Chapter 2 Page 1
Refrigerants are heat-carrying mediums which absorb heat at a low temperature level and can be compressed (increased in pressure) to a higher temperature where they are able to give off the absorbed heat. The ideal refrigerant would be one that could discharge all of the heat it is capable of absorbing.
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The requirements of a good refrigerant are:
1. Low boiling point.
2. Safe and nontoxic.
3. Easy to liquefy at a moderate pressure and temperature.
4. High latent-heat value (able to absorb a large quantity of BTU heat units).
5. Capable of changing state under normal pressure changes.
6. Able to mix well with oil.
7. Noncorrosive to metal.
Lets explain these properties
1. Low Boiling Point
What is Boiling? We will use water as an example. When water is heated the water molecules begin to move rapidly. This is because heat is energy - science defines heat as the flow of energy from a warm object to a cooler object. Water turns from a liquid "State" to a vapor "State" at sea level once it reaches 212 Degrees Fahrenheit or 100 Degrees Celsius. As the water absorbs the heat it turns to vapor. Intern if the vapor was to release the heat it would turn back into water.
Lets look at natures water cycle to help you understand the refrigeration cycle
Since water boiling is done by adding heat it could be used as a refrigerant but its boiling point is too high. EXAMPLE: If you were to use water in an air conditioning system, your home would only be about 90 degrees. This is not very high heat and the water would not absorb very much heat. This is because refrigerant has to be a n average of 15 degrees colder than the space or air we are trying to cool. Every Ac and Refrigeration Instructor will tell you there is no such thing as cold it is just the removal of heat. To get a room to 70 degrees would require the water to be a minimum of 55 degrees. So for refrigerator with a freezer would require the water in the system to be a minimum of -15 degrees. Water freezes at 32 degrees so this will not work.
This is why we have refrigerants - R134a for example has a very low boiling point of -15.34 Degrees Fahrenheit.
Since R134a has a boiling point of -15.34 degrees, this means that is where this refrigerant turns from liquid to vapor. This is heat absorption. Unlike a pot that is boiling this is what we see when we look at a freeze evaporator and see the frost pattern. The frost on the tubing is an indication of refrigerant boiling inside the evaporator. An evaporator with a frost pattern from the Entrance - Capillary tubing to the Exit - Suction line this would be the sign of a properly charged system. Evaporators with a partial frost pattern means we have a sealed system problem. This will be discussed later in our troubleshooting chapter.