# Refrigeration and Air-conditioning - Mechanical Engineering test

## Refrigeration and Air-conditioning - Mechanical Engineering test

1) For a domestic refrigerator the COP is

a) More than 1
b) Less than 1
c) Equal to 1
d) Unpredictable.

ANSWER: a) More than 1

2) Relative COP is equal to

a) Actual C.O.P / theoretical C.O.P
b) Actual C.O.P x theoretical C.O.P
c) Theoretical C.O.P / actual C.O.P
d) None of these.

ANSWER: a) Actual C.O.P / theoretical C.O.P

3) How is the capacity of a refrigerating machine expressed?

a) Inside volume of the cabinet.
b) Lowest temperature attained.
c) Rate of abstraction of heat from the space being cooled.
d) Gross weight of machine is tonnes.

ANSWER: c) Rate of abstraction of heat from the space being cooled.

4) The critical pressure of a liquid is

a) The pressure above which a liquid will explode.
b) The pressure above which a liquid will always convert into a vapour.
c) The pressure above which a liquid will remain a liquid.
d) The pressure below which a liquid will always be a vapour form.

ANSWER: c) The pressure above which a liquid will remain a liquid.

5) The highest temperature of refrigerant in a mechanical refrigeration system occurs

a) Before expansion valve.
b) In evaporator.
c) Between evaporation and condenser.
d) Between compressor and condenser.

ANSWER: d) Between compressor and condenser.

6) When does the refrigerant exist as saturated liquid in a vapour compression cycle?

a) After passing through the expansion valve
b) After passing through the condenser
c) Before passing through the condenser
d) Before entering through the compressor

ANSWER: b) After passing through the condenser

7) What is the effect of superheating in a refrigeration cycle?

a) Does not change COP
b) Decreases COP
c) Increases COP
d) None of these

ANSWER: b) Decreases COP

8) In a refrigeration cycle a capillary tube is used

a) To produce cooling effect.
b) To control the temperature of refrigerated space.
c) To convert refrigerant from liquid to vapour state.
d) To control the flow of refrigerant.

ANSWER: d) To control the flow of refrigerant.

9) ……………….is the most distinguishing feature of absorption type refrigerator.

a) Small size for the same refrigerating machine.
b) Only low grade of energy in the form of heat used.
c) Higher C.O.P
d) Quieter operation.

ANSWER: d) Quieter operation.

10) Ammonia is preferred as a refrigerant in large commercial installations because

a) It has low latent heat.
b) It is non-toxic.
c) It is relatively cheap.
d) It has low working pressure.

ANSWER: c) It is relatively cheap.

11) The diameter of the suction pipe of refrigerating unit compressor, in comparison to delivery side is

a) Bigger.
b) Smaller.
c) Equal.
d) Unpredictable.

12) Which among the following advantages are entailed by dry compression?

a) It permits complete evaporation in the evaporator.
b) It permits higher speeds to be used.
c) It results in high volumetric and mechanical efficiencies.
d) All of these.

ANSWER: d) All of these.

13) A clicking sound may be heard in the expansion valve of a newly charged ammonia compressor system due to

a) Less charge of ammonia.
b) Excessive charge of ammonia.
c) Leakage of ammonia.
d) Choking of evaporator coils.

ANSWER: a) Less charge of ammonia.

14) Flash chamber in the refrigeration circuit is installed

a) To reduce the size of evaporator by avoiding vapour going to evaporator.
b) To improve overall heat transfer co-efficient.
c) To reduce pressure losses through the evaporator.
d) All of these.

ANSWER: d) All of these.

15) If R-22 refrigeration system is charged with R-12 then

a) It will not function.
b) It will have considerable fluctuations in the operating pressures.
c) Its refrigeration capacity will be reduced to about one-third.
d) It will operate at low temperature.

ANSWER: c) Its refrigeration capacity will be reduced to about one-third.

16) In a flooded evaporator ………………type of expansion device is employed?

a) Self-actuated expansion valve.
b) Capillary tube.
c) Thermostatic device.
d) Float valve.

