Compressors Gas Dynamics and Gas Turbines

Q1: A rocket works with maximum overall efficiency when air-craft velocity is __________ the jet velocity.

A equal to

B one-half

C double

Q2: The increase in pressure in a vane blower takes place first due to compression and then due to back flow of air.

A Correct

B Incorrect

Q3: The compressed air may be used

A in gas turbine plants

B for operating pneumatic drills

C in starting and supercharging of I.C. engines

D all of the above

Q4: The increase in pressure in a roots blower is entirely due to back flow of air.

A Agree

B Disagree

Q5: Only rocket engines can be propelled to space because

A they can generate very high thrust

B they have high propulsion efficiency

C these engines can work on several fuels

D they are not air-breathing engines

Q6: The maximum temperature in a gas turbine is

A 200°C

B 500°C

C 700°C

D 1000°C

Q7: The clearance volume in the compressor is kept minimum because it effects on volumetric efficiency.

A Correct

B Incorrect

Q8: Which of the following statement is correct?

A The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency.

B The compression ratio for the compressor is always greater than unity.

C The compressor capacity is the ratio of workdone per cycle to the stroke volume.

D During isothermal compression of air, the workdone in a compressor is maximum.

Q9: The maximum delivery pressure in a rotary air compressor is

A 10 bar

B 20 bar

C 30 bar

D 50 bar

Q10: An open cycle gas turbine works on the same cycle as that of a closed cycle gas turbine.

A Yes

B No

Q11: Intercooling in gas turbines

A decreases net output but increases thermal efficiency

B increases net output but decreases thermal efficiency

C decreases net output and thermal efficiency both

D increases net output and thermal efficiency both

Q12: The type of rotary compressor used in gas turbines, is of

A centrifugal type

B axial flow type

C radial flow type

D none of these

Q13: The efficiency of a jet engine is higher at

A low speeds

B high speeds

C low altitudes

D high altitudes

Q14: The type of rotary compressor used in aeroplanes, is of

A centrifugal type

B axial flow type

C radial flow type

D none of these

Q15: The maximum combustion pressure in gas turbine is __________ as compared to I.C. engine.

A more

B less

Q16: In a reciprocating air compressor, the compression work per kg of air

A increases as clearance volume increases

B decreases as clearance volume increases

C is independent of clearance volume

D increases as clearance volume decreases

Q17: A large clearance Volume in a reciprocating compressor results in

A reduced volume flow rate

B increased volume flow rate

C lower suction pressure

D lower delivery pressure

Q18: The ratio of workdone per cycle to the stroke volume of the compressor is known as

A compressor capacity

B compression ratio

C compressor efficiency

D mean effective pressure

Q19: The stagnation pressure rise in a centrifugal compressor takes place

A in the diffuser only

B in the impeller only

C in the diffuser and impeller

D in the inlet guide vanes only

Q20: Intercooling in multi-stage compressors is done

A to cool the air during compression

B to cool the air at delivery

C to enable compression in two stages

D to minimise the work of compression

Q21: The compressed air may be used

A in gas turbine plants

B for operating pneumatic drills

C in starting and supercharging of I.C. engines

D all of the above

Q22: In a single acting reciprocating compressor, the suction, compression and delivery of air takes place in __________ of the piston.

A one stroke

B two strokes

C three strokes

D four strokes

Q23: 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)

A D1/D2 =  p1p2

B D1/D2 =  p1/p2

C D1/D2 =  p2/p1

D none of these

Q24: The rotary compressors are suitable for large discharge of air at low pressure.

A True

B False

Q25: An aftercooler is used to

A remove impurities from air

B reduce volume of air

C cause moisture and oil vapour to drop out

D cool the air

Q26: Gas turbine as compared to steam turbine

A requires less space for installation

B has compressor and combustion chamber

C has less efficiency

D all of these

Q27: In a jet propulsion

A the propulsive matter is ejected from within the propelled body

B the propulsive matter is caused to flow around the propelled body

C its functioning does not depend upon presence of air

D none of the above

Q28: The compression ratio in a gas turbine is

A 4

B 1

C 9

D 12

Q29: Workdone by a two-stage reciprocating air compressor per cycle is equal to the workdone in LP. cylinder and H.P. cylinder.

