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

1. The comfort conditions in air conditioning are at (where DBT = Dry bulb temperature, and RH = Relative humidity)
A. 25°C DBT and 100% RH
B. 20°C DBT and 80% RH
C. 22°C DBT and 60% RH
D. 25°C DBT and 40% RH
Answer : C

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

3. While designing the refrigeration system of an aircraft, the prime consideration is that the
A. System has high C.O.P.
B. Power per TR is low
C. Mass of refrigerant circulated in the system is low
D. Mass of the refrigeration equipment is low
Answer : D

4. Hydrogen is used in Electrolux refrigeration system so as to _________ the rate of evaporation of the liquid ammonia passing through the evaporator.
A. Equalise
B. Reduce
C. Increase
D. None of these
Answer : C

5. Most air cooled condensers are designed to operate with a temperature difference of
A. 5°C
B. 8°C
C. 14°C
D. 22°C
Answer : C

6. The specific humidity during cooling and dehumidification
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : C

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

8. In which of the following refrigeration system, waste heat can be effectively used?
A. Vapour compression cycle
B. Vapour absorption cycle
C. Air refrigeration cycle
D. None of these
Answer : B

9. The COP of a domestic refrigerator
A. Is less than 1
B. Is more than 1
C. Is equal to 1
D. Depends upon the make
Answer : B

10. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be
A. Positive
B. Negative
C. Zero
D. None of these
Answer : B

11. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is
A. Ammonia
B. Carbon dioxide
C. Freon
D. Brine
Answer : B

12. Moisture should be removed from refrigerants to avoid
A. Freezing at the expansion valve
B. Restriction to refrigerant flow
C. Corrosion of steel plates
D. All of these
Answer : D

13. A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be
A. Lack of cooling water
B. Water temperature being high
C. Dirty condenser surface
D. All of these
Answer : D

14. A refrigerant with the highest critical pressure is
A. R-11
B. R-12
C. R-22
D. Ammonia
Answer : D

15. In vapour compression cycle using NH? as refrigerant, initial charge is filled at
A. Suction of compressor
B. Delivery of compressor
C. High pressure side close to receiver
D. Low pressure side near receiver
Answer : C

16. The bypass factor (B. P. F.) in case of sensible heating of air is (Where td? = Dry bulb temperature of air entering the heating coil, td? = Dry bulb temperature of air leaving the heating coil, and td? = Dry bulb temperature of heating coil)
A. (td? - td?)/(td? - td?)
B. (td? - td?)/(td? - td?)
C. (td? - td?)/(td? - td?)
D. (td? - td?)/(td? - td?)
Answer : B

17. The thermostatic expansion valve is also called
A. Constant pressure valve
B. Constant temperature valve
C. Constant superheat valve
D. None of these
Answer : C

18. A condenser of refrigeration system rejects heat at the rate of 120 kW, while its compressor consumes a power of 30 kW. The coefficient of performance of the system will be
A. 1/4
B. 1/3
C. 3
D. 4
Answer : D

19. In aircraft, air refrigeration Cycle is used because of
A. Low weight per tonne of refrigeration
B. High heat transfer rate
C. Low temperature at high altitudes
D. Higher coefficient of performance
Answer : A

20. The coefficient of performance of a domestic refrigerator is ________ as compared to a domestic air-conditioner.
A. Same
B. Less
C. More
D. None of these
Answer : B

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

22. The dry bulb temperature lines, on the psychrometric chart are
A. Vertical and uniformly spaced
B. Horizontal and uniformly spaced
C. Horizontal and non-uniformly spaced
D. Curved lines
Answer : A

23. Which of the following statement is correct for ammonia as a refrigerant?
A. It is toxic to mucous membranes.
B. It requires large displacement per TR compared to fluoro carbons.
C. It reacts with copper and its alloys.
D. All of these
Answer : D

24. 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

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

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

27. The operating temperature of a cold storage is 2°C. The heat leakage from the surrounding is 30 kW for the ambient temperature of 40°C. The actual C.O.P. of refrigeration plant used is one fourth that of ideal plant working between the same temperatures. The power required to drive the plant is
A. 1.86 kW
B. 3.72 kW
C. 7.44 kW
D. 18.6 kW
Answer : D

