Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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1. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

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

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

3. Air conditioning means

All of these

Dehumidifying

Heating

Cooling

4. The relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

Theoretical COP/actual COP

None of these

5. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

None of these

Increases C.O.P.

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

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Solid and dry ice

Water at 0°C

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

Equal

Anything

High

Small

8. During cooling and dehumidification, dry bulb temperature

Increases

None of these

Remains constant

Decreases

9. During sensible cooling,

Relative humidity remains constant

Wet bulb temperature increases

Partial pressure of vapour remains constant

Specific humidity increases

10. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

Corrosion of whole system

High power consumption

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

Less than 2 kg

There is no such consideration

More than or equal to 3.65 kg

More than 10 kg

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

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

13. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Carnot cycle

None of the above

Rankine’s cycle

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

Compression

Indirect

Absorption

Direct

15. Which of the following statement is correct?

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

All of these

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

The constant enthalpy lines are also constant wet bulb temperature lines

16. The advantage of dry compression is that

It permits complete evaporation in the evaporator

It permits higher speeds to be used

All of the above

It results in high volumetric and mechanical efficiency

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

Less

Same

More or less depending on ambient conditions

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

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

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

Effective temperature

None of these

Mean radiant temperature

Dew point temperature

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

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21. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

0.622 Pv / (Pb - Pv)

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

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

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

DX coil

None of these

Dry

Flooded

24. The specific humidity during dehumidification process

None of these

Decreases

Remains constant

Increases

25. The specific humidity during heating and humidification process.

Increases

None of these

Decreases

Remains constant

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

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Compression of the refrigerant vapour

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

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

All of these

Halide torch

Soap and water

Sulphur sticks

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

None of the above

Both room sensible heat and latent heat loads

Room latent heat load only

Room sensible heat load only

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

Compressor and evaporator

Condenser and expansion valve

Compressor and condenser

Expansion valve and evaporator

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31. The Freon group of refrigerants are

Zoetrope refrigerants

Inorganic refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

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

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

Will be lower

Will be higher

Will remain unaffected

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

All of the above

Heat of compression

Enthalpy increase in compressor

Work done by compressor

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

Absolute

None of these

Relative

Specific

35. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

Maximum work input

36. 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)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

37. 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

2 kW

1 kW

4 kW

38. Air refrigeration operates on

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

Brayton cycle

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

Higher than

Same as

None of these

Lower than

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

Freon-22

CO2

NH3

Freon-12

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41. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Freon-11

Air

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

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

Of adiabatic saturation of incoming stream

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

43. 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

1.2

0.2

44. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

45. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

Refrigeration & Air-Conditioning Practice Set-4

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