1000+ Refrigeration & Air-Conditioning Multiple Choice Question Answer [Solved]

1. Which of the following statement is correct?
A. In vapour absorption refrigerator, the compression of refrigerant is avoided.
B. Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser.
C. In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.
D. All of the above
Answer : D

2. 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

3. 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

4. In a refrigeration cycle, the flow of refrigerant is controlled by
A. Compressor
B. Condenser
C. Evaporator
D. Expansion valve
Answer : D

5. 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

6. 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

7. The sensible heat factor during cooling and dehumidification process is given by (where h? = Enthalpy of air entering the cooling coil, h? = Enthalpy of air leaving the cooling coil, and hA = Enthalpy of air at the end of dehumidification process)
A. (hA - h2)/ (h1 - h2)
B. (h2 - hA)/ (h1 - h2)
C. (h1 - h2)/ (hA - h2)
D. (hA - h1)/ (h2 - h1)
Answer : A

8. The optimum effective temperature for human comfort is
A. Higher in winter than in summer
B. Lower in winter than in summer
C. Same in winter and summer
D. Not dependent on season
Answer : B

9. Vapour compression refrigeration is somewhat like
A. Carnot cycle
B. Rankines cycle
C. Reversed Carnot cycle
D. None of the above
Answer : D

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

11. The C.O.P. of a heat pump working on a reversed Carnot cycle is
A. T?/(T? - T?)
B. (T? - T?)/T?
C. (T? - T?)/T?
D. T?/(T? - T?)
Answer : D

12. 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

13. 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

14. The thermostatic expansion valve is used in __________ type of evaporators.
A. Flooded
B. DX coil
C. Dry
D. None of these
Answer : C

15. Which of the following statement is wrong?
A. The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures.
B. In vapour compression cycle, the useful part of the heat transfer is at the condenser.
C. In ammonia-hydrogen (Electrolux) refrigerator, no compressor, pump or fan is required.
D. The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.
Answer : D

16. 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

17. Chaperon equation is applicable for registration at
A. Saturation point of vapour
B. Saturation point of liquid
C. Sublimation temperature
D. Triple point
Answer : A

18. The bank of tubes at the back of domestic refrigerator is
A. Condenser tubes
B. Evaporator tubes
C. Refrigerant cooling tubes
D. Capillary tubes
Answer : A

19. The evaporator used in household refrigerators is
A. Frosting evaporator
B. Non-frosting evaporator
C. Defrosting evaporator
D. None of these
Aswer : A

20. As relative humidity decreases, the dew point temperature will be ________ wet bulb temperature.
A. Same as
B. Lower than
C. Higher than
D. None of these
Answer : B

21. The value of C.O.P in vapour compression cycle is usually
A. Always less than unity
B. Always more than unity
C. Equal to unity
D. Any one of the above
Answer : B

22. In a psychrometric process, the sensible heat added is 30 kJ/s and the latent heat added is 20 kJ/s. The sensible heat factor for the process will be
A. 0.3
B. 0.6
C. 0.67
D. 1.5
Answer : B

23. Pick up the correct statement about giving up of heat from one medium to other in ammonia absorption system
A. Strong solution to weak solution
B. Weak solution to strong solution
C. Strong solution to ammonia vapour
D. Ammonia vapours to weak solution
Answer : B

24. An evaporator is also known as
A. Freezing coil
B. Cooling coil
C. Chilling coil
D. All of these
Answer : D

25. 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

26. 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

27. In vapour compression cycle, the condition of refrigerant is saturated liquid
A. After passing through the condenser
B. Before passing through the condenser
C. After passing through the expansion throttle valve
D. Before entering the expansion valve
Answer : A

28. Aqua ammonia is used as refrigerant in the following type of refrigeration system
A. Compression
B. Direct
C. Indirect
D. Absorption
Answer : D

29. In refrigerators, the temperature difference between the evaporating refrigerant and the medium being cooled should be
A. High, of the order of 25°
B. As low as possible (3 to 11°C)
C. Zero
D. Any value
Answer : B

30. 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

31. A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in ________ power per tonne of refrigeration.
A. Same
B. Lower
C. Higher
D. None of these
Answer : B

32. For air conditioning the operation theatre in a hospital, the percentage of outside air in the air supplied is
A. Zero
B. 20
C. 50
D. 100
Answer : D

33. The COP of a vapour compression plant in comparison to vapour absorption plant is
A. More
B. Less
C. Same
D. More/less depending on size of plant
Answer : A

34. The operating pressure for refrigerating units using R-12 as a refrigerant is
A. 2 bar
B. 8 bar
C. 15 bar
D. 30 bar
Answer : B

35. In a vapour compression cycle, the refrigerant immediately after expansion valve is
A. Liquid
B. Sub-cooled liquid
C. Saturated liquid
D. Wet vapour
Answer : D

36. The curved lines on a psychrometric chart indicates
A. Dry bulb temperature
B. Wet bulb temperature
C. Dew point temperature
D. Relative humidity
Answer : D

37. 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

38. Reducing suction pressure in refrigeration cycle
A. Lowers evaporation temperature
B. Increases power required per ton of refrigeration
C. Lowers compressor capacity because vapour is lighter
D. All of the above
Answer : D

39. 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

40. The formation of frost on cooling coils in a refrigerator
A. Increases heat transfer
B. Improves C.O.P. of the system
C. Increases power consumption
D. Reduces power consumption
Answer : C

41. 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

42. The lower horizontal line of the refrigeration cycle plotted on pressure-enthalpy diagram represents
A. Condensation of the refrigerant vapour
B. Evaporation of the refrigerant liquid
C. Compression of the refrigerant vapour
D. Metering of the refrigerant liquid
Answer : B

43. In a vapour compression system, the condition of refrigerant before entering the expansion or throttle valve is
A. High pressure saturated liquid
B. Wet vapour
C. Very wet vapour
D. Dry vapour
Answer : A

44. Chaperon equation is a relation between
A. Temperature, pressure and enthalpy
B. Specific volume and enthalpy
C. Temperature and enthalpy
D. Temperature, pressure, specific volume and enthalpy
Answer : D

45. One ton refrigeration corresponds to
A. 50 kcal/ min
B. 50 kcal/ hr
C. 80 kcal/ min
D. 80 kcal/ hr
Answer : A

46. The material of pipe lines for a system using Freon as a refrigerant should be
A. Brass
B. Copper
C. Steel
D. Aluminium
Answer : B

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

48. The refrigerant for a refrigerator should have
A. High sensible heat
B. High total heat
C. High latent heat
D. Low latent heat
Answer : C

49. R-12 is generally preferred over R-22 in deep freezers since
A. It has low operating pressures
B. It gives higher coefficient of performance
C. It is miscible with oil over large range of temperatures
D. All of the above
Answer : C

50. The difference between dry bulb temperature and wet bulb temperature, is called
A. Dry bulb depression
B. Wet bulb depression
C. Dew point depression
D. Degree of saturation
Answer : B