As the refrigerant flows into the evaporator, it vaporizes and absorbs thermal energy from the inside of the refrigerator (the energy transfers involved in vaporization will also be discussed in Key Idea 5: Energy and Phase Changes). Because thermal energy is lost from the inside of the refrigerator, the temperature inside the refrigerator falls. Since the refrigerant absorbs energy, its internal energy increases. The refrigerant then reenters the compressor and flows through the cycle again.
Worked Example
What is the overall effect of the flow of the refrigerant through the refrigeration cycle? Refer to the Refrigeration Learning Tool. as necessary.
Overall, in the refrigeration cycle, energy is transferred from the one part of the surroundings to another. Energy is removed from the inside of the refrigerator and released to the air outside the refrigerator. (You may have noticed that warm air comes out from the back or bottom of your refrigerator.) However, the thermal energy that is absorbed from the inside of the refrigerator is less than the thermal energy that is released to the surrounding air. This is because, to transfer energy from the cold interior of the refrigerator to the relatively warm air in the room surrounding the refrigerator, the input of energy as work is required. Therefore, the thermal energy that the refrigerant releases to the surroundings is equal to the energy absorbed as thermal energy from the inside of the refrigerator plus the energy gained as work from the compressor.
Now, we can answer the question that was presented at the beginning of this section.
Your Turn
Can you cool your house by opening the refrigerator door? Explain why or why not. Use the Refrigeration Learning Tool. if necessary.
No. Although the refrigerator will cool the air near the evaporator, the air near the condenser will be warmed. In fact, opening the refrigerator will actually warm up the house, because the thermal energy released at the condenser includes both the energy absorbed as thermal energy at the evaporator and the energy added to the system as work by the compressor. Therefore, while opening the refrigerator door causes more thermal energy to be absorbed from the air near the evaporator, even more energy is released to the air near the condenser.
Question For Thought
An air conditioner functions very similarly to a refrigerator – why can you cool your home with an air conditioner?