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Original title: Approaching the past life of refrigeration technology

 Danfoss Global Refrigeration R&D Test center in Tianjin.A liquid-free helium dilution chiller at a science and technology exhibition.Xinhua News Agency photo.

 In April,climatologists at the European Union's Copernicus Climate Change Service said global average temperatures could hit a new high in 2023 or 2024,driven by climate change and the expected return of the El Nino weather phenomenon.This year may be the hottest summer on record.

 According to the traditional Chinese almanac,"Three years after the summer solstice".It means that from the third"Geng day"after the summer solstice,the fall begins.The dog days are the hottest time of the year.It is reported that this year is one of the earliest years of fall in the 21st century.Beginning on July 11,the dog days last for 40 days.In fact,since the beginning of the fall,the heat wave has been rolling across the country.The continuous high temperature weather has made"relieving the heat"the key word in many people's lives.At this time,many people cannot help feeling that air conditioning is really a great invention.

 Today,we bring you a technology closely related to air conditioning-refrigeration technology.After more than a century of development,modern refrigeration technology has brought a lot of convenience to people's production and life,and has become one of the indispensable key technologies in many industries and fields.

 The origin of refrigeration technology:How do humans prevent summer heat

 When you think of summer,what comes to mind?Air conditioning,ice cream,cold watermelon?When you sit in an air-conditioned room and drink cold drinks in summer,it is inevitable that you will wonder how ancient people spent the summer before the invention of air conditioning.

 Ice is the ancient people's"sharp weapon"to cool down the summer.As early as the pre-Qin period,the royal family and nobles could already use ice to cool down the summer heat and keep food fresh.According to the"Zhou Rites"records,in the Zhou Dynasty,there was already a special organization and person in charge of ice management.In winter,a special person is responsible for collecting ice and storing it in the ice cellar;In the summer,the emperor would give ice cubes to his officials as a benefit.The ice was kept in a wooden or bronze box,called an"ice mirror,"which served as an air conditioner and refrigerator.

 At the end of the Tang Dynasty,when craftsmen were producing gunpowder,they accidentally found that saltpeter dissolved in water would make the surrounding water cool and freeze.So they began to use saltpeter to make ice.After the saltpeter is dissolved in water,it can be extracted by cooling crystallization or evaporation crystallization method and reused.With this method,the cost of producing and storing ice is greatly reduced.In the Song Dynasty,in the bustling market,citizens could already eat a variety of ice drinks.Poet Yang Wanli has poetry cloud:"Sell ice a sound across the water,pedestrians do not eat heart eyes open."

 In addition to using ice cubes to cool down,people have also invented a variety of refrigeration devices and buildings,such as seven-wheel fans,self-rain pavilions,and cooling halls.The design of Hanliang Hall in the Tang Dynasty is very clever.The hall is equipped with many water carts.The flowing water drives the fan to rotate,and the cold water vapor and cold wind are sent into the palace.The rotating fan brings cold water to the roof,and then flows down the eaves to form an artificial water curtain,which plays the role of summer cooling.

 Mechanical refrigeration,on the other hand,was not realized until the 19th century.

 In 1834,the British Jacobi Perkins made a steam compression refrigerator.This refrigerator uses ether as the working medium and can work continuously.In 1844,a doctor in the United States created an air refrigerator with air as the medium.The chiller is used to make ice and cool air for hospitals.Initially,researchers used natural substances such as air as refrigerants.Later,with the advancement of technology and in-depth research,freon has become the most widely used refrigerant.This has also greatly promoted the development of refrigeration and air conditioning technology.

 It is interesting that the air conditioner,which is almost indispensable to people in summer today,was not born to cool human life.

 In 1902,a printing plant in the United States was affected by the unsteady air temperature and humidity.To solve this problem,engineer Willis Carrier invented the first modern electric air conditioner.This equipment is recognized by the industry as the birth of the air conditioning industry,and he is therefore known as the"father of air conditioning".

 After the appearance of air conditioning,with the advantages of adjusting the temperature and humidity in the production process,it entered many industries such as chemical,pharmaceutical,and food.Later,some public places,such as department stores,office buildings,cinemas,etc.,were also equipped with air conditioning.Air conditioning is getting closer and closer to People's Daily life.

 Air conditioning refrigeration technology was named by the American Academy of Engineering as one of the 20 greatest engineering achievements of the 20th century.Its importance is now more evident than ever.

 With the development of the air conditioning industry,there are more and more brands of air conditioners,lower and lower energy consumption,and better and better performance.While ensuring comfort,energy saving and environmental protection have also become the focus of the air conditioning industry.

 Application of refrigeration technology:from social life to scientific research

 With the development of refrigeration technology,human's daily life,industrial production,and even the research and development of high-tech have been inseparable from refrigeration technology.

 120K is a key node of refrigeration technology according to the temperature range obtained by refrigeration."K"stands for Kelvin,a unit of temperature in the International System of Units.Kelvin starts at absolute zero,which is 120K=-153.15°C.

 More than 120K refrigeration technology,for ordinary refrigeration.

 Ordinary refrigeration technology can be said to be the most commonly used refrigeration technology in our daily life.Shopping malls,cinemas,exhibition halls and other public places,cars,trains,planes and other public transport,the air conditioning used in these places belong to the application of ordinary refrigeration technology.Secondly,in the process of production,storage and transportation of food and drugs,in order to prevent the deterioration of goods,it is necessary to freeze or refrigerate them with refrigerators,freezers,etc.,which cannot be separated from ordinary refrigeration technology.Common refrigeration technology provides a lot of convenience for our life.

