Passive Desalination Discovers How To Avoid Salt-Clogging

Saltwater is plentiful, but no good for drinking. Desalinization is the obvious solution, but a big problem isn’t taking the salt out, it’s where all that leftover salt goes. Excess salt accumulates, crystallizes, collects, and clogs a system. Dealing with this means maintenance, which means higher costs, which ultimately limits scalability.

The good news is that engineers at MIT and in China have succeeded in creating a desalination system that avoids this problem by intrinsically flushing accumulated salt as it is created, keeping the system clean. And what’s more, the whole thing is both scalable and entirely passive. The required energy all comes from gravity and the sun’s heat.

To do this, the device is constructed in such a way that it mimics the thermohaline circulation of the ocean on a small scale. This is a process in which temperature and density differentials drive a constant circulation and exchange. In the team’s system, this ultimately flushes concentrations of salt out of the system before it has a chance to collect.

The entirely passive nature of the device, its scalability, and the fact that it could desalinate water without accumulating salt for years means an extremely low cost to operate. The operating principle makes sense, but of course, it is careful engineering that shows it is actually possible. We have seen projects leveraging the passive heating and circulation of water before, but this is a whole new angle on letting the sun do the work.

Will Nickel-Hydrogen Cells Be The Energy Storage Holy Grail?

You may have heard us here remarking in the past, that if we had a pound, dollar, or Euro for every miracle battery technology story we heard that was going to change the world, we would surely be very wealthy by now. It’s certainly been the case that many such pronouncements refer to promising chemistries that turn out only to be realizable in a lab, but here there’s news of one with a bit of pedigree. Nickel hydrogen batteries have a long history of use in space, and there’s a startup producing them now for use on the ground. Could they deliver the energy storage Holy Grail?

The cathode in a nickel-hydrogen battery is formed by nickel hydroxide, and the anode is formed of hydrogen. If a gas as an anode sounds far fetched, we’re guessing that their structure is similar to the zinc-air battery, in which zinc hydroxide forms in a paste of powdered zinc, and works against oxygen from the air over a porous conductive support. What gives them their exciting potential is their ability to take more than 30,000 charge/discharge cycles, and their relative safety when compared to lithium ion cells. Hydrogen in a pressure vessel might not seem the safest of things to have around, but the chemistry is such that as the pressure increases it reacts to form water. The cost of the whole thing is reduced further as new catalysts have replaced the platinum used by NASA on spacecraft.

We really hope that these batteries will be a success, but as always we’ll wait and see before calling it. They may well be competing by then with the next generation of zinc-air cells.

Hackaday Prize 2023: Computer Vision Guides This Farm Mower

It’s a problem common to small-scale mixed agriculture worldwide, that of small areas of grass and weeds that need mowing. If you have a couple of sheep and enough electric fence there’s one way to do it, otherwise, if you rely on machinery, there’s a lot of hefting and pushing a mower in your future. Help is at hand, though, thanks to [Yuta Suito], whose pylon-guided mower is a lightweight device that mows an area defined by a set of orange traffic cones. Simply set the cones around the edge of the plot, place the mower within them, and it does the rest.

At its heart is a computer vision system that detects the cones and estimates distance from them by their perceived size. It mows in a spiral pattern by decreasing the cone height at which it turns, thus covering the whole area set out. Inside is a Raspberry Pi doing the heavy lifting, and because it’s designed for farmland rather than lawns, it has an adaptive track system to deal with obstacles. In its native Japan there is an ageing rural population, so it is particularly suitable for being operated by an older person. See it in action in the video below the break.

A robotic mower aimed at farms is certainly unusual here, but we’ve seen a lot of more conventional lawnmowers.

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Hackaday Prize 2023: A 3D Printed Vertical Wind Turbine

We feature a lot of off-grid power projects here at Hackaday, whether they’re a micropower harvester or something to power a whole house. Somewhere in the middle lies [esposcar90]’s 3D-printed vertical wind turbine, which it is claimed can deliver 100 watts from its diminutive tabletop package.

It’s designed to be part of a package with another turbine but makes a very acceptable stand-alone generator. The arms have large scoop-like 3D-printed vanes and drive a vertical shaft up the centre of the machine. This drives a set of satellite gears connected to a pair of DC permanent magnet motors, which do the work of generating. For different wind situations, there are even some differing STL gear choices to speed up the motors. The motors are 12V devices, so we’re guessing the output voltage will be in that ballpark. However, it’s not made entirely clear in the write-up.

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Hackaday Prize 2023: AutoDuct Smart Air Duct

Modern building techniques are relying more and more on passive elements to improve heating and cooling efficiencies, from placing windows in ways to either absorb sunlight or shade it out to using high R-value insulation to completely sealing the living space to prevent airflow in or out of the structure. One downside of sealing the space in this fashion, though, is the new problem of venting the space to provide fresh air to the occupants. This 3D printed vent system looks to improve things.

Known as the AutoDuct, the shutter and fan combination is designed to help vent apartments with decentralized systems. It can automatically control airflow and also reduces external noise passing through the system using a printed shutter mechanism which is also designed to keep out cold air on windy days.

A control system enables features like scheduling and automatic humidity control. A mobile app is available for more direct control if needed. The system itself can also integrate into various home automation systems like Apple’s HomeKit.

A 100% passive house that’s also as energy-efficient as possible might be an unobtainable ideal, but the closer we can get, the better. Some other projects we’ve seen lately to help climate control systems include this heat pump control system and this automatic HVAC duct booster fan system.

Clean Water, From A Plant-Based Filter

If you’re an outdoors person, one of the earliest things you learned was probably that in-field water sources can’t always be trusted as drinkable. A clear mountain stream could have a dead sheep in it just upstream, for example. Maybe you learned to boil it, or perhaps add chemical tablets. Up-to-date campers have a range of filters at their disposal thanks to nanotechnology, but such devices aren’t the only options to avoid sickness. [BeraAjan] has built one using plant xylem.

The inspiration for this filter came from an MIT paper, and the plant xylem in question isn’t the thin layer we were expecting but a far thicker one found in young conifer branches. In fact, the whole twig without its bark is placed in a tube, and the water filters through it.

It’s fair to say that this isn’t the fastest of filters though, as you can see in the video below the break. He’s combined a few individual filters, but maybe it’s not for the easily bored.

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Road Salt? Bah! New Roadway Material Promises A Better Solution To Snow And Ice

If you’ve ever lived somewhere it gets properly cold, you’ll know that winter’s icy grasp brings the inevitable challenge of keeping roadways safe. While road salt and gritting have long been the go-to solutions, their detrimental environmental impact and the potential for infrastructure degradation are well-documented.

However, a game-changing new development might just offer a brighter, greener solution. Just imagine it—roads that stay ice free without requiring regular attention. 

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