Power Plant Engineering Multiple Choice Questions 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 & hf is the enthalpy of saturated water at that pressure?
a) h + hf
b) h x hf
c) h – hf
d) none of the mentioned
Answer: c
Clarification: 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 – hf.
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)
Answer: d
Clarification: 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: c
Clarification: 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 hper 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) hper heater = (a-b)/ (n + 1)
b) hper heater = (a-b) x (n – 1)
c) hper heater = (a-b) + (n – 1)
d) hper heater = (a-b) – (n + 1)
Answer: a
Clarification: 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,
hper heater = (a-b)/ (n + 1).
8. If n denotes the number of heater, tOA denotes the overall temperature difference & Tfw denotes the total temperature rise of feedwater. The expression for Tfw is?
a) (n/(n+1)) x tOA
b) (n/(n-1)) x tOA
c) (n/(n+1)) / tOA
d) (n/(n+1)) – tOA