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1 Introduction Chlorofluorocarbons and hydrochlorofluorocarbons (CFCs, HCFCs) are ozone-depleting substances (ODS). The Montreal Protocol of 1987 established a schedule to restrict the production and consumption of certain chlorofluorocarbon compounds that cause damage to the ozone layer； The Seventh Meeting of the Parties to the Montreal Protocol, held in Vienna in December 1995, further established a specific schedule for restricting CFCs and hydrochlorofluorocarbons. To fulfill this commitment, on September 15, 2006, five ministries and commissions – the **General Administration of Environmental Protection**, the **Development and Reform Commission**, the Ministry of Commerce, the General Administration of Customs, and the **General Administration of Quality Supervision, Inspection and Quarantine** – jointly issued a statement announcing that a regulation banning the production, sale, import, and export of household appliances that use chlorofluorocarbons (CFCs) as refrigerants or blowing agents would be issued by the end of 2006. It was also stipulated that, starting from January 1, 2007, no enterprise shall produce household appliances that utilize CFCs as refrigerants or blowing agents ； CFCs must not be used as cleaning agents in the production of household appliances. As of May 1, 2007, no enterprise shall sell or import/export household appliances that use CFCs as refrigerants or blowing agents. In search of alternatives to ODS-based refrigerants, countries around the world are developing substitutes such as carbon dioxide, liquid ammonia, R134a, isobutane (R600a), and others. However, due to the high liquefaction pressure of carbon dioxide and the high toxicity of liquid ammonia, which make them unsuitable for civilian use, the ODS substitutes that have been truly commercialized on a large scale are mainly R134a and R600a; the United States and Japan use R134a, while Europe uses R600a. In our country, the ODS substitutes include both R134a and R600a; R134a products are mainly exported to the United States and Japan, while R600a is used domestically as well as exported to the European Union. Recently, dimethyl ether (DME) has come to the attention as a promising alternative to ODSs, thanks to its excellent thermodynamic properties, ample market supply, and low cost. Based on a comparison of the physical property data of DME, R22, R134a, and R600a, this paper analyzes the possibility of DME being used as a refrigerant ； The cooling performance under ideal refrigeration cycle conditions was calculated ； The safety, environmental friendliness, and economic viability of DME as a refrigerant were analyzed. The results show that DME has good cooling efficiency; it is an environmentally friendly and cost-effective refrigerant. With appropriate safety measures in place, it can certainly become a refrigerant with promising prospects for development. 2 Feasibility Analysis of Using DME as a Refrigerant to Replace Freon 2.1 Properties of DME The property data of DME compared with those of the refrigerants commonly used in the refrigeration industry, namely R22, R134a, and R600a, are shown below: http://www.nmtech.com.cn/jishuwang/upload1/0710251638527548.jpg http://www.nmtech.com.cn/jishuwang/upload1/0710251643274268.jpg http://www.nmtech.com.cn/jishuwang/upload1/0710251644031091.jpg http://www.nmtech.com.cn/jishuwang/upload1/0710251644449543.jpg It can be seen that DME has many advantages as a refrigerant: ① It has a higher critical temperature compared to R134a and R22; its standard evaporation temperature is similar to that of R134a, and theoretically it should have a higher coefficient of performance (COP value) than R134a ； ②At normal condensation temperatures, the condensation pressure is low; therefore, the pressure resistance requirements for the equipment are reduced, which lowers the likelihood of leaks and helps save on manufacturing costs ； ③The vaporization latent heat is high; it is more than twice that of R134a and R22, and about 23% higher than that of R600a. For the same cooling capacity, the mass flow rate of the working fluid is low, resulting in less refrigerant required ； ④The viscosities of both the gas and liquid phases are low, which helps to reduce resistance losses on the refrigerant side and improve system performance ； ⑤Both the gas and liquid phases have high thermal conductivity, which facilitates heat transfer in evaporators and condensers and reduces the area required for the heat exchanger ； ⑥Compared to R600a, it has a lower standard evaporation temperature, allowing for use in a lower temperature range than R600a ； The