Tag Archives: cooling

Researchers create the “whitest paint” — it reflects 98% of sunlight

What if paint could cool off a building enough to not need air conditioning? A group of US researchers has produced just that: the whitest ever paint. It cooled surfaces by 4.5ºC below the ambient temperature and reflected 98% of sunlight.

Image credit: Flickr / Marco Verch

Cooling represents a significant sector of energy consumption in both residential and commercial applications. This is set to become a growing problem as the climate heats up more and more, as more people buy air conditioning equipment to cope with rising temperatures. Urban areas are especially problematic: cities act as “hot islands” as vegetation is replaced with concrete and asphalt, infrastructure that’s darker and absorbs more heat. 

White-painted roofs have long been considered a solution to cool buildings. They are currently used all around the world, from New York to India — but there’s a problem. The reflective white paints currently on the market only reflects 80-90% of sunlight and absorb UV light. This means that oftentimes, they can’t cool surfaces below ambient temperature.

Last year, researchers from Purdue University in the United States created an ultra-white paint that pushed limits on how white paint can be. But now they have outdone their work, creating a newer paint that isn’t just whiter but can also keep surfaces cooler than the formulation that the researchers had previously demonstrated.

“If you were to use this paint to cover a roof area of about 1,000 square feet, we estimate that you could get a cooling power of 10 kilowatts. That’s more powerful than the central air conditioners used by most houses,” Xiulin Ruan, a Purdue professor of mechanical engineering, said in a statement. 

The researchers argue this new white is probably the closest equivalent of the blackest black, known as “Vantablack,” which absorbs up to 99.9% of visible light. The paint formulation reflects up to 98.1% of sunlight – compared with the 95.5% of the white they developed in 2020 – and sends infrared heat away from the surface as well. 

The new paint was revealed in a paper in the journal ACS Applied Materials & Interfaces, in which the researchers explained the reasons behind the paint’s cooling performance. They used barium sulphate as the pigment at a 60% concentration, which, unlike conventional titanium dioxide pigment, doesn’t absorb UV light. 

At the same time, the researchers used another trick: pigment particles of different sizes. The amount of light dispersed by a particle depends on its size, so using a range distributes more of the light spectrum from the sun. The team tried out over 100 different materials and tested around 50 formulations for each of the most promising. 

“We looked at various commercial products, basically anything that’s white,” Xiangyu Li, a postdoctoral researcher at MIT, who worked on this project as a Purdue Ph.D. student, said in a statement. “We found that using barium sulfate, you can theoretically make things really, really reflective, which means that they’re really, really white.”

The new paint is the result of six years of research, building on attempts going back to the 1970s to develop radiative cooling paint. As it uses a standard acrylic solvent, the paint could be manufactured like any other, the researchers argued. It would also be similar in price, they argued, as barium sulphate is actually cheaper than titanium dioxide. 

The university and the research team have already filed a patent for the paint and are now working with large companies towards commercialization. They believe that the paint will be widely available in the market in one or two years. This could help address cooling’s growing emissions and at the same time bring down the heat in big cities.

Researchers develop a new, more efficient way to keep cool — the ‘Cold Tube’

With the world getting hotter, finding energy-efficient ways to cool down is more important than ever. A team of researchers from the University of British Columbia, Princeton University, the University of California, Berkeley and the Singapore-ETH Centre plan to help us do just that with the ‘Cool Tube’.

The experimental pavilion setup in Singapore.
Image credits Lea Ruefenacht.

Air conditioning can be a blessing in the hot summer months, but they also consume a lot of power. Added up on a city- or country-wide scale this translates to a huge drain on our grids and vast quantities of CO2 emissions. Air conditioning can also contribute to respiratory complications by keeping germs in suspension in the air (by keeping it in constant motion).

The team behind Cold Tube wanted to change how we manage our personal temperature during such times, and their approach doesn’t involve cooling or moving air at all.

Cool cooling ideas

“Air conditioners work by cooling down and dehumidifying the air around us—an expensive and not particularly environmentally friendly proposition,” explains co-lead author Adam Rysanek, assistant professor of environmental systems at UBC’s school of architecture and landscape architecture.

