Chapter 6 Introduction to Refrigerants
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Azeotropic Refrigerant Blends
Azeotropes are refrigerant blends that respond
to changes in pressure and temperature like a single
refrigerant—with fixed boiling and condensing points.
An azeotrope maintains consistent properties during
all operational conditions. At atmospheric pressure,
the individual refrigerants will not separate as the
blend evaporates or condenses. R-500 and R-502 are
examples of azeotropic refrigerants. R-500 consists of
R-12 and R-152a, and R-502 consists of R-22 and R-115.
Because most azeotropic blends contain a phased-out
refrigerant, their use may decrease with time, unless
new azeotropic mixtures are developed.
Zeotropic Refrigerant Blends
Zeotropes are refrigerant blends in which each
individual refrigerant that makes up the blend responds
differently to conditions based on its individual char-
acteristics. Therefore, a zeotropic blend operates under
a range of boiling and condensing points that corre-
sponds to the range of its individual refrigerants and
the percentage of the blend that each refrigerant makes
up. Near-azeotropes react similarly to zeotropes but
respond over a smaller range of boiling and condens-
ing points. Near-azeotropes are technically zeotropes,
but allowing them their own category helps to differ-
entiate them more precisely.
Zeotropic refrigerants separate into their indi-
vidual components more easily than azeotropic
refrigerants. The separating of a zeotropic blend’s indi-
vidual refrigerants during phase change is known as
fractionation. Fractionation can be thought of as the
refrigerant splitting up or “fracturing” into its base
components. This occurs because the different refriger-
ants in a zeotropic blend have different boiling points.
The refrigerant with the lowest boiling point boils first.
For example, R-401A is a zeotropic refrigerant
blend composed of R-22, R-152a, and R-124. At atmo-
spheric pressure, R-22 has a boiling point of –41°F
(–40.5°C), R-152a has a boiling point of –13°F (–25°C),
and R-124 has a boiling point of 10.5°F (–12°C). As the
refrigerant blend enters the evaporator, R-22 vaporizes
first, followed by R-152a. As a result, the refrigerant
vapor early in the evaporation process is composed
mainly of R-22 and R-152a, while the liquid refrigerant
is composed of R-124 and some R-152a. As the evapora-
tion process continues, the ratio of refrigerants in the
vapor gradually returns to what it was when the liq-
uid refrigerant entered the evaporator. The component
refrigerants undergo a similar separation when the
refrigerant blend condenses.
The impact of fractionation is that a zeotropic
refrigerant blend can have different temperatures at
any given pressure, depending on whether it is a liquid
or vapor. This temperature difference is called tem-
perature glide. Temperature glide is the temperature
difference between the vapor and liquid state during
evaporation or condensation at a constant pressure.
Temperature glide is a unique characteristic of
zeotropic blends because normally a substance evapo-
rates or condenses while maintaining a constant tem-
perature. When water reaches 212°F (100°C), it does
not immediately become vapor. Additional heat, called
latent heat, must be absorbed to provide the energy for
a phase change from liquid to vapor, but the additional
heat does not raise the temperature of the water as it
changes. Zeotropes can change phase and temperature
at the same time, and each zeotropic refrigerant blend
has its own temperature glide. The common range for
temperature glide is 0.3°F–10°F (0.2°C–6°C).
The temperature at which the first component of a
zeotropic refrigerant begins to boil is called the bubble
point. The temperature at which the last component
of a zeotropic refrigerant is completely vaporized is
called the dew point.
Caution
Mixing Refrigerant Blendss
Zeotropic and azeotropic refrigerants are patented
refrigerants. The manufacturing process is complicated.
Service technicians should never attempt to make their
own mixtures.
6.3 Identifying Refrigerants
Refrigerants are identified by a standardized num-
bering system developed by the American Society of
Heating, Refrigerating, and Air-Conditioning Engineers
(ASHRAE). Refrigerants are assigned a unique num-
ber that follows the letter R, which stands for refriger-
ant. You should become familiar with both refrigerant
numbers and names. Refrigerant numbers are not just
randomly assigned. The first digit indicates the refrig-
erant series to which a particular refrigerant belongs.
The numbers that follow have a different significance
depending on the refrigerant’s classification.
6.3.1 Chemical Classifi cations
Refrigerants are first categorized by their molecu-
lar structure. Figure 6-4 shows the various classifica-
tions of refrigerants. Methane-, ethane-, and propane-based
refrigerants contain carbon as their main component,
making them organic compounds. Cyclic organic refrig-
erants are organic refrigerants that have double bonds
between atoms. Miscellaneous organic refrigerants are
carbon-based refrigerants that do not fall under any of
Mixing Refrigerant Blend
Z eotropic and azeotropic refrigerants are patented
refrigerants. The manufacturin g process is complicated.
S ervice technicians should never attempt to make their r
own mixtures.