Amprobe ACDC-620T Clamp-On-Multimeter - Manual (Page 57)

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REFRIGERATIN THEORY
Thermocouples are widely used in the process control and refrigeration industry. A
review of basic refrigeration theory will help you to apply the meter in refrigeration
applications.
In any refrigeration application the goal is to transfer heat from one place to another.
The transfer is made by pumping a refrigerant from one area to another area whose
temperature is different.
The refrigerant has a low boiling point and a high latent heat of vaporization. That is,
a great deal of heat is required to convert the refrigerant from a liquid to a gas at its
boiling temperature. The resulting gas is at the same temperature, but it contains
more heat energy than the liquid did.
At atmospheric pressure, common refrigerant gasses such as Freon and Ammonia
boil far below water freezing point, and absorb heat from their surroundings in the
process. Likewise, as gasses condense, they release heat back into their environ-
ment.
We can control the boiling point by raising or lowering the pressure, forcing the gas
to dissipate heat or absorb it. If we raise the pressure enough by compressing, it will
become liquid. In a refrigeration system there is a compressor and a system of
valves to change the pressure of a contained gas. The gas absorbs or dissipates
heat in heat exchangers called evaporators or condensers, depending on how they
are used. Figure 25 shows the basic parts of a refrigerator.