“The Cold Tube works by absorbing the heat directly emitted by radiation from a person without having to cool the air passing over their skin. This achieves a significant amount of energy savings.”

The system consists of a series of rectangular panels that can be fitted to walls or ceilings. These elements are kept cool by chilled water being circulated through them.

The idea behind the Cold Tube is that heat naturally radiates from hot surfaces to colder ones — that’s how heat from the Sun makes it to Earth. When you sit under or near one of these elements, your body heat will radiate towards it. The team describes this effect as similar to the sensation of cold air flowing over your body, even when ambient temperatures are high.

It’s not a new concept — in fact, it’s been in use in industrial settings for several decades now. What Cold Tube does differently, however, is to use a special coating that does away with the need to dehumidify air.

A look inside a pavilion incorporating the Cold Tube system
A look inside the pavilion.
Image credits Lea Ruefenacht.

Humidity in the air condenses on cold surfaces, which can cause hygiene issues and damage surfaces and materials. The team developed an airtight, water-repellent membrane that encases their panels, and prevents condensation from forming (but still allows the system to function as intended).

The researchers tested their system in an outdoor setting in Singapore last year. The temperature outside during the test was 30 degrees Celsius (86 degrees Fahrenheit) on average. Yet, participants reported feeling ‘cool’ and ‘comfortable’ despite the heat, and the panels remained dry throughout the day.

“Because the Cold Tube can make people feel cool without dehumidifying the air around them, we can look towards shaving off up to 50 percent of typical air conditioning energy consumption in applicable spaces,” said Eric Teitelbaum, a senior engineer who oversaw the demonstration project while working at the Singapore-ETH Centre.

“This design is ready. It can obviously be used in many outdoor spaces—think open-air summer fairs, concerts, bus stops, and public markets. But the mission is to adapt the design for indoor spaces that would typically use central air conditioning.”

The system doesn’t rely on cooling air, like a traditional air conditioner, so it can even be used with an open window, or in open spaces. The team hopes that its low operating cost will make the Cold Tube an attractive option for both developed and developing countries. A commercially viable version of the system is expected for 2022.

The paper “Membrane-assisted radiant cooling for expanding thermal comfort zones globally without air conditioning” has been published in the journal PNAS.

Huge dinosaurs evolved cooling systems to escape heat stroke

Growing big has its advantages — like escaping those nasty predators — but it also brings new problems. For giant dinosaurs, dealing with overheating was a massive issue, but they managed to overcome it by developing specialized cooling systems.

Detail of a painting of an Upper Jurassic scenery showing a sauropod. Credits: Gerhard Boeggemann.

Dinosaurs were an extremely varied group, and size is one regard in which their variability went off the charts. Some dinosaurs were as small as hummingbirds, weighing only a few grams, while others could weight as much as 100 tons.

Sauropods were the largest and heavier dinosaurs — larger than everything else in their ecosystem, and an order of magnitude more massive than anything that ever walked the Earth until them.

There are several advantages to growing this much. For starters, you can simply outgrow predators, and become too big for predation. Secondly, you can also use energy more efficiently, and also gain significant longevity. But there are a few issues to overcome too. Thermal inertia is such an issue.

“Small dinosaurs could have just run into the shade to cool off,” said study co-author Professor Lawrence Witmer, “but for those giant dinosaurs, the potential for overheating was literally inescapable. They must have had special mechanisms to control brain temperature, but what were they?”

Different dinosaur groups had different physiological strategies to deal with high heat loads in the brain. Small-bodied dinosaurs had a balanced pattern of blood supply with no particular emphasis on any one site of heat exchange whereas larger-bodied dinosaurs had a more focused thermal strategy, emphasizing blood flow to different parts of the head. Credits: Courtesy of WitmerLab at Ohio University.

If you want to cool down, one of the best things you can do is use evaporation. It’s what many creatures do through sweat, and it’s also what air conditioning units do. This process is particularly important around the head, where some of the most sensitive organs (like the brain and eyes) lie. Chemical analyses of fossil sauropod teeth previously suggested that, despite their massive bodies, the animals maintained body temperatures similar to those of modern mammals, so we know that they were successful in their thermoregulation.

