Volumetric efficiency of air compressors is of the order of
20 - 30 %
40 - 50 %
60 - 70 %
70 - 90 %
Correct Answer :
D. 70 - 90 %
Related Questions
When the temperature of air leaving the intercooler, in a two stage compression with intercooler, is ________ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.
Equal to
Less than
More than
None of these
The air entry velocity m a rocket as compared to aircraft is
Same
More
Less
Zero
Reheating in a gas turbine
Increases the thermal efficiency
Increases the compressor work
Increases the turbine work
Decreases the thermal efficiency
Pick up the wrong statement
Large gas turbines employ axial flow compressors
Axial flow compressors are more stable than centrifugal type compressors but not as efficient
Axial flow compressors have high capacity and efficiency
Axial flow compressors have instability region of operation
Which of the following statement is wrong?
In a two stage reciprocating air compressor with complete intercooling, maximum work is saved.
The minimum work required for a two stage reciprocating air compressor is double the work required for each stage.
The ratio of the volume of free air delivery per stroke to the swept volume of the piston is called volumetric efficiency.
None of the above
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
An aftercooler is used to
Remove impurities from air
Reduce volume of air
Cause moisture and oil vapour to drop out
Cool the air
Pick up the correct statement
Gas turbine uses low air-fuel ratio to economise on fuel
Gas turbine uses high air-fuel ratio to reduce outgoing temperature
Gas turbine uses low air-fuel ratio to develop the high thrust required
All of the above
A centrifugal compressor works on the principle of
Conversion of pressure energy into kinetic energy
Conversion of kinetic energy into pressure energy
Centripetal action
Generating pressure directly
The material commonly used for air craft gas turbine is
Stainless steel
High alloy steel
Duralumin
Timken, Haste alloys
Free air is the air at
Atmospheric conditions at any specific location
20°C and 1 kg/cm² and relative humidity of 36%
0°C and standard atmospheric conditions
15°C and 1 kg/cm²
Gas turbines use following type of air compressor
Centrifugal type
Reciprocating type
Lobe type
Axial flow type
Maximum work is done in compressing air when the compression is
Isothermal
Adiabatic
Polytropic
None of the above
1 m of air at atmospheric condition weighs approximately
0.5 kg
1.0 kg
1.3 kg
2.2 kg
In jet propulsion power unit, the inlet duct of diverging shape is used in order to
Collect more air
Convert kinetic energy of air into pressure energy
Provide robust structure
Beautify the shape
The propulsive power of the rocket is (where v₁ = Jet velocity, and v₂ = Aircraft velocity)
(v₁² -v₂²)/2g
(v₁ - v₂)²/2g
(v₁² -v₂²)/g
(v₁ - v₂)²/g
A closed cycle gas turbine gives ________ efficiency as compared to an open cycle gas turbine.
Same
Lower
Higher
None of these
For slow speed large capacity compressor, following type of valve will be best suited
Poppet valve
Mechanical valve of the Corliss, sleeve, rotary or semi rotary type
Disc or feather type
Any of the above
The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is
Pressure drop across the valves
Superheating in compressor
Clearance volume and leakages
All of these
The volumetric efficiency of a compressor falls roughly as follows for every 5°C increase in atmospheric temperature
0.1 %
0.5 %
1 %
5 %
In air compressors, free air delivery means the
Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
Volume of air delivered by the compressor
Volume of air sucked by the compressor during its suction stroke
None of the above
The capacity of a compressor is 5 m /min refers to
Standard air
Free air
Compressed air
Compressed air at delivery pressure
The type of rotary compressor used in gas turbines, is of
Centrifugal type
Axial flow type
Radial flow type
None of these
The maximum delivery pressure in a rotary air compressor is
10 bar
20 bar
30 bar
50 bar
Which one of the following is the effect of blade shape on performance of a centrifugal compressor?
Backward curved blades has poor efficiency
Backward curved blades lead to stable performance
Forward curved blades has higher efficiency
Forward curved blades produce lower pressure ratio
The inlet pressure is always ________ the discharge pressure.
Equal to
Less than
More than
None of these
The ratio of work done per cycle to the swept volume in case of compressor is called
Compression index
Compression ratio
Compressor efficiency
Mean effective pressure
Inter cooling in compressors
Cools the delivered air
Results in saving of power in compressing a given volume to given pressure
Is the standard practice for big compressors
Enables compression in two stages
The axial flow compressor is preferred in aircraft gas turbines because of
Low frontal area
Higher thrust
High pressure rise
None of these
The ratio of the net work obtained from the gas turbine plant to the turbine work is known as
Compression ratio
Work ratio
Pressure ratio
None of these