1 National Alternatives to Atmospheric Ozone Destructive Substances In accordance with the requirements of environmental protection requirements at home and abroad, China signed the revised Montreal Protocol on Substances that Deplete the Ozone Layer in 1991. According to this Protocol, China will fulfill its commitment to the world on time and meet the requirements of environmental protection, and will gradually phase out CFC working fluids that have a destructive effect on the ozone layer. Now, many users of CFC working fluid compressors are not very clear about the serious consequences of CFC's destruction of the atmospheric ozone layer on human living environment. Therefore, in order to improve our living environment, we must limit the use of CFC refrigerant, and must be effectively managed. According to the newly-recognized situation, the government has the following policies on CFC working fluids: 1. 1 industrial refrigeration Under the premise that the refrigeration compressor production transformation project can reach full capacity production in 2003, the industrial and commercial refrigeration industry will stop the CFC-12 (R 12) maintenance refilling in 2003. 1. 2 home appliance industry In 1999 and 2003, 40% and 80% of the refrigerants used in newly produced refrigerators and freezers were replaced by R 134a instead of R 12 . At the same time, strive to meet the maintenance needs of refrigerators and freezers by using recycling methods. 1. 3CFC alternative production plan Existing CFC production units will be gradually dismantled, while a similar quota system to the fire protection industry is used to limit production. By 2010, in addition to the individual approved essential use and maintenance CFC, other aspects of CFC consumption and production will be completely stopped, replaced by R 134a. According to the latest report, the country is restricting the production of R 12 year by year, and it is not allowed to establish a new R 12 production point. The annual use of R 12 manufacturers should not exceed the average of three years in 1995, 1996 and 1997. Year by year, from July 1, 1999, according to the needs of the environmental protection situation, the country began to strictly restrict the use of R 12, and reduced the amount of use year by year, and completely banned use in 2005. 2 The possibility of replacing R12 with R134a As an alternative to R 12 , R 134a has been widely recognized in the refrigeration industry after years of research and testing. R 134a is characterized by zero coefficient of damage ( ODP ) to the atmospheric ozone layer and a global warming effect ( GWP ) of 0.26. It is non-flammable, non-toxic and has no corrosive effect on the lining. R 134a and R 12 are significantly different in processing, processing and application, but it is feasible to use it instead of R 12 . The following analysis is from several aspects. 2. 1 properties of the refrigerant (1) The pressure/temperature curve of R 134a and R 12 is as shown, the intersection temperature of the two curves is about 17. 7 ° C. Above this temperature, the saturation pressure of R 134a is higher than R 12 ; below this temperature, the saturation pressure of R 134a is lower than R 12 . DDR 12□DDR 134a pressure and temperature curve ( 2) Evaporation temperature from - 17. 8 ° C to + 10 ° C, condensation temperature at 48.8 ° C, R 134a and R 1 2 relative cooling curve shown, intersection The temperature will change as the condensing temperature changes. The higher the condensing temperature, the higher the intersection point. (3) is a comparison of some characteristics of R 12, R 134a and R 22, the data is measured under standard refrigerant conditions (-15 °C evaporation temperature, + 30 °C condensation temperature). (4) When the same degree of subcooling is used, the cooling effect of R 134a is better than that of R 12 . DDR 12□DDR 134a Cooling and evaporation temperature curves R 12, R 134a and R 22 Comparison characteristics of certain characteristics R 12 R 134a R 22 Chemical formula CCl 2 F 2 CF 3 CH 2 F CHClF 2 Evaporation pressure / psig 11. 8 9. 1 28. 2 Condensation pressure / psig 93. 3 97 158. 2 Saturated gas density ( - 15 ° C) / ( kg / m 3) 10. 98 8. 21 13. 48 Saturated liquid density ( 30 ° C) / ( Kg/ m 3)1 292. 8 1 190. 2 1 174. 2 Latent heat of evaporation ( - 15 ° C) / ( kcal / kg ) 1 092. 5 1 430. 