Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

Soap and water

Halide torch

All of these

Sulphur sticks

3. Air refrigeration operates on

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

Brayton cycle

4. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Relative humidity remains constant

Wet bulb temperature increases

5. The relative coefficient of performance is

Actual COP/theoretical COP

Theoretical COP/actual COP

Actual COP × theoretical COP

None of these

6. The specific humidity during heating and humidification process.

Remains constant

Increases

Decreases

None of these

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

None of these

Lower than

Same as

Higher than

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

Effective temperature

Mean radiant temperature

None of these

Dew point temperature

9. During cooling and dehumidification, dry bulb temperature

Decreases

Remains constant

Increases

None of these

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

DX coil

None of these

Dry

Flooded

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

Decrease

May increase or decrease depending on the type of refrigerant used

Remain unaffected

Increase

12. The sub-cooling in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

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,

Will be lower

Will be higher

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

Will remain unaffected

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

Mixture of ice and water under equilibrium conditions

Solid and dry ice

Ice at 4°C

Water at 0°C

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

Before passing through the condenser

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

Compressor and condenser

Condenser and expansion valve

Expansion valve and evaporator

Compressor and evaporator

17. The superheating in a refrigeration cycle

Does not alter C.O.P.

None of these

Decreases C.O.P.

Increases C.O.P.

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

Compression

Indirect

Direct

Absorption

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

There is no such consideration

Less than 2 kg

More than or equal to 3.65 kg

More than 10 kg

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

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

20°C DBT and 60% RH

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21. 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

0.2

1.2

22. 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

23. Vapour compression refrigeration is somewhat like

None of the above

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

24. 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)

25. 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

All of these

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

26. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

Freon-11

Air

CO2

27. Superheating in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

28. 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 - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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

Dry saturated vapour

Superheated vapour

Wet vapour

Saturated liquid

30. 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

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

Small

Equal

High

Anything

32. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

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

None of these

Specific

Absolute

Relative

34. The advantage of dry compression is that

It permits complete evaporation in the evaporator

All of the above

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

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

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

37. Moisture in Freon refrigeration system causes

High power consumption

Ineffective refrigeration

Freezing automatic regulating valve

Corrosion of whole system

38. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

39. The specific humidity during dehumidification process

Remains constant

Increases

Decreases

None of these

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

Freon-22

CO2

NH3

Freon-12

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41. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

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

None of these

42. 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 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

43. 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

44. Air conditioning means

Heating

Dehumidifying

Cooling

All of these

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

Both room sensible heat and latent heat loads

None of the above

Room latent heat load only

Room sensible heat load only

Refrigeration & Air-Conditioning Practice Set-4

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