ANSWER: d) Float valve.

17) A pressure gauge on the discharge side of compressor

a) Gives an idea about the C.O.P of the cycle.
b) Gives a warning when the pressure reaches a dangerous point.
c) Confirms the flow of refrigerant in cycle.
d) None of these.

ANSWER: b) Gives a warning when the pressure reaches a dangerous point.

18) In a vapour compression system, a thermometer is installed in the main line close to the compressor as

a) It helps the operator to adjust compressor for greater efficiency.
b) Temperature helps in calculating the C.O.P.
c) Temperature indicates whether liquid or vapour refrigerant is going to compressor.
d) None of these.

ANSWER: a) It helps the operator to adjust compressor for greater efficiency.

19) Which refrigerants will be preferred if space occupied by the refrigerating plant and cost are the major considerations?

a) Methyl chloride.
b) Ammonia.
c) Sulphur dioxide.
d) Carbon dioxide.

ANSWER: d) Carbon dioxide.

20) In vapour absorption system using ammonia, water is required for

a) Condenser only.
b) Separator only.
c) Absorber, separator and condenser.
d) Absorber only.

ANSWER: c) Absorber, separator and condenser.

21) What is the function of brine agitator in an ice plant?

a) To reduce compressor power.
b) To obtain uniform temperature of brine.
c) To increase C.O.P.
d) None of these.

ANSWER: b) To obtain uniform temperature of brine.

22) Which of the following statement is correct?

a) Dew point temperature is the saturation temperature corresponding to the partial pressure of the water vapour in moist air.
b) Dew point temperature can be measured with the help of thermometer.
c) Dew point temperature is the same as the thermodynamic wet bulb temperature.
d) For saturated air, dew point temperature is less than the web bulb temperature.

ANSWER: a) Dew point temperature is the saturation temperature corresponding to the partial pressure of the water vapour in moist air.

23) Relative humidity is

a) It denotes the amount of water vapour actually present in air as a percentage of maximum amount that could be present at that particular temperature.
b) It represents the ratio of mass of water vapour to the mass of dry air in a given volume of air water vapour mixture.
c) It is the mass of water vapour per unit volume of air water vapour mixture.
d) None of these.

ANSWER: a) It denotes the amount of water vapour actually present in air as a percentage of maximum amount that could be present at that particular temperature.

24) In a psychrometric chart what does the vertical lines parallel to the ordinate indicates

a) Wet bulb temperature.
b) Specific humidity.
c) Dew point temperature.
d) Dry bulb temperature.

ANSWER: d) Dry bulb temperature.

25) …………………… can be measured by a sling psychrometer.

a) Absolute humidity.
b) Dry bulb as well as wet bulb temperatures.
c) Specific humidity.
d) Wet bulb temperature.

ANSWER: b) Dry bulb as well as wet bulb temperatures.

26) Among the following which statement is incorrect regarding “dehumidification process”?

a) Enthalpy of saturation increases.
b) Dry bulb temperature remains unchanged.
c) Moisture is removed.
d) Specific humidity and relative humidity decreases.

ANSWER: a) Enthalpy of saturation increases.

27) What does the curved lines on a psychrometric chart indicates?

a) Dew point temperature.
b) Relative humidity.
c) Specific humidity.
d) Dry bulb temperature.

ANSWER: b) Relative humidity.

28) Which of the following decreases during sensible cooling of air?

a) Specific humidity.
b) Wet bulb temperature.
c) Dry bulb temperature.
d) None of these.

ANSWER: c) Dry bulb temperature.

29) Dew point temperature is constant as long as there is no change in

a) Volume of air.
b) Relative and specific humidity of air.
c) Moisture content of air.
d) WBT and DBT.

ANSWER: c) Moisture content of air.

30) Sensible heat factor is given by

a) (LH – SH)/SH
b) (LH + SH)/SH
c) SH/(LH - SH)
d) SH/(LH + SH)

ANSWER: d) SH/(LH + SH)