SSC JE Exam - air compressors refrigeration cycles refrigeration plant nozzles steam turbines Question Bank with Options

1. In a centrifugal compressor, the pressure rise is achieved by:

A) The centrifugal force acting on the fluid

B) The reciprocating motion of a piston

C) The expansion of the fluid through a nozzle

D) The reduction of fluid velocity in a converging section

2. The efficiency of a nozzle is defined as the ratio of:

A) Actual kinetic energy at exit to isentropic kinetic energy at exit

B) Isentropic kinetic energy at exit to actual kinetic energy at exit

C) Actual kinetic energy at exit to the enthalpy drop

D) Enthalpy drop to actual kinetic energy at exit

3. What is the main cause of 'th trusting' in steam turbine blades?

A) High steam velocity

B) Centrifugal forces

C) Steam leakage past blades

D) Moisture erosion

4. Which type of steam turbine uses multiple stages of nozzles and rotors to extract energy from the steam progressively?

A) Simple impulse turbine

B) Simple reaction turbine

C) Multi-stage turbine

D) Back pressure turbine

5. What is the primary energy conversion occurring in the nozzle of a steam turbine?

A) Mechanical energy to thermal energy

B) Thermal energy to kinetic energy

C) Kinetic energy to mechanical energy

D) Pressure energy to kinetic energy

6. In a converging-diverging nozzle, if the back pressure is equal to the pressure at the exit of the diverging section under choked conditions, what is the Mach number at the exit?

A) Less than 1

B) Equal to 1

C) Greater than 1

D) Cannot be determined without knowing the specific heat ratio

7. Which of the following is a characteristic of a 'supercritical' fluid in the context of refrigeration?

A) It exists as a liquid and vapor mixture.

B) It has a distinct boiling and condensation point.

C) It exists above its critical temperature and critical pressure.

D) It can be easily liquefied by increasing pressure alone.

8. What is the purpose of a muffler in an air compressor system?

A) To increase the discharge pressure

B) To reduce the noise level of the compressed air

C) To remove moisture from the compressed air

D) To cool the compressed air

9. The 'flash gas' in a refrigeration system causes:

A) Increased cooling capacity

B) Reduced compressor efficiency

C) Lower discharge pressure

D) Higher suction pressure

10. Which statement about R-744 (Carbon Dioxide) as a refrigerant is correct?

A) It operates in a transcritical cycle at typical conditions.

B) It has a very low critical temperature.

C) It is highly flammable.

D) It has a high Global Warming Potential (GWP).

11. In a vapor-compression cycle, the refrigerant enters the compressor as:

A) Saturated liquid

B) Saturated vapor

C) Superheated vapor

D) Wet vapor

12. Which type of rotary compressor is known for its high volumetric efficiency and ability to handle large volumes of air or gas?

A) Rotary vane compressor

B) Rotary lobe (Roots) blower

C) Rotary screw compressor

D) Centrifugal compressor

13. What is the effect of increasing the compression ratio in a reciprocating compressor, assuming constant stroke volume and speed?

A) Increased volumetric efficiency

B) Decreased volumetric efficiency

C) No change in volumetric efficiency

D) Increased discharge temperature only

14. The volumetric efficiency of a reciprocating compressor is defined as the ratio of:

A) Actual volume of air delivered to the swept volume

B) Swept volume to the actual volume of air delivered

C) Volume of air at suction conditions to the swept volume

D) Volume of air at discharge conditions to the swept volume

15. Which problem is most likely to occur in the later stages of a steam turbine operating with wet steam?

A) Erosion of blades

B) Corrosion of blades

C) Overheating of blades

D) Cavitation

16. What is the 'degree of reaction' in a steam turbine?

A) The ratio of pressure drop in the moving blades to the total pressure drop

B) The ratio of enthalpy drop in the moving blades to the total enthalpy drop

C) The ratio of kinetic energy change in the moving blades to the total kinetic energy change

D) The ratio of work done by the moving blades to the total work done

17. In a steam turbine, blade speed is crucial. For maximum efficiency in an impulse turbine, the blade speed should ideally be:

A) Equal to the steam jet velocity

B) Half the steam jet velocity

C) Twice the steam jet velocity

D) Independent of the steam jet velocity

18. What is the primary advantage of using a Curtis turbine (a type of velocity-compounded impulse turbine)?

A) High efficiency at all steam flow rates

B) Compact design for a given power output

C) Low blade speeds required, reducing centrifugal forces

D) Ability to handle superheated steam only

19. The efficiency of a steam turbine is generally higher for which type of turbine?

A) Pure impulse turbine

B) Pure reaction turbine

C) Multi-stage impulse-reaction turbine

D) Single-stage turbine

20. In a de Laval nozzle (converging-diverging), if the back pressure is reduced below the pressure corresponding to the Mach number at the exit, what happens to the flow?

