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.
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 2nd 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 xe2x88x9235xcx9cxe2x88x9215xc2x0 C. The refrigerant for middle back pressure condition and the refrigerant for high back pressure condition are xe2x88x9215xcx9c+5xc2x0 C. and xe2x88x9210xcx9c+10xc2x0 C., respectively. As a representative example of the refrigerant for low back pressure condition, CFC-12 (CF2Cl2, 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 (NH3) 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 (CH2FCF3), 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 (CO2=1, 100 yr), which is very high.
Although R-500 (CF2Cl2/CHF2Cl2) 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 (CO2=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 5xcx9c6xc2x0 C. of temperature grade during condensing and evaporating processes as well as flammability and explosiveness.
In addition, ammonia (NH3) 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.
Therefore, the object of the present invention is to provide a composition of refrigerant mixture for low back pressure condition, which is environmentally friendly and is applied, with the adjustment of the amount of the refrigerant, directly to the conventional refrigerator systems adopting CFC-12 refrigerant without any systemic change.
Another object of the present invention is to provide a composition of refrigerant mixture for low back pressure condition which has excellent coefficient of performance and safety to environment and human, condensing and evaporating pressures almost identical to that of CFC-12, excellent compatibility with a refrigerating oil, and enhanced non-flammability and non-explosiveness.
The objects and other objects described in the description can be achieved by providing a composition of refrigerant mixture for low back pressure condition, containing isobutane and 1,1-difluoroethane, and optionally an additive which increases non-flammability.
According to the first aspect of the present invention, there is provided a composition of refrigerant mixture for low back pressure condition containing isobutane and 1,1-difluoroethane.
According to the second aspect of the present invention, there is provided a composition of refrigerant mixture for low back pressure condition containing 25xcx9c35 wt % of isobutane and 65xcx9c75 wt % of 1,1-difluoroethane.
According to the third aspect of the present invention, there is provided a composition of refrigerant mixture for low back pressure condition isobutane and 1,1-difluoroethane and an additive selected from the group consisting of carbon dioxide (CO2), trifluoromethyl iodide (CF3I) and mixture thereof to increase non-flammability.
According to the fourth aspect of the present invention, there is provided a refrigerator system comprising as a refrigerant the composition of refrigerant mixture for low back pressure condition.
The present invention relates to a composition of refrigerant mixture for low back pressure condition, which is environment-friendly and can be directly dropped in refrigerator systems adopting CFC-12 refrigerant, which is main cause of destruction of ozone layer and of induction of green house effect of earth.
The composition according to the present invention contains azeotropic mixture of isobutane and 1,1-difluoroethane, and optionally an additive which improves non-flammability.
More specifically, the composition according to the present invention contains 25xcx9c35 wt % of hydrocarbon refrigerant isobutane and 65xcx9c75 wt % of HFC refrigerant 1,1-difluoroethane (CHF2CH3), and optionally less than 5 wt % of an additive, which is selected from the group consisting of carbon dioxide (CO2), trifluoromethyl iodide (CF3I) and mixture thereof in order to improve non-flammability, based on the total weight of refrigerant mixture.
According to the particular preferred embodiment of the present invention, a composition of refrigerant mixture for low back pressure condition comprising 29xcx9c31 wt % of isobutane, 68xcx9c70 wt % of 1,1-difluoroethane, 1xcx9c2 wt % of an additive selected from the group consisting of carbon dioxide (CO2), trifluoromethyl iodide (CF3I), and mixture thereof gave most preferred result.
The additive, carbon dioxide (CO2) or trifluoromethyl iodide (CF3I), which is used to prevent flammability of the hydrocarbon refrigerant, has additional role to improve volumetric cooling capacity and mobility of the refrigerant oil in the evaporator. According to another preferred embodiment of the present invention, addition of 1.5 wt % and 5 wt % of the additive to the refrigerant mixture raised the ignition point of the refrigerant composition to about 745xcx9c725xc2x0 C. and to about 830xcx9c850xc2x0 C., respectively, and the ignition point was increased in proportional to the content thereof. However, since the excess content of the carbon dioxide (CO2) and/or trifluoromethyl iodide (CF3I) could lower the cooling capacity, it is desirable for the composition to contain less than 5 wt % of the additive, based on the total weight of refrigerant mixture.
The composition according to the present invention can be prepared by removing air from an airtight vessel with a vacuum pump, followed by introducing the hydrocarbon refrigerant isobutane [CH(CH3)3] and HFC refrigerant 1,1-difluoroethane into the vessel and mixing the refrigerant mixture for a certain time. If necessary, carbon dioxide (CO2) and trifluoromethyl iodide (CF3I) can be added to the mixture in order to prevent flammability of the hydrocarbon refrigerant and to increase mobility of the refrigerating oil in the evaporator and volumetric cooling capacity of the refrigerant composition. The obtained product can be put into valve-equipped gas vessels and shipped. These processes can be performed at normal temperature.
According to the preferred embodiment of the present invention, the composition according to the present was proven to have high coefficient of performance and volumetric cooling capacity. As thus, it can be widely used in the refrigerator systems composed of a compressor, a condenser, and an expansion valve, and an evaporator. It can be also used in refrigerator systems equipped with an oil separator and a liquid separator additionally. Especially, the composition exhibits similar behaviors with CFC-12 in terms of vapor pressure, such that it can be directly dropped without any systemic change or modification in the conventional refrigerator systems in which CFC-12 is used as a refrigerant, comprising reciprocal, rotary or scrolling compressor.
In addition, since the composition according to the present invention is environment-friendly and no harm to the ozone layer and green house effect of earth, disadvantages resulted from CFC-12, HFC and HCFC refrigerant compositions can be avoided.
Further, since the composition has the excellent compatibility with the refrigerating oil which is used in order to prevent the abrasion of the parts such as a compressor, various refrigerating oils defined in the standard (ISOVG 10xcx9c50) of the International Standards Organization (ISO) can be widely used. Especially, differently from HFC-134a, mineral oils, which have been used most widely, can be used as a refrigerating oil.
The composition according to the present invention is also applicable to the refrigerators adopting the heat pump method, where the heat emitted from the condenser of the refrigerating cycle is used as the heating source. For example, the composition can be applied to the heat pump air-conditioner, which can be used for heating and cooling, by obtaining heat from the air in an evaporator located in the outdoor, and then warming the air in the indoor with the heat emitted from a condenser.