Refrigeration & Air-Conditioning Practice Set-4

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

Compression

Direct

Absorption

Indirect

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

Dry

None of these

DX coil

Flooded

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

Room latent heat load only

None of the above

Room sensible heat load only

Both room sensible heat and latent heat loads

4. 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 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

Of adiabatic saturation of incoming stream

5. The advantage of dry compression is that

All of the above

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

It permits complete evaporation in the evaporator

6. The specific humidity during heating and humidification process.

Increases

Remains constant

Decreases

None of these

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

Mean radiant temperature

Dew point temperature

Effective temperature

None of these

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

20°C DBT and 60% RH

26°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

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

Decrease

Remain unaffected

Increase

May increase or decrease depending on the type of refrigerant used

10. 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)]

None of these

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

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

Freon-12

NH3

Freon-22

CO2

12. 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 be higher

Will remain unaffected

13. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Rankine’s cycle

None of the above

Carnot cycle

14. 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

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

Compressor and evaporator

Expansion valve and evaporator

Condenser and expansion valve

Compressor and condenser

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

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

Small

Equal

High

Anything

19. 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

5

0.2

6

1.2

20. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Very little work input

Maximum work input

Zero work input

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21. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

Freon-11

CO2

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

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

Halide torch

Soap and water

Sulphur sticks

All of these

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Ice at 4°C

Water at 0°C

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

More

More or less depending on ambient conditions

Less

Same

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

Work done by compressor

Enthalpy increase in compressor

Heat of compression

All of the above

27. The sub-cooling in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

None of these

Decreases C.O.P.

28. During cooling and dehumidification, dry bulb temperature

None of these

Remains constant

Decreases

Increases

29. Moisture in Freon refrigeration system causes

Corrosion of whole system

Ineffective refrigeration

High power consumption

Freezing automatic regulating valve

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

None of these

Absolute

Relative

Specific

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31. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

Theoretical COP/actual COP

32. Air conditioning means

Cooling

All of these

Heating

Dehumidifying

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

Same as

Higher than

None of these

Lower than

34. 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)

35. The specific humidity during dehumidification process

Decreases

None of these

Increases

Remains constant

36. 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

4 kW

2 kW

1 kW

37. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

Relative humidity remains constant

38. Air refrigeration operates on

Reversed Carnot cycle

Rankine’s cycle

Brayton cycle

Carnot cycle

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

Evaporation of the refrigerant liquid

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

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41. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

42. 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)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

43. Superheating in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

44. Which of the following statement is correct?

The constant enthalpy lines are also constant wet bulb temperature lines

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

45. The superheating in a refrigeration cycle

Increases C.O.P.

Does not alter C.O.P.

Decreases C.O.P.

None of these

Refrigeration & Air-Conditioning Practice Set-4

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