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This set of Thermal Engineering 1 Multiple Choice Questions & Answers (MCQs) focuses on Air Compressors Set 1
Q1 | An ideal air compressor cycle with clearance on p-v diagram can be represented by following processes
- one adiabatic, two isobaric, and one constant volume
- two adiabatic and two isobaric
- two adiabatic, one isobaric and one constant volume,
- one adiabatic, one isobaric and two constant volume
Q2 | The work done per unit mass of air in compression will be least when n is equal to
- 1
- 1.2
- 1.3
- 1.4
Q3 | Isothermal compression though most efficient, but is not -practicable because
- it requires very big cylinder
- it does not increase pressure much
- it is impossible in practice
- compressor has to run at very slow speed to achieve it
Q4 | Ratio of indicated H.P. and brake H.P. is known as
- mechanical efficiency
- volumetric efficiency
- isothermal efficiency
- adiabatic efficiency
Q5 | The ratio of work doen per cycle to the swept volume in case of compressor is called
- compression index
- compression ratio
- compressor efficiency
- mean effective pressure
Q6 | Cylinder clearance in a compressor should be
- as large as possible
- as small as possible
- about 50% of swept volume
- about 100% of swept volume
Q7 | Ratio of compression is the ratio of
- gauge discharge pressure to the gauge intake pressure
- absolute discharge pressure to the absolute intake pressure
- pressures at discharge and suction corresponding to same temperature
- stroke volume and clearance volume
Q8 | Clearance volume in actual reciprocating compressors is essential
- to accommodate Valves in the cylinder head
- to provide cushioning effect
- to attain high volumetric efficiency
- to provide cushioning effect and also to avoid mechanical bang of piston with cylinder head.
Q9 | The net work input required for compressor with increase in clearance volume
- increases
- decreases
- remains same
- increases/decreases depending on compressor capacity
Q10 | Ratio of indicated h.p. to shaft h.p. is known as
- compressor efficiency
- isothermal efficiency
- volumetric efficiency
- mechanical efficiency
Q11 | Volumetric efficiency is
- the ratio of stroke volume to clearance volume
- the ratio of the air actually delivered to the amount of piston displacement
- reciprocal of compression ratio
- index of compressor performance
Q12 | Volumetric efficiency of a compressor with clearance volume
- increases with increase in compression ratio
- decreases with increase in compression ratio
- is not dependent upon compression ratio
- may increase/decrease depending on compressor capacity
Q13 | Volumetric efficiency of a compressor without clearance volume
- increases with increase in compression ratio
- decreases with increase in compression ratio
- is not dependent upon compression ratio
- may increase/decrease depending on compressor capacity
Q14 | The clearance volume of the air compressor is kept minimum because
- it allows maximum compression to be achieved
- it greatly affects volumetric efficiency
- it results in minimum work
- it permits isothermal compression
Q15 | Which is false statement about multistage compression.
- Power consumption per unit of air delivered is low
- Volumetric efficiency is high
- It is best suited for compression ratios around 7:1
- The moisture in air is condensed in the intercooler
Q16 | Reciprocating air compressor is best suited for
- large quantity of air at high pressure
- small quantity of air at high pressure
- small quantity of air at low pressure
- large quantity of air at low pressure
Q17 | Rotary compressor is best suited for
- large quantity of air at high pressure
- small quantity of air at high pressure
- small quantity of air at low pressure
- large quantity of air at low pressure
Q18 | After-cooler is used to
- cool the air
- decrease the delivery temperature for ease in handling
- cause moisture and oil vapour to drop out
- reduce volume
Q19 | The compressor performance at higher altitude compared to sea level will be
- same
- higher
- lower
- dependent on other factors
Q20 | Pick up the wrong statement about advantages of multistage compression
- better lubrication is possible advantages of multistage
- more loss of air due to leakage past the cylinder
- mechanical balance is better
- air can be cooled perfectly in between
Q21 | Losses in a centrifugal compressor are due to
- inlet losses
- impeller channel losses
- diffuser losses
- all of the above
Q22 | For supplying intermittent small quantity of air at high pressure, following compressor is best suited
- centrifugal
- reciprocating
- axial
- screw
Q23 | For minimum work in multistage compression, assuming same index of compression in all stages
- work done in first stage should be more
- work done in subsequent stages should increase
- work done in subsequent stages should decrease
- work done in all stages should be equal
Q24 | Diffuser in a compressor is used to
- increase velocity
- make the flow stream-line
- convert pressure energy into kinetic energy
- convert kinetic energy into pressure energy
Q25 | Phenomenon of choking in compressor means
- no flow of air
- fixed mass flow rate regardless of pressure ratio
- reducing mass flow rate with increase in pressure ratio
- increased inclination of chord with air steam