Quiz: Mechanical Engineering 18 June 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

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

Q1. Availability of a system at any given stage is
(a) a property of the system
(b) the total energy of the system
(c) the minimum work obtainable as the system goes to dead state
(d) the maximum useful work obtainable as the system goes to dead state

Q2. The irreversibility associated with the process is defined as
(a) Loss of qualitative energy
(b) Loss of energy
(c) Loss of enthalpy
(d) Loss of entropy

Q3. Which one of the following methods is more effective to improve the efficiency of the Rankine cycle used in thermal power plant?
(a) Increasing the condenser temperature
(b) Decreasing the condenser temperature
(c) Decreasing the boiler temperature
(d) Increasing the boiler temperature

Q4. Air pre-heater
(a) increases evaporative capacity of a boiler
(b) increases the efficiency of boiler
(c) enables low grade fuel to be burnt
(d) all of the above

Q5. The work output of theoretical Otto cycle
(a) Increases with increase in compression ratio
(b) Increases with increase in pressure ratio
(c) Increases with increase in adiabatic index
(d) All of the above

Q6. In emission measuring equipments, the HC is measured using
(a) Gas Chromatograph
(b) Flame ionization detector
(c) Chemiluminescence detector
(d) NDIR analyser

Q7. If the pressure range of compressor is low, then the COP will be
(a) low
(b) high
(c) remains unchanged
(d) cannot be determined

Q8. Multi-evaporator systems with a single compressor and a pressure reducing valve:
(a) Yield very high COP as compared to single stage systems
(b) Yield lower compressor discharge temperature compared to single stage systems
(c) Yield slightly higher refrigeration effect in the low temperature evaporator
(d) Yield slightly high refrigeration effect in high temperature evaporator compared to single stage systems

Q9. If the ratio of emission of a body to that of a black body at a given temperature is constant for all wavelengths, the body is called:
(a) Black body
(b) Gray body
(c) White body
(d) Opaque body

Q10. Steel and cast-iron pipes carrying fluid under pressure are regarded as hydraulically smooth when
(a) the boundary surface is relatively smooth
(b) the roughness projections are of low height
(c) the roughness elements are completely covered by the laminar sub-layer
(d) the laminar layer is thin as compared to the average height of roughness element

Solutions

S1. Ans.(d)
Sol. Availability of a system at any given stage is defined as the maximum useful work obtainable as the system goes to dead state.

S2. Ans.(a)
Sol. The loss of qualitative energy or degradation of energy is associated with the irreversibility of the system.

S3. Ans.(b)
Sol. There are following methods to increase the efficiency of Rankine cycle:
1. Lowering the condenser pressure
2. Super-heating the steam to high temperature
3. Increasing the boiler pressure

S4. Ans.(d)
Sol. Air preheater has following effects in a power plant
1.Increases in evaporative capacity of a boiler
2.Increases the efficiency of boiler
3.Enables low grade fuel burning

S5. Ans.(d)
Sol. Work output of Otto cycle increases with pressure ratio, compression ratio and adiabatic index.

S6. Ans.(b)
Sol. HC is measured with the help of flame ionization detector. The flame ionization detector passes sample and carrier gas from the column through a hydrogen-air flame. The hydrogen-air flame alone creates few ions, but when an organic compound is burned there is an increase in ions produced. A polarizing voltage attracts these ions to a collector located near the flame.

S7. Ans.(b)
Sol. If pressure range is low then the compressor work done will be low and hence, COP will be high.

S8. Ans.(d)
Sol. Multi-evaporator system with a single compressor and a pressure reducing valve yield slightly higher refrigeration effect in the high temperature evaporator compared to single stage systems.

S9. Ans.(b)
Sol. If the ratio of emission of a body to that of a black body at a given temperature is constant for all wavelengths, the body is called Gray body.

S10. Ans.(c)
Sol. When the thickness of laminar sub-layer is more than the average height of roughness then it is called hydraulically smooth surface.

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