lower explosion limit is high, resulting in relatively high safety levels ； ⑦Both the ODP and GWP values are zero; it is environmentally friendly, non-toxic, and poses no harm to humans, making it an eco-friendly refrigerant. However, as a refrigerant, DME also has many drawbacks: firstly, DME is flammable, with an explosion limit of 3.4%, and it falls into Category 3 in terms of safety classification, which is close to Category 2 (3.5%), but it still has an explosion limit almost twice as high as that of R600a ； Secondly, compared to R134a and R22, the gas has a larger specific volume; therefore, with the device remaining unchanged, the mass flow rate of the refrigerant is lower ； Again, DME has high specific heats for both gas and liquid phases; under the same amount of heat recovery, the degree of subcooling is low, making flash formation more likely during throttling. An analysis of the basic physical properties of DME shows that it possesses many excellent characteristics suitable for use as a refrigerant. 2.2 Calculation of the theoretical refrigeration cycle for DME The schematic diagram of the theoretical cycle for dimethyl ether in a refrigerator is shown in Figure 4. http://www.nmtech.com.cn/jishuwang/upload1/0710251645204212.jpg The operating conditions used in the calculations are as follows: evaporation temperature (°C) – 23.3, condensation temperature (°C) 54.4, subcooling temperature (°C) 32.2, superheating temperature (°C) 32.2, and ambient temperature (°C) 32.2. The gas equation of state adopted is the PR equation, whose basic form is shown in: http://www.nmtech.com.cn/jishuwang/upload1/0710251645548683.jpg The calculations for the refrigeration cycle are carried out using the method described in the literature. The calculation results, along with literature comparisons of the cooling performance of R22, R134a, and R600a in refrigerator cycles, are shown in Table 2. http://www.nmtech.com.cn/jishuwang/upload1/0710251646451258.jpg The results show that DME has the highest cooling capacity per unit mass; therefore, the least amount of refrigerant is required, which helps to reduce manufacturing costs as well as refrigerant costs ； The highest refrigeration efficiency COP indicates the best energy-saving effect of COP. However, due to the lower specific volume of DME, its cooling capacity per unit volume is lower than that of R22, but it remains higher than that of R600a and R134a. To achieve the best cooling effect, it is necessary to increase the air inlets of the R134a and R22 compressors. Therefore, DME is performance-wise viable as a substitute for ODS refrigerants. 2.3 Safety and Environmental Impact As can be seen from Table 3, the ODS and GWP values of DME are 0; therefore, it does not cause any damage to the ozone layer or contribute to the greenhouse effect. Although R134a does not cause ozone layer damage, it has a significant greenhouse effect. According to the environmental standards set by the European Union, R134a fails to meet these environmental requirements. Of course, DME is explosive and flammable, posing certain safety risks. However, compared to R600a used in China and the EU at present, it has a much higher explosion limit, and thus is significantly safer. As long as safety standards are strictly followed during manufacturing and maintenance, no danger will arise. http://www.nmtech.com.cn/jishuwang/upload1/0710251647296907.jpg 2.4 Economic viability: At present, as traditional Freon-based products are gradually phased out, the prices of R134a and R600a have risen sharply, and there is a shortage of supply. Meanwhile, as domestic and international production of DME increases rapidly, its output is gradually declining; therefore, DME has certain economic advantages. http://www.nmtech.com.cn/jishuwang/upload1/0710251648042349.jpg 3 Conclusions Based on the analysis of DME’s physical properties, the calculation of its cooling efficiency, as well as economic and environmental considerations, the following conclusions can be drawn: 1) DME exhibits good performance and meets the requirements to serve as a substitute refrigerant for ODSs. 2) Compared to R22, DME has a slightly lower cooling capacity per unit volume; it is necessary to modify the compressor’s inlet to increase the amount of air entering it. For existing R600a and R134a refrigerators or other cooling devices, no adjustments to the compressor parameters are required – they can be filled with DME directly. 3) Using DME as a condensing fluid, it is more environmentally friendly than R22 and R134a ； Its safety performance exceeds that of R600a. 4) Using DME as the working fluid provides good economic efficiency.