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Thermal Engineering Mcqs

Q:

Which of the following statement is TRUE about balanced draught?

A) No fan/blower is installed B) A fan/blower is installed in the middle of the chimney
C) One fan/blower is installed at the base of the boiler and one near the base of the chimney D) Two fans/blowers are installed both at the base of the boiler
 
Answer & Explanation Answer: C) One fan/blower is installed at the base of the boiler and one near the base of the chimney

Explanation: Balanced draught is the combination of forced draught and induced draught. In forced draught the fan/blower is located near or at the base of the chimney. In induced draught the fan/blower is located near the base of the boiler.

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2164
Q:

Radial flow of steam is observed in _____

A) down-flow type surface condenser B) central-flow type surface condenser
C) regenerative type surface condenser D) evaporative Surface condenser
 
Answer & Explanation Answer: B) central-flow type surface condenser

Explanation: In central-flow type surface condenser, the suction pipe of air extraction pump is located at the center of the tubes. This results in radial flow of the steam. In this case the pressure drop of steam is less.

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1237
Q:

Steam issues from the nozzle with a velocity of 1000 m/s in a De Laval turbine. The nozzle angle is 20°, mean blade velocity is 350 m/s. The inlet and outlet angles of the blades are equal. The mass of the steam flowing through the turbine per second is 0.3 kg. Calculate the tangential force on the blades. Take blade velocity coefficient as 0.8.

A) 451 N B) 256 N
C) 318 N D) 196 N
 
Answer & Explanation Answer: C) 318 N

Explanation: Not available for this question

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1028
Q:

LMTD in case of condenser will ________ for counter and parallel flow heat exchanger.

A) Remain same B) Not be equal
C) Cannot be determined D) Will not change with time
 
Answer & Explanation Answer: A) Remain same

Explanation: In case of condenser and evaporator ?T1 and ?T2 remains same in case of counter and parallel flow heat exchanger. Therefore LMTD in case of condenser will be same for counter and parallel flow heat exchangers.

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919
Q:

Following observations were made after the trial of a boiler for 24 hours.
Mass of coal burnt = 1300 kg
Mass of steam generated = 14000 kg
Mean effective pressure of steam = 10 bar
Temperature of the feed water = 40°C
Calorific value of coal = 30000 kJ/kg
Calculate the boiler efficiency if the dryness fraction of the steam generated is 0.95.

A) 90% B) 80%
C) 70% D) 60%
 
Answer & Explanation Answer: A) 90%

Explanation: Not available for this question

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832
Q:

Which of the following is a fixed factor on which boiler efficiency depends?

A) Actual firing rate B) Humidity of combustion air
C) Condition of heat absorbing surfaces D) Properties of the fuel burnt
 
Answer & Explanation Answer: D) Properties of the fuel burnt

Explanation: The efficiency of a boiler depends on two types of factors – fixed factors and variable factors. Boiler design, Heat recovery equipment, built in loses, rated rate of firing and properties and characteristics of the fuel burnt are all fixed factors. Actual firing rate, humidity of combustion air, condition of heat absorbing surfaces are variable factors.

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771
Q:

In a Parson’s reaction turbine, the outlet angle of blade is 25°. Calculate the work done per second by the blades if the blade mean blade speed is 60 m/s and the absolute velocity of the steam leaving the nozzle is 120 m/s. The mass flow rate of steam is 0.1 kg per second.

A) 756 W B) 854 W
C) 945.12 W D) 1065 W
 
Answer & Explanation Answer: C) 945.12 W

Explanation: Not available for this question

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760
Q:

In an impulse turbine, the axial force on the blades is zero if _____

A) the whirl components of the inlet and outlet absolute velocities are equal B) the flow components of the inlet and outlet absolute velocities are equal
C) the exit velocity of steam is axial D) the flow and whirl component of inlet velocity are equal
 
Answer & Explanation Answer: B) the flow components of the inlet and outlet absolute velocities are equal

Explanation: Not available for this question

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