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0 Kelvin is equal to:
0 °F.
0 °C.
-273,16 °C.
+273,16 °C.
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During automatic operation of a refrigeration system the starting and stopping of the compressor is usually achieved by which of the following?
Low pressure cut out.
Thermostatic switch.
Temperature in the cold room.
Manual on/off switch.
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From the following options select those, which may cause the refrigeration system high pressure cut out to operate and stop the compressor?
Loss of condenser coolant.
Oil carry over.
Ice on the evaporator coils.
Overcharge of refrigerant.
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If a running system regularly requires change of refrigerant, what should be done?
Find the leak and rectify the problem before the system is charged.
Charge the system, modern refrigerants and cheap and do not harm the environment.
Change the system, find the leak and rectify the problem.
Replace the lost refrigerant with nitrogen.
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Put in the correct words. According to the second law of thermodynamics heat can only transfer naturally from a region of high temperature to a region of ____ unless mechanical work is done on the system.
High pressure.
Low temperature.
Equal temperature.
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The closed cycle refrigeration system works on the principle of which of the following?
Rapid expansion and loss of refrigerant.
Rapid expansion and recirculation of the refrigerant.
Vapour compression with loss of refrigerant.
Vapour compression and recirculation of the refrigerant.
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The ideal temperature of a freeze room is:
-26 °C to -30 °C.
-5 °C to -10 °C.
-18 °C to -25 °C.
0 °C to -5 °C.
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The operation of the automatic expansion valve is based on:
Constant evaporator pressure and temperature.
Constant evaporator pressure.
Constant evaporator temperature.
Constant flow of refrigeration medium.
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The operation of the thermostatic expansion valve is based on:
Constant degree of superheat in the vapour at the evaporator.
Constant flow of refrigeration medium.
Constant evaporator pressure.
Constant temperature in the condenser.
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The term “specific enthalpy” of a fluid, measured in kJ/kg, is used to quantity the energy per unit mass due to:
The internal energy.
The sum of the internal energy plus the volume.
The sum of the pressure plus the volume.
The sum of the internal energy plus the product of the pressure and volume.
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To be able to evaporate a medium at -20 °C and to condense the same medium at 30 °C we have to:
Increase the pressure.
Decrease the pressure.
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What are the disadvantages of ammonia as a refrigerant?
It is toxic and inflammable.
It is very expensive.
It can only be used on very large refrigeration systems.
It cannot be used in refrigeration systems with screw compressor.
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What are the main components in a closed refrigeration cycle?
Compressor, condenser, expansion valve and receiver.
Compressor, condenser, expansion valve and evaporator.
Compressor, oil separator, expansion valve and evaporator.
Compressor, condenser and evaporator.
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What is absolute pressure?
It is the same as 100 % vacuum.
Atmospheric pressure plus gauge pressure.
It is equal to atmospheric pressure.
It is the same as gauge pressure.
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What is the disadvantage of the manually operated expansion valve?
It can only be used with modern refrigerants.
It responds to quickly to changes in load.
It cannot be used with modern refrigerants.
It is unresponsive to changes in load.
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What is the main problem with Carbon dioxide as a refrigerant?
Extremely inflammable.
Extremely low working pressure.
Extremely high cost.
Extremely high working pressure.
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What is the saturation temperature?
The temperature at which a fluid boils or condenses, it varies with pressure.
The temperature at which a fluid boils or condenses, it is independent of pressure.
It is the point where the ice starts to melt.
It is the same as critical point for a gas.
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What will be an adequate allowance for oil circulation in a refrigeration system?
One litre of oil for every thirty kilo of refrigerant charge.
One litre of oil for every twenty kilo of refrigerant charge.
One litre of oil for every kilo of refrigerant charge.
One litre of oil for every two kilo of refrigerant charge.
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When the desired cold room temperature is reached in a refrigeration system operating on the direct expansion principle, which of the following shuts off the evaporator for the room?
Thermostatically controlled expansion valve.
Low pressure cut out.
High pressure cut out.
Solenoid valve operated by thermostatic switch.
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Which of the following components are parts of the high-pressure side in a refrigeration system?
Condenser.
Evaporator.
Receiver.
Suction line.
Liquid line.
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Which of the following does the term latent heat describe when referring to a refrigerant?
The temperature.
Heat required to cause evaporation at constant boiling temperature and pressure.
The heat required to superheat the refrigerant gas.
The heat required to raise the liquid temperature to boiling point.
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Which of the following indicates refrigerant undercharge?
Low head pressure.
High receiver level.
Vapour bubbles in the liquid line sight glass.
Compressor running continuously.
High head pressure.
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