SSC JHT - Refrigeration & Air-Conditioning 1000+ MCQ [Solved] PDF Download

1. Air conditioning means
A. Cooling
B. Heating
C. Dehumidifying
D. All of these
Answer : D

2. The specific humidity during heating and humidification process.
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : B

3. In air-conditioning of aeroplanes, using air as a refrigerant, the cycle used is
A. Reversed Carnot cycle
B. Reversed Joule cycle
C. Reversed Brayton cycle
D. Reversed Otto cycle
Answer : C

4. In case of sensible cooling of air, the coil efficiency is given by
A. B.P.F. - 1
B. 1 - B.P.F.
C. 1/ B.P.F.
D. 1 + B.P.F.
Answer : B

5. Freon group of refrigerants are
A. Inflammable
B. Toxic
C. Non-inflammable and toxic
D. Nontoxic and non-inflammable
Answer : D

6. Air refrigeration operates on
A. Carnot cycle
B. Reversed Carnot cycle
C. Rankines cycle
D. Brayton cycle
Answer : D

7. An Electrolux refrigerator is called a __________ absorption system.
A. Single fluid
B. Two fluids
C. Three fluids
D. None of these
Answer : C

8. The ratio of heat extracted in the refrigerator to the work-done on the refrigerant is called
A. Coefficient of performance of refrigeration
B. Coefficient of performance of heat pump
C. Relative coefficient of performance
D. Refrigerating efficiency
Answer : A

9. The wet bulb temperature during sensible heating of air
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : B

10. Most thermostatic expansion valves are set for a superheat of
A. 5°C
B. 10°C
C. 15°C
D. 20°C
Answer : A

11. In a domestic vapour compression refrigerator, the refrigerant commonly used is
A. CO?
B. Ammonia
C. R-12
D. All of these
Answer : C

12. The refrigerant used in small tonnage commercial machines (hermetically sealed units) is
A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12
Answer : C

13. When the air is passed through an insulated chamber having sprays of water maintained at a temperature higher than the dew point temperature of entering air but lower than its dry bulb temperature, then the air is said to be
A. Cooled and humidified
B. Cooled and dehumidified
C. Heated and humidified
D. Heated and dehumidified
Answer : A

14. The thermal diffusivity for gases is generally __________ those for liquids.
A. Equal to
B. Less than
C. Greater than
D. None of these
Answer : C

15. The total pressure exerted by the mixture of air and water vapour is equal to the sum of pressures which each constituent would exert, if it occupied the same space by itself. This statement is called
A. Kinetic theory of gases
B. Newton's law of gases
C. Dalton's law of partial pressures
D. Avogadro's hypothesis
Answer : C

16. During dehumidification process, __________ remains constant.
A. Wet bulb temperature
B. Relative humidity
C. Dry bulb temperature
D. Specific humidity
Answer : C

17. The air cooling system mostly used in transport type aircrafts is
A. Simple air cooling system
B. Simple evaporative air cooling system
C. Bootstrap air cooling system
D. All of these
Answer : C

18. The process of under-cooling is generally brought about by
A. Circulating more quantity of cooling water through the condenser
B. Using water colder than the main circulating water
C. Employing a heat exchanger
D. Any one of the above
Answer : D

19. Efficiency of a Carnot engine is given as 80%. If the cycle direction be reversed, what will be the value of COP of reversed Carnot Cycle?
A. 1.25
B. 0.8
C. 0.5
D. 0.25
Answer : D

20. Air refrigeration cycle is used in
A. Domestic refrigerators
B. Commercial refrigerators
C. Air conditioning
D. Gas liquefaction
Answer : D

21. The vapour compression refrigerator employs the following cycle
A. Rankine
B. Carnot
C. Reversed Rankine
D. Reversed Carnot
Answer : D

22. Pick up the wrong statement. A refrigerant should have
A. Tow specific heat of liquid
B. High boiling point
C. High latent heat of vaporisation
D. Higher critical temperature
Answer : B

23. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T? = Loest absolute temperature, and T? = Highest absolute temperature)
A. T? / (T? - T?)
B. (T? - T?)/T?
C. (T? - T?)/T?
D. T?/ (T? - T?)
Answer : A

24. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to
A. Collect liquid refrigerant and prevent it from going to compressor
B. Detect liquid in vapour
C. Superheat the vapour
D. Collect vapours
Answer : A

25. Vertical lines on pressure-enthalpy chart show constant
A. Pressure lines
B. Temperature lines
C. Total heat lines
D. Entropy lines
Answer : C

26. During heating and dehumidification process, dry bulb temperature
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : B

