Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

Show paginator

Hide paginator

20%

Page 1 of 5

1. 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

4 kW

2 kW

2. The specific humidity during dehumidification process

Decreases

Remains constant

Increases

None of these

3. During cooling and dehumidification, dry bulb temperature

Remains constant

Decreases

Increases

None of these

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

Solid and dry ice

Mixture of ice and water under equilibrium conditions

Water at 0°C

Ice at 4°C

5. 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

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

Of adiabatic saturation of incoming stream

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

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

7. 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

8. Vapour compression refrigeration is somewhat like

Reversed Carnot cycle

Rankine’s cycle

Carnot cycle

None of the above

9. The sub-cooling in a refrigeration cycle

Does not alter C.O.P.

Decreases C.O.P.

Increases C.O.P.

None of these

10. 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

Page 2 of 5

11. 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

1.2

0.2

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

Less than 2 kg

There is no such consideration

More than 10 kg

More than or equal to 3.65 kg

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

Lower than

Same as

Higher than

None of these

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

None of these

Relative

Absolute

Specific

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

Halide torch

All of these

Soap and water

Sulphur sticks

16. Air conditioning means

All of these

Heating

Dehumidifying

Cooling

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

High

Anything

Small

Equal

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

NH3

CO2

Freon-12

Freon-22

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

Flooded

Dry

None of these

DX coil

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

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

Page 3 of 5

21. 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)/(td₃ - td₂)

(td₃ - td₁)/(td₂ - td₃)

(td₃ - td₂)/(td₃ - td₁)

(td₂ - td₃)/(td₃ - td₁)

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

23. Refrigeration in aeroplanes usually employs the following refrigerant

Freon-11

CO2

Freon-22

Air

24. 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

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

Less

Same

More or less depending on ambient conditions

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

Compression of the refrigerant vapour

Condensation of the refrigerant vapour

Metering of the refrigerant liquid

Evaporation of the refrigerant liquid

27. The advantage of dry compression is that

All of the above

It permits higher speeds to be used

It permits complete evaporation in the evaporator

It results in high volumetric and mechanical efficiency

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

Direct

Compression

Indirect

Absorption

29. The relative coefficient of performance is

Theoretical COP/actual COP

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

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

Room sensible heat load only

Room latent heat load only

None of the above

Both room sensible heat and latent heat loads

Page 4 of 5

31. Ammonia absorption refrigeration cycle requires

Maximum work input

Zero work input

Very little work input

Nearly same work input as for vapour compression cycle

32. The specific humidity during heating and humidification process.

Increases

Decreases

Remains constant

None of these

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

34. 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

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

Heat of compression

Work done by compressor

Enthalpy increase in compressor

All of the above

36. Moisture in Freon refrigeration system causes

Corrosion of whole system

High power consumption

Freezing automatic regulating valve

Ineffective refrigeration

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

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

38. The superheating in a refrigeration cycle

Does not alter C.O.P.

Increases C.O.P.

None of these

Decreases C.O.P.

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

Expansion valve and evaporator

Compressor and condenser

Condenser and expansion valve

Compressor and evaporator

40. Air refrigeration operates on

Reversed Carnot cycle

Carnot cycle

Rankine’s cycle

Brayton cycle

Page 5 of 5

41. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

42. 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

43. During sensible cooling,

Partial pressure of vapour remains constant

Specific humidity increases

Wet bulb temperature increases

Relative humidity remains constant

44. Superheating in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

45. The Freon group of refrigerants are

Halocarbon refrigerants

Zoetrope refrigerants

Hydrocarbon refrigerants

Inorganic refrigerants

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