1. In a domestic icebox type refrigerator, the ice block is kept at the top because __________
a) it is easy for the user to operate
b) disposal of water is easier
c) hot air can be easily removed from the top
d) cold air can flow down due to buoyancy effect
Explanation: Buoyancy effect acts similar to the gravitational force that occurs on the surface outside, hence the more dense cold air comes to the bottom and the hot air goes at the top, but there is no chance of hot air in the refrigerator.
2.Why are vapour absorption system better than compression system?
a) Uses low grade thermal energy
b) Uses no energy
c) Uses refined petroleum energy to produce least pollution
d) Uses high grade thermal energy
Explanation: It uses low grade of thermal energy, hence it can easily be operated for greater output, and economically
3. In a triple fluid vapour absorption refrigeration system, why is the hydrogen gas used?
a) Improve system performance
b) Reduce the partial pressure of vapour in the evaporator
c) Calculate the refrigerant
d) Provide the vapour seal
Explanation: Hydrogen gas is lighter and less dense than many of the gases. Hence it is used to reduce the partial pressure in the vapour in the evaporator.
4. Why low temperature refrigeration is produced in an air standard refrigeration system?
a) Evaporation of liquid air
b) Throttling of air
c) Expansion of air in turbine
d) Condensing of air
Explanation: Due to expansion of air in turbines, the pressure in the air decreases and the loss of pressure results in the fall of temperature. Hence low temperature is obtained in air standard refrigeration system.
5. The required input to the steam jet refrigeration systems is in the form of?
a) Mechanical energy
b) Thermal energy
c) High pressure, motive steam
d) Both mechanical and thermal
Explanation: For a Steam jet refrigeration, the velocity at input is an important part to produce the Jet effect. Hence the input pressure must be high enough as possible.
6. What is the common application of Air standard refrigeration system?
a) Domestic refrigerators
b) Aircraft air conditioning
c) Cold storage
d) Car air conditioning system
Explanation: As sufficient amount of air is obtained while aviation of air crafts, the only thing is to reduce its velocity, and then it can be used for air conditioning in air crafts.
7. Why is a nozzle used in a steam jet refrigeration system?
a) To convert the high pressure motive steam into high velocity steam
b) To reduce energy consumption
c) To improve safety aspects
d) To improve thermal conductivity
Explanation: Nozzle is a device which has one of its end converging whereas the other end diverging, when the steam enters from larger end and exit at smaller end, its velocity increases that produces Jet effect. Hence nozzle is used for it.
8. Which properties are essential for thermoelectric refrigeration?
a) High electrical and thermal conductivity
b) Low electrical and thermal conductivity
c) Low electrical conductivity and high thermal conductivity
d) High electrical conductivity and low thermal conductivity
Explanation: For producing thermoelectric effect, high thermal conductivity is a desirable property, but for producing refrigerating effect the thermal conductivity should be lowest to reduce the loss of cooling due to conduction through walls.
9. Why is fast freezing done in various products ?
a) To reduce the cell damage due to ice crystal growth.
b) To reduce energy consumption of refrigerator
c) To reduce the bacterial activity
d) To save time
Explanation: If the refrigeration in allowed to occur at a slow rate, the cells may get damage due to ice formation in the form of crystals because of the moisture content present in it.
10. In a refrigerating machine, heat rejected is ________ the heat absorbed.
a) equal to
b) less than
c) in unity with
d) greater than
Explanation: Heat rejected in refrigerating machine is always more than the heat absorbed because as the evaporation increases i.e. heat rejection, more will be the refrigerating effect.