Quiz:Mechanical Engineering 11 April 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Thermal Engineering

Each question carries 3 mark.
Negative marking: 1 mark
Time: 10 Minute

Q1. An inventor says that his new concept of an engine, while working between temperature limits of 27°C and 327°C rejects 45% of heat absorbed from the source. His engine is then equivalent to which one of the following engines?
(a) Carnot engine
(b) Diesel engine
(c) An impossible engine
(d) Ericsson engine

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q2. Consider the following statements:
1.Availability is generally conserved.
2.Availability can either be negative or positive.
3.Availability is the maximum theoretical work obtainable.
4.Availability can be destroyed in irreversibilities.
Which of these statements are correct?
(a) 3 and 4
(b) 1 and 2
(c) 1 and 3
(d) 2 and 4

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q3. Consider the following statements:
The increase in metacentric height
1.Increases stability
2.Decreases stability
3.Increases comfort for passengers in a ship
4.Decreases comfort for passengers in a ship
Which of the above statements are correct?
(a) 1 and 3
(b) 1 and 4
(c) 2 and 3
(d) 2 and 4

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q4. In centrifugal compressor terminology, vaneless space refers to the space between
(a) The inlet and blade inlet edge
(b) Blades in the impeller
(c) Diffuser exit and volute casing
(d) Impeller tip and diffuser inlet edge

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q5. In a steam nozzle, to increase the velocity of steam above sonic velocity by expanding steam below critical pressure
(a) A vacuum pump is added
(b) Ring diffusers are used
(c) Divergent portion of the nozzle is necessary
(d) Abrupt change in cross-section is needed

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q6. In a single-stage open-cycle gas turbine, the mass flow through the turbine is higher than the mass flows through compressor, because
(a) the specific volume of air increases by use of inter-cooler
(b) the temperature of air increases in the reheater
(c) the combustion of fuel takes place in the combustion chamber
(d) the specific heats at constant pressure of incoming air and exhaust gases are different

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q7. For quick response of a thermo-couple to observe varying temperature of fluids
(a) wire diameter must be large
(b) wire material density must be large
(c) wire material specific heat must be large
(d) wire surface heat transfer coefficients must be large

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q8. For the same type of shapes, the value of Radiation Shape Factor will be higher when surfaces are
(a) Closer only
(b) Moved further apart
(c) Smaller and held closer
(d) Larger and held closer

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q9. Consider the following statements for multi-jet carburetor:
1.Acceleration jet is located just behind the throttle valve.
2.Idle jet is located close to the choke.
3.Main jet alone supplies petrol at normal engine speed.
Which of these statements are correct?
(a) 1, 2 and 3
(b) 1 and 2
(c) 2 and 3
(d) 1 and 3

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q10. The refrigerant used for absorption refrigerators working heat from solar collectors is mixture of water and
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Lithium bromide
(d) Freon 12

L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Solutions

S1. Ans (c)
Sol. Efficiency of Carnot engine,
η = 1-T2/T1 = 1-(300/600)= 0.5
But according to the inventor’s claim
Efficiency of engine = 1–0.45=0.55
∵ Efficiency of actual engine cannot be greater than Carnot efficiency. So, this is an
impossible engine.

S2. Ans (a)
Sol. The availability is the maximum useful work obtainable from a system as it reaches the dead state. Conversely, availability can be regarded as the minimum work required to bring the closed system from the dead state to given state. The value of availability cannot be negative. As energy is always conserved, availability is not generally conserved but is destroyed by irreversibility.

S3. Ans (b)
Sol.

S4. Ans (d)
Sol.

S5. Ans (c)
Sol.

S6. Ans (c)
Sol. After the compression of air, same amount of fuel is added in the combustion chamber which undergoes combustion. After combustion the flue gases are expanded in the turbine which is more than the mass flow rate of only air in the compressor.

S7. Ans (d)
Sol. If surface that transfer coefficient is large then the rate of heat transfer will be more and hence thermo-couple will be quick to respond to varying temperature of fluids.

S8. Ans(d)
Sol. The value of radiation shape factor is high if surfaces are large and closer to each other.

S9. Ans (d)
Sol. Idle jet is located close to butterfly valve (Throttle)

S10. Ans (c)
Sol. Absorption refrigerators working by solar collector uses mixture of water and Lithium bromide (Water-LiBr).

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