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 TM 9-8000
CHAPTER 37
PRINCIPLES OF REFRIGERATION
Section I. GENERAL
pressure reduces it. These gases also provide good
37-1. Ambient Temperature. The temperature of the
heat transfer qualities and do not deteriorate system
air surrounding an object is referred to as ambient
components. There are two gases used in the
temperature. As ambient temperature increases, it
refrigeration process: Refrigerant- 12 and Refrigerant-22.
causes the molecules to interact more violently and
Extreme caution should be used if they are handled.
increase their length of travel. This results in an increase
Refrigerant-12, otherwise known as R-12, Freon-12, or
in physical size. If this principle were applied to a closed
F-12, boils at -21.70F (-29.80C) when at sea level.
system, the result would be an increase in pressure.
Because of this low boiling point and its ability to pass
The opposite happens when the ambient temperature is
through the system endlessly, R-12 is an ideal
lowered. The interaction of molecules is less violent and
refrigerant. If the R-12 is pressurized enough, the
their length of travel is reduced, which results in a
boiling point would be moved well above the
decrease in closed system pressure. Figure 37-1 shows
temperatures endured on the hottest day.
the effects of ambient temperature on a closed system.
Table 37-1 indicates the pressure of Refrigerant-12 at
37-2. Gases Used in Refrigeration. With the
various temperatures. For instance, a drum of
exception of changes in state, gases used in refrigeration
Refrigerant at a temperature of 800F (26.60C) will have
are recycled much like engine coolant. Different
a pressure of 84.1 psi (579.9 kPa). If it is heated to
pressures and temperatures cause the gas to change
1250F (51.60C), the pressure will increase to 167.5 psi
state from liquid to gas and back to a liquid again. The
(1154.9 kPa). It also can be used conversely to
boiling point of the refrigerant changes with system
determine the temperature at which Refrigarent-12 boils
pressure. High pressure raises the boiling point and low
under various
Figure 37-1. Effects of Ambient Temperature on Closed Systems
37-1
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