New technology for refrigeration and air conditioning, have you got it?

- Jul 08, 2019-

1、Electrothermal refrigeration is realized by using organic thermoelectric materials

Thermoelectric materials can realize the direct conversion between temperature difference and electric energy, which is one of the important energy materials. As a new thermoelectric material system, organic thermoelectric materials have broad application prospects in flexible, low-cost power supply devices and self-powered sensors.

The key laboratory of organic solids, institute of chemistry, Chinese academy of sciences, has been devoted to the research of organic thermoelectric materials for a long time. Recently, the ministry of science and technology research and development of the national key project, strategy the forerunner of the Chinese academy of sciences research plan and the support of the national natural science foundation project, researchers study organic thermoelectric devices parr post effect of the heat effect of complex and mutual interference problems, combined with the preparation of suspension device and vacuum system structures, reduce the heat loss, the in situ by using high speed/phase-locked infrared technology realizes the parr stick effect and joule heating and heat .

2、"Defrost with ice"

A research team at Virginia tech university has developed the world's first surface design process for passive defrosting materials.

Moisture and low temperature are important conditions for frost formation. Traditional methods of defrosting, including using antifreeze, heating or applying salt to the surface, are sometimes less than ideal and prone to contamination. The coating technology of recent years can also avoid frosting on the surface, but its durability is poor.

Researchers at Virginia tech have demonstrated a new surface design process that USES the properties of ice to defrost. They created tiny raised grooves on the surface of aluminum, into which water is injected at low temperatures to create "ice streaks." Ice streaks trap moisture in the air around them, keeping the aluminum surfaces around them dry and preventing frost from forming. According to the report, the total area of the "ice stripes" only accounts for about 10 percent of the material surface, sacrificing this area for the other 90 percent of the material surface without frost.

Researchers believe the new process could reduce environmental pollution by replacing traditional defrosting and deicing chemicals. This new process can be considered as a priority for manufacturing outdoor air conditioning systems.

The research is published in the new issue of applied materials and interfaces, a journal of the American chemical society.

3, the new coating can effectively reduce arbitrary surface temperature

Houses in Greece and other sunny countries are often painted white to reflect as much sunlight as possible. Now researchers are reinterpreting this ancient strategy by using a new type of "passive radiation cooling" material to reduce the heat from sunlight. Most of these technologies don't take advantage of existing roofs and walls, but a team of researchers in the United States has now created a cooling coating that can cover any surface, lowering the temperature by about six degrees Celsius. The new paint can be applied directly to any surface texture and can be combined with different pigments to give different colors. The development highlights "tremendous progress in the field," said Xiaobo Yin, a materials scientist at the university of Colorado, boulder. His team developed a passive, radiation-cooled plastic film and founded a start-up called radi-cool, which aims to commercialise it. The new materials could reduce cooling costs by as much as 15 percent in some climates, Yin said. "That's a big number." He said. In the United States, 17 percent of homes have electric air conditioners, so the savings are huge.

White paint typically reflects only about 80 percent of visible light, and they still absorb ultraviolet and near-infrared rays, which can heat buildings. To do better, the new material will first combine materials or structures that reflect almost all of the sun's rays, including near-infrared rays and, in some cases, even ultraviolet rays. They also need to contain polymers or other substances to use their chemical composition to dissipate the extra heat at wavelengths of 8 to 13 microns. The atmosphere does not block these wavelengths of radiation, allowing the material to efficiently release excess heat into space without heating the surrounding air.

In a paper published in nature in 2014, a team of researchers led by Shanhui Fan, an electrical engineer at Stanford university in palo alto, California, showed that by alternating layers of silicon dioxide and hafinium dioxide, they had created a highly reflective surface that was 5 ° c cooler than the surrounding air. Last year, Fan and his colleagues used another material -- a polymer and silver film combination -- to cool air conditioning water. The team says the technology could potentially save 21 percent of the cost of air conditioning in the summer. Since then, Fan's team has launched its own startup, SkyCool Systems.

Yin and his colleague Ronggui Yang took another step forward last year: a plastic film embedded with tiny glass beads that lowers surface temperatures by 10 degrees Celsius. In Australia, applied physicists Angus Gentle and Geoff Smith of the university of technology in Sydney reported in a 2015 paper that a cool roofing material made from two polymers could cool a roof by 3 ° c at midday and 6 ° c at night, respectively, compared with the surrounding air.

