R12 SUBSTITUTE MIXED REFRIGERANT AND REFRIGERANT SYSTEM

Technical Field

[1] The present invention relates to a dimethyl ether (hereinafter, referred to

"DME")-iso-butane mixed refrigerantused as a refrigerant (hereinafter, referred to as "R") in steam compression refrigerators and air conditioners, and more particularly to a mixed refrigerant substituted for an R12 (CFC 12) or an R 134a (HFC 134a), which is widely applied to household refrigerators and car air conditioners. Background Art

[2] Generally, chlorofluorocarbon (hereinafter, referred to "CFC") and hydrochloroflu- orocarbon (hereinafter, referred to "HCFC"), which are derived from methane or ethane, have been mainly used as refrigerants of refrigerators, air conditioners, and heat pumps. Particularly, CFC12 having a boiling point of -29.75 ⁰ C and a molecular weight of 120.93D/kD is widely used in household refrigerators and car air conditioners.

[3] However, the destruction of an ozone layer in the stratosphere by CFCs and HCFCs is an important global environmental issue. Thereby, the production and consumption of CFCs and HCFCs destroying the ozone layer in the stratosphere is restricted by the Montreal Protocol made in 1987. Since the ozone depletion potential (hereinafter, referred to as "ODP") of CFC12 is 0.9, the use of the CFC12 is completely abolished in developed countries based on the Montreal Protocol. Accordingly, most countries use HFC 134a having an ODP of 0.0 as a refrigerant.

[4] Recently, global warming as well as the destruction of the ozone layer is another important global environmental issue. The Kyoto Protocol made in 1997 strongly advises persons to restrain the use of HFCshaving a high global warming potential (hereinafter, referred to as "GWP"). In order to satisfy the above trend, refrigerator manufacturers in Europe and Japan use hydrocarbon, such as iso-butane, instead of CFC12 and HFC134a, as a refrigerant.

[5] Table 1 states environmental potentials of several refrigerants.

[6] Table 1

[Environmental potentials of refrigerants]

[7]

[8] (*) ODPs of the above refrigerants are value in case that the ODP of CFC 11 is set to 1.0.

[9] (**) GWPs of the above refrigerants are value in case that the GWP of carbon dioxide is set to 1.0 on the basis of 100 years.

[10]

[11] As stated in Table 1, propane, iso-butane, and DME respectively have ODPs of 0.0, and GWPs, which are remarkably lower than those of other refrigerants. Due to the above characteristics, refrigerants, which have ODPs of 0.0, and GWPs being lower than those of CFC12 or HFC134a, are mixed in EU, Japan, and other Asia countries, thereby obtaining desired thermodynamic characteristics, improving efficiency, and increasing interchangeability with oil. Iso-butane and DME are suitable to the above requirements.

[12] In order to use a material as a substitutefor a conventional refrigerant, the material must have a coefficient of performance (hereinafter, referred to as "COP) similar to that of the conventional refrigerant. Here, the COP means the total refrigerating effect against force applied to a compressor. The higher the COP is, the higher the energy efficiency of a refrigerator or an air conditioner is. In order to use the compressor without modifying the compressor, the substitute refrigerant must have a steam pressure similar to that of the conventional refrigerant, and provide a volumetric capacity (hereinafter, referred to as "VC") similar to that of the conventional refrigerant. Here, the VC means the refrigerating effect per unit volume, and is a factor representing the size of the compressor. The VC is in proportion to the steam pressure, and is expressed in terms of kJ/D. In case that the substitute refrigerant has a VC similar to that of the conventional refrigerant, a manufacturer can manufacture refrigerators and air conditionerswithout changing or modifying the compressor, thus being advantageous. However, in viewof the results so far achieved, in case that a refrigerant made of a pure materialis substituted for the conventional refrigerant, since the substitute refrigeranthas a VC differing from that of the conventional refrigerant, it is necessary to change or modify the compressor and the substitute refrigerant cannot have a COP similar to that of the conventional refrigerant.

[13] In order to solve the above problems, a mixed refrigerant is used. Components of the mixed refrigerant are well mixed so that the mixed refrigerant has a COP similar to that of the conventional refrigerant and a VC similarto that of the conventional refrigerant, thereby not requiring the modification of a compressor. Due to these charac-

teristics of the mixed refrigerant, various mixedrefrigerants, which are substituted for CFC 12, have been proposed. Some of the above mixed refrigerants contain HCFCs, the use of which was inhibited by the Montreal Protocol, thus not being a suitable substitute for the conventional refrigerant from a long-term point of view.

