Note: Descriptions are shown in the official language in which they were submitted.
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R~RI~.~ANT C~MPOSITIONS
m e present invention relates to non-azeotropic refrigerant
compositions and more particularly to non-azeotropic refrigerant
compositions which can be used in the low temperature refrigeration
applications currently satisfied by refrigerant R-502 which is an
azeotropic mixture of chlorodifluoromethane (refrigerant R-22) and
chloropentafluoroethane (refrigerant R-115).
Heat transfer devices of the m~h~nical compression type such as
refrigerators, freezers, heat pumps and air conditioning systems are
well known. In such devices a refrigerant liquid of a suitable
boiling point evaporates at low pressure taking heat from a
surrounding heat transfer fluid. m e resultiny vapour is then
compressed and passes to a con~ncer where it con~nces and gives off
heat to another heat transfer fluid. The con~n~te is then returned
through an expansion valve to the evaporator so completing the cycle.
The m~h~n;cal energy required for compressing the vapour and pumping
the liquid may be provided by an electric motor or an internal
combustion engine.
In addition to having a suitable boiling point and a high latent
heat of vaporisation, the properties preferred of a refrigerant
include low toxicity, non-flamm bility, non-corrosivity, high
stability and freedom from objectionable odour.
Hitherto, heat transfer devices have tended to use fully and
partially halogenated chlorofluorocarbon refrigerants such as
trichlorofluoromethane (refrigerant R-11), dichlorodifluoromethane
(refrigerant R-12), chlorodifluoromethane (refrigerant R-22) and the
azeotropic mixture of chlorodifluoromethane and
chloropentafluoroethane (refrigerant R-llS); the azeotrope being
refrigerant R-502. Refrigerant R-S02, for example, has been widely
used in low temperature refrigeration applications.
However, the fully and partially halogenated chlorofluorocarbons
have been implicated in the destruction of the earth's protective
ozone layer and as a result the use and production thereof has been
limited by international agreement. I
Whilst heat transfer devices of the type to which the present
invention relates are essentially closed systems, loss of refrigerant
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to the atmosphere can occur due to leakage during operation of the
equipment or during maintenance procedures. It is important, . r
therefore, to replace fully and partially halogenated
chlorofluorocarbon refrigerants by materials having low or zero ozone
depletion potentials.
In addition to the possibility of ozone depletion, it has been
suggested that significant concentrations of chlorofluorocarbon
refrigerants in the atmosphere might contribute to global warming
(the so-called greenhouse effect). It is desirable, therefore, to use
refrigerants which have relatively short atmospheric lifetimes as a
result of their ability to react with other atmospheric constituents
such as hydroxyl radicals.
Replacements for some of the chlorofluorocarbon refrigerants
presently in use have already been developed. These replacement
refrigerants tend to comprise selected hydrofluoroalkanes, i.e.
compounds which contain only carbon, hydrogen and fluorine atoms in
their structure. Thus, refrigerant R-12 is generally-being replaced
by 1,1,1,2-tetrafluoroethane (R-134a~.
Although suitable repl~c~nt refrigerants are available, there
is always a need for new refri~erants having a low or zero ozone
depletion potential that are capable of replacing the
chlorofluorocarbon refrigerants presently in use such as R-502.
Furthermore, very real benefits could be realised by a new
replacement refrigerant having a higher refrigeration capacity than
the replacement refrigerants known in the art.
The present invention provides a non-azeotropic refrigerant
composition comprising a mixture of compounds having low or zero
ozone depletion potentials which can be used in the low temperature
refrigeration applications currently satisfied by refrigerant R-502.
The non-azeotropic refrigerant composition of the invention can
exhibit an advantageously high refrigeration capacity.
According to the present invention there is provided a
non-azeotropic (zeotropic) refrigerant composition comprising:
(A) carbon dioxide (C02);
(B) pentafluoroethane (R-125); and
(C) l,l,l-trifluoroethane (R-143a).