“The brain and sense organs like the eye are very sensitive to temperature,” said Ruger Porter, Assistant Professor of Anatomical Instruction and lead author of the study. “Animals today often have elaborate thermoregulatory strategies to protect these tissues by shuttling hot and cool blood around various networks of blood vessels. We wanted to see if dinosaurs were doing the same things.”

In order to see how this process took place, researchers looked at blood vessels — the body’s natural cooling system. Thankfully for the researchers, blood vessels basically inscribe themselves into bones and well-preserved fossils can reveal the ridges associated with blood vessels.

Credits: Courtesy of WitmerLab at Ohio University.

The team started out with carcasses of birds and reptiles, using CT scans to trace blood flow from sites of evaporative cooling to the brain. They also measured the bony canals and grooves that conveyed the blood vessels. They were then able to take what they’ve learned from this process and adapt it to information from dinosaur fossils. They found that different dinosaurs used different cooling strategies.

“The discovery that different dinosaurs cooled their brains in a variety of ways not only provides a window into the everyday life of dinosaurs, it also serves as an exemplar of how the physical constraints imposed by specific environmental conditions have shaped the evolution of this diverse and unique group,” said Sharon Swartz, a program director at the National Science Foundation, which funded the research. “Using a combination of technological innovation and biological expertise, these researchers were able to take a direct reading from the fossil record that provides new clues about how dinosaur skeletal form and function evolved.”

A key factor that decided how dinosaurs regulated their temperature was body size. Smaller dinosaurs had balanced blood flows, whereas larger dinosaurs favored blood flow to different parts of the head — the blood vessel patterns that researchers found goes way beyond what is necessary for simple nourishment. This unbalanced pattern allowed thermal strategies to be more focused, emphasizing one or more cooling regions.

For a while, the team also had a puzzling question. Most of the giant dinosaurs were herbivores, but large predators (such as the 10-ton Tyrannosaurus Rex) also existed — and the researchers’ analysis showed that they had a balanced vascular pattern, like the small dinosaurs.

“This finding had us scratching our heads until we noticed the obvious difference–theropods like Majungasaurus and T. rex had a huge air sinus in their snouts,” Witmer said. But the eureka moment came when the team found evidence that this antorbital air sinus was richly supplied with blood vessels. Witmer had previously shown that air circulated through the antorbital air sinus like a bellows pump every time the animal opened and closed its mouth.

“Boom! An actively ventilated, highly vascular sinus meant that we had another potential cooling region. Theropod dinosaurs solved the same problem…but in a different way,” concluded Witmer.

The team now wants to expand the research to other species of dinosaurs.

The study has been published in the journal Anatomical Record.

Credit: Pexels.

Solid-state refrigerators based on “plastic crystals” could one-day revolutionize cooling

Credit: Pexels.

Credit: Pexels.

The refrigerator is one of the most useful and valuable modern inventions. It forever changed our way of life, allowing food to be stored for much longer without having to change its taste or texture by pickling, potting, drying or salting it (the traditional way of preserving food before mechanical refrigeration appeared). But despite the fact that they’ve been around for more almost a century, refrigerators haven’t changed that much. They’re still essentially bulky boxes powered by compressors that move environmentally-taxing chemicals — but this seemingly timeless design may soon change.

Researchers at the University of Cambridge are experimenting with a new kind of refrigerating agent called “plastic crystals” which switch from a disordered phase into an ordered phased when pressed by a mechanical force. During the phase switch, the temperature rises and this extra heat is absorbed by the environment. This leads to a drop in pressure that forces the crystals back into an ordered state, causing the temperature to drop.

This pressure and temperature cycle is the same as the one used by a conventional refrigerator. However, your kitchen fridge cools things with a compressor (which is very bulky, constraining the product’s design) that raises the pressure of hydrofluorocarbons (HFCs). The gases — also used to cool cars and buildings — pose a rapidly growing climate threat, trapping heat in the atmosphere. They’re nearly 10,000 times as potent as carbon dioxide and unless their growth is checked, their emissions could double by 2020 and triple by 2030, according to U.S. data.

“If we can do the same job with a solid, it will be better for the environment,” Xavier Moya, a materials scientist at Cambridge University in the U.K., told Inside Science.

