 0.5 (a – b).

3. What happens to the feedwater that enters the economiser?

a) Feedwater is heated to the saturation temperature at the boiler pressure

b) Feedwater is heated to the boiler temperature at the saturation pressure

c) Feedwater is cooled to the saturation temperature

d) Feedwater is cooled at the boiler pressure

View Answer

Explanation: The function of an economiser is to heat the feedwater to the saturation temperature at the boiler temperature. Naturally, this is what happens to the feedwater in the Economiser.

4. The economiser can also be assumed as?

a) Feedwater cooler

b) Feedwater heater

c) Economiser has nothing to do with Feedwater

d) None of the mentioned

View Answer

Explanation: The function of an economiser is to heat the feedwater to the saturation temperature at the boiler temperature. Hence, it is assumed as ‘feedwater heater’.

5. The feedwater in the Economiser _________

a) is heated by bled turbine steam

b) is cooled by bled turbine steam

c) is heated by outgoing flue gases

d) is cooled by outgoing flue gases

View Answer

Explanation: The function of an economiser is to heat the feedwater to the saturation temperature at the boiler temperature. This heating of feedwater occurs by the heat given to the feedwater by outgoing flue gases.

6. The temperature rise from condenser to boiler saturation is divided __________ among the feedwater heaters for maximum gain in efficiency.

a) unequally

b) partially

c) equally

d) remains undivided

View Answer

Explanation: The total enthalpy rise or the temperature rise from condenser to boiler saturation is divided equally among the feedwater heaters for maximum gain in the efficiency.

7. What is the expression for enthalpy of each heater h_{per heater} if a represents the enthalpy of heated feedwater from the economiser and b represents the enthalpy at condenser & n represents the number of heaters?

a) h_{per heater} = (a-b)/ (n + 1)

b) h_{per heater} = (a-b) x (n – 1)

c) h_{per heater} = (a-b) + (n – 1)

d) h_{per heater} = (a-b) – (n + 1)

View Answer

Explanation: the expression for enthalpy of each heater h if a represents the enthalpy of heated feedwater from the economiser and b represents the enthalpy at condenser & n represents the number of heaters is given by,

h

_{per heater}= (a-b)/ (n + 1).

8. If n denotes the number of heater, t_{OA} denotes the overall temperature difference & T_{fw} denotes the total temperature rise of feedwater. The expression for T_{fw} is?

a) (n/(n+1)) x t_{OA}

b) (n/(n-1)) x t_{OA}

c) (n/(n+1)) / t_{OA}

d) (n/(n+1)) – t_{OA}

View Answer

Explanation: If n denotes the number of heater, t

_{OA}denotes the overall temperature difference & T

_{fw}denotes the total temperature rise of feedwater. The expression for T

_{fw}is given by the following relation,

T

_{fw}= (n/(n+1)) x t

_{OA}.

9. The expression for the overall temperature difference T_{OA} is given by?

a) t_{OA} = boiler saturation temperature – condenser temperature

b) t_{OA} = boiler saturation temperature + condenser temperature

c) t_{OA} = boiler saturation temperature x condenser temperature

d) t_{OA} = boiler saturation temperature / condenser temperature

View Answer

Explanation: The expression for the overall temperature difference t is given by,

t

_{OA}= boiler saturation temperature – condenser temperature.

10. Efficiency gain follow the law of ____________

a) diminishing forward motion

b) increasing return

c) decreasing return

d) none of the mentioned

View Answer

Explanation: The gain in cycle efficiency is proportional to the gain in feedwater temperature, the efficiency gain thereby follows the law of diminishing return with the increase in the number of heaters.

11. The number of heaters for a plant is fixed by?

a) Mass Balance

b) Energy balance

c) Heat balance

d) None of the mentioned

View Answer

Explanation: The number of heaters for a plant is fixed by Energy Balance of the whole plant when it is found that cost of adding another heater does not justify the saving in heat supply or marginal increase in cycle efficiency.

12. The effect on the degree of regeneration due to an increase in feedwater temperature is?

a) degree of regeneration increases

b) degree of regeneration decreases

c) degree of regeneration remain same

d) degree of regeneration is optimised

View Answer

Explanation: An increase in feedwater temperature reduces the heat absorption from the outgoing flue gases in the economiser & may cause a reduction in boiler efficiency. The number of heaters & the degree of regeneration thus get optimised.

13. The expression for efficiency when a & b are two constants corresponding to alpha & beta and c corresponds to gamma, is?

a) Efficiency = 1 – ((b^{2}))/((b + c)(a + b – c)))

b) Efficiency = 1 + ((b^{2}))/((b + c)(a + b – c)))

c) Efficiency = ((b^{2}))/((b + c)(a + b – c)))

d) Efficiency = 1 / ((b^{2}))/((b + c)(a + b – c)))

View Answer

Explanation: The expression for efficiency when a & b are two constants corresponding to alpha & beta and c corresponds to gamma, is given as,

Efficiency = 1 – ((b

^{2}))/((b + c)(a + b – c))).

14. What is the relation between a & c if a & c correspond to alpha & gamma respectively, for maximum efficiency of a cycle?

a) a = 3c

b) c = 2a

c) c = (a/3)

d) a = 2c

View Answer

Explanation: The relation between a & c if a & c correspond to alpha & gamma respectively, for maximum efficiency of a cycle is given by,

c = (a/2).

15. The expression for efficiency gain due to regeneration if a, b, n correspond to alpha, beta, cycle efficiency respectively, is?

a) n = ((a x a x b)/((a + b)(a + 2b)^{2}))

b) n = ((a x a x b)/((a – b)(a + 2b)^{2}))

c) n = ((a x a x b)/((a + b)(a + b)^{2}))

d) n = ((a x a x b)/((a + b)(a + 2b)^{3}))

View Answer

Explanation: The expression for efficiency gain due to regeneration if a, b, n correspond to alpha, beta, cycle efficiency respectively is given by,

n = ((a x a x b)/(a + b)(a + 2b)

^{2})).

**Sanfoundry Global Education & Learning Series – Power Plant Engineering.**

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