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Multiple choice question for engineering

Set 1

1. The cycle of evaporation and rain in nature can be assumed to be a kind of Carnot cycle. If ocean water instead of evaporation are boiled by the heat of Sun at a constant temperature of 100 deg C and the condensation of steam into water droplets within the clouds occur at constant temperature of -20 deg C. Find the thermal efficiency of Carnot cycle of nature?
a) 0.2777
b) 0.3030
c) 0.3333
d) 0.50

Answer: b [Reason:] Carnot thermal efficiency= 1-( Mean temperature of heat addition)/( Mean temperature of heat rejection).

2. How is it advantageous to expand steam at 250 deg C in a turbine as compared to expanding saturated steam in similar turbine?
a) Enhances the thermal efficiency of the cycle
b) Reduces the mechanical damage caused to turbine blades due to wet steam
c) Increases the mean temperature of heat addition
d) All of the mentioned

Answer: d [Reason:] Superheating steam makes expansion within turbine to take place in dry region to a greater extent.

3. In a steam turbine power plant, the boiler feedwater temperature is marked as 30 deg C, ocean as sink with temperature 20 deg C and desired thermal efficiency of the plant is 0.46. Find the temperature of steam entering the turbine?
a) 500degC
b) 505.55degC
c) 507.62degC
d) 509.18degC

Answer: d [Reason:] Mean temperature of heat addition= ( Temperature of feedwater + Temperature of steam entering turbine)/2.

4. In a newly developed innovative idea brought up by CSIR in India, gas turbine exhaust gas are being utilized to convert feedwater into steam. Certain data of the experiment are as follows: mass flow rate of exhaust gas= 40 kg/hr, enthalpy of exhaust gas at the time of their exit from gas turbine is 600 kJ/kg, steam turbine output as measured by brake dynamometer=60 hp-sec, thermal efficiency of steam power plant is 0.25, efficiency of exhaust gas in converting feedwater into steam is taken as 50%. Find the enthalpy of exhaust gas remaining after they generate steam from feedwater?
a) 350.0KJ/Kg
b) 241.2KJ/Kg
c) 112.45KJ/Kg
d) 512.56KJ/Kg

Answer: b [Reason:] Heat added= difference of enthalpies * efficiency of exhaust gas in converting feedwater into steam and then apply thermal efficiency formula for Carnot efficiency.

5. Why does Carnot cycle has maximum efficiency?
a) Since all the processes in Carnot cycle are completely reversible
b) Since only process of expansion and compression are reversible
c) Since only the process of heat addition and heat rejection are reversible
d) Since all processes involved are irreversible

Answer: a [Reason:] All the processes in Carnot cycle are completely reversible.

6. A researcher during an experiment found that mean temperature of heat addition and heat rejection for a steam power plant operating on a Carnot cycle is 127 deg C and 27 deg C respectively. Later, he calculated the thermal efficiency of the steam cycle. Can you predict what was it?
a) 0.20
b) 0.25
c) 0.30
d) 0.35

Answer: b [Reason:] Thermal efficiency of a Carnot cycle is given by ( Mean temperature of heat addition-Mean temperature of heat rejection)/(Mean temperature of heat addition).

7. If Carnot cycle has maximum possible thermal efficiency, then why don’t the steam turbine power plants run on Carnot cycle?
a) Because the process of heat addition is at constant temperature
b) As mean temperature of heat addition is quite low in case of Carnot cycle
c) Since work consumed by compressor is approximately equal to work produced by turbine
d) Because boiler can’t be maintained at constant pressure in Carnot cycle

Answer: c [Reason:] As compressor and turbine both work on wet steam, therefore they don’t have significant difference in their work.

8. The mass of coal(lignite) used in boiler of a steam power plant is 20 ton per hour and calorific value of lignite is 13600 KJ/kg. Also, if the entropy of steam entering turbine is =750 J/K and that of feedwater entering the boiler is =550J/K. Find the mean temperature of heat addition?
a) 100 deg C
b) 115 deg C
c) 110 deg C
d) 105 deg C

Answer: d [Reason:] Tmean= Q/( change in entropy).

9. In a solar operated steam power plant, water is converted into steam via solar heat. If the effective area of solar plate is 200m^2, value of solar constant is 1.362KW per m^2, efficiency of solar components is 17% and overall thermal efficiency of steam cycle desired is 12%. Find the turbine power output ?
a) 45KW
b) 22.46KW
c) 5.55KW
d) 16.54KW

Answer: c [Reason:] Efficiency of steam cycle=( Turbine power output/ ( solar constant*area*solar efficiency)).

10. A boiler feed pump is used to raise:
a) Static pressure of feedwater
b) Dynamic pressure of feedwater
c) Static & Dynamic pressure of feedwater
d) None of the mentioned

Answer: a [Reason:] Since water needs to be brought to boiler pressure and is not in motion.