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The zeotropic refrigerant composition of the invention comprises
~ three separate components,
- The first component (component (A)) is carbon dioxide (CO2)
which exhibits a low temperature refrigeration action subliming at
around -78.5 C. The second component (component (B)) is
pentafluoroethane (R-125) which has a boiling point of around
-48.5 C. m e third component (component (C)) is 1,1,1-trifluoroethane
(R-143a) which has a boiling point of around -47.6 C.
The refrigerant composition of the invention may-also contain
1,1,1,2-tetrafluoroethane (R-134a) which has a boiling point of
around -26.5 c.
The amounts of the CO2, R-125 and R-lg3a and the amount of the
R-134a (if included) in the refrigerant composition may be varied
within wide limits, but typically the refrigerant composition will
comprise from 1 to 20 % by weight CO2, from 25 to 70 ~ by weight
R-125, from 25 to 70 ~ by weight,R-143a and from 0 to 25 % by weight
(for example, from 1 to 25 % by weight) R-134a.
When the optional R-134a is not included, a preferred
refrigerant composition of the invention in terms of its suitability
as a replacement for refrigerant R-502 is one comprising from 2 to
15 % by weight CO2, from 28 to 70 % by weight R-125 and from 28 to
70 % by weight R-143a.
When the optional R-134a is not included, a particularly
preferred refrigerant composition of the invention in terms of its
suitability as a repl~ t for refrigerant R-502 is one comprising
from 2 to 12 % by weight, more particularly from 2 to 10 ~ by weight,
CO2, from 38 to 60 % by weight, more particularly from 45 to 50 % by
weight, R-125 and from 38 to 60 % by weight, more particularly from
45 to 50 % by weight, R-143a.
When the optional R-134a is included, a preferred refrigerant
composition of the invention in terms of its suitability as a
replacement for refrigerant R-502 is one comprising from 2 to 15 ~ by
weight CO2, from 27 to 70 % by weight R-125, from 27 to 70 % by
weight R-143a and from 1 to 25 % by weight R-134a.
When the optional R-134a is included, a particularly preferred
refrigerant composition of the invention in terms of its suitability
j as a replacement for refrigerant R-502 is one comprising from 2 to
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15 % by weight, more particularly from 2 to 12 % by weight, CO2, from
37 to 60 % by weight, more particularly from 35 to 45 % by weight,
R-125, from 37 to 60 % by weight, more particularly from 43 to 53 %
by weight, R-143a and from 1 to 10 % by weight, more particularly
from 1 to 5 % by weight, R-134a.
m e refrigerant composition of the invention may also be
combined with one or more hydrocarbon compounds in an amount which is
sufficient to allow the composition to transport a mineral oil or
alkyl benzene type lubricant around a refrigeration circuit and
return it to the compressor. In this way, inexpensive lubricants
based on mineral oils or alkyl benzenes may be used to lubricate the
compressor.
Suitable hydrocarbons for use with the refrigerant composition
of the invention are those cont~;ning from 2 to 6 carbon atoms, with
hydrocarbons cont~ining from 3 to 5 carbon atoms being preferred.
Propane and pentane are particularly preferred hydrocarbons, with
pentane being especially preferred.
Where a hydrocarbon is combined with the refrigerant composition
of the invention, it will preferably be present in an amount of from
1 to 10 % by weight on the total weight of the refrigerant
composition.
