Single phase motor working theory

Single Phase Induction motor:-

》The single phase induction motor operation can be described by two methods double revolving field theory and cross field theory 113 is perhaps the easier of the two explanation to understand so we will discuss the double revolving theory only

Double revolving field theory:-

》》A single phase AC current supplies the man winding that produce a pulsating magnetic field 》》Mathematically Rakul setting friend would be divided into two field which are rotating in opposite direction
》》 the interaction between the field and current induced in the road Charbagh generates opposing torque

Starting torque:-

》》Single phase motor starting torque is zero  of the pulsating  single phase magnetic flux
》》 the starting of the motor requires the generation of a rotating magnetic flux similar to the rotating flux in three phase motor
》》 two perpendicular coil That Give current 90° out of phase can generate the necessary rotating magnetic field which start the motor
》》There are single phase Motors are built with  two perpendicular winding

》 the best gift is achieved by connecting
• A  resistance
• An inductance or
• A capacitor in series with the starting winding.

》 Most frequently used is a capacitor to generate the starting torque

》 Single phase induction motor are classified and name according to the method employed to make them self starting

(I).  split phase induction motor:- started by phase motor section through the use of auxiliary for starting winding
(II). Capacitor Motors:- standard 5 phase motor connection through the use of an auxilliary  and capacitor these are 

classified as:-
(a). Capacitor start induction run motor
(b). Capacitor run induction motor
(c). capacitor start capacitor run induction motor
(III). Shaded pole induction motor:- started by the motion of the magnetic field produced by means of shading coil around

☆ split phase induction motor☆

In this motor having two winding main winding and auxiliary winding ,hence these winding are 90° electrically each other and same 90° phase angle in these  winding. there are main winding having low resistance and high reactance and auxiliary winding have high resistance and low reactance .switch motor when attain 75% of its rated speed.
  》Working:-

Is lags by V because low reactance and high resistance and Im lag V by very large due to high reactance hence its starting torque proportional to sign thita . it disconnect after attain 75% speed from rated .

Centrifugal switch operation:-
                                                        It is connected in series with the head salary winding and mounted on the rotor shaft when the motor started and reaches 75% of synchronous speed centrifugal switch is mechanically  opened and in running condition auxiliary  winding remains  cut out from the circuit
Therefore motor run only with main winding

Characteristics:-

a.) Starting torque 1.5 times to 2 times the full load torque
b.) Starting current 6 to 8 time the full load current
c.) Low operating power factor 0.55 to .65
d.) Low efficiency 60 to 65%
e.) Power rating 1/20 to 1/2 kW
f.) Speed range 2875rpm to 700 rpm

Applications :-
                            It has low starting current and moderate starting torque. It is used for easily started load and typical applications  including fan, saw, washing machine, blower, centrifugal
pumps. etc.

Capacitor induction motor:-
1.) Capacitor start motor
2.) Capacitor run motor
3.) Capacitor start capacitor run motor

Capacitor start motor :-

                                           In this motor electrolytic capacitor used for starting the motor .in this  motor 90° phase angle for starting purpose the motor . Im' and Is' Im lags V' due to high reactance of main winding in there Is'lead V' due to capacitor  Im'and Is' angle is 90° . this motor having high starting torque .it is used in Lathes , drilling , fan, etc.

Cheracteristcs :-
a.) Starting torque 3.5 to 4.5 times the full load torque
b.) ∝30° to 80° from starting torque can be improved
c.) power factor very from 0.65 to 0 .75.
d.)Power rating 1/10 to 3/4 kW

Requirement of capacitor
》 Electrolytic capacitor are used as  starting capacitor value around 50 microfarad to a few hundred micro farad
》 Capacitor designed for extremely short time duty service and is guaranteed for not more then 29 period of operation / hr each period not axceed 3 seconds

Applications :-
This motor has high starting torque and therefore is used for hard start load such as pumps compressor refrigerator units machine tools etc.

Capacitor start capacitor run 

characteristics 

a ) starting torque 3 to 3.5 time the full load
b.) 60% efficiency opprox.
c.) Power factor .09
d.) Power rating 1/8 to 3/4 HP
e.) Pull out torque up to 260% of rated torque

Applications :-
》It combines the advantage of capacitor start and permanent capacitors and used for hard to start loads such compressor ,pump conveyors etc.
》 These motors are often employed requiring a quite operating motor such as in hospitals and  studios

Shadded pole motor theory of operations :-

 Small motor requiring only small starting torque may be made self starting by using low resistance copper bands called shadding bands. The emf induced in the shadding band cause a current to flow in the band . This current oppose the change of flux to which it is due and thus there is a time lag between the fluxes in the shadded and unshadded portion of the pole . The flux in the shadded portion of tge pole lags the flux in the rottor portion . the result is like a rotating field moving in the direction from the unshadded to the shadded portion of the pole and a starting torque is produced

characteristics :-
a.) Low starting torque 0.4 to 0.8 times the full load torque
b.) Efficiency 35% approximate
c.) Power factor 0.45 approx.
d.) Pull out torque 15% of full load torque
e.) Power rating 1/300 to 20HP ( 2.5 W to 40W)

Applications :- Because their poor starting torque low power factor and poor efficiency such motor are only suitable for low power applications such as for toys, portable fan, electric clock, hair drier, humidifier , photocopy machine etc.

