Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

Theoretical COP/actual COP

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

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

Compressor and evaporator

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

Anything

Small

High

Equal

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

Specific

None of these

Absolute

Relative

5. Air conditioning means

Cooling

Heating

Dehumidifying

All of these

6. The Freon group of refrigerants are

Halocarbon refrigerants

Hydrocarbon refrigerants

Zoetrope refrigerants

Inorganic refrigerants

7. Refrigeration in aeroplanes usually employs the following refrigerant

CO2

Air

Freon-22

Freon-11

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

20°C DBT and 50% RH

20°C DBT and 60% RH

26°C DBT and 60% RH

26°C DBT and 50% RH

9. Superheating in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

Other factors decide C.O.P

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

Dew point temperature

Mean radiant temperature

Effective temperature

None of these

Page 2 of 5

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

Soap and water

Sulphur sticks

Halide torch

All of these

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

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

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

Flooded

None of these

DX coil

Dry

14. 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

1 kW

2 kW

4 kW

15. 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)

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

0.622 Pv / (Pb - Pv)

None of these

μ/[1 - (1 - μ) (Ps/Pb)]

16. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

High power consumption

Ineffective refrigeration

Corrosion of whole system

17. 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

18. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Nearly same work input as for vapour compression cycle

Zero work input

19. The advantage of dry compression is that

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

All of the above

20. 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

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

Page 3 of 5

21. 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

Increase

Decrease

Remain unaffected

22. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Brayton cycle

Rankine’s cycle

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

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Water at 0°C

Solid and dry ice

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

Same

More or less depending on ambient conditions

More

Less

25. The superheating in a refrigeration cycle

None of these

Increases C.O.P.

Decreases C.O.P.

Does not alter 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)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

Freon-12

Freon-22

NH3

CO2

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

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Compression of the refrigerant vapour

Evaporation of the refrigerant liquid

29. 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 higher

Will remain unaffected

Will be lower

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

30. Vapour compression refrigeration is somewhat like

Rankine’s cycle

None of the above

Carnot cycle

Reversed Carnot cycle

Page 4 of 5

31. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

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

None of the above

Both room sensible heat and latent heat loads

Room latent heat load only

Room sensible heat load only

33. The sub-cooling in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

35. 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

36. The specific humidity during dehumidification process

Remains constant

None of these

Increases

Decreases

37. During cooling and dehumidification, dry bulb temperature

None of these

Decreases

Remains constant

Increases

38. The specific humidity during heating and humidification process.

Increases

Decreases

Remains constant

None of these

39. 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

5

6

1.2

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

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Page 5 of 5

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

Compression

Absorption

Direct

Indirect

42. 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

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

44. During sensible cooling,

Relative humidity remains constant

Specific humidity increases

Partial pressure of vapour remains constant

Wet bulb temperature increases

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

None of these

Same as

Lower than

Higher than

Refrigeration & Air-Conditioning Practice Set-4

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection

Refrigeration & Air-Conditioning Practice Set-4

Share this Now with Friends:

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection