Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
2003-03-05
2003-11-18
Hardee, John R. (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
Reexamination Certificate
active
06649079
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a composition of refrigerant mixtures for low back pressure condition, which is environment-friendly and can be directly dropped in the conventional refrigerator system adopting CFC-12 refrigerant without any systemic change such that it can be effectively used as a substitution material for Freon refrigerant CFC-12 which is the main cause of ozone layer destroy and green house effect of earth. More specifically, the present invention relates to the composition of refrigerant mixtures for low back pressure condition, containing isobutane, 1,1-difluoroethane, and, optionally an additive. The composition according to the present invention is environmentally friendly, therefore minimizes destroy of the ozone layer and global green house effect. Further, it has many excellent properties such as high volumetric-cooling capacity or the vapor pressure similar with CFC-12 to minimize the systemic modification of the refrigerator systems adopting Freon refrigerant CFC-12, and azeotropic characteristic to minimize the temperature grade during evaporation and condensation processes.
DESCRIPTION OF THE BACKGROUND ART OF THE INVENTION
Refrigerating cycle is composed of a compressor, a condenser, an evaporator, an expansion valve, a dryer, an oil separator, a liquid separator, and so forth. Based on the 2
nd
law of thermodynamics, the refrigerator absorbs heat from the low heat supply and emits it to the high heat supply with the assistance of the compressor's work. Refrigerant used in the refrigeration cycle absorbs the heat from the surrounding and evaporates in the evaporator under the low temperature. In the compressor, the refrigerant is compressed to the gas having high temperature and high pressure and then, it is cooling again in the condenser and the phase thereof is changed to the liquid having high pressure. Finally, the pressure thereof is decreased to the initial value on passing through the expansion valve. During these cycles, the heat is transferred from the low heat supply, i.e., surrounding to the high heat supply and the refrigerant performs continuous cooling of the surrounding.
According to operation temperature, the refrigerant is classified into 3 classes: a refrigerant for low back pressure condition, a refrigerant for high back pressure condition, and a refrigerant for middle back pressure condition. The refrigerant for low back pressure condition operates at a temperature of −35~−15° C. The refrigerant for middle back pressure condition and the refrigerant for high back pressure condition are −15~+5° C. and −10~+10° C., respectively. As a representative example of the refrigerant for low back pressure condition, CFC-12 (CF
2
Cl
2
, simply, R-12), one of CFC (Chlorofluorocarbon) refrigerant, can be mentioned. Due to its high coefficient of performance and low flammability, CFC-12 has being widely used in small refrigerators such as household and industrial air-conditioner. However, the use thereof is strictly restricted for being a main cause of ozone layer destroy and global green house effect.
For these reasons, the development of CFC-12 substitution refrigerants has been continuously progressed. HFC (Hydrofluorocarbon) refrigerants such as HFC-134a (or R-134) or HFC-152a (or R-152a), azeotropic refrigerants such as R-500, HC (Hydrocarbon) refrigerants such as R-600a, and an organic compound ammonia (NH
3
) were suggested as substitution refrigerants for CFC-12.
HFC refrigerants have been widely used as a substitution refrigerant for CFC-12, but there are questions as to the environmental safety of such HFC's. Especially, since HFC-134a (CH
2
FCF
3
), most widely used among HFC refrigerants, has lower volumetric cooling capacity and coefficient of performance with high compressing ratio than CFC, it consumes more electricity than CFC-12 refrigerant does. Because of its poor compatibility with a refrigerating oil, special oils like ester oils or poly alkylene glycol (PAG) oils are necessarily required rather than mineral oils. However, the ester oils or PAG oils may cause significant damages to a refrigerator by the absorption of moisture when they are exposed to the air. For these reasons, they cannot be directly dropped in the refrigerator systems adopting CFC-12 refrigerant. That is, systemic changes of the conventional refrigerator systems such as a compressor and the manufacturing equipments are necessarily required. Also, the HFC refrigerants are not environment-friendly. Specifically, the global warming potential (GWP) of HFC-134a is about 300 (CO
2
=1, 100 yr), which is very high.
Although R-500 (CF
2
Cl
2
/CHF
2
Cl
2
) is an excellent refrigerant showing azeotropic behavior, which is a mixture of 2 kinds of refrigerants but acts as a single refrigerant, the use thereof is also restricted because it contains Freon refrigerant which causes environmental pollution and destroys ozone layer.
The hydrocarbon refrigerants have been actively researched as a substitution refrigerant for CFC-12, because of its excellent thermodynamic properties and low global warming potential, specifically 3 (CO
2
=1, 100 yr). For instance, isobutane, R600a refrigerant is suggested as a refrigerator for use in household. Despite of its excellent thermodynamic properties, it suffers from disadvantages that it requires systemic changes or modifications of the CFC-12 refrigerator systems such as a compressor because of its low volumetric cooling capacity. Further, it may also be susceptible to flammability and explosiveness. In addition, R-290 (propane) having high. volumetric cooling capacity, which is one of the refrigerant for high back pressure condition, cannot be directly dropped in the conventional refrigerators because it has much higher vapor pressure than CFC-12. Non-azeotropic refrigerant containing mixture of isobutane and propane is also suffered from non-azeotropic behavior showing 5~6° C. of temperature grade during condensing and evaporating processes as well as flammability and explosiveness.
In addition, ammonia (NH
3
) shows excellent refrigerant feature in cooling capacity, but it is a poisonous gas and susceptible to flammability and explosiveness. Further, it erodes copper and its alloy by the absorption of moisture. Therefore, it cannot be used in the refrigerator for use in household.
Meanwhile, U.S. Pat. No. 5,624,595 disclosed a refrigerant composition comprising silicone oil as an additive in order to improve flammability of the refrigerant. However, the amount of silicone oil added is strictly restricted because it circles through the refrigerating cycle as liquid state and reduces the cooling capacity and accumulation thereof in the evaporator may cause significant damages to the refrigerator. Further, since it is separated from the refrigerant while it is stored for a long time after being manufactured, the improvement in flammability is relatively low when the real refrigerant is discharged as a gas from the vessel.
As a result, in order to use the refrigerants suggested in the above, systemic changes or modifications of the refrigerator systems adopting CFC-12 refrigerant is necessarily required for the reason that they have different properties than CFC-12 in terms of cooling capacity, condensing pressure, evaporating pressure, and so forth. This systemic changes waste enormous cost and resources and the cost required for modifying manufacturing equipments is incalculably high.
Therefore, it has been demanded to develop new azeotropic refrigerant, which could be directly dropped in the conventional refrigerator systems in which CFC-12 was used as a refrigerant such that systemic changes can be minimized, which has excellent volumetric cooling capacity, high performance coefficient, and evaporating pressure feature without showing temperature grade during evaporating and condensing processes, and which is compatible with components of the refrigerator system such as refrigerating oil.
SUMMARY OF THE INVENTION
Therefore, the object of the p
ACM Tech
Bachman & LaPointe P.C.
Hardee John R.
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