Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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

Condenser and expansion valve

Expansion valve and evaporator

Compressor and condenser

Compressor and evaporator

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

3. Moisture in Freon refrigeration system causes

High power consumption

Corrosion of whole system

Freezing automatic regulating valve

Ineffective refrigeration

4. 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

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

All of the above

Heat of compression

Work done by compressor

Enthalpy increase in compressor

6. 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

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

Halide torch

All of these

Soap and water

Sulphur sticks

8. 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

9. 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

Dew point temperature

Mean radiant temperature

10. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Freon-11

Freon-22

Air

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11. Air conditioning means

Cooling

All of these

Heating

Dehumidifying

12. Ammonia absorption refrigeration cycle requires

Very little work input

Zero work input

Nearly same work input as for vapour compression cycle

Maximum work input

13. 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 remain unaffected

Will be lower

Will be higher

14. 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

15. The specific humidity during dehumidification process

Decreases

None of these

Increases

Remains constant

16. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

17. The specific humidity during heating and humidification process.

None of these

Remains constant

Increases

Decreases

18. Air refrigeration operates on

Carnot cycle

Rankine’s cycle

Brayton cycle

Reversed Carnot cycle

19. Superheating in a refrigeration cycle

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

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21. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Reversed Carnot cycle

None of the above

Carnot cycle

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

Anything

High

Equal

Small

23. 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)

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

Relative

Specific

None of these

Absolute

25. The relative coefficient of performance is

None of these

Actual COP × theoretical COP

Actual COP/theoretical COP

Theoretical COP/actual COP

26. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

It permits higher speeds to be used

All of the above

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

Higher than

Lower than

None of these

Same as

28. 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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

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

Solid and dry ice

Water at 0°C

Mixture of ice and water under equilibrium conditions

Ice at 4°C

30. 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

3 kW

1 kW

2 kW

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31. 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)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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

More than or equal to 3.65 kg

There is no such consideration

Less than 2 kg

More than 10 kg

33. 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 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

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

DX coil

Dry

None of these

Flooded

35. 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

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

26°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

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

Direct

Indirect

Compression

Absorption

38. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

None of these

Does not alter C.O.P.

Increases C.O.P.

39. The Freon group of refrigerants are

Inorganic refrigerants

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

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

Freon-22

CO2

NH3

Freon-12

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41. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

Wet bulb temperature increases

42. 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)

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

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

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

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

44. During cooling and dehumidification, dry bulb temperature

Increases

None of these

Remains constant

Decreases

45. 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

Remain unaffected

Increase

Decrease

Refrigeration & Air-Conditioning Practice Set-4

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