Refrigerant invention and development to promote the progress of refrigeration technology

In the hot summer, people naturally think of air conditioners that bring in cool breezes and comfortable surroundings. Drinking a refreshing drink from the refrigerator can also be refreshing. All this is a great gospel of refrigeration technology brought to mankind. In the rapid development of modern refrigeration technology, the invention and development of refrigerants play a crucial role.

There are currently about 30 kinds of industrial refrigerants. Commonly used Freon and ammonia (Ammonia).

Freon is currently the most widely used refrigerant is a general term for saturated hydrocarbon halogen derivatives, including the writing of FC for FC, CFC for chlorofluorocarbons, HFC for hydrogen-containing writing, and writing for both HCFC. Commercial freon number according to the rules from left to right the first is the number of carbon minus one; the second is the number of hydrogen plus one; the third is the number of fluorine atoms, chlorine atoms are not numbered, if also contains bromine atoms, The first number according to the above principles, coupled with the letter B and the number of bromine atoms. According to this principle, CBrF3 is written as FC-13B1. CFC-12 is widely used in the production of refrigerators due to its non-toxic and odorless, non-flammable and non-explosive, good stability and good lubricating effect on equipment. Other products such as CFC- 11, HCFC-22, HCFC-113, HCFC-114 are also widely used.

Ammonia to use earlier, as the refrigerant earlier than freon for 60 years, widely used in refrigeration, cold storage and other large refrigeration equipment, its main advantage is the unit volume of large capacity, low cost, not with metal and refrigerated oil Reaction, good thermal stability, but there are also significant toxicity, the obvious shortcomings of corrosion of organic parts.

However, Freon, as a refrigerant, has a fatal flaw. It is a "greenhouse gas" with 1,700 times more greenhouse gases than carbon dioxide, and more dangerously, it destroys ozone in the atmosphere. In the 1980s, two scholars in California of the United States took the lead in pointing out that CFCs (Chlorofluorocarbons) emit chlorine atoms under the action of ultraviolet rays. Chlorine atoms react with ozone to generate free radical chains. One chlorine atom can consume tens of thousands of ozone molecules, thus affecting Ozone molecules 250-320 nm UV absorption, so that the excess UV reaches the Earth's surface, a direct impact on the survival of humans and other organisms. In particular, the chemical properties of CFCs are very stable. Emissions of CFCs reach the stratosphere stably for 40 to 150 years and cause long-term damage to the ozone layer. Owing to the destruction of the ozone layer by Freon, scientists have even found the ozone hole over the poles of the Earth. Therefore, the Montreal agreement of 1990 stipulates that all countries in the world will stop production and emission of Freon by the end of this century. Countries are now looking for alternatives to Freons, which are referred to as "green refrigerants" for environmental compliance. It is a very difficult task to find alternative products that are both environmentally friendly and practical in use. The possible products are CFC-22, HFC-134a, HFC-152a and so on.

In addition, researchers have developed various alternative technologies, including magnetic refrigeration and adsorption refrigeration. Magnetic cooling is also called "paramagnetic salt adiabatic cooling." Paramagnetic salt contains iron or rare earth elements, the 3d, 4f layer electron is not full, it has a magnetic, in the process of excitation and demagnetization will endothermic or exothermic, the development of this type of refrigeration technology with high cooling efficiency, cost Low, simple structure and other advantages, the most attractive is that it does not pollute the environment, so very promising. For example, with magnesium nitrate as a cryogenic magnetic refrigerator cooling can be close to OK. Adsorption refrigeration is the use of adsorption or desorption of endothermic or exothermic nature of the refrigeration, commonly used refrigerant systems include metal hydride - hydrogen, zeolite-H2O, activated carbon - nitrogen, praseodymium oxide (ceria) - oxidation system . Taking full account of the refrigerant and environmental compatibility and the requirements of sustainable development, the new refrigeration technology is vividly called "green refrigeration", which is a trend of the development of refrigeration technology in the future and should be the one I catch for the refrigeration industry Opportunity to meet the challenge of the mainstream.

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