[14] Dupont Co. in U.S. developed ternary mixed refrigerants, such as MP39

(53%R22/34%R124/13%R152a) and MP66 (61%R22/28%R124/l l%R152a), which contain HCFC and hydrofluorocarbon (hereinafter, referred to as "HFC"), and sold the refrigerants on the market. Monroe Air Tech. developed a ternary mixed refrigerant called GHG-X3 (65%R22/4%R600a/31%R142b), which contains HCFC and iso- butane, and sells the refrigerant on the market. Further, other companies put various mixed refrigerants on the market. However, most of the above mixed refrigerants have ODPs higher than 0.0 to contaminate global environment, and energy efficiencies lower than that of CFC 12 to indirectly accelerate global warming. Further, most of the above mixed refrigerants contain HCFC and HFC, the use of which was inhibited bythe Kyoto Protocol, thus not being considered as suitable substitutes for the conventional refrigerants from a long-term point of view. Disclosure of Invention Technical Problem

[15] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a mixed refrigerant, which has an ODP of 0.0, so as not to influence an ozone layer in the stratosphere, and a GWP lower than those of other conventional substitute refrigerants, and is used as a substitute for CFC12 and HFC134a without modifying the conventional compressor. Technical Solution

[16] In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a binary mixed refrigerant for refrigerants and air conditioners, including 55-99 % by weight of RE170 (dimethyl ether) and 1-45 % by weight of R600a (iso-butane).

[17] Preferably, 75-95 % by weight of RE170 (dimethyl ether) and 5-25 % by weight of R600a (iso-butane) are mixed.

[18] Further, preferably, 60-90 % by weight of RE170 (dimethyl ether) and 10-40 % by weight of R600a (iso-butane) are mixed.

Advantageous Effects

[19] The mixed refrigerant of the present invention has an ODP of 0.0 so as not to influence an ozone layer in the stratosphere, thus being more advantageous than CFC 12 and HFC 134a in terms of environmental preservation. Compared to HFC 134a having a high ODP, which is inhibited by the Kyoto Protocol, the mixed refrigerant of

the present invention contains DME and iso-butane, which have low ODPs, and reduce the amount of HFC used, thus reducing global warming. Brief Description of the Drawings

[20] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[21] FIG. 1 is a circuit diagram of a refrigerating system used in a refrigerator or an air conditioner using a refrigerant in accordance with the present invention; and

[22] FIG. 2 is a graph illustrating the relation between a variation of temperature and a variation of the composite ratio of DME and iso-butane of a binary mixed refrigerant. Best Mode for Carrying Out the Invention

[23] Now, the composition and functional effect of a binary mixed refrigerant substituted for R12 in accordance with the present invention will be described in detail with reference to the annexed drawings.

[24] The binary mixed refrigerant of the present invention has an ODP of 0.0 so as not to influence an ozone layer in the stratosphere, and a GWP lower than those of other substitute refrigerants, and is used as a substitute for CFC12 and HFC134a without modifying the conventional compressor.

[25] More specifically, the binary mixed refrigerant of the present invention contains

RE170 (dimethyl ether, "DME") and R600a (iso-butane). The binary mixed refrigerant of the present invention has an ODP of 0.0, a GWP lower than those of other substitute refrigerants, and a COP and a VC, which are similar to or higher than those of CFC12 and HFC 134a.

[26] In order to develop the mixed refrigerant substituted for R 12, the present inventor made a program, which simulates the performance of a refrigerator or an air conditioner. FIG. 1 is a circuit diagram of a general refrigerating system of a refrigerator or an air conditioner used in the present invention. The refrigerating system comprises an evaporator, a condenser, a compressor, and an expansion valve. In FIG. 1, Qc represents a direction of the flow of heat in the condenser (refrigerants air), Qe represents a direction of the flow of heat in the evaporator (air→refrigerant), TSl represents an inlet temperature of air in the evaporator, TS7 represents an outlet tem- peratureof air in the evaporator, TS3 represents an outlet temperature of air in the condenser, and TS 6 represents an inlet temperature of air in the condenser. The program performed thermodynamics and heat transfer analysis of parts of the refrigerating system of the refrigerator or the air conditioner, for example, of a heat exchanger and the compressor, and finally combinedthem. One of important factors for determining the accuracy of the program is a physical property value of the refrigerant.

This program calculated physical property values of all refrigerants using theCarnahan- Starling-De Santis (CSD) state equation, which is used as a standard in U.S. and Japan. The CSD state equation, which is known as REFPROP, was developed by the National Institute of Standards and Technology in U.S., and the accuracy and the application of the CSD state equation were proved, thus being most widely used in leading companies, research institutes and universities regarding refrigerators and air conditioners all over the world. Real data were substantially used as input data for developing and performing the program.