Set 2

1. Centrifugal compressors are also know as ____________
a) turbo compressors
d) none of the mentioned

2. In idealized turbo machinery pressure rise is done by adding _______
a) Temperature
b) Mass
c) Kinetic energy
d) None of the mentioned

Answer: c [Reason:] In idealized turbo machinery the pressure rise is done by adding kinetic energy.

3. The pressure rise in impeller is _________ the rise in diffuser.
a) equal to
b) greater than
c) equal to or greater than
d) none of the mentioned

Answer: d [Reason:] Not in all cases pressure rise in diffuser equals to pressure rise in impeller in some cases pressure rise in impeller will be more than that of diffuser.

4. In centrifugal compressor velocity of flow leaving the impeller is equals to _______ in many cases.
a) Speed of sound
b) Double the speed of sound
c) Triple the speed of sound
d) None of the mentioned

Answer: a [Reason:] Initially the flow enters straightly into the impeller and the impeller pushes the flow inwards to spin faster and finally when the flow is leaving impeller it has almost speed of sound.

5. ________ are used as stationary compressors in steam turbines.
a) moving vanes
b) Guide vanes
c) moving & Guide vanes
d) None of the mentioned

Answer: b [Reason:] Guide vanes are used as stationary compressors where guide vanes reduces the velocity and according to the Bernoulli’s theorem when velocity is reduced its pressure is increased.

6. ________________ has large change in inlet to exit radius when compared to centrifugal compressors.
a) Axial compressors
b) Axial & Centrifugal compressors
c) Centrifugal compressors
d) None of the mentioned

Answer: c [Reason:] Centrifugal compressors has large change in inlet to exit temperature when compared to axial compressor.

7. The first part in both centrifugal compressor and axial compressor are similar.
a) True
b) False

Answer: a [Reason:] The first in both centrifugal compressor and axial compressor are similar.

8. Centrifugal compressor __________ the energy by increasing the radius where as centrifugal fan decreases the energy.
a) increases
b) decreases
d) none of the mentioned

Answer: b [Reason:] Both centrifugal compressor and centrifugal fan are similar as both increases the energy by reducing the radius.

9. Centrifugal compressors increases the density of fluid more than ________
a) 1%
b) 3%
c) 5%
d) None of the mentioned

Answer: c [Reason:] Centrifugal compressors increases the density of fluid more than 5 %.

10. Centrifugal fan has relative fluid velocities ______
a) Mach number more than 0.3
b) mach number less than 0.1
c) Mach number less than 0.3
d) None of the mentioned

Answer: c [Reason:] Centrifugal fans often operate at fluid velocities less than mach number 0.3.

Set 3

1. No of dimensions used in centrifugal compressors are____________
a) 1
b) 2
c) 3
d) None of the mentioned

Answer: c [Reason:] Centrifugal compressors use three dimensions. They are Mass Length Time.

2. Flow in a centrifugal compressor is inversely proportional to _______
a) Time
b) Square of time
c) Cube of time
d) None of the mentioned

Answer: a [Reason:] Flow in centrifugal compressor is inversely proportional to the time.

3. Head in centrifugal compressor is __________ to square of the time.
a) directly proportional
b) equal to
c) inversly proportional
d) none of the mentioned

Answer: c [Reason:] Head in centrifugal compressor is inversely proportional to square of the time.

4. Continuity equation can be applied to centrifugal compressor.
a) True
b) False

Answer: a [Reason:] Continuity equation also known as conservation of mass can be applicable to centrifugal compressor.

5. Navier stokes equation is conservation of ______
a) Mass
b) Momentum
c) Both of the mentioned
d) None of the mentioned

Answer: b [Reason:] Navier stokes equation is conservation of momentum.

6. Centrifugal compressor is an _______
a) irreversible process
b) quasi static process
c) reversible process
d) none of the mentioned

Answer: c [Reason:] Under some circumstances centrifugal compressor is reversible process.

7. In centrifugal compressor flow is ____________
b) Perpendicular
d) none of the mentioned

8. In centrifugal compressor centrifugal energy present in the gas is utilized to _____
a) compress
b) increase temperature
d) none of the mentioned

Answer: a [Reason:] In centrifugal compressor centrifugal energy present in the gas is utilized to do work.

9. Centrifugal compressor delivers _______ flow capacity.
a) high
b) low
c) medium
d) none of the mentioned

Answer: b [Reason:] Centrifugal compressor delivers low flow capacity.

10. Rotating speed of centrifugal compressor is _______ function of diameter to be maintained.
a) inverse
b) direct
c) point
d) none of the mentioned

Answer: a [Reason:] Rotating speed of centrifugal compressor is inverse function of diameter to be maintained.