In a recent study published in Nature Communications, Moya and colleagues showed that plastic crystals of neopentylglycol (CH3)2C(CH2OH)2 display thermal changes comparable to HFCs.

In the future, solid-state refrigeration could lead to more compact and flexible devices compared to traditional ones. Vapor compression systems generally occupy a lot of space. Without the need for a bulky compressor and extensive pipes for vapor, solid refrigerators could theoretically be small enough to cool microchips.

Before solid-state fridges become a reality, there are some engineering challenges that need to be solved. One is hysteresis, which occurs when the system’s output depends not only on its present inputs but also on past inputs (when the system exhibits memory so to speak). In this particular case, the temperature of the plastic crystals doesn’t return all the way back down to its original temperature, so each cooling cycle becomes less efficient. Another downside is that plastic crystals require a huge pressure to operate, hovering at around 2,500 bars, compared to only 50-100 bars in traditional refrigerators.

According to the Cambridge researchers, it might a decade before plastic crystal refrigerators enter the consumer market. They are currently testing the technology under a spinoff which is already collaborating with manufacturers.

The porous polymer coating reflects sunlight and emits heat to passively cool off buildings. Credit: Jyotirmoy Mandal/Columbia Engineering.

Polymer paint passively cools down any surface

The porous polymer coating reflects sunlight and emits heat to passively cool off buildings. Credit: Jyotirmoy Mandal/Columbia Engineering.

The porous polymer coating reflects sunlight and emits heat to passively cool off buildings. Credit: Jyotirmoy Mandal/Columbia Engineering.

Heat-waves are on the rise all over the world, becoming more frequent and more intense. Developing countries are the hardest hit: not only are heat waves more extreme than in other parts of the world but cooling methods are also more difficult to implement due to cost. In such situations, passive cooling — which doesn’t require electricity or any kind of energy input — is the way to go.

Plastics and other cheap polymers are actually excellent heat radiators, which would make them ideal for passive daytime radiative cooling (PDRC) if scientists could figure out how to get these normally transparent surfaces to reflect sunlight without using silver mirrors.

Researchers at Columbia University have finally been able to accomplish this. Reporting in the journal Science, the authors described a PDRC polymer coating with nano- and micro-scale voids that act as passive air coolers. The amazing part is that the coating can be applied like paint on rooftops, buildings, vehicles — basically anything.

Apply and cool

A passive cooling surface is effective when it has a high solar reflectance and emittance. In other words, if these two variables are high enough, there’s a net heat loss effect ever under intense sunlight.

The cheapest and, often times, most practical PDRC is white paint. If you’ve ever switched a black shirt for a white shirt on a hot summer day, you must know how much of a difference this can make.

The problem with white paint, however, is that it doesn’t reflect longer wavelengths of light, so its cooling performance is modest.

Passive daytime radiative cooling (PDRC) works by reflecting sunlight and emitting heat in order to achieve a net heat loss. This way, a surface can attain sub-ambient temperatures. Credit: Jyotirmoy Mandal.

Passive daytime radiative cooling (PDRC) works by reflecting sunlight and emitting heat in order to achieve a net heat loss. This way, a surface can attain sub-ambient temperatures. Credit: Jyotirmoy Mandal.

Using phase-inversion, the Columbia Engineering team was able to introduce light-scattering air-voids in polymers. The process involved mixing the polymer with a solvent alongside water, in which the polymer is insoluble. Ultimately, the pigments in white paint were replaced with air voids that reflect all wavelengths of light, from UV to infrared. And even though there were no pigments, the polymer still turned white.

What you get is a far better performance than typical white paint and even better than some state-of-the-art PDRCs that are complex and costly. What’s more, there’s the convenience that the polymer coating can be applied like paint to virtually any surface.

During tests, the coating kept surfaces significantly cooler than the surrounding environment under widely different skies. For instance, the polymer paint cooled surfaces by 6°C in the warm, arid desert in Arizona and 3°C in the foggy, tropical environment of Bangladesh.

Another selling point is stability. For instance, cellulose, which is the main component of paper, turns yellow over time. The porous films developed at Columbia, however, did not seem to change one bit over the course of a month in the field.