A) The flow becomes subsonic throughout

B) The flow remains sonic at the throat and supersonic at the exit

C) The flow becomes detached from the nozzle surface

D) The flow remains choked at the throat and expands further in the diverging section

21. For a converging nozzle, the maximum mass flow rate occurs when:

A) The back pressure is equal to the atmospheric pressure

B) The back pressure is slightly below the critical pressure

C) The back pressure is equal to or below the critical pressure

D) The inlet pressure is very low

22. What is the primary difference between a nozzle and a diffuser?

A) A nozzle increases velocity and decreases pressure; a diffuser decreases velocity and increases pressure.

B) A nozzle decreases velocity and increases pressure; a diffuser increases velocity and decreases pressure.

C) A nozzle converts kinetic energy to pressure energy; a diffuser converts pressure energy to kinetic energy.

D) A nozzle operates with subsonic flow; a diffuser operates with supersonic flow.

23. Which component in a refrigeration plant is responsible for removing heat from the cooled space?

A) Condenser

B) Compressor

C) Expansion valve

D) Evaporator

24. In a vapor-compression cycle, the heat rejected in the condenser is equal to:

A) Enthalpy of liquid refrigerant leaving condenser - Enthalpy of vapor refrigerant entering condenser

B) Enthalpy of vapor refrigerant entering evaporator - Enthalpy of liquid refrigerant leaving expansion valve

C) Enthalpy of vapor refrigerant leaving evaporator - Enthalpy of liquid refrigerant entering evaporator

D) Enthalpy of vapor refrigerant leaving condenser - Enthalpy of vapor refrigerant entering evaporator

25. The theoretical COP of a vapor-compression refrigeration cycle can be increased by:

A) Increasing the condenser pressure

B) Decreasing the evaporator pressure

C) Increasing the superheat at compressor inlet

D) Decreasing the subcooling at condenser outlet

26. Which of the following refrigerants has the highest Ozone Depletion Potential (ODP)?

A) R-134a

B) R-22

C) R-717 (Ammonia)

D) R-600a (Isobutane)

27. A centrifugal compressor is characterized by:

A) Positive displacement of gas

B) Continuous flow with no moving valves

C) Reciprocating motion of a piston

D) Expansion and compression of gas in the same chamber

28. Which factor has the most significant impact on reducing the work of compression in a multi-stage compressor with intercooling?

A) Increasing the number of stages

B) Lowering the interstage pressure

C) Increasing the clearance volume

D) Using a more efficient compressor design

29. The term 'isentropic efficiency' of a compressor refers to the ratio of:

A) Actual work input to isentropic work input

B) Isentropic work input to actual work input

C) Actual work output to isentropic work output

D) Isentropic work output to actual work output

30. What is the main disadvantage of using a single-stage impulse turbine for high-pressure applications?

A) Low efficiency

B) High blade speeds required, leading to mechanical stress

C) Excessive steam leakage

D) Requires very low inlet steam temperature

31. In an isentropic nozzle, the velocity of the steam increases as it passes through. What happens to the temperature and pressure of the steam?

