Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. The sub-cooling in a refrigeration cycle

None of these

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

2. The bypass factor (B. P. F.) in case of sensible heating of air is (Where t_d₁ = Dry bulb temperature of air entering the heating coil, t_d₂ = Dry bulb temperature of air leaving the heating coil, and t_d₃ = Dry bulb temperature of heating coil)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

3. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

Maximum work input

4. In refrigerator, liquid receiver is required between condenser and flow controlling device, if quantity of refrigerant for system is

There is no such consideration

Less than 2 kg

More than or equal to 3.65 kg

More than 10 kg

5. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

6. Air conditioning means

Heating

Cooling

All of these

Dehumidifying

7. A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be

3 kW

1 kW

4 kW

2 kW

8. The alignment circle is marked on the psychrometric chart at

20°C DBT and 60% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

9. During sensible cooling,

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

10. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

Of adiabatic saturation of incoming stream

Which lies between the wet bulb and dew point temperatures of the incoming stream

Which is lower than the dew point temperature of the incoming stream

Which lies between the dry bulb and wet bulb temperatures of the incoming stream

Page 2 of 5

11. The thermostatic expansion valve is used in ________ type of evaporators.

None of these

Flooded

Dry

DX coil

12. The condition of refrigerant as it leaves the compressor in a vapour compression system is

Saturated liquid

Wet vapour

Dry saturated vapour

Superheated vapour

13. The refrigeration effect in a dry evaporator compared to flooded evaporator in a similar plant is

More

Same

Less

More or less depending on ambient conditions

14. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

15. Aqua ammonia is used as refrigerant in the following type of refrigeration system

Indirect

Direct

Compression

Absorption

16. The condensing pressure due to the presence of non-condensable gases, as compared to that actually required for condensing temperatures without non-condensable gases,

Will be higher

May be higher or lower depending upon the nature of non-condensable gases

Will remain unaffected

Will be lower

17. The wet bulb depression indicates _________ humidity of the air.

None of these

Relative

Specific

Absolute

18. The conditioned air supplied to the room must have the capacity to take up

Both room sensible heat and latent heat loads

Room latent heat load only

None of the above

Room sensible heat load only

19. The lower horizontal line of the refrigeration cycle plotted on pressure-enthalpy diagram represents

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

20. In vapour compression cycle, the condition of refrigerant is very wet vapour

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

Page 3 of 5

21. In vapour compression refrigeration system, refrigerant occurs as liquid between

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

Expansion valve and evaporator

22. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

None of these

Remains constant

23. The sensible heat factor during the heating and humidification process is given by (where h₁ = Enthalpy of air entering the heating coil, h₂ = Enthalpy of air leaving the heating coil, and h_A = Enthalpy of air at the end of humidification process)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

24. The leakage in a refrigeration system using Freon is detected by

Sulphur sticks

Halide torch

Soap and water

All of these

25. The specific humidity during heating and humidification process.

Increases

Decreases

None of these

Remains constant

26. A standard ice point temperature corresponds to the temperature of

Water at 0°C

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

27. The relative coefficient of performance is

Theoretical COP/actual COP

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

28. The specific humidity during dehumidification process

None of these

Decreases

Remains constant

Increases

29. The boiling point of ________ is 10.5°C.

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

30. Which of the following refrigerants has lowest freezing point?

Freon-12

Freon-22

CO2

NH3

Page 4 of 5

31. The index which correlates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as

Dew point temperature

Effective temperature

Mean radiant temperature

None of these

32. The wet bulb temperature at 100% relative humidity is ________ dew point temperature.

None of these

Same as

Higher than

Lower than

33. Relative humidity is given by (where p_v = Partial pressure of water vapour, p_b = Barometric pressure, p_s = Pressure of saturated air, p_d = Pressure at dry bulb temperature, p_w = Saturation pressure corresponding to wet bulb temperature, and μ = Degree of saturation)

None of these

0.622 Pv / (Pb - Pv)

[Pv (Pb - Pd)]/ [Pd (Pb - Pv)]

μ/[1 - (1 - μ) (Ps/Pb)]

34. The Freon group of refrigerants are

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

35. The coefficient of performance is the ratio of the refrigerant effect to the

Work done by compressor

Enthalpy increase in compressor

All of the above

Heat of compression

36. The advantage of dry compression is that

All of the above

It permits complete evaporation in the evaporator

It permits higher speeds to be used

It results in high volumetric and mechanical efficiency

37. The C.O.P. of a refrigeration cycle with lowering of condenser temperature, keeping the evaporator temperature constant, will

May increase or decrease depending on the type of refrigerant used

Decrease

Increase

Remain unaffected

38. Air refrigeration operates on

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

Carnot cycle

39. Vapour compression refrigeration is somewhat like

None of the above

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

40. Superheating in a refrigeration cycle

Increases C.O.P

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Page 5 of 5

41. Which of the following statement is correct?

The wet bulb temperature is a measure of enthalpy of moist air

The wet bulb and dry bulb temperature are equal at saturation condition

All of these

The constant enthalpy lines are also constant wet bulb temperature lines

42. A refrigeration cycle operates between condenser temperature of + 27°C and evaporator temperature of -23°C. The Carnot coefficient of performance of cycle will be

0.2

5

6

1.2

43. Which of the following refrigerant has the highest freezing point.

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

44. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-11

Air

Freon-22

45. For better C.O.P of refrigerator, the pressure range corresponding to temperature in evaporator and condenser must be

Small

Anything

Equal

High

Refrigeration & Air-Conditioning Practice Set-4

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