Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

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

Anything

High

Small

Equal

2. Vapour compression refrigeration is somewhat like

Carnot cycle

Reversed Carnot cycle

Rankine’s cycle

None of the above

3. 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

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

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

5. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₁)/(td₃ - td₂)

6. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

Remains constant

None of these

7. 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 be lower

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

Will remain unaffected

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

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

Ice at 4°C

Water at 0°C

Mixture of ice and water under equilibrium conditions

Solid and dry ice

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

Page 2 of 5

11. 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 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

Which lies between the wet bulb and dew point temperatures of the incoming stream

12. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

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

Freon-12

NH3

Freon-22

CO2

14. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

15. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Freon-22

Air

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

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Condensation of the refrigerant vapour

Compression of the refrigerant vapour

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

More

More or less depending on ambient conditions

Same

Less

18. The relative coefficient of performance is

None of these

Actual COP/theoretical COP

Actual COP × theoretical COP

Theoretical COP/actual COP

19. 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)

20. The advantage of dry compression is that

It permits higher speeds to be used

All of the above

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

Page 3 of 5

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

Higher than

None of these

Lower than

Same as

22. Air refrigeration operates on

Carnot cycle

Brayton cycle

Rankine’s cycle

Reversed Carnot cycle

23. Moisture in Freon refrigeration system causes

High power consumption

Freezing automatic regulating valve

Corrosion of whole system

Ineffective refrigeration

24. 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

Mean radiant temperature

Dew point temperature

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

Less than 2 kg

More than or equal to 3.65 kg

More than 10 kg

There is no such consideration

26. 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

1 kW

3 kW

2 kW

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

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

26°C DBT and 60% RH

20°C DBT and 60% RH

26°C DBT and 50% RH

20°C DBT and 50% RH

29. The specific humidity during heating and humidification process.

Decreases

Increases

Remains constant

None of these

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

Relative

Specific

Absolute

None of these

Page 4 of 5

31. The superheating in a refrigeration cycle

None of these

Decreases C.O.P.

Increases C.O.P.

Does not alter C.O.P.

32. The Freon group of refrigerants are

Halocarbon refrigerants

Inorganic refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

33. Superheating in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

34. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

Very little work input

35. Air conditioning means

All of these

Cooling

Dehumidifying

Heating

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

Sulphur sticks

Halide torch

Soap and water

All of these

37. 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)

μ/[1 - (1 - μ) (Ps/Pb)]

None of these

38. The specific humidity during dehumidification process

Increases

None of these

Remains constant

Decreases

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

Flooded

Dry

DX coil

None of these

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

Absorption

Direct

Compression

Indirect

Page 5 of 5

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

Compressor and condenser

Expansion valve and evaporator

Compressor and evaporator

Condenser and expansion valve

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

43. 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

1.2

6

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

Work done by compressor

Enthalpy increase in compressor

All of the above

Heat of compression

45. 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

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