【用阳光煮水的海绵】

【用阳光煮水的海绵】麻省理工学院的研究人员结合泡沫、导热材料和气泡膜创造新型海绵,完全使用阳光就可以把水煮沸。它充分利用铜的特性吸收电磁波谱的各个部分,当暴露在阳光下时吸收热量,把通过的水变成蒸汽,再使用气泡膜包围海绵确保水加热到沸腾。该成果可用于家庭取暖和医疗灭菌,价格低廉。

The sponge that can BOIL water using nothing but sunlight
By GIAN VOLPICELLI
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Scientists have created a sponge-like device that can boil water using only sunlight.
Researchers at the Massachusetts Institute of Technology (MIT) combined foam, heat-conducting materials and bubble wrap to create the sponge.
They believe the device could provide a new way to heat water in houses or industrial facilities at a low cost.
Traditional methods to produce steam from solar radiations rely on expensive lenses and mirrors to focus light.
The new invention, however, is relatively cheap and makes the most of low-tech components.
The sponge is essentially a piece of copper that is treated to absorb various parts of the electromagnetic spectrum.
This means that when you expose it to the sun, it absorbs the heat.
When water is forced through it, it heats up that water, causing it to turn into steam.
By wrapping the sponge in bubble wrap, it focuses sunlight on the sponge to make sure the water heats up until it boils.
Researchers George Ni and Gang Chen at MIT came up with their water-heating design in 2014.
The floating device, made up of carbon foam and graphite, soaks up water through small pores.
It then transform 85 percent of sunlight into steam.
Still, the device had been only tested using an artificial light source ten times as intense as sunlight in normal conditions.
Building on that precedent,  the scientists tried to devise a gadget that could achieve comparable results when exposed to natural sunlight, for instance when left on a rooftop.
They ultimately swapped graphite for a 'spectrally-selective absorber', a thin blue film with exceptional absorptive properties that retains heat.
But after testing it in a water container, they discovered that a lot of heat was still being lost as a result of convection - with hot molecules of air swirling around and cooling down the device and the water.
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That hurdle was eventually overcome thanks to Chen's 16-year-old daughter, who was using transparent bubble wrap to build a makeshift greenhouse for a school project.
Chen noticed how his child's contraption could reach temperatures as high as  160 degrees Fahrenheit (71 C) in winter, and decided to give the method a try.
Combining their structure with a layer of bubble wrap, Chen and Ni succeeded in trapping heat inside the device.
When they tested their 'sponge' in water again, the invention boiled the liquid - converting about 20 per cent of sunlight into steam.
Importantly, the device could heat up water even on cool or cloudy days.
'I was very skeptical of the idea at first,' Ni said in a statement.
'I thought [bubble wrap] was not a high-performance material.
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'But we tried the clearer bubble wrap with bigger bubbles for more air trapping effect, and it turns out, it works. Now because of this bubble wrap, we don't need mirrors to concentrate the sun.'
The researchers envisage larger versions of their device  being used for domestic heating, sterilisation or for desalinating sea water.
While most mirror-based systems harnessing sunlight to boil water are both expensive and durable (up to 20 years), Ni explained that his invention could probably last up to two years at the most.
Still, the short lifespan would be offset by the device's low cost.
'Even so, the cost is pretty competitive,' Ni commented.
'It's kind of a different approach, where before, people were doing high-tech and long-term [solar absorbers]. We're doing low-tech and short-term.'
http://www.dailymail.co.uk/sciencetech/article-3760135/The-sponge-BOIL-water-using-sunlight.html#userconsent#

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