MCQ on Refrigerator & AC 51-105

51. One ton refrigeration corresponds to
(A) 50 kcal/ min✔
(B) 50 kcal/ hr
(C) 80 kcal/ min
(D) 80 kcal/ hr

52. 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

53. The leaks in a refrigeration system using Freon are detected by
(A) Halide torch which on detection produces greenish flame lighting✔
(B) Sulphur sticks which on detection gives white smoke
(C) Using reagents
(D) Smelling

54. The reduced ambient air cooling system has
(A) One cooling turbine and one heat exchanger
(B) One cooling turbine and two heat exchangers
(C) Two cooling turbines and one heat exchanger✔
(D) Two cooling turbines and two heat exchangers

55. 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

56. Which of the following refrigerant has the maximum ozone depletion potential in the stratosphere?
(A) Ammonia
(B) Carbon dioxide
(C) Sulphur dioxide
(D) Fluorine✔

57. 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

58. Hydrogen is used in Electrolux refrigeration system so as to _________ the rate of evaporation of the liquid ammonia passing through the evaporator.
(A) Equalize
(B) Reduce
(C) Increase✔
(D) None of these

59. 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

60. The pressure at the inlet of a refrigerant compressor is called
(A) Suction pressure✔
(B) Discharge pressure
(C) Critical pressure
(D) Back pressure

61. Condensing temperature in a refrigerator is the temperature
(A) Of cooling medium
(B) Of freezing zone
(C) Of evaporator
(D) At which refrigerant gas becomes liquid✔

62. 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

63. Highest pressure encountered in a refrigeration system should be
(A) Critical pressure of refrigerant
(B) Much below critical pressure✔
(C) Much above critical pressure
(D) Near critical pressure

64. The refrigerant used for absorption refrigerators working on heat from solar collectors is a mixture of water and
(A) Carbon dioxide
(B) Sulphur dioxide
(C) Lithium bromide✔
(D) R-12

65. One ton of the refrigeration is
(A) The standard unit used in refrigeration problems
(B) The cooling effect produced by melting 1 ton of ice
(C) The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours✔
(D) The refrigeration effect to produce 1 ton of ice at NTP conditions

66. The dry bulb temperature during sensible heating of air
(A) Remains constant
(B) Increases✔
(C) Decreases
(D) None of these

67. Vertical lines on pressure-enthalpy chart show constant
(A) Pressure lines
(B) Temperature lines
(C) Total heat lines✔
(D) Entropy lines

68. During heating and dehumidification process, dry bulb temperature
(A) Remains constant
(B) Increases✔
(C) Decreases
(D) None of these

69. The evolution of heat of solution takes place in ammonia absorption plant when
(A) Ammonia vapour goes into solution✔
(B) Ammonia vapour is driven out of solution
(C) Lithium bromide mixes with ammonia
(D) Weak solution mixes with strong solution

70. 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

71. In vapour compression cycle, the condition of refrigerant is high pressure saturated liquid
(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 expansion valve✔

72. In a bootstrap air evaporative cooling system, the evaporator is provided
(A) Between the combustion chamber and the first heat exchanger
(B) Between the first heat exchanger and the secondary compressor
(C) Between the secondary compressor and the second heat exchanger
(D) Between the second heat exchanger and the cooling turbine✔

73. 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

74. 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

75. The higher temperature in vapour compression cycle occurs at
(A) Receiver
(B) Expansion valve
(C) Evaporator
(D) Compressor discharge✔

76. 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

77. 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

78. The evaporator changes the low pressure liquid refrigerant from the expansion valve into
(A) High pressure liquid refrigerant
(B) Low pressure liquid and vapour refrigerant
(C) Low pressure vapour refrigerant✔
(D) None of these

79. 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

80. Carbon dioxide is
(A) Colourless
(B) Odourless
(C) Non-flammable
(D) All of these✔

81. 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✔

82. 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

83. If a gas is to be liquefied, its temperature must be
(A) Increased to a value above its critical temperature
(B) Reduced to a value below its critical temperature
(C) Equal to critical temperature✔
(D) None of the above

