Refrigeration Multiple Choice Questions on “Refrigerants – Physical Properties”.
1. What is the temperature till which Freon group refrigerants remain stable?
a) 545°C
b) 535°C
c) 555°C
d) 565°C
Answer: b
Clarification: Freon group refrigerants remain stable until the temperature of 535°C. The temperature above this, refrigerants become unstable and by decomposing produce corrosive and poisonous products.
2. From the following refrigerants, which is one of the most stable refrigerants?
a) Ammonia
b) R – 12
c) Carbon dioxide
d) Sulphur dioxide
Answer: d
Clarification: Sulphur dioxide is one of the most stable refrigerants among the given refrigerants. The temperature at which it starts decomposing is 1645°C. The temperature above this, Sulphur dioxide becomes unstable and by decomposing produce corrosive and poisonous products.
3. A refrigerant should show stability and inertness.
a) True
b) False
Answer: a
Clarification: To avoid the reaction of metal with the refrigerant, refrigerant should be stable and inert. If not, then the disintegration of refrigerant produces non-condensable gases which increase condenser pressure and vapour lock, which affects the operation.
4. In the presence of which of the following, Sulphur dioxide becomes corrosive?
a) R – 12
b) Ammonia
c) Water
d) Carbon dioxide
Answer: c
Clarification: Sulphur dioxide is non-corrosive with almost every metal, but if the water is present, then it forms sulphuric acid in the presence of water. So, Sulphur dioxide should be used where water is absent.
5. Which of the following is true about refrigerants?
a) Should be corrosive
b) Should not be stable
c) Should have high viscosity
d) Should have low viscosity
Answer: d
Clarification: As the pressure drop in the liquid and suction line is smaller, hence for refrigerant to pass through these lines should possess low viscosity for easier operation. Heat transfer through condenser and evaporator is improved by low viscosity.
6. Which of the following has the least viscosity at a liquid temperature of -15°C and atmospheric pressure?
a) R – 764
b) R – 744
c) R – 717
d) R – 11
Answer: c
Clarification: Among the given refrigerants, R – 744, i.e. Carbon dioxide has the least viscosity at given conditions, valued at 0.115 whereas, R – 764, R – 717 and R – 11 have liquid viscosities at given conditions as 0.503, 0.250 and 0.650.
7. Which of the following has the least viscosity at a vapour temperature of -15°C and atmospheric pressure?
a) R – 764
b) R – 744
c) R – 12
d) R – 11
Answer: d
Clarification: Among the given refrigerants, R – 11 has the least viscosity at given conditions, valued at 0.0096 whereas, R – 764, R – 744 and R – 12 have liquid viscosities at given conditions as 0.0111, 0.0132 and 0.0114.
8. What is the criterion to find out leakage of ammonia?
a) Solubility
b) Corrosiveness
c) Colour
d) Odour
Answer: d
Clarification: Ammonia is soluble in water and corrosive in nature, but these things have nothing to do with leakage detection. As it is a colourless gas so, the pungent odour of ammonia is the only criterion to find out the leakage in the system.
9. Which of the following has the highest thermal conductivity at a liquid temperature of 40°C?
a) R – 22
b) R – 113
c) R – 12
d) R – 11