“The fact that cooling is achieved in both desert and tropical climates, without any thermal protection or shielding, demonstrates the utility of our design wherever cooling is required,” Yuan Yang, assistant professor of materials science and engineering, said in a statement.

“Now is a critical time to develop promising solutions for sustainable humanity,” Yang added, “This year, we witnessed heat waves and record-breaking temperatures in North America, Europe, Asia, and Australia. It is essential that we find solutions to this climate challenge, and we are very excited to be working on this new technology that addresses it.”

Until not too long ago, white was thought to be the most challenging color to manufacture. The new research, however, shows that, in fact, white can be the most attainable color.

“It can be made using nothing more than properly sized air voids embedded in a transparent medium. Air voids are what make snow white and Saharan silver ants silvery,” Nanfang Yu, associate professor of applied physics said in a statement.

Stanford researchers develop the coolest clothes – literally

Stanford engineers have developed cheap, low-cost textiles that can cool your body much more efficiently than existing clothes.

The clothes can make you feel cooler than wearing nothing at all. Photo by AhmetSelcuk.

Naturally, a logical application for this technology would be in hot climates, especially where air conditioning is not available. But even when air conditioning is available, the cooling clothes could help save a lot of energy. Detailing their work in Science, the researchers explain:

“If you can cool the person rather than the building where they work or live, that will save energy,” said Yi Cui, an associate professor of materials science and engineering at Stanford and of photon science at SLAC National Accelerator Laboratory.

There are two mechanisms through which the material cools the body. The first one is not innovative, and is something that already exists in some fabrics: it lets perspiration evaporate through the material. But the second mechanism is indeed revolutionary: it allows heat that the body emits as infrared radiation to pass through the plastic textile. This means that the wearer feels almost 4 degrees Fahrenheit cooler than if they wore cotton clothing.

The anti-blanket

All existing bodies in the universe give off infrared radiation, which is invisible to the human eye. To easily visualize this, think of night-vision goggles – they see the heat given away by bodies. When you put a blanket on, it doesn’t heat you directly, but it traps the heat you radiate close to you. This material does kind of the opposite, allowing most of this energy to be released.

“Forty to 60 percent of our body heat is dissipated as infrared radiation when we are sitting in an office,” said Shanhui Fan, a professor of electrical engineering who specializes in photonics, which is the study of visible and invisible light.

“But until now there has been little or no research on designing the thermal radiation characteristics of textiles.”

Stanford researchers began with a sheet of polyethylene and modified it with a series of chemical treatments, resulting in a cooling fabric. (Image credit: L.A. Cicero)

While the idea sounds fairly simple, the technology behind it is anything but. The team implemented nanotechnology, photonics, and chemistry to give polyethylene – the common, transparent plastic often used as kitchen wrap – a number of desirable characteristics. For example, they made it allow thermal radiation to pass right through it. The same goes for air and water vapor. They also made it opaque (not transparent).

But people don’t wear plastic, so they had to change it once more. To make this thin material more fabric-like, they created a three-ply version: two sheets of treated polyethylene separated by a cotton mesh for strength and thickness.

Better than wearing nothing at all

The end result was that the clothes keep you cooler than your own skin, which is quite an achievement.

“Wearing anything traps some heat and makes the skin warmer,” Fan said. “If dissipating thermal radiation were our only concern, then it would be best to wear nothing.”

When they compared it with regular cotton, it made the skin surface 3.6 F colder. This might not seem like much, but it can make a huge difference – the difference between turning the air conditioning on or leaving it off, or the difference between making a person feel comfortable or uncomfortable.

The team is now working on making different textures and colors, making it suitable for mass production. The material and the thermal treatment is quite cheap, and it could be suitable for countries in hot climates.