84. The capacity of a domestic refrigerator is in the range of
(A) 0.1 to 0.3 TR✔
(B) 1 to 3 TR
(C) 3 to 5 TR
(D) 5 to 7 TR

85. The lowest thermal diffusivity is of
(A) Iron
(B) Lead
(C) Aluminium
(D) Rubber✔

86. In a vapour compression cycle, the refrigerant immediately after expansion valve is
(A) Liquid
(B) Sub-cooled liquid
(C) Saturated liquid
(D) Wet vapour✔

87. 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✔

88. Critical pressure of a liquid is the pressure
(A) Above which liquid will remain liquid✔
(B) Above which liquid becomes gas
(C) Above which liquid becomes vapour
(D) Above which liquid becomes solid

89. 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

90. Formation of frost on evaporator in refrigerator
(A) Results in loss of heat due to poor heat transfer✔
(B) Increases heat transfer rate
(C) Is immaterial
(D) Can be avoided by proper design

91. 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✔

92. The suction pipe diameter of refrigerating unit compressor in comparison to delivery side is
(A) Bigger✔
(B) Smaller
(C) Equal
(D) Smaller/bigger depending on capacity

93. The coefficient of performance (C.O.P.) of a refrigerator working as a heat pump is given by
(A) (C.O.P.)P = (C.O.P.)R + 2
(B) (C.O.P.)P = (C.O.P.)R + 1✔
(C) (C.O.P)P = (C.O.P)R - 1
(D) (C.O.P)P = (C.O.P)R

94. Presence of moisture in a refrigerant affects the working of
(A) Compressor
(B) Condenser
(C) Evaporator
(D) Expansion valve✔

95. 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

96. Which of the following cycles uses air as the refrigerant?
(A) Ericson
(B) Stirling
(C) Carnot
(D) Bell Coleman✔

97. The curved lines on a psychrometric chart indicates
(A) Dry bulb temperature
(B) Wet bulb temperature
(C) Dew point temperature
(D) Relative humidity✔

98. 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✔

99. 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

100. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration
(A) 0.1 to 0.5 h.p. per ton of refrigeration
(B) 0.5 to 0.8 h.p. per ton of refrigeration
(C) 1 to 2 h.p. per ton of refrigeration✔
(D) 2 to 5 h.p. per ton of refrigeration

101. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is
(A) 0.376
(B) 0.4
(C) 0.6✔
(D) 0.67

102. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.
(A) More✔
(B) Less
(C) Equally
(D) Unpredictable

103. Most thermostatic expansion valves are set for a superheat of
(A) 5°C✔
(B) 10°C
(C) 15°C
(D) 20°C

104. In a refrigeration system, heat absorbed in comparison to heat rejected is
(A) More✔
(B) Less
(C) Same
(D) More for small capacity and less for high capacity

105. 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

MCQ on Refrigerator & AC 1-50

1. Freon group of refrigerants are
(A) Inflammable
(B) Toxic
(C) Non-inflammable and toxic
(D) Nontoxic and non-inflammable✔

2. The boiling point of ammonia is
(A) -10.5°C
(B) -30°C
(C) -33.3°C✔
(D) -77.7°C

3. For obtaining high COP, the pressure range of compressor should be
(A) High
(B) Low✔
(C) Optimum
(D) Any value

4. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be
(A) 1.33
(B) 2.33✔
(C) 3.33
(D) 4.33

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

6. The freezing point of sulphur dioxide is
(A) -56.6°C
(B) -75.2°C✔
(C) -77.7°C
(D) -135.8°C

7. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of
(A) 1: 1
(B) 1: 9✔
(C) 9: 1
(D) 1: 3

8. In a refrigeration system, the expansion device is connected between the
(A) Compressor and condenser
(B) Condenser and receiver
(C) Receiver and evaporator✔
(D) Evaporator and compressor

9. The vapour compression refrigerator employs the following cycle
(A) Rankine
(B) Carnot
(C) Reversed Rankine
(D) Reversed Carnot✔

10. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about
(A) 1
(B) 1.25✔
(C) 2.15
(D) 5.12

11. Rating of a domestic refrigerator is of the order of
(A) 0.1 ton✔
(B) 5 tons
(C) 10 tons
(D) 40 tons

12. 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)

13. The bank of tubes at the back of domestic refrigerator is
(A) Condenser tubes✔
(B) Evaporator tubes
(C) Refrigerant cooling tubes
(D) Capillary tubes

14. In a lithium bromide absorption refrigeration system
(A) Lithium bromide is used as a refrigerant and water as an absorbent
(B) Water is used as a refrigerant and lithium bromide as an absorbent✔
(C) Ammonia is used as a refrigerant and lithium bromide as an absorbent
(D) None of the above

15. The condition of refrigerant after passing through the condenser in a vapour compression system is
(A) Saturated liquid✔
(B) Wet vapour
(C) Dry saturated vapour
(D) Superheated vapour