m e refrigerant composition of the invention may also be used in
combination with the types of lubricants which have been specially
developed for use with hydrofluorocarbon based refrigerants. Such
lubricants include those comprising a polyoxyalkylene glycol base
oil. Suitable polyoxyalkylene glycols include hydroxyl group
initiated polyoxyalkylene glycols, e.g. ethylene and/or propylene
oxide oligomers/polymers initiated on mono- or polyhydric alcohols
such as methanol, butanol, pentaerythritol and glycerol. Such
polyoxyalkylene glycols may also be end-capped with suitable t~rmin~l
groups such as alkyl, e.g. methyl groups. Another class of lubricants
which have been developed for use with hydrofluorocarbon based
refrigerants and which may be used in combination with the present
refrigerant compositions are those comprising a neopentyl polyol
ester base oil derived from the reaction of at least one neopentyl
polyol and at least one aliphatic carboxylic acid or an esterifiable
derivative thereof. Suitable neopentyl polyols for the formation of
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the ester base oil include pentaerythritol, polypentaerythritols such
as di- and tripentaerythritol, trimethylol islk~n-~c such as
trimethylol ethane and trimethylol propane, and neopentyl glycol. The
esters may be formed with linear and/or br~nrhe-l aliphatic carboxylic
acids, such as linear and/or branched alkanoic acids. Preferred acids
are selected ~rom the Cs8, particularly the Cs 7~ linear alkanoic
acids and the Cslo~ particularly the Csg, branched alkanoic acids. A
minor proportion of an aliphatic polycarboxylic acid, .e.g. an
aliphatic dicarboxylic acid, may also be used in the synthesis of the
ester in order to increase the viscosity thereof. Usually, the amount
of the carboxylic acid(s) which is used in the synthesis will be
sufficient to esterify all of the hydroxyl groups contained in the
polyol, although residual hydroxyl functionality may be acceptable.
The zeot'ropic refrigerant composition of the present invention
may be used to provide the desired cooling in heat transfer devices
such as low temperature refrigeration systems by a method which
involves con~ cing the refrigerant composition and thereafter
evaporating it in a heat exchange relationship with a heat transfer
fluid to be cooled. In particular, the refrigerant composition of the
invention may be employed as a repl~ ~m~nt for refrigerant R-502 in
low temperature refrigeration applications.
The present invention is now illustrated but not limited with
reference to the following example.
~rle 1
The performance of five refrigerant compositions of the invention in
a low temperature refrigeration cycle was investigated using standard
refrigeration cycle analysis techniques in order to assess the
suitability thereof as a repl~c~m~nt for R-502. The followinçl
refrigerant compositions were subjected to the cycle analysis:
(1~ A composition comprising 2 % by weight C~2~ 43.1 96 by weight
R-12S, 51 % by weight R-143a and 3.9 96 by weight R-134a.
(2) A composition comprising 5 96 by weight C~2 ~ 41.8 96 by weight
R-125, 49.4 ~ by weight R-143a and 3.8 % by weight R-134a.
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(3) A composition comprising 10 ~ by weight CO2, 39.6 ~ by weight
R-125, 46.8 % by weight R-143a and 3.6 % by weight R-134a.
(4) A composition comprising 2 % by weight C03, 49 % by weight R-125
and 49 % by weight R-143a.
(5) A composition comprising 5 % by weight co2, 47.5 ~ by weight
R-125 and 47.5 % by weight R-143a.
The following operating conditions were used in the cycle analysis.
Mean Evaporator Temperature: -40 C
Mean Condenser Temperature: 40'C
Amount of Superheat: lO'C
Amount of Subcooling: 5'C
Isentropic Compressor Efficiency: 75 %
Cooling Duty: 1 kW
The results of analysing the performAnce of the five refrigerant
compositions in a low temperature refrigeration cycle using these
operating conditions are given in Table 1.
The performance parameters of the refrigerant compositions which
are presented in Table 1, i.e. con~n~er pressure, evaporator
pressure, discharge temperature, refrigeration capacity (by which is
meant the cooling duty achieved per unit swept volume of the
compressor), coefficient of performance (COP) (by which is meant the
ratio of cooling duty (refrigeration effect) achieved to m~ch~nical
energy supplied to the compressor), and the glides in the evaporator
and condenser (the temperature range over which the refrigerant
composition boils in the evaporator and condenses in the con~n~er),
are all art recognised parameters.
The performance of refrigerant R-502 under the same operating
conditions is also shown in Table 1 by way of comparison.
It is apparent from Table 1 that the refrigerant compositions of
the invention exhibited as good as or better refrigeration capacities
than refrigerant R-502 and that the refrigeration capacity increased
as the C03 content in the composition increased. It is also apparent
from the results given in Table 1 that the performance of the
refrigerant composition of the invention in a low temperature
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refrigeration cycle is such that it could make an acceptable
replA~m~nt for refrigerant R-502.
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