“If you want to make a textile, you have to be able to make huge volumes inexpensively,” Cui concluded.

passive cooling system

A simple coating cools solar panels by reflecting the heat into outer space

No kidding, Stanford researchers actually showed it’s possible to cool solar panels by applying a special coating that reflects some of the heat back into space. The coating, called a  photonic crystal cooling system, is transparent. This allows the light to reach the PV cells so these can generate energy, but – crucially – some of the heat is reflected back in space. It’s so good that the researchers showed their PV panels can even stay below ambient temperature, which is incredible by itself. If you know a thing or two about solar panels, then you’ll remember their efficiency is directly related to temperature. The cooler a panel is, the more of the sun’s energy it can convert into electricity. And we’re talking about a mere coating, which shouldn’t be too difficult to scale. Bit by bit, you if you multiply the extra efficiency by millions of panels you end up with a huge useful energy gain. This may be a game changer.

passive cooling system

Illustration: Nicolle R. Fuller/Sayo-Art

Previously, the same team at Stanford made headlines after their turned cooling upside down. A radiator is the most basic cooling part and implies transferring the heat out of your system, to the ambient. Take your refrigerator, for instance. It uses energy to cool food inside, but it also release heat into the room its kept, which is then absorbed and released outside and so on. Same with a car, where a simple grilled metal part stays in contact with both the engine and the air to move away the heat. What’s innovative about the new solution developed at Stanford, however, is that heat is thrown out of the planetary system itself. The heat literally ends up in outer space. When they first showcased their passive cooling prototype, the researchers reported they could lower the temperature of anything that it’s placed on by up to five degrees Celsius by absorbing heat, then re-emitting it at an infrared frequency which can pass through the atmosphere. This way, you use the Universe as a heat sink. Brilliant.

The silica coating over a the Stanford logo.

The researchers were interested, however, in making this work for solar panels, but their initial prototype also reflected 97% of the sun’s rays which is obviously impractical for solar power generation. Now, they’ve found a workaround: they’ve designed a thin film of pattern silica which is transparent to visible light, which makes up most of the energy that solar panels use, but essentially absorbs infrared light (heat). In the paper published in PNAS, the researchers report cooling a solar panel layered with such a film by up to 13 degrees Celsius, which is huge! In terms of efficiency, this translates in increased performance of at least 1% in absolute efficiency.

All matter dissipates heat under the form of far infrared waves, be it rocks, trees or cells. Humans, at normal body temperature, radiate most strongly in the infrared at a wavelength of about 10 microns, which can be viewed with special thermal vision goggles. Heat is dissipated in wavelengths between 6 and 30 micrometers, but air molecules can only absorb, and thus emit, heat in the lower and upper range. Anything that’s between 8 and 13 micrometers passes right through the air and into space. So the trick lies in building a surface that reflects lower and upper ranges, while radiating microwaves that can’t be absorbed by air. The polished fused silica coating is very thin, only 500-μm thick, and patterned with of 6-μm wide, 10-μm deep holes. In the lab, it was etched using photographically which doesn’t sound too practical for large scale but other manufacturing methods could be used.

A multilayer stack cools surfaces below it by radiating heat into space. Credit: FAN LAB, STANFORD ENGINEERING

Cooling of the future: just send the heat into space

Since ancient times, people living in hot climates learned if they paint their rooftops white, then their quarters would stay cooler during the scorching heat. In an attempt to curve energy consumed on air conditioning, which accounts for 15% of all electricity consumed in the US, scientists have devised a multi-layered surface that acts in two ways to expel heat: a traditional heat reflecting mechanism and a high-tech, innovative heat transfer system which expels radiation from inside the house and into space.

Expelling heat into space

A multilayer stack cools surfaces below it by radiating heat into space. Credit: FAN LAB, STANFORD ENGINEERING

A multilayer stack cools surfaces below it by radiating heat into space. Credit: FAN LAB, STANFORD ENGINEERING

The first step you need to take in order to cool a surface is make sure as much incoming heat from the sun is reflected. White surfaces and mirrors are great for this. Cooling rooms without air conditioning is a bit trickier, and to understand how the engineers at  Stanford University in Palo Alto devised their system we first need to grasp how heat is transferred.

All matter dissipates heat under the form of far infrared waves, be it rocks, trees or cells. Humans, at normal body temperature, radiate most strongly in the infrared at a wavelength of about 10 microns, which can be viewed with special thermal vision goggles. Heat is dissipated in wavelengths between 6 and 30 micrometers, but air molecules can only absorb, and thus emit, heat in the lower and upper range. Anything that’s between 8 and 13 micrometers passes right through the air and into space. So the trick lies in building a surface that reflects lower and upper ranges, while radiating microwaves that can’t be absorbed by air.