16. In a refrigeration cycle, the flow of refrigerant is controlled by
(A) Compressor
(B) Condenser
(C) Evaporator
(D) Expansion valve✔

17. The colour of the flame of halide torch, in case of leakage of Freon refrigerant, will change to
(A) Bright green✔
(B) Yellow
(C) Red
(D) Orange

18. For air conditioning the operation theater in a hospital, the percentage of outside air in the air supplied is
(A) Zero
(B) 20
(C) 50
(D) 100✔

19. In vapour compression cycle using NH₃ 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

20. 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

21. Absorption system normally uses the following refrigerant
(A) Freon-11
(B) Freon-22
(C) CO2
(D) Ammonia✔

22. 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✔

23. 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✔

24. The C.O.P. of a Carnot refrigerator in winter will be _________ as compared to C.O.P. in summer.
(A) Same
(B) Lower
(C) Higher✔
(D) None of these

25. 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✔

26. During humidification process, __________ increases.
(A) Wet bulb temperature
(B) Relative humidity✔
(C) Dry bulb temperature
(D) Specific humidity

27. Where does the lowest temperature occur in a vapour compression cycle?
(A) Condenser
(B) Evaporator✔
(C) Compressor
(D) Expansion valve

28. The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure, is called
(A) Humidity ratio
(B) Relative humidity✔
(C) Absolute humidity
(D) Degree of saturation

29. Under cooling in a refrigeration cycle
(A) Increases C.O.P✔
(B) Decreases C.O.P
(C) C.O.P remains unaltered
(D) Other factors decide C.O.P

30. In a domestic vapour compression refrigerator, the refrigerant commonly used is
(A) CO₂
(B) Ammonia
(C) R-12✔
(D) All of these

31. 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

32. The fluids used in Electrolux refrigerator are
(A) Water and hydrogen
(B) Ammonia and hydrogen
(C) Ammonia, water and hydrogen✔
(D) None of these

33. Domestic refrigerator working on vapour compression cycle uses the following type of expansion device
(A) Electrically operated throttling valve
(B) Manually operated valve
(C) Thermostatic valve
(D) Capillary tube✔

34. The condition of refrigerant after passing through the expansion or throttle valve, in a vapour compression system is
(A) High pressure saturated liquid
(B) Wet vapour
(C) Very wet vapour✔
(D) Dry vapour

35. 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

36. The centrifugal compressors are generally used for refrigerants that require
(A) Small displacements and low condensing pressures
(B) Large displacements and high condensing pressures
(C) Small displacements and high condensing pressures
(D) Large displacements and low condensing pressures✔

37. Rick up the incorrect statement
(A) Lithium bromide used in vapour absorption cycle is non volatile
(B) Lithium bromide plant can't operate below 0°C
(C) A separator is used in lithium bromide plant to remove the unwanted water vapour by condensing✔
(D) Concentration of solution coming out of lithium bromide generator is more in comparison to that entering the generator

38. During dehumidification process, the relative humidity
(A) Remains constant
(B) Increases
(C) Decreases✔
(D) None of these

39. The refrigerant widely used in domestic refrigerators is
(A) Ammonia
(B) Carbon dioxide
(C) Sulphur dioxide
(D) R-12✔

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

41. During sensible cooling of air ________ decreases.
(A) Wet bulb temperature
(B) Relative humidity
(C) Dry bulb temperature✔
(D) Specific humidity

42. At lower temperatures and pressures, the latent heat of vaporisation of a refrigerant
(A) Decreases
(B) Increases✔
(C) Remain same
(D) Depends on other factors

43. The wet bulb depression is zero when relative humidity is
(A) Zero
(B) 0.5
(C) 0.75
(D) 1.0✔

44. The C.O.P of a refrigeration cycle with increase in evaporator temperature, keeping condenser temperature constant, will
(A) Increase✔
(B) Decrease
(C) Remain unaffected
(D) May increase or decrease depending on the type of refrigerant used

45. During humidification process, dry bulb temperature
(A) Remains constant✔
(B) Increases
(C) Decreases
(D) None of these

46. The vapour pressure of refrigerant should be
(A) Lower than atmospheric pressure
(B) Higher than atmospheric pressure✔
(C) Equal to atmospheric pressure
(D) Could be anything

47. 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.✔

48. 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✔

49. For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then
(A) Bigger cabinet should be used
(B) Smaller cabinet should be used
(C) Perfectly tight vapour seal should be used✔
(D) Refrigerant with lower evaporation temperature should be used

50. During sensible heating of air _________ decreases.
(A) Wet bulb temperature
(B) Relative humidity✔
(C) Dry bulb temperature
(D) Specific humidity