28. Nusselt number (N_N) is given by
A. N_N = hl/k
B. N_N = ? c_p/k
C. N_N = ? V l /?
D. N_N = V²/t.c_p
Answer : A

29. Wet bulb temperature is the temperature of air recorded by a thermometer, when
A. It is not affected by the moisture present in the air
B. Its bulb is surrounded by a wet cloth exposed to the air
C. The moisture present in it begins to condense
D. None of the above
Answer : B

30. The sub-cooling in a refrigeration cycle
A. Does not alter C.O.P.
B. Increases C.O.P.
C. Decreases C.O.P.
D. None of these
Answer : B

31. The boiling point of ammonia is
A. 100°C
B. 50°C
C. 33.3°C
D. 0°C
Answer : C

32. For obtaining high COP, the pressure range of compressor should be
A. High
B. Low
C. Optimum
D. Any value
Answer : B

33. In a pressure enthalpy chart, the space to the left of the saturated liquid line represents
A. Wet vapour region
B. Superheated vapour region
C. Sub-cooled liquid region
D. None of these
Answer : C

34. It is desired to condition the outside air from 70% relative humidity and 45° C dry bulb temperature to 50% relative humidity and 25° C dry bulb temperature (room condition). The practical arrangement will be
A. Dehumidification
B. Cooling and humidification
C. Cooling and dehumidification
D. Dehumidification and pure sensible cooling
Answer : C

35. Cooling water is required for following equipment in ammonia absorption plant
A. Condenser
B. Evaporator
C. Absorber
D. Condenser, absorber and separator (rectifier)
Answer : D

36. Dry bulb temperature is the temperature of air recorded by a thermometer, when
A. It is not affected by the moisture present in the air
B. Its bulb is surrounded by a wet cloth exposed to the air
C. The moisture present in it begins to condense
D. None of the above
Answer : A

37. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called
A. Sub-cooling or under-cooling
B. Super-cooling
C. Normal cooling
D. None of these
Answer : A

38. The bypass factor of a cooling coil decreases with
A. Decrease in fin spacing and increase in number of rows
B. Increase in fin spacing and increase in number of rows
C. Increase in fin spacing and decrease in number of rows
D. Decrease in fin spacing and decrease in number of rows
Answer : A

39. The process, generally used in summer air conditioning to cool and dehumidify the air, is called
A. Humidification
B. Dehumidification
C. Heating and humidification
D. Cooling and dehumidification
Answer : D

40. In a psychrometric chart, specific humidity (moisture content) lines are
A. Vertical and uniformly spaced
B. Horizontal and uniformly spaced
C. Horizontal and non-uniformly spaced
D. Curved lines
Answer : B

41. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the
A. Heat dissipated to the surroundings
B. Heat stored in the human body
C. Sum of (A) and (B)
D. Difference of (A) and (B)
Answer : C

42. In a vapour compression system, the condition of refrigerant before passing through the condenser is
A. Saturated liquid
B. Wet vapour
C. Dry saturated vapour
D. Superheated vapour
Answer : D

43. 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

44. If the evaporator temperature of a plant is lowered, keeping the condenser temperature constant, the h.p. of compressor required will be
A. Same
B. More
C. Less
D. More/less depending on rating
Answer : B

45. 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

46. The specific humidity during dehumidification process
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : C

47. 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

48. In a domestic refrigerator, a capillary tube controls the flow of refrigerant from the
A. Expansion valve to the evaporator
B. Evaporator to the thermostat
C. Condenser to the expansion valve
D. Condenser to the evaporator
Answer : A

49. In vapour compression cycle the condition off refrigerant is dry saturated vapour
A. After passing through the condenser
B. Before passing through the condenser
C. After passing through the expansion or throttle valve
D. Before entering the compressor
Answer : D

50. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called
A. Wet bulb temperature
B. Dry bulb temperature
C. Dew point temperature
D. None of these
Answer : B