Refrigeration & Air-Conditioning Practice Set-4

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

2. 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 10 kg

More than or equal to 3.65 kg

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

Same as

Higher than

None of these

Lower than

4. During sensible cooling,

Wet bulb temperature increases

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

5. The specific humidity during heating and humidification process.

None of these

Increases

Remains constant

Decreases

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

Freon-12

CO2

Freon-22

NH3

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

Small

Equal

Anything

High

8. 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

4 kW

1 kW

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

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

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

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

Of adiabatic saturation of incoming stream

10. Air conditioning means

Cooling

Dehumidifying

Heating

All of these

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11. The specific humidity during dehumidification process

Decreases

Increases

Remains constant

None of these

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

Increase

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

13. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

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

All of these

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

15. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Does not alter C.O.P.

Increases C.O.P.

16. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

17. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-11

Freon-22

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

Compressor and evaporator

19. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

None of these

Increases C.O.P.

Decreases C.O.P.

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 50% RH

26°C DBT and 60% RH

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

Room latent heat load only

Both room sensible heat and latent heat loads

Room sensible heat load only

None of the above

22. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

23. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

24. 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 remain unaffected

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

Will be lower

Will be higher

25. 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)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

26. Ammonia absorption refrigeration cycle requires

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

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

All of these

Halide torch

Soap and water

Sulphur sticks

28. Vapour compression refrigeration is somewhat like

None of the above

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

29. During cooling and dehumidification, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

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

Heat of compression

Work done by compressor

Enthalpy increase in compressor

All of the above

32. 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)

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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

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

Compression

Absorption

Direct

Indirect

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

Less

More or less depending on ambient conditions

Same

More

35. Air refrigeration operates on

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

Carnot cycle

36. 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

5

1.2

0.2

6

37. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Ineffective refrigeration

Corrosion of whole system

High power consumption

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

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

39. The relative coefficient of performance is

Actual COP × theoretical COP

Theoretical COP/actual COP

None of these

Actual COP/theoretical COP

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

DX coil

Dry

None of these

Flooded

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

None of these

Mean radiant temperature

Dew point temperature

Effective temperature

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

44. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

It permits higher speeds to be used

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

None of these

Absolute

Specific

Relative

Refrigeration & Air-Conditioning Practice Set-4

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