However, there is still a problem with applying these coatings to roofing and siding materials. Highly reflective compounds can be incorporated into traditional wood and clay tiles for use in new buildings or renovations. But for existing buildings, it is difficult to have more choices.

This is where new passive cooling coatings come in.

Applied physics and applied mathematics at Columbia University Yuan Yang and Nanfang Yu team in a new period of the United States in a paper published in the journal science, points out that the development of their new material is a kind of multiscale pore structure of micro-nano polyvinylidene fluoride - hexafluoropropylene copolymer ", use the material made of thin film in the sunlight band high reflectivity, with 96% to 99.6% in the infrared radiation window has a high radiation rate of 97%, without power refrigeration can be realized in the daytime.

The test results showed that the surface temperature of the film was 5.9℃ lower than the ambient temperature in the dry environment with sufficient light. In the humid environment, the membrane temperature is about 2.9℃ lower than the ambient temperature.

According to the report, the porous film, polyvinylidene fluoride and air refractive index is very different, can effectively scatter sunlight, including ultraviolet, visible and near-infrared light, so as to achieve a high reflectivity, will not be heated by sunlight; The micron porous structure improves the radiation rate and increases the heat radiation outward.

It is known that the preparation of similar functional materials requires complex vacuum deposition equipment, and it is difficult to directly cover the surface of any shape and texture. The new materials have the advantages of low cost and strong applicability, and can be directly coated on any surface such as plastic, metal and wood.

Yang said that building surfaces tend to be colour-sensitive, and that the material can be combined with pigments to reflect the near-infrared light from sunlight in different colours, significantly lowering the building's temperature compared with traditional paints.

"It looks good for widespread use." Gentle said. The new paint costs about five times as much as conventional paint, says Ronnen Levinson, a roofing cooling specialist at Lawrence Berkeley national laboratory in California. But the increased costs have brought benefits. "All these really cool coatings make the middle of the day cool like at night," Gentle says.

4. The new film automatically reflects sunlight when heated

A new type of film has been developed by us and Chinese researchers. It can be used on Windows to help save energy.

Susan fang, a professor of mechanical engineering at the Massachusetts institute of technology, points out that smart Windows on the market have "electrochromic" Windows, but they require electrical power to change the transparency of the glass, so they are not very energy-efficient.

Working with researchers at the university of Hong Kong in China, Ms. Fang discovered a "thermochromic" material that is transparent at low temperatures, but whose internal structure changes when the temperature exceeds 32 degrees Celsius, becoming translucent and reflecting 70 percent of the sun's heat.

The experiment shows that, under the light source of simulated sunlight, the temperature of the heat-measuring chamber without the film wrapping can reach 38.9℃, while when there is this kind of film wrapping, the temperature of the heat-measuring chamber is only 33.9℃. So the researchers believe applying the film to Windows in buildings could help reduce air-conditioning costs and save energy.

The paper appears in the new issue of the journal joule.

5. Use refrigeration to remove air pollutants

British scientists have found that cooling can be used to remove air pollutants.

International research by the Chinese academy of sciences and Nottingham trent university in the UK could suggest a new way for simple retrofit of air conditioners and humidifiers that could clean up polluted indoor air.

The study, led by professor pan gang of Nottingham trent university in the UK, tested the effectiveness of low-temperature indoor air cleaning by removing air pollutants and particles caused by smoke

The team found that when the smog-polluted air circulates through a cryogenic condenser, fine particles attract themselves to the condenser tube as they fall by gravity, resulting in clean air. This method removes 99% of the particles. At the same time, NO2 can be condensed and removed from the air at -50℃, indicating that this method is effective for removing a variety of indoor pollutants with high boiling points. By modifying air conditioners and humidifiers, low-temperature condensation may continue to purify indoor air, with health considerations more important than energy consumption, researchers say.

"Experiments show that simply circulating polluted air through a small freezer can remove most particulate matter and gas pollutants," said professor pan gang. At the same time, the research makes it possible to add 'clean air' features to household appliances, especially when the air is heavily polluted. "By controlling indoor air pollution and improving air quality in this way, this research work will greatly improve public health."