Set 4

1. Gas turbine controls are classified into ____ types.
a) 1
b) 2
c) 3
d) None of the mentioned

Answer: b [Reason:] Gas turbine drives are classified into two types.

2. DSC interface is used in __________
a) compressor drive
b) turbine drive
c) compressor & turbine drive
d) none of the mentioned

Answer: c [Reason:] Both DSC interface and Graphic interface is used in both compressor drive and turbine drive.

3. In gas turbines Load control is available in _______
a) compressor drives
b) generator drives
c) compressor & generator drive
d) none of the mentioned

Answer: b [Reason:] Load control is available in generator drives as load can be applied or decreased only on the generator not on the compressor.

4. Communication interfaces are ___________ in steam drives.
a) available
b) not available
c) depends on the usage
d) none

Answer: a [Reason:] Communication interface is available in steam drives.

5. Steam turbine performance is expressed in _______
a) heat rate
b) steam rate
c) heat & steam rate
d) none of the mentioned

Answer: b [Reason:] Steam turbine performance is expressed in steam rate.

6. Gas turbine performance is expressed in terms of _______
a) heat & steam rate
b) steam rate
c) heat rate
d) none of the mentioned

Answer: c [Reason:] Gas turbine performance is expressed in terms of heat rate while steam turbine is expressed in terms of steam rate.

7. Gas turbine performance is directly proportional to the ______
a) inlet air density
b) inlet air temperature
c) both of the mentioned
d) none of the mentioned

Answer: a [Reason:] Gas turbine performance is directly proportional to inlet air density as inlet air density increases its inlet air mass which increases the performance of gas turbine.

8. In a gas turbine power produced is _________ to inlet air density.
a) indirectly proportional
b) directly proportional
c) not proportional
d) one

Answer: b [Reason:] As inlet air density is directly related to performance of gas turbine, When inlet air density is increased its performance increased which means the power produced by gas turbine is increased.

9. In a gas turbine when firing temperature is __________ engine efficiency changes.
a) increased
b) decreased
c) remained constant
d) none of the mentioned

Answer: a [Reason:] When firing temperature is increased its environmental air conditions are altered so that its engine efficiency changes.

10. In steam turbines vapor and vapor conditions change with time.
a) True
b) False

Answer: a [Reason:] In steam turbine both vapor and vapor conditions are constant and that’s what makes calculating the steam turbine performance easy where as in gas turbines both vapor and vapor conditions are not constant and that makes it difficult for calculating performance.

Set 5

1. Radial vibration measurement measures ____________
a) unbalanced masses
b) cracked shafts
c) oil whirl
d) all of the mentioned

Answer: d [Reason:] Radial vibration measurement measures all the unbalanced masses, cracked shafts and also oil whirls.

2. Vibration measurements in steam turbines can be made in _______ planes
a) 1
b) 2
c) 1 or 2
d) None of the mentioned

Answer: c [Reason:] Vibration measurements in steam turbines can be measured in single plane or two planes.

3. Absolute shaft measurement is done when __________
a) weight of the rotating assemble is five times more than casing
b) weight of rotating assembly is two time more than the casing
c) weight of the rotating assembly is thrice the casing weight
d) none of the mentioned

Answer: a [Reason:] Absolute shaft measurement measures the shaft motion with respect to the free space. It is done when weight of the shaft assembly is five times more than the weight of casing.

4. Phase measurement is required for accurate balancing of the rotor.
a) True
b) False

Answer: a [Reason:] Phase measurement is required for accurate balancing of any rotor. Because phase is defined as angle between reference mark and heavy spot on the rotor.

5. Eccentricity measurement is used to indicate ______
a) bent shafts
b) when the rotor can be bought to the high speeds
c) both of the mentioned
d) none of the mentioned

Answer: c [Reason:] Eccentricity measurement makes us to know about the sag or bow in a rotor which helps us to get knowledge about whether to increase the speed or not.

6. DE measurement is used to get the knowledge about distance between case and rotor.
a) True
b) False

Answer: a [Reason:] As turbine casing has more weight than rotor , when turbine is under operation it should be taken care that there should not be any contact between turbine and casing due to thermal expansion as turbine has more expansion when compared to casing.

7. Rotor thrust measurement is done in order to _______
a) monitor thrust
b) monitor bearing wear
c) monitor thrust & bearing wear
d) none of the mentioned

Answer: c [Reason:] Rotor thrust measurement is done in order to monitor thrust and also bears wear.

8. Thrust position measurements are taken within _____ inches of thrust bearing.
a) 10
b) 12
c) 20
d) none of the mentioned

Answer: b [Reason:] Thrust position measurement is done within 12 inches of thrust bearing.

9. Thrust measurement taken out of 12 inches are effected by ______
a) thrust forces
b) thrust forces & thermal expansions
c) thermal expansions
d) none of the mentioned