At present, climate change and ozone hole caused by environmental warming have become global environmental problems, which will pose a severe challenge to human survival and development if not controlled. Therefore, in the research process of automobile air conditioning refrigerant substitution, we should strengthen the awareness of protecting the ecological environment, not only see the immediate benefits, but also pay attention to the coordinated and sustainable development of the ecological environment and human beings.
Influence of Refrigerant on Atmospheric Environment
Refrigerant is the working medium to complete the refrigeration cycle in the refrigeration process. Halogenated hydrocarbon refrigerants are mainly used for air conditioning refrigeration, among which those without hydrogen atoms are called chlorofluorocarbons (CFC), those with hydrogen atoms are called hydrochlorofluorocarbons (HCFC) and those without chlorine atoms are called hydrofluorocarbons (HFC). The influence of air-conditioning refrigerants on the atmospheric environment mainly has two aspects, one is to destroy the atmospheric ozone layer, and the other is the greenhouse effect that warms the global climate.
In halogenated hydrocarbons, with the increase of chlorine atoms, the damage to the ozone layer is more serious. Therefore, CFC has the most serious damage to the ozone layer, HCFC has relatively little damage to the ozone layer, and HFC has no damage to the ozone layer. The extent to which refrigerants damage the ozone layer is expressed by ozone depletion potential (ODP).
The emission of refrigerants will produce the greenhouse effect of global warming, and its influence degree is expressed by global warming potential (GWP).
Elimination and substitution of refrigerant CFC- 12
Before the Montreal Protocol was signed, most automobile air conditioning systems used CFCl2 as refrigerant. CFC-L2 is an ideal refrigerant, its boiling point and molar mass are -29.79℃ and 120.93kg/kmol, respectively, but its ODP value is high. According to Montreal Protocol, CFC 12 is a first-class prohibited refrigerant.
In order to find new refrigerants to replace CFC substances, the air conditioning industry has carried out extensive research and made a lot of efforts to find new refrigerants with zero ODP value. In these studies, the refrigerant HFC 134a developed by DuPont has been successfully applied to the refrigeration industry. The main characteristics of refrigerant HFC 134a are: no chlorine atom; It has good safety performance; The physical properties are close to CFCl2, so it is easy to reform the refrigeration system. The heat transfer performance is better than CFCl2, and the amount of refrigerant can be greatly reduced. The evaporation pressure of HFC 134a and CFC-L2 is similar, with zero ODP value and only 0.29 GWP value, and there is no obvious toxicity (long-term chronic toxicity test is still in progress). The following table lists the ODP value, GWP value and service life of refrigerants commonly used in automobile air conditioners in the atmosphere.
HFC 134a is immiscible with the existing mineral refrigeration oil, so we must find a new compressor oil for it. Through repeated tests and screening, two kinds of oils miscible with HFC 134a were developed. Their codes are PAG and POE, and PAG oil is widely used. However, there are still the following problems: its high moisture absorption capacity is easy to cause ice resistance of throttling elements (capillary or expansion valve) in refrigeration system, so it is necessary to increase the amount of desiccant in the system or improve its moisture absorption capacity; At high temperature, the solubility with HFC 134a is reduced, even insoluble. Therefore, special attention should be paid to improving the condensation conditions of the system and not to make the condensation temperature too high; The lubricity is slightly worse than mineral oil; It has infiltration or corrosion effect on rubber seals currently used in refrigeration system, not only involving rubber seals, but also involving refrigerant delivery hoses; The price is 4-5 times more expensive than the current refrigerator oil. In view of the above problems, the design of automobile air conditioning refrigeration system should be changed as follows: the displacement of refrigeration compressor is unchanged, and the original model can be maintained, but all rubber seals must be HNBR；; The design of condenser (including liquid storage dryer) needs to be modified to improve the heat dissipation ability and the ability to absorb moisture in refrigerant and oil; The evaporator can keep the original structure unchanged; Thermal expansion valve must increase the damping value of the original throttle element, so it is necessary to reduce its throttle hole and change the sealing material, and the model is shown as HFC134 A; For refrigerant pipelines (including hoses and connectors), it is necessary to change the material of seals in connectors. The hose adopts multi-layer composite structure, and a layer of nylon is sandwiched in PAG oil-resistant rubber lining to improve the permeability resistance.
At present, HFC 134a has been commercialized and widely used in refrigeration and air conditioning, especially in automobile air conditioning. This is because, firstly, the characteristics of HFC 134a, and secondly, by selecting a single refrigerant, the composition of the refrigerant can be prevented from changing when it passes through the rubber hose. At present, 50% of HFC 134a refrigerants produced worldwide are used in automobile air conditioners. Due to the special working conditions of automobile air conditioners, refrigerants are usually filled in the sea every two years.
In 2006, China's new car consumption was about 6,550 tons, and the maintenance consumption was about 2,950 tons, totaling 9,500 tons, up 25% year-on-year, accounting for 56% of the total consumption of HFC 134a. This shows that the automobile air conditioning market in China is huge, and the demand for refrigerants is also huge.
