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Keeping Things Cool:  A Look Inside Your Refrigerator

        Ever wonder how a refrigerator works?  The most important thing to remember about refrigeration is that you don't
move cool air in, but rather you move heat out.  By definition, "cold" is nothing more than the absence of heat.  Many people think that refrigerants (such as Freon) are used to cool air from the outside and then pump it into the refrigerator.   This is absolutely FALSE!  In fact, the exact opposite happens.   Refrigerants are used to remove heat from inside the refrigerator.   This explains the warm air that exits the back of your refrigerator.  Let's take a closer look at refrigerators.

    Assume that your refrigerator uses a refrigerant called Freon-12, which it probably does.  Freon-12 (dichlorodifluoromethane) boils at about -21 0F at atmospheric pressure.  What this means is that Freon-12 would boil and evaporate instantaneously at a room temperature of 68 0F.  So, here is what is happening inside your refrigerator:

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    Let's start inside the evaporator where we have cold, liquid Freon.  The heat inside the refrigerator is enough to evaporate the Freon which boils at the low temperatures.  This is why refrigerants have to be used, they evaporate at low temperatures so the heat inside the refrigerator moves into the evaporator.  If a liquid that boiled at a higher temperature than the inside of the refrigerator was used, you'd actually be moving heat into the refrigerator....not exactly what you need!  Now the evaporated refrigerant moves into the compressor (a vital part of any refrigerator as you know!).  Here, the refrigerant is pressurized and as with any pressurized vapor, the refrigerants temperature increases.  In the case of Freon-12, the compressor raises the temperature to about 130 0F!   This explains why you can find some "warm" coils in the back of the refrigerator.  From the compressor, the hot vapor moves to the condenser where the condenser coils are in contact with ambient air.  As long as the air is below about 105 0F, the heat from the Freon-12 is passed out to the surrounding air and this causes the hot vapor to cool slightly, but enough to condense back into the liquid phase.  At this point, heat from inside the refrigerator has been successfully moved outside of the refrigerator.  At this point, the Freon must be cooled further in preparation for its entry back into the evaporator to repeat the cycle.  This is accomplished be releasing the pressure from the Freon (added by the compressor), by use of an expansion valve.  By releasing the pressure, the Freon cools back down. 

    The thermostat monitors the temperature inside the refrigerator.  When the temperature is above the thermostat setting, the compressor is started and the cycle runs and cools the refrigerator.  When the temperature inside the refrigerator reaches the thermostat temperature, the compressor is stopped.

    So why is it so important to keep the refrigerator door sealed?  To keep the cool air inside? keep the warm air out!

    To summarize how a refrigerator operates:

    Indoor coils (evaporator) and outdoor coils (condenser) are where the refrigerant changes phase, absorbing or releasing heat through evaporation or condensation.  The compressor and expansion valve facilitate the pressure changes, increased by the compressor and reduced by the valve.

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