 Refrigeration technology below 120K,for low temperature refrigeration.In daily life,we hardly use cryogenic refrigeration technology.However,low-temperature refrigeration technology can promote the development of many high-tech,and has a wide range of applications in scientific research,aerospace,materials,energy,medicine and many other fields.

 In the field of energy,scientists use cryogenic refrigeration technology to liquefy gases.If you liquefy hydrogen to liquid hydrogen.Liquid hydrogen has a high energy density and is safer than hydrogen during transportation,making it one of the best storage and transportation methods for hydrogen energy.Cryogenic liquid propellant composed of liquid hydrogen and liquid oxygen is widely used in space launch.China's Long March 5 carrier rocket used liquid hydrogen and oxygen propellant to launch the space exploration experiment module.Compared with the traditional propellant,the engine using liquid hydrogen and liquid oxygen as propellant has higher specific impulse performance,more green environmental protection,and is suitable for repeated use.

 Deep space exploration is inseparable from cryogenic refrigeration technology.The high vacuum and extremely low temperature environment of the universe require space telescopes and instruments used for exploration to maintain extremely low temperatures.Many spacecraft,including the Planck probe and the James Webb Space Telescope,are equipped with cryogenic refrigeration systems.This not only extends the life of the detector,but also improves the accuracy of the detector.

 Cryogenic refrigeration technology also plays an extremely important role in the field of chip manufacturing.In March this year,the"domestic extremely low temperature dilution refrigerator for quantum computing"independently developed by a domestic research team successfully passed the identification committee.The project has set two domestic records for the lowest continuous operating temperature and cooling capacity that have been publicly reported."Domestic extremely low temperature dilution refrigerator for quantum computing"is a high-end scientific research instrument that can provide a low temperature environment close to absolute zero.It can meet the temperature and cold capacity requirements of quantum computing,and is one of the key core devices for developing quantum computing and researching quantum technology.

 It can be said that low-temperature refrigeration technology plays an irreplaceable role in the fields of science and technology.

 The future of refrigeration technology:green and energy efficient

 Not long ago,a report in the journal Nature Geoscience said that between 2010 and 2020,the concentration of five chlorofluorocarbons(CFCs)that deplete the ozone layer in the Earth's atmosphere increased rapidly,and part of the source may point to the by-product of the production of hydrofluorocarbons(HFCs).

 Over the past few decades,global efforts to protect the ozone layer have made some progress.The international community adopted the Montreal Protocol in 1987 to phase out the use of ozone-depleting chemicals such as chlorofluorocarbons.As substitutes,HFCS have now replaced CFCS in many applications.However,this research results show that in order to cope with global climate change and protect the environment,the development of more green and energy-saving refrigeration technology is still a topic that needs to be continuously explored in the field of refrigeration technology research around the world.

 In recent years,in addition to traditional compressor refrigeration or adsorption refrigeration,some new refrigeration technologies are developing rapidly.

 Solar cooling.According to different energy conversion methods,solar energy refrigeration mainly through two ways:one is to achieve the conversion of light to electricity,the use of electricity refrigeration;The second is to achieve the conversion of light to heat,the use of thermal energy cooling.Compared with conventional refrigeration technology,the working medium of solar refrigeration technology does not contain substances such as freon,which is of great significance for the protection of the ozone layer.In addition,solar refrigeration equipment almost does not need to consume conventional energy such as electricity,which can save costs.At present,this technology is still in the experimental stage in China.It is believed that with the deepening of research,this technology will be able to enter thousands of households in the near future.

 Magnetic refrigeration.Magnetic refrigeration is the use of magnetothermal effect refrigeration.The magnetic material is used as the refrigeration working medium,which is not only conducive to protecting the environment,but also has high efficiency and reliability.Magnetic refrigeration is widely used in many fields.The industry believes that magnetic refrigeration may play an important role in space exploration and development.

 Geothermal cooling.Geothermal refrigeration mainly uses geothermal steam or geothermal water to provide heat energy to drive absorption refrigeration equipment.Geothermal energy can be renewable energy,high heat flux,easy to collect,stable parameters and easy to use.These advantages make geothermal refrigeration technology energy saving,environmental protection,reliable performance,is widely used in many fields.

 In addition,there are some researchers"alternative path",put forward a lot of quite creative ideas.

 Researchers at the University of Cambridge in the UK have developed a color nanomaterial.The material is made from plant cellulose and is usually white in color.When the film made of the new material is placed in sunlight,the average temperature of the film is nearly 4.4°C lower than the surrounding air,and one square meter of the film can generate more than 120 watts of cooling power,a property that is comparable to many types of home air conditioners.Cellulose is very abundant in nature.The researchers believe that the new material has the potential to be an environmentally friendly,cheap and sustainable means of refrigeration.

 Researchers at the Chinese Academy of Sciences have found that normal alkane(the main chemical component of paraffin)can achieve cooling effects through liquid solid phase transformation under a certain pressure.According to reports,the cost of normal alkane is low,the physical and chemical properties are stable,the phase change process does not produce harmful emissions,and it is easy to miniaturize refrigeration equipment,and has broad application prospects in the field of refrigeration.This opens up new ideas for the development of green and environmentally friendly new refrigeration technology.

 Today,refrigeration technology has become an indispensable key technology for human production and life.How to make this technology better serve all mankind while saving energy and protecting the environment is a long-term topic for researchers in the future.(He Yishu)