Substitution of refrigerant HFC 134a
According to the requirements of the Regulation on the Control of Fluorine-containing Greenhouse Gases adopted by the European Union, the European Union will ban the use of refrigerants with GWP greater than 1 50 in newly produced automobile air conditioners from 201June 7+10/day. HFC 134a has a GWP value of/. From 20 111October1to 20171/October 65438, the GWP was greater than/kloc-. Starting from 20 17 and 1, all automobile air conditioners will be prohibited from using refrigerants with GWP greater than 150. Therefore, it is a trend and necessity to use low GWP refrigerants in automobile air conditioners. CO2, hydrocarbons, HFC 152a and some mixtures that can be used as refrigerants in automobile air conditioners have become research hotspots. @page@
(1) synthetic refrigerant
Since 2002, Honeywell Company of the United States began to research and develop a mixture substitute of HFC 134a, and developed a binary mixture composed of tetrafluoropropene (CF3CF=CH2) and trifluoroiodomethane (CF3l), named Fluid H. It is reported that the GWP value of this mixture is less than 10, which is non-combustible, has low slip temperature and is similar to the original one. At present, toxicity and system stability tests, compressor tests, system tests and car body tests are being carried out.
American companies such as Delphi and General Motors are developing automobile air conditioning systems with HFC 152a as refrigerants. According to the research and test results, it can be seen that using HFC 152a as refrigerant in automobile air conditioning system basically does not need to change the pipeline components and production lines of the existing automobile air conditioning system using HFC 134a as refrigerant. Compared with the current HFC 134a system, it can provide equivalent or even better refrigeration effect and higher performance coefficient.
In 2003, the test vehicle using HFC 152a was well received at the SAE New Refrigerant Seminar held in Phoenix, Arizona, USA.
In addition, DuPont and lneos also announced that they are developing a substitute for HFC 134a, which meets the requirements of the European Union.
At home, Shandong Dongyue Chemical Co., Ltd. actively followed the development trend at home and abroad, and developed the substitute of HFC 134a for automobile air conditioning refrigerant according to the requirements of the European Union. Its ODP value is zero, and its GWP value is 1 15, which is compatible with the existing automobile air conditioning system with HFC 134a as the refrigerant and has better energy efficiency. At present, application testing and system testing are under way.
Although the above-mentioned enterprises have done a lot of research and development and test work on HFC 134a substitutes for automobile air conditioners, there are still many aspects to be improved for the large-scale production and application of these substitutes. It is expected that HFC 134a will still be one of the research hotspots in the near future.
(2) Application of natural refrigerants
hydrocarbon
At present, the main hydrocarbons used as refrigerants are propane (R290), butane (R600) and isobutane (R600a), among which R600a has been widely used in refrigerators in Europe and some developing countries, and meets the requirements of Kyoto Protocol, with ODP=0, GWP= 15, good environmental protection performance, low cost and low working pressure. In addition, the mixed refrigerant composed of R290 and R600a has also been developed and utilized.
Ammonia (R7 17)
Ammonia has been used for 120 years and is still in use today. Its ODP=0, GWP=0, and it has excellent thermal performance, low price and easy leak detection. However, ammonia is toxic and flammable. It should be noted that although the use record of 100 years shows that the accident rate of ammonia is very low. Better safety measures must be found in the future, such as reducing the filling amount of ammonia, adopting screw compressor and introducing plate heat exchanger. However, its oil solubility, incompatibility with some materials and high exhaust temperature also need to be solved reasonably.
Carbon dioxide (R744)
CO2 is a natural substance with ODP=0 and GWP= 1. Wide source, low cost, safety, non-toxic, non-flammable, suitable for lubricating oil of various common mechanical parts materials, even at high temperature, it does not decompose to produce harmful gases. The latent heat of evaporation of CO2 is large, and the refrigerating capacity per unit volume is quite high, so the compressor and its components are small. The adiabatic index is higher, K= 1.30, and the compressor pressure ratio is about 2.5-3.0, which is lower than other refrigeration systems, and the volumetric efficiency is higher, which is close to the optimal economic level and has great development potential.
The main natural working medium used in automobile air conditioning is CO2 refrigerant. The refrigeration performance of CO2 has been recognized. However, its stability is questioned, and it is not allowed to leak into the car, affecting passengers in the CO2 system. The energy consumption of CO2 system is relatively high, and the price of accessories is also very high, which is not suitable for economical cars. The noise and vibration of this kind of system are also technical problems that need to be solved urgently, and it is not easy to maintain.
development trends
Although the international community is calling for the replacement of HFC 134a, it has little impact on the domestic market. HFC 134a is in the development stage in China, even in Europe and America, its replacement has just started. This is because it takes a long time to develop and formally apply a refrigerant, and domestic refrigerants have always been subject to the patents of large companies. Only independent research and development can be in an invincible position in the market.
To sum up, under the dual pressure of environmental protection and energy saving, it is the general trend to develop green refrigerants. Due to the unsatisfactory commercial mass production (substitution) of refrigerants in the world, researchers at home and abroad are still making unremitting exploration and have made some achievements and breakthroughs in some fields, but the continuous research and development of new products still needs to continue. I found you a passage. I hope it helps you.