A) Temperature and pressure increase

B) Temperature decreases, pressure increases

C) Temperature increases, pressure decreases

D) Temperature and pressure decrease

32. What is the purpose of compounding in a steam turbine?

A) To increase the efficiency by reducing blade speed

B) To increase the volumetric flow rate of steam

C) To reduce the moisture content of steam

D) To prevent cavitation

33. Which type of steam turbine is typically used for high-power generation in thermal power plants?

A) Impulse turbine

B) Reaction turbine

C) Compound turbine

D) Multi-stage turbine

34. A reaction turbine is characterized by:

A) Pressure drop occurring only in the stationary nozzles

B) Pressure drop occurring in both stationary and moving blades

C) Significant velocity increase in the moving blades

D) No pressure change across the moving blades

35. What is the primary function of the nozzle in a steam turbine?

A) To increase the steam pressure

B) To convert the thermal energy of steam into kinetic energy

C) To extract work from the steam

D) To condense the steam

36. In a steam turbine, the expansion of steam occurs across:

A) A stationary blade row

B) A rotating blade row

C) Both stationary and rotating blade rows

D) The nozzle

37. Choked flow in a nozzle occurs when:

A) The back pressure is significantly higher than the ambient pressure

B) The Mach number at the throat reaches unity

C) The flow velocity is zero

D) The nozzle exit area is very small

38. What is the critical pressure ratio for air expanding from stagnation conditions to sonic velocity at the throat of a nozzle?

A) Approximately 0.528

B) Approximately 0.833

C) Approximately 1.0

D) Depends on the specific heat ratio

39. For a converging-diverging nozzle, what is the condition at the throat for supersonic flow to exist in the diverging section?

A) The flow must be subsonic throughout

B) The Mach number at the throat must be unity (M=1)

C) The Mach number at the throat must be greater than 1

D) The pressure at the throat must be equal to the back pressure

40. A nozzle is a device designed to:

A) Increase the pressure of a fluid by decreasing its velocity

B) Decrease the pressure of a fluid by increasing its velocity

C) Maintain constant pressure and velocity of a fluid

D) Convert thermal energy into mechanical work

41. What is the primary purpose of a receiver in a refrigeration plant?

A) To store excess refrigerant

B) To act as a surge drum for the evaporator

C) To ensure a liquid supply to the expansion device

D) To remove non-condensable gases

42. The Bell-Coleman cycle, also known as the air refrigeration cycle, is best suited for applications requiring:

A) High cooling capacity at low temperatures

B) Low cooling capacity at moderate temperatures

C) Cooling with a non-condensable fluid

D) High COP at low temperature differences

43. Which refrigerant is commonly used in domestic refrigerators and has a high COP but is flammable?

A) R-134a

B) R-410A

C) R-22

D) R-600a (Isobutane)

44. In a vapor-compression refrigeration cycle, the expansion valve (or capillary tube) is responsible for:

A) Increasing the pressure of the refrigerant

B) Cooling the refrigerant to a lower temperature and pressure

C) Evaporating the refrigerant

D) Condensing the refrigerant

45. Which refrigeration cycle is considered the ideal vapor-compression cycle?

A) Bell-Coleman cycle

B) Rankine cycle

C) Carnot cycle

D) Vapor-compression cycle with saturated vapor at compressor inlet and saturated liquid at condenser outlet

46. The Coefficient of Performance (COP) for a refrigeration system is defined as:

A) Heat rejected to the hot reservoir / Work input

B) Work input / Heat absorbed from the cold reservoir

C) Heat absorbed from the cold reservoir / Work input

D) Heat rejected to the hot reservoir / Heat absorbed from the cold reservoir

47. A rotary vane compressor utilizes vanes that slide in and out of slots in a rotor. What is the main advantage of this type of compressor?

A) High efficiency at very low pressures

B) Compact size and low noise levels

C) Ability to handle large volumes of gas at high pressures

D) Low initial cost

48. What is the primary function of an intercooler in a multi-stage reciprocating compressor?

A) To increase the final discharge pressure

B) To reduce the work done per unit mass of air compressed

C) To increase the volumetric efficiency

D) To prevent oil contamination

49. In a reciprocating compressor, the clearance volume significantly affects the volumetric efficiency. What is the typical range for clearance volume as a percentage of the stroke volume?

A) 0.1% to 1%

B) 1% to 5%

C) 5% to 10%

D) 10% to 20%

50. Which type of compressor uses a rotating impeller to impart velocity to the fluid, which is then converted to pressure energy in a diffuser?

A) Reciprocating compressor

B) Rotary screw compressor

C) Centrifugal compressor

D) Diaphragm compressor

air compressors refrigeration cycles refrigeration plant nozzles steam turbines - Question Bank