Refrigeration & Air-Conditioning Practice Set-4

Page 1 of 5

1. 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

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

More than 10 kg

There is no such consideration

More than or equal to 3.65 kg

Less than 2 kg

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

Higher than

None of these

Lower than

Same as

4. 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

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

Expansion valve and evaporator

Compressor and evaporator

Compressor and condenser

Condenser and expansion valve

6. Ammonia absorption refrigeration cycle requires

Nearly same work input as for vapour compression cycle

Zero work input

Maximum work input

Very little work input

7. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Carnot cycle

None of the above

Reversed Carnot cycle

8. Air refrigeration operates on

Carnot cycle

Rankine’s cycle

Brayton cycle

Reversed Carnot cycle

9. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

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

Direct

Indirect

Absorption

Compression

Page 2 of 5

11. Refrigeration in aeroplanes usually employs the following refrigerant

Air

CO2

Freon-22

Freon-11

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 higher

Will remain unaffected

Will be lower

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

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

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

14. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

15. Air conditioning means

Dehumidifying

All of these

Heating

Cooling

16. 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

17. The relative coefficient of performance is

None of these

Theoretical COP/actual COP

Actual COP/theoretical COP

Actual COP × theoretical COP

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

Superheated vapour

Saturated liquid

Wet vapour

Dry saturated vapour

19. 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

20. The sub-cooling in a refrigeration cycle

None of these

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

Page 3 of 5

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

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

Compression of the refrigerant vapour

22. 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

23. Superheating in a refrigeration cycle

Increases C.O.P

Decreases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

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

More or less depending on ambient conditions

Same

Less

More

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

None of these

Dry

DX coil

Flooded

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

27. 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

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

All of these

Sulphur sticks

Soap and water

Halide torch

29. The specific humidity during heating and humidification process.

None of these

Remains constant

Decreases

Increases

30. 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

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 - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₃ - td₁)/(td₃ - td₂)

32. 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

Mean radiant temperature

Dew point temperature

Effective temperature

33. 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

1.2

5

0.2

34. The Freon group of refrigerants are

Zoetrope refrigerants

Halocarbon refrigerants

Inorganic refrigerants

Hydrocarbon refrigerants

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

Freon-12

Freon-22

NH3

CO2

36. The specific humidity during dehumidification process

Increases

Decreases

Remains constant

None of these

37. 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

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

High

Small

Equal

Anything

39. The superheating in a refrigeration cycle

Decreases C.O.P.

Does not alter C.O.P.

Increases C.O.P.

None of these

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

Specific

None of these

Relative

Absolute

Page 5 of 5

41. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

It permits higher speeds to be used

It permits complete evaporation in the evaporator

All of the above

42. During cooling and dehumidification, dry bulb temperature

Decreases

Increases

None of these

Remains constant

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

26°C DBT and 60% RH

20°C DBT and 50% RH

26°C DBT and 50% RH

20°C DBT and 60% RH

44. During sensible cooling,

Specific humidity increases

Wet bulb temperature increases

Partial pressure of vapour remains constant

Relative humidity remains constant

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

Refrigeration & Air-Conditioning Practice Set-4

Related

Leave a ReplyCancel reply

Secured Payments

Protection

Refrigeration & Air-Conditioning Practice Set-4

Share this Now with Friends:

Related

Leave a ReplyCancel reply

Secured Payments

Protection