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Cooling Systems

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Cooling Systems

A refrigerator door makes a great message center. Its smooth metal surface is perfect for sticky notes and magnets. In most homes, a refrigerator is one of the hardest working appliances, but not just because it holds messages. Unlike most other home appliances, a refrigerator generally runs nonstop every day of the year. Can you think of another home appliance that gets such constant use?

Purpose of a Cooling System

A refrigerator is an example of a cooling system. Another example is an air conditioner. The purpose of any cooling system is to transfer thermal energy in order to keep things cool. A refrigerator, for example, transfers thermal energy from the cool air inside the refrigerator to the warm air in the kitchen. If you’ve ever noticed how warm the back of a running refrigerator gets, then you know that it releases a lot of thermal energy into the room.

Q: Thermal energy always moves from a warmer area to a cooler area. How can thermal energy move from the cooler air inside a refrigerator to the warmer air in a room?

A: The answer is work.

How a Refrigerator Works

A refrigerator must do work to reverse the normal direction of thermal energy flow. Work involves the use of force to move something, and doing work takes energy. In a refrigerator, the energy is usually provided by electricity. You can read in detail in the Figure below how a refrigerator does its work. For an animation of how a refrigerator works, go to this URL: http://www.chemistry.wustl.edu/~edudev/LabTutorials/CourseTutorials/LabTutorials/Thermochem/fridge_movie.html

The Refrigerant

The key to how a refrigerator or other cooling system works is the refrigerant. A refrigerant is a substance such as Freon™ that has a low boiling point and changes between liquid and gaseous states as it passes through the refrigerator. As a liquid, the refrigerant absorbs thermal energy from the cool air inside the refrigerator and changes to a gas. As a gas, it transfers thermal energy to the warm air outside the refrigerator and changes back to a liquid. Work is done by a refrigerator to move the refrigerant through the different components of the refrigerator.

Diagram illustrating how a refrigerator works

Summary

  • The purpose of a cooling system such as a refrigerator or air conditioner is to transfer thermal energy in order to keep things cool.
  • A refrigerator transfers thermal energy from the cool air inside the refrigerator to the warm air in the kitchen. Thermal energy normally moves from a warmer area to a cooler area, so a refrigerator must do work to reverse the normal direction of heat flow.
  • The key to how a refrigerator or other cooling system works is the refrigerant. A refrigerant is a substance with a low boiling point that changes between liquid and gaseous states as it passes through the refrigerator.

Explore More

At the following URL, watch the video “How Air Conditioners Work.” Then fill in the blanks in the statements below.

http://www.physics.org/explorelink.asp?id=537&q=air&currentpage=1&age=0&knowledge=0&item=5

  1. The basic concept behind an air conditioner is __________.
  2. The liquid in an air conditioner __________ at a very low temperature.
  3. Evaporation occurs inside metal __________.
  4. Air is cooled by being blown over the __________.
  5. The __________ turns the gas back into a liquid.

Review

  1. What is the purpose of a cooling system? What are examples of cooling systems?
  2. Outline how a refrigerator works.
  3. What is a refrigerant? Why is it the key to how a cooling system works?

Vocabulary

refrigerant

refrigerant

Substance with a low boiling point that is used to transfer thermal energy in a cooling system such as a refrigerator.

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