Azeotropics: The azeotropic mixtures
are usually binary mixtures that behaves like a pure fluid, i.e., under constant
pressure they condense and evaporate at a constant temperature and the
composition of the mixture in the vapour and liquid phases will be same. Since
the composition at which an azetropic mixture
is formed is a function of temperature, no true azeotropic
mixtures exist in refrigeration, however,
for most of the standard azeotropic mixtures,
the composition change is small. For example the popular cold storage
refrigerant R502 is a mixture of R22 and R152a.
Zeotropics: Zeotropic mixtures are also called as Non-Azeotropic Refrigerant
mixtures which exhibit a significant temperature variation during constant
pressure phase change process, such as condensation and evaporation. Also, at
equilibrium the composition in vapour and liquid phases will be different. The
fact that temperature varies during phase change can be used beneficially in
applications where the external heat source and sink temperature also have to
vary. Important non-ODS, zeotropic refrigerant mixture is R407c,
a mixture of (R32/R125/R134a).
From the refrigerant mixtures we can control the
toxicity, flammability, oil
miscibility with the help of different compositions. But due to leakage
the composition of zeotropics can change we should require to take at most care.
There are different types of synthetic refrigerants like :
Chlorofluorocarbons (CFCs): These are the refrigerants that are developed in
1930?s for household appliances, various industrial and commercial
applications. These refrigerants contain chlorine, Fluorine, Carbon. These
refrigerants are ideal that they did not react with other materials, non-toxic,
and non-reactive. But later discovered that the chlorine present in refrigerant
act as a catalyst for ozone depletion, which chlorine atom depletes the oxygen
molecule from the ozone which is not a environment safety. so Montreal protocol
has prohibited the usage of CFCs. Some of the examples of CFCs are R11, R12,
R13, R500, R502, R503.
(HCFCs): These are the refrigerants consists of hydrogen, chlorine, Fluorine, Carbon as its constituents.
These are eco friendly refrigerants having just 10% of ozone depletion level.
They are cost effective, Less toxic. But these HCFCs are responsible for
climate change, and global warming so Montreal protocol has prohibited the
usage of HCFCs. Examples of HCFCs are R22, R123,R124, R401A,R401B.
Hydroflurocarbons(HFCs): These refrigerants contain Hydrogen, Fluorine,
Carbon as its constituents. These are having less global warming potential than
HCFCs but they are having considerable amount of ozone depleting elements.
However R134a from the HFC family is now using in wide range of applications
because of its low global warming potential and ozone depletion level. These
refrigerants are also having less toxicity and energy efficient. Examples of
HFCs are R134a, R23, R407c, R507.
Generally the all refrigerants are characterised by two numbers:
Ozone depletion potential (ODP): Which means
reduction in the concentration of ozone in the ozone layer. According to
the Montreal protocol, the ODP of refrigerants should be zero.
should have as low a GWP value as possible to minimize the problem of global
There are also other factors that
we have to look while selecting the refrigerant
should be non toxic, they will cause suffocation when the concentration is
high. HFCs and CFCs are non toxic in nature when mixed up with air. But when
they came in to contact with heating element they decompose and forms high
refrigerants should be non-flammable and non-explosive. When any vehicle met
with an accident the refrigerant should not explosive.
stability: The refrigerant should have chemical stability when they are using as a
working fluid in the refrigeration system
Ease of leak
detection: If there is any leakage in the system, it should be easily identified.
Based on the requirements of the refrigerants and
considering the properties of the refrigerant we take R600a and R134a as a
working fluid in the refrigeration system.