Thursday, November 15, 2018

These Fluid-Filled Tiles Could Help Keep the Buildings of the Future Cool

Sunlight is the power source for nearly all life on Earth, but it can be destructive, too. When too much radiation—particularly the heat rays of the near-infrared—hits manmade structures, it can cause them to overheat, warp, and even fracture.

Nature, on the other hand, seems generally unconcerned about overheating. It turns out that many organisms have specialized circulatory systems to regulate temperature—a fact that intrigued Dr. Mark Alston and his research team at the University of Nottingham. A lot of humanity’s best “inventions” have been taken directly from nature’s playbook, so Alston wondered if he could mimic a natural mechanism to cope with sunlight in his own lab.

Although he was initially interested in the type of circulatory system found most often in mammals, Alston quickly realized that its basic mechanism—pumping heat to the extremities, where it gets discarded—isn’t best suited to most human applications. Instead, he says, “We were looking more for a recirculative system, to store energy…so we could put it back into the system.” In fact, he was quickly drawn to the way plants absorb energy from incident sunlight, stashing it as sugars in a fluid and then moving it out of the leaf so that the energy can be used for growth. If we could do something similar, he realized, we could prevent material stress and generate energy at the same time!

Leaves, of course, absorb and transport energy via fluid flowing through a complex system of veins, a system termed fluidics. “Although it sounds incredibly simple, nature is very complex, with order rules that are regulated to hierarchical scales that we have to mirror and match,” Alston says. In other words, you can’t expect things to behave the same when you scale them up or down in size; the capillary action that helps a plant pull water up its stem just won’t work if the channel is too large. But in an effort to replicate some of that complexity in synthetic materials, Alston developed an algorithm to design a network of tiny channels optimized for this kind of energy transport.

Leaves host highly intricate networks of veins, which transport energy to the rest of the plant.
Image Credit: By wiki user Star61; own work, (CC BY-SA 4.0
Once he was happy with the solution developed by his algorithm, Alston used lasers to etch the microchannels—varying in width from 2 millimeters to 3 millimeters—into two plates of a synthetic polymer, each 5 millimeters thick. After bonding the mirrored pieces together, he had created a leaf-mimicking patch of material measuring about 6” x 8.5”. Following more computations to ensure uniform flow in all the patch’s channels, he set distilled water flowing through it and cranked a test lamp up to 1000 lux—about the brightness of an overcast day. Measuring the amount of energy absorbed and transported to an external heat reservoir, Alston found he was able to achieve a temperature difference between the inflowing water and the outflowing water difference of 14°C, which translated to several dozen Watts of heating power.

Excited by these initial results, Alston envisions a future where panels of similar material would be outfitted with sensors and precisely controlled pumps that would allow them to work in tandem—much like the leaves of a tree. As he points out, it’s not uncommon that part of a structure faces full sun while another portion is partially shaded. In a scenario such as this, numerous panels mosaiced together make a lot of sense. “Each one would be able to regulate its own temperature with relation to its specific area or environment, which could be completely different to its neighbor,” he says.

A depiction of what panels working together might look like.
Image Credit: Mark Alston
Of course, there’s a lot of work to be done before we get there. Right now, Alston is on the lookout for industrial partners to help scale up the project; while he’s confident that the production process isn’t too complicated to adapt for mass production, he does want to experiment with more advanced energy-capturing fluids in the hope of increasing efficiency. In his search for partners, Alston envisions aerospace companies using his creation to shield their capsules and equipment from the sun’s rays. He’s also courting the medical industry; when the microchannels are embedded in silicon the temperature-regulating properties are largely unchanged but the material becomes a flexible patch that could be applied to burns to rapidly cool off damaged tissue.

Whether we first see Alston’s self-regulating material on spaceships, in hospitals, or in some other application he hasn’t thought of yet, it’s one more exciting advancement in materials research to watch out for. Of course, you already see the original version in action every day—yet another reason to show our green spaces a little appreciation.

—Eleanor Hook

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