A white roof reflects heat away and keeps your home cool. Image: vtecoliving.blogspot.com

A white roof reflects heat away and keeps your home cool. Image: vtecoliving.blogspot.com

Shanhui Fan placed a surface made up of seven layers alternating between silicon dioxide (SiO2) and hafnium dioxide (HfO2) onto a silicon wafer. At the very top, a thin silver coating was applied to act as a first line of reflection. The first four ultra thin layers of SiO2 and HfO2 reflect nearly all the rest of the energy that wasn’t reflected in the first place by the silver layer. Together, this stack reflects 97% of incoming radiation. The bottom three layers – two thicker SiO2 layers separated by a thick HfO2 layer – absorbed heat from below and radiated it wavelengths between 8 and 13 micrometers.

When tested, even during full sunlight, the coating cooled surfaces below it by 5 degrees Celsius.

This is definitely a most interesting solution, considering the high cooling potential without any energy input whatsoever. It remains to be seen if the system can be scale efficiently enough to be cost effective. The space radiator was described in a paper published in Nature.

A novel technique cools electronic devices faster and cheaper

Researchers at  North Carolina State University have developed a new technique of cooling electronic devices which they claim and prove through their findings that it can lead to an increase of performance by improving the rate of heat exchange, while also lowering the cost of manufacturing. The scientists’ findings might lead to a new generation of more efficient heat sinks, as well as better cooling for devices that generate a lot of heat, such as lasers and power devices.

The technique is centered around what the researchers call a “heat spreader”, a copper-graphene composite, which is attached to the electronic device using an indium-graphene interface film. Together, the materials provide a much higher thermal conductivity than the conventional lonesome copper used ubiquitously for standard cooling of electronic devices. To be more precise, copper-graphene composite films with thickness greater than 200 microns showed an improvement in thermal conductivity over that of electrolytic copper from 380 W/m.K to 460 W/m.K at 300 K – more than 20%.

Besides the remarkable improvement in thermal conductivity, the researchers point out that the copper-graphene composite is also low-cost and easy to produce, using an electrochemical deposition process “Copper is expensive, so replacing some of the copper with graphene actually lowers the overall cost,” conclude the researchers.

Their findings have been published in the journal Metallurgical and Materials Transactions B.

source: NCSU

Taking a look at the ‘little ice age’ of 1810

ice-ageGlobal warming is one of the main concerns on everybody’s lips, causing more and more damage to the environment every year, sometimes in ways that seem hard to believe; everyday there seems to be a new report about something that went, is going, or will be going terribly wrong. However, in the early 1800s, the situation was in diametric contradiction with everybody being worried about a global cooling that seemed to come out of nowhere.

It all peaked in 1816, when in most places of the world there was actually no summer at all ! That year’s chill was blamed by climatologists on the eruption of the Indonesian volcano called Tambora, but why the few years before 1816 were also way colder than usually remained a mystery. However, newly uncovered evidence from the ice of Antarctica and Greenland suggests that another volcanic eruption was probably responsible for it.

Jihong Cole-Dai, a chemistry professor at South Dakota State University led the expeditions that cleared this intriguing question that seemed to be without an answer. He found evidence of another eruption some 6 years before the 1815 one (which was responsible for the 1816 cooling). Here’s why major volcano eruptions have such a big influence:  they practically dump immense quantities of sulfur dioxide and ash that act pretty much like an umbrella, shading the Earth and reflecting sunlight for several years.

However, it’s obvious that a single volcanic eruption couldn’t be responsible for ‘freezing’ a whole decade. Cole-Dai and his team found evidence of one more eruption that helped trigger the mini ice age. However, they weren’t able to pinpoint the volcano, saying that they only know it has to be somewhere close to the equator and really big. I don’t know for sure but I’m guessing that a more detailed analysis will give some more clues regarding this volcano and researchers will be able to find it, despite the fact that it seems to be a ‘needle in the haystack’ kind of search.