Refrigeration & Air-Conditioning Practice Set-4

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

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

2. The Freon group of refrigerants are

Hydrocarbon refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

3. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

4. 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

2 kW

1 kW

3 kW

4 kW

5. 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

6. Air conditioning means

Cooling

Heating

Dehumidifying

All of these

7. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

It permits complete evaporation in the evaporator

All of the above

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

Soap and water

All of these

Sulphur sticks

Halide torch

9. 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

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

Decrease

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

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

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

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

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

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

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

After passing through the condenser

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

Room latent heat load only

Room sensible heat load only

None of the above

Both room sensible heat and latent heat loads

15. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

16. During sensible cooling,

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

Relative humidity remains constant

17. Vapour compression refrigeration is somewhat like

Carnot cycle

None of the above

Reversed Carnot cycle

Rankine’s cycle

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

Dry

DX coil

Flooded

None of these

19. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

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

Solid and dry ice

Ice at 4°C

Water at 0°C

Mixture of ice and water under equilibrium conditions

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

26°C DBT and 50% RH

20°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

22. 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

6

5

23. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

24. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Air

Freon-11

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

Indirect

Direct

Absorption

Compression

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

Anything

Equal

Small

High

27. During cooling and dehumidification, dry bulb temperature

Remains constant

Decreases

Increases

None of these

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

Same as

None of these

Higher than

Lower than

29. The specific humidity during dehumidification process

Increases

None of these

Remains constant

Decreases

30. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

Carnot cycle

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31. 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 lower

Will remain unaffected

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

Will be higher

32. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

None of these

Relative

Specific

Absolute

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

Work done by compressor

Heat of compression

All of the above

Enthalpy increase in compressor

35. Ammonia absorption refrigeration cycle requires

Zero work input

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

36. Superheating in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

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

Same

Less

More or less depending on ambient conditions

More

38. 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

Dew point temperature

Effective temperature

Mean radiant temperature

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

40. 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)]

0.622 Pv / (Pb - Pv)

None of these

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

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41. The specific humidity during heating and humidification process.

Increases

None of these

Remains constant

Decreases

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

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

CO2

NH3

Freon-22

Freon-12

44. 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

45. Moisture in Freon refrigeration system causes

Ineffective refrigeration

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

Refrigeration & Air-Conditioning Practice Set-4

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