Wax on, wax off, wax push
Phase change materials are interesting things. I first came across them as materials for building: most people will have noticed that buildings made of stone or concrete tend to be quite cool inside, even when the weather is extremely hot. This is because the materials can absorb a great deal of heat and prevent it passing to the interior of the building – it’s known as “thermal mass”. Phase-change materials mimic this effect without the need for stone, by exploiting a property of matter. When a substance changes state – a solid melting into a liquid or a liquid vaporising into a gas – it absorbs heat without changing temperature. So pack a panel for building a wall with capsules of wax, heat up one side, and the wax melts, absorbing the heat and preventing it passing through to the other side.
Researchers from the university of Santa Barbara have designed a device which uses another property of melting wax to turn it into a passive motor for a ventilation system. Liquid wax occupies a larger volume than the same mass of solid wax; constrain it in a container with one wall that can move and when it melts, the moving wall becomes a piston. In December, Charlie Xiao, Elliot Hawkes and Bolin Liao published a paper in the journal Device (https://www.cell.com/device/fulltext/S2666-9986(23)00304-6) explaining how they incorporated this device into a roof tile, with the wax-powered system opening a louvre in the tile to allow hot air to escape. When the temperature falls, the wax solidifies and contracts, closing the louvre. The researchers selected a wax which melts at 18.5°C (65.3°F).
In hotter countries than my UK home, a huge amount of electricity is used for indoor air conditioning. As summers warm here, even I’ve succumbed and bought a small air conditioning machine to cool my workspace when the mercury rises above 30°C. Were my house made from concrete or stone, I wouldn’t need it. Similarly, buildings in hot countries with thermal mass don’t need as much or any aircon. But It’s very difficult to add thermal mass to an existing building. Putting a passive wax-powered roof tile in would be easier, cheaper and provide at least some cooling.
I’m indebted to Roger Highfield, former New Scientist editor and before that science editor of the Daily Telegraph, editor and now science director of the Science Museum, for pointing this item out.
As I mentioned on Monday, this week I’ve interviewed one of the key engineers involved in the effort to send people back to the moon. One of the things the new generation of moonwalkers will certainly be doing is collecting moondust. Technically known as regolith, it’s quite nasty stuff: composed mostly of a pulverised glassy material, it’s sharp-edged and has tendency to get everywhere. For the Apollo astronauts of the 1960s and 1970s it clogged machinery and space-suit joints. It smells a bit like gunpowder and one of the astronauts, Harrison Schmidt, was allergic to it, breaking out into a sneezing fit on removing his helmet in the lunar lander after a period working outside. But it’s also one of the main research targets for lunar return missions, as it is likely to contain traces of water that could be the source of rocket fuel and will form the basis for construction materials to build permanent habitation on the moon’s surface.
As regolith is such an aggressive material, collecting it is likely to be done by robots. But these will be operated by astronauts (control from Earth would be more cumbersome because of the timelag of radio signals), and a team at the University of Bristol’s robotics laboratory, have developed a virtual model of moondust, mimicking its properties like density and stickiness and behaviour under lunar gravity, which they plan on incorporating into a videogame-like system for training future astronauts. The idea is that they will start with this simulation, then progress to physical models in a moon-like landscape before they travel up to the moon to operate the real thing. Team leader Joe Louca comments “Our primary focus throughout this project was on enhancing the user experience for operators of these systems – how could we make their job easier?” In a paper in the journal Frontiers in Space Technology, Space Section Exploration (https://www.frontiersin.org/articles/10.3389/frspt.2024.1303964/full), Louca explains how the team started with a simulation developed by researchers at the German space agency DLR which had high accuracy but was limited by only being able to simulate small amounts of regolith and modified it to make it scalable to larger amounts. “Then we conducted a series of experiments – half in a simulated environment, half in the real world – to measure whether the virtual moondust behaved the same as its real-world counterpart.” Louca’s team’s next task is to see whether the model can be used in simulation of regolith-collecting robots, and if successful, they plan on modifying it to mimic Martian soil for future missions to the Red Planet and, in the shorter term to train scientists who will handle and analyse Martian regolith from a planned sample-return mission.
The astronauts of the Artemis missions scheduled for the next few years are still likely to curse moondust as it makes their suits’ knee-joints creak and grind and it might make them sneeze. But Louca’s team’s work will indirectly help them breathe, ferry them up and down from the surface to the Lunar Gateway orbital station that’s soon to begin construction, protect them on the surface and even power the next step into the Solar System.
While lunar missions hope to find water, on Earth the quality of water is a concern for millions. In central Bangladesh, deposits of arsenic leach into the waters of the River Mengha and into groundwater, putting local people at risk from its ferocious toxicity. Tom Varner, a doctoral student at the University of Texas at San Antonio, is investigating an odd phenomenon known as he natural reactive barrier in the Mengha and its neighbour the Hooghly where oxygen-rich river water mixes with groundwater with reducing (electron-donating) properties, leading to the formation of iron oxides which have the ability to bind onto arsenic and remove it from the river water. “Understanding more about these processes and the natural reactions that occur between river and aquifer will provide the groundwork for future studies to understand how contaminants behave in the environment,” Varner says. As well as helping improve the health of communities at risk from water toxicity, the studies could help land remediation projects, he adds (https://www.utsa.edu/today/2024/02/story/utsa-doctoral-student-studies-water.html).
The interest from the university of Texas stems from aquifers associated with the deltas of the Brazos River and the Mississippi, where there are also elevated arsenic levels and sediments rich in iron compounds. Arsenic occurs in many locations and is often associated with copper deposits, including in Cornwall.