A True

B False

Q30: The inlet pressure is always __________ the discharge pressure.

A equal to

B less than

C more than

Q31: The degree of reaction in an axial flow compressor is defined as the ratio of static enthalpy rise in the

A rotor to static enthalpy rise in the stator

B stator to static enthalpy rise in the rotor

C rotor to static enthalpy rise in the stage

D stator to static enthalpy rise in the stage

Q32: In axial flow compressor, exit flow angle deviation from the blade angle is a function of

A blade camber

B blade camber and incidence angle

C space-chord ratio

D blade camber and space-chord ratio

Q33: The actual volume of air delivered by a compressor, When reduced to the normal temperature and pressure conditions is called compressor capacity.

A Yes

B No

Q34: A closed cycle gas turbine gives __________ efficiency as compared to an open cycle gas turbine.

A same

B lower

C higher

Q35: A rotary compressor is driven by an

A electric motor

B engine

C either (a) or (b)

D none of these

Q36: The ratio of the indicated power to the shaft power or brake power of the motor or engine required to drive the compressor, is called

A compressor efficiency

B volumetric efficiency

C isothermal efficiency

D mechanical efficiency

Q37: In a centrifugal compressor, an increase in speed at a given pressure ratio causes

A increase in flow

B decrease in flow

C increase in efficiency

D increase in flow and decrease in efficiency

Q38: In a four stage compressor, if the pressure at the first and third stage are 1 bar and 16 bar, then the delivery pressure at the fourth stage will be

A 1 bar

B 16 bar

C 64 bar

D 256 bar

Q39: The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as

A compressor efficiency

B volumetric efficiency

C isothermal efficiency

D mechanical efficiency

Q40: The volume of air delivered by the compressor is called

A free air delivery

B compressor capacity

C swept volume

D none of these

Q41: 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.

A equal to

B less than

C more than

Q42: The capacity of a compressor is expressed in

A kg/m2

B kg/m3

C m3/min

D m3/kg

Q43: Rotary compressors are used for delivering

A small quantities of air at high pressures

B large quantities of air at high pressures

C small quantities of air at low pressures

D large quantities of air at low pressures

Q44: An axial compressor gives optimum performance at high speeds and large volume flows.

A Agree

B Disagree

Q45: Intercooling in compressors results in saving of power in compressing given volume of air to a given pressure.

A Correct

B Incorrect

Q46: For a two stage reciprocating compressor, compression from p1 to p3 is with perfect intercooling and no pressure losses. If compression in both the cylinders follows the same polytropic process and the atmospheric pressure is pa, then the intermediate pressure p2 is given by

A p2 = (p1 + p3)/2

B p2 =  p1.p3

C P2 = Pa x p3/p1

D p2 = pa  p3/p1

Q47: The total heat rejected in a reciprocating air compressor is equal to the sum of the heat rejected during polytropic compression per kg of air and heat rejected in the intercooler per kg of air.

A True

B False

Q48: High air-fuel ratio in gas turbines

A increases power output

B improves thermal efficiency

C reduces exhaust temperature

D do not damage turbine blades

Q49: In the aircraft propellers

A the propulsive matter is ejected from within the propelled body

B the propulsive matter is caused to flow around the propelled body

C its functioning does not depend upon the presence of air

D none of the above

Q50: The volumetric efficiency for reciprocating air compressors is about

A 10 to 40%

B 40 to 60%

C 60 to 70%

D 70 to 90%

Q51: Which of the following statement is wrong?

A In a two stage reciprocating air compressor with complete intercooling, maximum work is saved.

B The minimum work required for a two stage reciprocating air compressor is double the work required for each stage.

C The ratio of the volume of free air delivery per stroke to the swept volume of the piston is called volumetric efficiency.

D none of the above


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