Propulsion efficiency of the following order is obtained in practice
34 %
50 %
60 %
72 %
Correct Answer :
C. 60 %
Related Questions
In a jet propulsion unit, the products of combustion after passing through the gas turbine are discharged into
Atmosphere
Vacuum
Discharge nozzle
Back to the compressor
In the aircraft propellers
The propulsive matter is caused to flow around the propelled body
Propulsive matter is ejected from within the propelled body
Its functioning does not depend on presence of air
All of the above
Reheating in a multistage expansion gas turbine __________ compressor work.
Has no effect on
Decreases
Increases
None of these
The overall thermal efficiency of an ideal gas turbine plant is (where r = Pressure ratio)
r -1
1 - r -1
1 - (1/r) -1/
1 - (1/r) /-1
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
A closed gas turbine in which fuel is burnt directly in the air is not possible because of
Paucity of O2
Increasing gas temperature
High specific volume
High friction losses
The criterion of the thermodynamic efficiency for rotary compressor is
Isentropic compression
Isothermal compression
Polytropic compression
None of the above
A 3 m³/min compressor means that it
Compresses 3 m³/min of standard air
Compresses 3 m³/ min of free air
Delivers 3 m³/ min of compressed air
Delivers 3 m³/ min of compressed air at delivery pressure
The maximum temperature in a gas turbine is
200°C
500°C
700°C
1000°C
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
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
In jet engines the products of combustion after passing through the gas turbine are discharged into
Atmosphere
Back to the compressor
Discharge nozzle
Vacuum
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
Euler's equation is applicable for
Centrifugal compressor
Axial compressor
Pumps
All of the above
The working fluid in a turbine is
In two phases
In three phases
In a single phase
In the form of air and water mixture
The overall isothermal efficiency of the compressor is defined as the ratio of
Work required to compress the air isothermally to the actual work required to compress the air for the same pressure ratio
Isothermal power to the shaft power or B.P. of the motor or engine required to drive the compressor
Volume of free air delivery per stroke to the swept volume of the piston
Isentropic power to the power required to drive the compressor
Air-fuel ratio in a jet engine will be of the order of
10 : 1
15 : 1
20 : 1
60 : 1
In gas turbines, high thermal efficiency is obtained in
Closed cycle
Open cycle
Both of the above
Closed/open depending on other considerations
Ramjet engine
Is self operating at zero flight speed
Is not self operating at zero flight speed
Requires no air for its operation
Produces a jet consisting of plasma
Pick up the wrong statement
Centrifugal compressors deliver practically constant pressure over a considerable range of capacities
Axial flow compressors have a substantially constant delivery at variable pressures
Centrifugal compressors have a wider stable operating range than axial flow compressors
Axial flow compressors are bigger in diameter compared to centrifugal type
If p₁, is the pressure of air entering the L.P. cylinder and p₂ is the pressure of air leaving the L.P. cylinder (or intercooler pressure), then the ratio of cylinder diameters for a single acting, two stage reciprocating air compressor with complete intercooling is given by (where D₁ = Dia. of L.P. cylinder, and D₂ = Dia. of H.P. cylinder)
D₁/D₂ = p₁ p₂
D₁/D₂ = p₁/p₂
D₁/D₂ = p₂/p₁
None of these
The compressor capacity with decrease in suction temperature
Increases
Decreases
Remain unaffected
May increase or decrease depending on compressor capacity
The fuel consumption in gas turbines is accounted for by
Lower heating value
Higher heating value
Heating value
Higher calorific value
The minimum work required for a three stage reciprocating air compressor is ________ the work required for each stage.
Equal to
Double
Three times
Six times
The type of rotary compressor used in aeroplanes, is of
Centrifugal type
Axial flow type
Radial flow type
None of these
Water is injected in gas turbine cycle to
Control temperature
Control output of turbine
Control fire hazards
Increase efficiency
Reheating in multistage expansion gas turbine results in
High thermal efficiency
Reduction in compressor work
Decrease of heat loss in exhaust
Maximum work output
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
If p₁ is the pressure of air entering the L.P, cylinder and p₃ is the pressure of air leaving the H.P. cylinder, then the ratio of cylinder diameters for a single acting, two stage reciprocating compressor with complete intercooling is given by
D₁/D₂ = (p₁ p₃)1/2
D₁/D₂ = (p₁/p₃)1/4
D₁/D₂ = (p₁ p₃)1/4
D₁/D₂ = (p₃/p₁)1/4
The volumetric efficiency of a compressor falls roughly as follows for every 5°C increase in atmospheric temperature
0.1 %
0.5 %
1 %
5 %