Refrigeration & Air-Conditioning Practice Set-4

June 7, 2021

Show paginator

Hide paginator

20%

Page 1 of 5

1. Moisture in Freon refrigeration system causes

Freezing automatic regulating valve

Corrosion of whole system

High power consumption

Ineffective refrigeration

2. 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 is lower than the dew point temperature of the incoming stream

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

Of adiabatic saturation of incoming stream

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

More than or equal to 3.65 kg

There is no such consideration

More than 10 kg

Less than 2 kg

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

Soap and water

All of these

Sulphur sticks

Halide torch

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

6. 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 - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

7. The relative coefficient of performance is

Actual COP/theoretical COP

None of these

Actual COP × theoretical COP

Theoretical COP/actual COP

8. During cooling and dehumidification, dry bulb temperature

Increases

Decreases

Remains constant

None of these

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

None of these

Specific

Absolute

Relative

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

Higher than

Same as

Lower than

None of these

Page 2 of 5

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

Compression

Indirect

Absorption

Direct

12. Refrigeration in aeroplanes usually employs the following refrigerant

Air

Freon-22

Freon-11

CO2

13. Air conditioning means

Heating

All of these

Cooling

Dehumidifying

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

15. 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)

(td₂ - td₃)/(td₃ - td₁)

(td₃ - td₂)/(td₃ - td₁)

16. Ammonia absorption refrigeration cycle requires

Very little work input

Maximum work input

Zero work input

Nearly same work input as for vapour compression cycle

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

Equal

Anything

Small

High

18. Air refrigeration operates on

Carnot cycle

Rankine’s cycle

Reversed Carnot cycle

Brayton cycle

19. The sub-cooling in a refrigeration cycle

Increases C.O.P.

None of these

Does not alter C.O.P.

Decreases C.O.P.

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

Effective temperature

Dew point temperature

None of these

Mean radiant temperature

Page 3 of 5

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

Solid and dry ice

Ice at 4°C

Mixture of ice and water under equilibrium conditions

Water at 0°C

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

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

Freon-12

Freon-22

CO2

NH3

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

None of the above

Room latent heat load only

Both room sensible heat and latent heat loads

Room sensible heat load only

27. 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

3 kW

2 kW

1 kW

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

Remain unaffected

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

29. Vapour compression refrigeration is somewhat like

Rankine’s cycle

Reversed Carnot cycle

None of the above

Carnot cycle

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

Compressor and evaporator

Compressor and condenser

Expansion valve and evaporator

Condenser and expansion valve

Page 4 of 5

31. The advantage of dry compression is that

It results in high volumetric and mechanical efficiency

All of the above

It permits complete evaporation in the evaporator

It permits higher speeds to be used

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

None of these

DX coil

Dry

Flooded

33. 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)

None of these

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

μ/[1 - (1 - μ) (Ps/Pb)]

0.622 Pv / (Pb - Pv)

34. The specific humidity during dehumidification process

Remains constant

Increases

Decreases

None of these

35. 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

36. The Freon group of refrigerants are

Hydrocarbon refrigerants

Inorganic refrigerants

Halocarbon refrigerants

Zoetrope refrigerants

37. During sensible cooling,

Specific humidity increases

Relative humidity remains constant

Wet bulb temperature increases

Partial pressure of vapour remains constant

38. 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 remain unaffected

Will be lower

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

Will be higher

39. Which of the following statement is correct?

The wet bulb temperature is a measure of enthalpy of moist air

The wet bulb and dry bulb temperature are equal at saturation condition

The constant enthalpy lines are also constant wet bulb temperature lines

All of these

40. Superheating in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

C.O.P remains unaltered

Page 5 of 5

41. 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

42. The specific humidity during heating and humidification process.

Decreases

None of these

Increases

Remains constant

43. The superheating in a refrigeration cycle

Increases C.O.P.

Decreases C.O.P.

None of these

Does not alter C.O.P.

44. 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

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

26°C DBT and 50% RH

26°C DBT and 60% RH

20°C DBT and 60% RH

20°C DBT and 50% RH

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