Refrigeration & Air-Conditioning Practice Set-4

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1. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

2. 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

3. The specific humidity during heating and humidification process.

Increases

Decreases

Remains constant

None of these

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

Enthalpy increase in compressor

Heat of compression

All of the above

Work done by compressor

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

NH3

Freon-22

CO2

Freon-12

6. 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 wet bulb and dew point temperatures of the incoming stream

Of adiabatic saturation of incoming stream

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

7. During cooling and dehumidification, dry bulb temperature

Remains constant

Decreases

None of these

Increases

8. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

High power consumption

Ineffective refrigeration

Corrosion of whole system

9. The advantage of dry compression is that

It permits higher speeds to be used

All of the above

It results in high volumetric and mechanical efficiency

It permits complete evaporation in the evaporator

10. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Very little work input

Maximum work input

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11. 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)]

None of these

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

0.622 Pv / (Pb - Pv)

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

Lower than

None of these

Same as

Higher than

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

14. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP × theoretical COP

Actual COP/theoretical COP

None of these

15. 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

16. 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 - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

(td₂ - td₃)/(td₃ - td₁)

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

Condenser and expansion valve

Compressor and condenser

Expansion valve and evaporator

Compressor and evaporator

18. 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

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

Will remain unaffected

Will be higher

19. 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

Effective temperature

Dew point temperature

Mean radiant temperature

20. Vapour compression refrigeration is somewhat like

Carnot cycle

Rankine’s cycle

None of the above

Reversed Carnot cycle

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

Small

Equal

Anything

High

22. 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 60% RH

20°C DBT and 50% RH

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

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

24. 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

5

0.2

1.2

25. The superheating in a refrigeration cycle

Decreases C.O.P.

None of these

Does not alter C.O.P.

Increases C.O.P.

26. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

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

Absorption

Direct

Indirect

Compression

29. 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

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

Less

Same

More

More or less depending on ambient conditions

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31. Air refrigeration operates on

Carnot cycle

Reversed Carnot cycle

Brayton cycle

Rankine’s cycle

32. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

Decreases C.O.P.

None of these

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

Dry

Flooded

DX coil

None of these

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

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

More than 10 kg

More than or equal to 3.65 kg

Less than 2 kg

There is no such consideration

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

Absolute

None of these

Specific

Relative

37. Air conditioning means

Dehumidifying

Heating

All of these

Cooling

38. The specific humidity during dehumidification process

Increases

Decreases

None of these

Remains constant

39. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-22

CO2

Air

Freon-11

40. Which of the following statement is correct?

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

The constant enthalpy lines are also constant wet bulb temperature lines

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

Sulphur sticks

Soap and water

Halide torch

All of these

42. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

43. During sensible cooling,

Partial pressure of vapour remains constant

Wet bulb temperature increases

Specific humidity increases

Relative humidity remains constant

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

Before passing through the condenser

45. 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

Refrigeration & Air-Conditioning Practice Set-4

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