• The home refrigerator works according to just a few simple principles.Jupiterimages/Photos.com/Getty Images
  
  The home refrigerator relies on just a few basic principles to function. Its ability to cool is essentially based upon the movement of a fluid, called "coolant", through a long, continuous system of tubing. The fluid within the tubes changes states between gas and liquid as it circulates. As heat always flows toward cold, this fluid can continuously move, creating the cold environment within the refrigerator.
  
  

Heat Transfer

• As heat will always travel from a relatively warm place to a cooler place, a refrigerator works by exposing its interior air to an even cooler surface. As the fluid-filled tubing winds around within the refrigerator, it draws warmth from the surrounding air. At this stage, the fluid is a cold gas. As the gas becomes warmer, it continues moving through the tubing, drawing that warmth to the exterior. As a result, the temperature inside the refrigerator drops. To optimize the cooling effect, the tubes have a highly coiled shape, which increases their surface area and makes even greater heat transfer possible.
  
  

Compression

• As the cold gas passes through the refrigerator's tubing, it warms to around 43 degrees Fahrenheit just before it exits the refrigerator's interior and enters the compressor. At this stage of the refrigeration process, the compressor further heats the coolant gas, reaching around 110 degrees Fahrenheit. The increase in temperature occurs because of the tendency of compression to make a gas hotter. The hot, pressurized coolant then continues to flow through coiled tubing outside the refrigerator, known as condenser coils. As gas flows along these coils, it releases heat into the surrounding air. By the time the coolant has fully passed through the condenser coils, its temperature has dropped to around 90 degrees Fahrenheit, turning back into a liquid.
  
  

Evaporation

• When a liquid evaporates, it drops dramatically in temperature. For example, when you sweat, it's the evaporation of the beads of sweat that help your body to cool down. Based on this principle, the liquid coolant exits the condenser coils to pass through an expansion valve. This expansion valve works like a spray atomizer, just like a fine spray nozzle works. The valve turns a liquid into tiny droplets, which immediately evaporate into the air, dropping in temperature. The design of most refrigerators complements a secondary compartment for an attached freezer; this design works so well because the coolant is so cold on exiting the expansion valve. The same coolant passes through the freezer, and by the time it reaches the refrigerator, it begins to warm again.