5 1 493 ( 5) Solubility of water: Liquid R 134a is similar to R 22 and has a much higher water absorption than R 12 . Therefore, in the low temperature system, the use of R 134a is not easy to freeze, and it is not easy to cause capillary blockage. But the system still needs to be dry. (6) After extensive research and testing, it was confirmed that R 134a is compatible with the materials used in the current main imported compressors and condensing units. 2. 2 Lubricating Oil - POE Oil 2. 2. 1 mutual solubility (1) Mutual solubility refers to the ability of a refrigerant to mix with a refrigerant. In the operating temperature range of the refrigeration system, the mutual solubility is an important factor for the oil return of the compressor. (2) R 134a is incompatible with mineral oil. (3) POE oil and R 134a are compatible. The miscibility of POE oil and R 134a is similar to that of R 22 and the currently used refrigeration oil. Some POE oils are completely miscible with R 134a (such as alkyl benzene oils and R 22 ), while some POE oils and R 134a are partially soluble (such as mineral oil and R 22 ). 2. 2. 2 moisture (1) Although the POE oil is not as absorbent as the previously considered PAG oil, its water absorption is still 100 times that of mineral oil. The inhaled moisture is difficult to remove by heating and vacuuming. (2) Try to avoid moisture entering the refrigeration system. Do not expose the compressor or refrigeration system to the atmosphere for more than 15 minutes. A better method of installation is to remove the plug and block the cap before welding. After the system operation is completed, the maximum moisture content in the system cannot exceed 80 × 10 - 6. After the system is fitted with a suitable dryer, the moisture index should be 10 × 10 - 6 or lower. (3) When using R 134a, a suitable dryer must be used in the system. 2. 2. 3 compatibility (1) After extensive research and testing, it was confirmed that the POE oil approved by each imported compressor manufacturer is completely compatible with the material of the fully enclosed compressor. (2) Although POE oil is theoretically compatible with mineral oil, it is not advisable to mix POE oil and mineral oil in a refrigeration system. Otherwise, the lubricant cannot be returned to the compressor or the evaporator can be lowered. Heat transfer efficiency. However, when the system is rebuilt in the field, if the remaining mineral oil in the system is less than 1%, adding POE oil will have no effect on the normal operation of the system. 2. 3 system design 2. 3. 1 compressor selection Manufacturers continue to design R 134a compressors that are compatible with refrigeration oils, refrigerants and materials. At the rated point, the R 134a compressor is designed to be very similar to the cooling capacity of the corresponding R 12 compressor. In most cases, especially in high-pressure compressors, the same displacement is used; and 21, 2000, No. 1 Zhang Yingkui: Regarding the replacement of R 134a refrigerant, in some cases, it is necessary to use the row of the first gear. Gas volume. This requires testing each compressor selected in the application to determine if the compressor used is suitable. Because of their different uses, their system operating conditions vary greatly. 2. 3. 2 capillary selection In general, R 134a has a higher cooling efficiency than R 12 . Thus, for a certain amount of cooling, the required flow rate is reduced, and therefore, the heat exchange capillary also needs to be changed. As with all capillary selections, a system test is performed to determine its length and size. 2. 3. 3 expansion valve selection Expansion valve manufacturers have designed expansion valves for R 134a. Ask the supplier when using the expansion valve. 2. 3. 4 return air / exhaust temperature Under similar conditions, the theoretical exhaust temperature of R 134a is slightly lower than R 12 . Therefore, the current R 12 back/exhaust temperature in the compressor manual should also apply to R 134a. In general, it is advantageous to limit the compressor discharge and motor temperature in the case where the return air temperature is slightly lower but there is no liquid return. 2. 3. 5 refrigerant charge The amount of refrigerant charge depends on the components in the system. According to the limited application data, the amount of liquid added to R 134a is 5% to 30% less than that of R 12 . 2. 3. 