27. The bypass factor, in case of sensible cooling of air, is given by (where td? = Dry bulb temperature of air entering the cooling coil, td? = Dry bulb temperature of air leaving the cooling coil, and td? = Dry bulb temperature of the cooling coil)
A. (td? -td?)/( td? -td?)
B. (td? -td?)/( td? -td?)
C. (td? -td?)/( td? -td?)
D. (td? -td?)/( td? -td?)
Answer : B

28. Air refrigerator works on
A. Reversed Carnot cycle
B. Bell Coleman cycle
C. Both (A) and (B)
D. None of these
Answer : C

29. A refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250 K. If the temperature at the end of constant pressure cooling is 300K and rise in the temperature of air in the refrigerator is 50 K, then the net work of compression will be (assume air as working substance with Cp = 1 kJ/kg)
A. 25 kJ/kg
B. 50 kJ/kg
C. 100 kJ/kg
D. 125 kJ/kg
Answer : B

30. The wet bulb temperature at 100% relative humidity is ________ dry bulb temperature.
A. Same as
B. Lower than
C. Higher than
D. None of these
Answer : A

31. An important characteristic of absorption system of refrigeration is
A. Noisy operation
B. Quiet operation
C. Cooling below 0°C
D. Very little power consumption
Answer : B

32. Choose the correct statement
A. A refrigerant should have low latent heat
B. If operating temperature of system is low, then refrigerant with low boiling point should be used
C. Pre-cooling and sub-cooling bf refrigerant are same
D. Superheat and sensible heat of a refrigerant are same
Answer : B

33. In mechanical refrigeration system, the refrigerant has the maximum temperature
A. In evaporator
B. Before expansion valve
C. Between compressor and condenser
D. Between condenser and evaporator
Answer : C

34. During heating and humidification, the final relative humidity of air
A. Can be lower or higher than that of the entering air
B. Is lower than that of the entering air
C. Is higher than that of the entering air
D. None of the above
Answer : A

35. Choose the wrong statement
A. Temperature of medium being cooled must be below that of the evaporator
B. Refrigerant leaves the condenser as liquid
C. All solar thermally operated absorption systems are capable only of intermittent operation
D. Frost on evaporator reduces heat transfer
Answer : A

36. A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called
A. Dry air
B. Moist air
C. Saturated air
D. Specific humidity
Answer : C

37. The index which correlates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as
A. Mean radiant temperature
B. Effective temperature
C. Dew point temperature
D. None of these
Answer : B

38. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process
A. Involves no change in volume
B. Takes place at constant temperature
C. Takes place at constant entropy
D. Takes place at constant pressure
Answer : D

39. The process, generally used in winter air-conditioning to warm and humidity the air, is called
A. Humidification
B. Dehumidification
C. Heating and humidification
D. Cooling and dehumidification
Answer : C

40. The moisture in a refrigerant is removed by
A. Evaporator
B. Safety relief valve
C. Dehumidifier
D. Driers
Answer : D

41. A thermostatic expansion valve in a refrigeration system
A. Ensures the evaporator completely filled with refrigerant of the load
B. Is suitable only for constant load systems
C. Maintains different temperatures in evaporator in proportion to load
D. None of the above
Answer : A

42. Allowable pressure on high pressure side or ammonia absorption system is of the order of
A. Atmospheric pressure
B. Slightly above atmospheric pressure
C. 24 bars
D. 56 bars
Answer : D

43. The higher temperature in vapour compression cycle occurs at
A. Receiver
B. Expansion valve
C. Evaporator
D. Compressor discharge
Answer : D

44. Carbon dioxide is
A. Colourless
B. Odourless
C. Non-flammable
D. All of these
Answer : D

45. A one tonne refrigerating machine means that
A. One tonne is the total mass of machine
B. One tonne refrigerant is used
C. One tonne of water can be converted into ice
D. One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min
Answer : D

46. The alignment circle is marked on the psychrometric chart at
A. 20°C DBT and 50% RH
B. 26°C DBT and 50% RH
C. 20°C DBT and 60% RH
D. 26°C DBT and 60% RH
Answer : B

47. In refrigerator, liquid receiver is required between condenser and flow controlling device, if quantity of refrigerant for system is
A. Less than 2 kg
B. More than or equal to 3.65 kg
C. More than 10 kg
D. There is no such consideration
Answer : B

48. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)
A. B.P.F. - 1
B. 1 - B. P.F.
C. 1/ B.P.F.
D. 1 + B.P.F.
Answer : B

49. Which of the following refrigerant has the lowest freezing point?
A. R-11
B. R-12
C. R-22
D. Ammonia
Answer : C

50. During cooling and dehumidification, dry bulb temperature
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : C