Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
1999-02-12
2001-07-10
Skane, Christine (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
C062S114000
Reexamination Certificate
active
06258292
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A “MICROFICHE APPENDIX”
Not Applicable
BACKGROUND OF THE INVENTION
Two of the most commonly used refrigerants for cooling (e.g., air conditioning) and refrigeration until recent years were R-12 and R-22. In January 1994, the further sale of R-12 (a chlorofluorocarbon) was banned rendering it unavailable for automotive use (its largest application). R-12 was also used with other refrigerants to achieve useful mixtures of other effective refrigerants. The refrigerant was known to exhibit good compatibility with mineral oils utilized for lubrication of compressors in the refrigeration system and performed the important role of returning refrigerant back to the compressor. Another common refrigerant is R-22, chlorodifluoromethane, though facing a ban in the future, still is widely used in freezers and ice making equipment.
The chlorofluorocarbons in wide use as refrigerants, such as R-12, are thought to have detrimental long term environmental effects and suitable alternatives have been vigorously sought since the realization of the detrimental effects. The accumulating evidence that the chlorofluorocarbons, because of their high stability, when released to the atmosphere, are able to reach the stratosphere has prompted substantial scientific study of the impact on the stratosphere. Evidence now supports the proposition that, under the influence of ultraviolet radiation, the chlorine atoms are released and undergo a chemical reaction with the ozone naturally occurring in the stratosphere. The observed effects of global warming is thought to be promoted by the thinning of the ozone layer occurring, at least in part, as a consequence of the chlorine-ozone reaction enabling greater amounts of ultraviolet light to reach the earth's surface.
The search for alternative refrigerants to harmful chlorofluorocarbons has been accelerated with the banning of the manufacture and sale in the United States of the refrigerant R-12, which was the refrigerant of choice for automotive and other portable commercial cooling systems. Alternatives such as the halocarbons, including fluorinated carbons, chlorinated carbons and brominated carbons are known and used as refrigerants. The most commonly used of the halocarbons are the fluorocarbons. The halocarbons have the desirable properties of being nonflammable and nontoxic.
Hydrocarbons, and particularly those of lower molecular weights (i.e., below about 70) have also been used as refrigerants. While being both effective and inexpensive, the hydrocarbon refrigerants are flammable which poses concerns when the refrigerant is leaked out of the system. When hydrocarbons are included as a constituent of a refrigerant, it is important for the refrigerant to exhibit azeotropic or near azeotropic properties such that any evaporation (loss) of the refrigerant experienced occurs in approximately the same rate as the other constituents. Only if the constituents exhibit this character, will the evaporated gas be nonflammable. Collaterally, it is important that during any experienced loss of refrigerant that the relative ratios of constituents not change appreciably, otherwise the thermodynamic properties of the refrigerant are likely to change causing the performance to deteriorate and perhaps damage the equipment. Irrespective of the satisfactory inclusion of hydrocarbons into compatible refrigerants improving the performance of such refrigerants, there are many elements of the refrigeration industry which still oppose the use of hydrocarbons for or in refrigerants.
R-22, a chlorodifluoromethane, is widely utilized in commercial refrigeration systems however, has the undesirable characteristic of requiring a low suction temperature in the compressor to avoid a rise in the discharge temperature. To overcome this characteristic, R-22 is commonly blended with smaller amounts of other refrigerants such as R-124, R-142
b,
R-152
a
or R-218 to produce a favorable vapor pressure/temperature curve.
An environmentally friendly commercial replacement for refrigerant R-12 is R-134
a
however, while the refrigerant exhibits a somewhat similar profile of the pressure/temperature curve of R-12, its performance capacity is noticeably less than R-12. R-134
a
does exhibit a different temperature relationship at higher operating temperatures than R-12. Were R-134
a
to be bled into a R-12 system, as a gradual replacement (i.e., topping off) the performance of the system at higher temperatures would gradually deteriorate, just when the system was in need. The point would be reached when the concentration of R-134
a
was sufficiently high that the system would shut down, unable to handle the higher pressures generated by R-134
a.
It is not uncommon for systems utilizing R-134
a
to require substantially more power for a given cooling or, alternatively, a considerably longer operating cycle to maintain a temperature in the system. In those systems which are already pressed to their capacities, the switch to R-134
a
from R-12 may render the system unable to maintain the set system temperatures under normal operating conditions. In such instances, the physical capacity of the system may have to be increased (retrofitting increased condenser and evaporation size) for satisfactory climate control.
Additionally, a substantial modification of the R-12 refrigerating/cooling system may be required before use of the replacement R-134
a.
R-134
a
is not compatible with the lubricating oils utilized with R-12, therefore it must be purged from the system before the charging with R-134
a.
Most systems including automotive systems utilizing R-12 include a lubricant, which is insoluble in R-134
a,
causing further incompatibility of the mixture. Changing the lubricant to the synthetic based oil required by R-134
a
may also require a change of seals if they are not compatible with R-134
a.
Or the oil required thereby With the cessation of sale of R-12, recharging of the refrigerant in the automotive system with R-134
a
thus requires an expensive retrofit to the system to accommodate the parameters of the replacement refrigerant and a complete purging of the system to ensure proper performance of the recharged system.
The quest for suitable substitutes for the harmful chlorofluorocarbons is complicated by the limited number of single fluorinated hydrocarbons which demonstrate the desirable refrigerant properties. Mixtures of known fluorinated hydrocarbons might be used if the desired combination of properties could be found in a given mixture. The creation of simple mixtures also generates problems for the design and operation of refrigeration systems in that the components may segregate in vapor and liquid phases. While concentration is accordingly directed to azeotropic blends or combinations, avoiding the segregation problems, the identification or formulation of such blends is not predictable, particularly when cost, flammability and toxicity are primary concerns.
SUMMARY OF THE INVENTION
The present invention is directed to a blend of a fluorocarbon and hexafluoropropylene in an homogeneous mixture which performs as a superior replacement refrigerant in systems designed for prior chlorofluorocarbons without retrofitting of the system, which operate in a manner essentially paralleling the temperature/pressure curve of the replaced refrigerant.
The novel composition of the refrigerant of the present invention may be varied in the weight percentages of components to exhibit the various vapor pressure/temperature curves of several present commercial refrigerants utilized in existing systems such that no retrofitting of the system is required.
The refrigerant of the present invention is particularly suitable for the replacement of R-12 and R-134
a
with a non-ozone depleting alternative yet being directly substitutable into such system without need for retrofitting since the refrigerant may be modified to exhibit similar operating parameters of the refrigerant to be replaced. When the present i
Garvey, Smith, Nehrbass & Doody, L.L.C.
Skane Christine
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