6 dryer (1) The POE oil used for R 134a is easily hydrolyzed, resulting in the formation of an acidic substance. Therefore, in every R 134a application system, the compressor manufacturer recommends using a suitable dryer. (2) The type of dryer that should be used is a molecular sieve dryer currently compatible with R 22 . It is recommended to use XH-6 (bonded core), XH-7 and XH-9 dryers. Since XH-6 (loose filled core) has a high wear rate, it is not recommended. (3) Solid core dryers with alumina absorb POE oil and moisture, and esters in POE oil may hydrolyze to produce acidic substances. If the installed dryer is too small to filter excess water from the system, the acid may return to the system. This is quite detrimental to the compressor. Therefore, compressor manufacturers recommend not using solid core dryers with alumina in systems that use POE oil. For special dryers, please contact your supplier. 2. 4 system processing 2. 4. 1 compatibility (1) Compared with R 134a, R 12 is more resistant to system treatment agents such as rust inhibitors, lubricants, and cleaning agents. These system treatments are insoluble in R 134a and can be blocked by the POE oil when it is flushed from the surface of the system. Therefore, these treatments must be carefully removed in the application so that they do not exist in the various components of the system. (2) The PAG oils of the earlier studies were completely incompatible with the chlorides, while the POE oils did not have this problem. As in the R 12 system, the chloride remaining on the surface of the refrigeration system must be removed as these chlorides are contaminants in the refrigeration system. 2. 4. 2 vacuum (1) The R 134a system and the R 12 system should have the same degree of vacuum (pumped to 200 m, vacuumed from both sides of the system). If the system is inadvertently allowed to enter moisture into certain parts of the system before installation, It is necessary to take a longer vacuum to make the moisture and non-condensate in the system meet the requirements. The compressor manufacturer recommends a maximum non-condensate ratio of 2% and a maximum moisture content of 80 × 10 - 6, but the water content in the system should be below 10 × 10 - 6 after the refrigeration system with the filter installed. (2) POE oil evaporates less than mineral oil at the same temperature and vacuum. Therefore, if the evaporation of the oil in the R 12 system treatment is not a problem, the evaporation of the oil during the R 134a system treatment should not be a problem. (3) Please contact the vacuum pump supplier when applying to confirm whether the vacuum pump currently used is used for the R 134a POE oil system. 2. 4. 3 leak detection (1) Leak detection equipment designed for R 134a testing or approved by the manufacturer for R 134a is required. Most manufacturers that produce leak detectors supply leak detectors for the R 134a and are developing more new products. (2) Please note that DuPont USA warns users not to use R 134a as a mixture with air for a pressure leak test. 2. 4. 4 filling refrigerant (1) Refrigerant filling equipment such as refills, valves, tubes, etc., which are generally compatible with R 22, are also compatible with R 134a (R 22 is more corrosive to gaskets and plastic than R 12 ). These devices are used for When R 134a, it needs to be recalibrated. Once the device is designated for R 134a, this device should only be used for R 134a. The equipment originally used for R 12 is used for R 134a. The remaining R 12 should be removed, a deep vacuum (25 to 50 m) should be drawn, and the R 134a refrigerant should be used for repeated flushing. When converting a device for R 12 to R 134a, ask the company that supplies the device. (2) R 134a can be charged in either gaseous or liquid form. A liquid line should be added to the liquid refrigerant, and the gaseous refrigerant can be added through the suction pipe while the compressor is running. It should be noted that the gaseous refrigerant must be injected to eliminate the vacuum before the compressor is first turned on. 200 - 300mm (7.87 - 11.81in.) Plastic Seals,Security Seals,Security Seal Polyurethane Parts,Rubber Sleeve Co., Ltd. , http://www.topstar-seals.com
The 21st century is a century of environmental protection, and green products will become the first choice for consumers. The refrigerant chlorofluorocarbon (CFC) used in refrigerators and freezers has a severe destructive effect on the atmospheric ozone layer. In order to protect the environment and stop using CFC, the international community is making unremitting efforts. According to the requirements of green technology at home and abroad, this paper intends to discuss the situation of environmentally friendly refrigerant R 134a instead of CFC-12.