[27] Judging from the fact in that the substitute refrigerant for refrigerators and air conditioners must have an ODP of 0.0 and a low GWP, the present inventor mixes RE170 (dimethyl ether, "DME") and R600a (iso-butane), so that the mixture is used as a substitute for CFC12 and HFC134a.

[28] FIG. 2 is a graph illustrating the relation between a variation of temperature and a variation of the composite ratio of DME and iso-butane of the binary mixed refrigerant at a pressure of 15OkPa. In the present invention, so far as any mention is not made, the composition ratio of a material is expressed by % by weight of arefrigerant having a low boiling point, i.e., a refrigerant having a high steam pressure, according to the international standard agreement.

[29] When RE 170 and R600a are mixed under the condition that the composition ratio of RE170 is more than 55 % by weight, a steam pressure is increased so that a saturated temperature is lowered at the same pressure. In this case, the mixed refrigerant has a refrigerating capacity higher than that of RE 170. Further, when RE 170 and R600a are mixed under the condition thatthe composition ratio of RE170 is 75-95 % by weight, the mixed refrigerant has a gliding temperature difference of substantially 0.0, thus becoming an azeotropic mixture. This composition ratio of the RE170/R600a mixed refrigerant is the most preferable.

[30] Table 2 states indexes of the substitute refrigerant of the present invention and CFC

12, serving as a reference material, using a computer analysis program under conventional conditions of a refrigerator or an air conditioner, which uses CFC 12 or HFC 134a.

[31] Table 2

[Comparison of performance of CFC 12 and substitute mixed refrigerant]

[32] [33] * Description of Abbreviation of Table 2 [34] COP: Coefficient of performance (total refrigerating effect/force applied to compressor)

[35] VC: Volumetric capacity [36] GTD: Gliding temperature difference [37] Tdis: Compressor discharge temperature [38] COPdiff: Difference of COPs between corresponding mixed refrigerant and CFC 12 [39] VCdiff: Difference of VCs between corresponding mixed refrigerant and CFC 12 [40] [41] As stated in Table 2, mixed refrigerants of examples 1 to 10 of the present invention have COPs higher than those of CFC 12 and R 134a, while having VCs similar to those of CFC 12 and R 134a. Further, since GTDs (below approximately 1?)

of the mixed refrigerants of the examples 1 to 10 of the present invention are remarkably lower than the GTD (approximately 7?) of a mixed refrigerant, which is commonly used now, the mixed refrigerants of the examples 1 to 10 of the present invention are useful. Moreover, since the Tdiss of the mixed refrigerants of the examples 1 to 10 of the present invention are similar to those of CFC 12 and HFC 134a or higher than those of CFC 12 and HFC 134a by 1O ⁰ C, the mixed refrigerants of the examples 1 to 12 of the present invention are useful also.

[42] Since the ODPs of the mixed refrigerants of the examples 1 to lOof the present invention are 0.0, the mixed refrigerants do not destroy an ozone layer, thus being advantageous in terms of environmental preservation, compared to CFC 12 and HFC 134a. HFC 134a, which has a high GWP, is restricted by the Kyoto Protocol. Accordingly, the mixed refrigerants contain DME and iso-butane, which have low GWPs, reduce the amount of HFC used, thus reducing global warming.

[43] With reference to Table 2, when the composition ratio of RE170 in the mixed refrigerant is less than 55 % by weight, the GTD of the mixed refrigerant exceeds I ⁰ C. Accordingly, preferably, the composition ratioof RE 170 in the mixed refrigerant is more than 55 % by weight. Particularly, in accordance with the examples 5 to 10, when the composition ratio of RE170 in the mixed refrigerant is more than 75 % by weight, the GTD of the mixed refrigerant is reduced less than 0.1 ⁰ C, so that the mixed refrigerant has the characteristic of an azeotropic mixed refrigerant similar to a pure refrigerant.

[44] With reference to Table 2, in order to allow a VCdiff to be less than 1%, the mixed refrigerant of the present invention preferably contains 60 to 90 % by weight of RE 170. The mixed refrigerants of the examples 2 to 7 of the present invention satisfy the above requirement.

[45] For the reference, mixed refrigerants having other composition ratios have excessively low VCs and excessively high GTDs, thus not being substantially applied to refrigerators and air conditioners. Industrial Applicability

[46] The mixed refrigerant of the present invention has an ODP of 0.0 so as not to destroy an ozone layer in the stratosphere, thus being more advantageous than CFC12 and HFC 134a in terms of environmental preservation. Compared to HFC 134a having a high GWP, which is restricted by the Kyoto Protocol, the mixed refrigerant of the present invention contains DME and iso-butane, which have low GWPs, and reduce the amount of HFC used, thus reducing global warming.

[47] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modi-

fications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.