Refrigeration & Air-Conditioning Practice Set-4

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1. 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

4 kW

2 kW

1 kW

3 kW

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

More

Less

More or less depending on ambient conditions

Same

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

Higher than

None of these

Same as

Lower than

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

None of these

Absolute

Specific

Relative

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

7. Which of the following statement is correct?

All of these

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

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

The constant enthalpy lines are also constant wet bulb temperature lines

8. The Freon group of refrigerants are

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

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

Expansion valve and evaporator

Condenser and expansion valve

Compressor and evaporator

Compressor and condenser

10. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

None of these

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

DX coil

Dry

Flooded

None of these

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 relative coefficient of performance is

Actual COP/theoretical COP

Actual COP × theoretical COP

None of these

Theoretical COP/actual COP

14. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

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

15. 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

16. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-22

Freon-11

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

Condensation of the refrigerant vapour

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

Metering of the refrigerant liquid

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

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

20°C DBT and 50% RH

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

20. 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 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

Of adiabatic saturation of incoming stream

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21. The specific humidity during heating and humidification process.

None of these

Decreases

Increases

Remains constant

22. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

Reversed Carnot cycle

None of the above

23. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

24. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Increases

Decreases

25. The specific humidity during dehumidification process

Remains constant

None of these

Decreases

Increases

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

Halide torch

All of these

Soap and water

Sulphur sticks

27. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

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

Both room sensible heat and latent heat loads

Room sensible heat load only

Room latent heat load only

None of the above

30. 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)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

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31. Air refrigeration operates on

Rankine’s cycle

Brayton cycle

Carnot cycle

Reversed Carnot cycle

32. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

33. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₂)/(td₃ - td₁)

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

Less than 2 kg

More than 10 kg

There is no such consideration

More than or equal to 3.65 kg

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

Indirect

Compression

Direct

Absorption

36. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

37. 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

None of these

Mean radiant temperature

38. Air conditioning means

Heating

Cooling

All of these

Dehumidifying

39. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

40. 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

6

1.2

0.2

5

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

Freon-12

CO2

NH3

Freon-22

42. During sensible cooling,

Specific humidity increases

Partial pressure of vapour remains constant

Relative humidity remains constant

Wet bulb temperature increases

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

Anything

High

Small

Equal

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

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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