Air Compressors Set 1

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
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