A Simple Stove, Built For Beans

Sitting around a campfire or fireplace is an aesthetically pleasing experience in most situations, and can even provide some warmth. But unless you have a modern wood-burning appliance, it’s likely that most of the energy available in the biomass is escaping as un-burned vapors. Surprisingly, solving this problem is almost as easy as buying a can of beans at the store, and the result is a very efficient stove which can be used for heat in a pinch.

[Robert] is demonstrating this gasifier stove, not with beans but using both a can of peas and a larger can of potatoes. Various holes are drilled in each can in a specific pattern, and then the smaller pea can is fitted inside the larger potato can. Once a fire is going, the holes allow for air to flow in a way which traps the escaping un-burned vapors from the fuel and burns them as they flow through the contraption. No moving parts are required; this is all powered by the natural airflow that’s produced by the heat of the fire.

The result of a build like this is not only a stove which can extract a much higher percentage of the available fuel, but also quires much less fuel for a given amount of heat, and produces a much cleaner, less smokey fire. [Robert] also added a screen mantle which allows for this to be used more as a heat source, but similar builds can also be used just as effectively for cooking, too.

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Fixing A Hot Shop, With Science

We know that pretty much everybody in the Northern hemisphere has had a hellish summer, and there’s little room for sympathy when someone busts out with, “Oh yeah? You think THAT’s hot? Well, lemme tell you…” But you’ve got to pity someone who lives in north Texas and has a steel Quonset hut for a shop. That’s got to be just stupidly hot.

But stupid hot can be solved — or at least mitigated — with a little smarts, which is what [Wesley Treat] brought to bear with this cleverly designed shop door heat shield. When it pushes past 42°C — sorry, that sounds nowhere near as apocalyptic as 108°F — the south-facing roll-up door of his shop becomes a giant frying pan, radiating heat into his shop that the air conditioner has trouble handling. His idea was to block that radiant heat with a folding barrier, but to make sure it would be worth the effort, he mocked up a few potential designs and took measurements of the performance of each. His experiments showed him that a layer of extruded polystyrene (XPS) foam insulation covered with reflective Mylar did better than just the foam or Mylar alone.

The finished heat shield is an enormous tri-fold plywood beast that snugs up against the door when things get toasty in the shop. There’s a huge difference in temperature between the metal door and the inside surface of the shield, which will hopefully keep the shop more comfortable. We imagine that the air between the door and the shield will still heat up, and convection could still distribute all that hot air into the shop. But at least he’s giving the AC a fighting chance.

In addition to great shop tips like this and his custom storage bins, [Wesley] is a talented signmaker. He’s pretty funny too — or maybe that’s just the heat talking.

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Hackaday Prize 2022: Upcycling Acrylic Scraps

Living and working in a remote rain forest may sound idyllic to those currently stuck in bland suburbia, and to be sure it does have plenty of perks. One of the downsides, though, is getting new materials and equipment to that remote location. For that reason, [Digital Naturalism Laboratories], also known as [Dinalab], has to reuse or recycle as much as they can, including their scraps of acrylic leftover from their laser cutter.

The process might seem straightforward, but getting it to actually work and not burn the acrylic took more than a few tries. Acrylic isn’t as thermoplastic as other plastics so it is much harder to work with, and it took some refining of the process. But once the details were ironed out, essentially the acrylic scraps are gently heated between two steel plates (they use a sandwich press) and then squeezed with a jack until they stick back together in one cohesive sheet. The key to this process is to heat it and press it for a long time, typically a half hour or more.

With this process finally sorted, [Dinalab] can make much more use of their available resources thanks to recycling a material that most of us would end up tossing out. It also helps to keep waste out of the landfill that would otherwise exist in the environment indefinitely. And, if this seems familiar to you, it’s because this same lab has already perfected methods to recycle other types of plastic as well.

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High Temp Heat Engine Achieves 40% Efficiency

People generate lots of waste heat. It makes sense that there is a desire to convert that heat into usable energy. The problem is one of efficiency. Researchers from MIT and the National Renewable Energy Lab have announced a new heat converter that they claim has 40% efficiency. Of course, there’s a catch. The temperature range for the devices starts at 1,900 °C .

The thermophotovoltaic cells are tandem devices with two cells mated on one substrate. Each cell is multiple layers of very thin and somewhat exotic materials. So this probably isn’t something you will cobble up in your basement anytime soon unless you’re already manufacturing ICs down there. It appears that the secret is in the multiple layers including a reflective one that sends any missed photons back through the stack.

The paper is pretty dense, but there’s a Sunday-supplement summary over on the MIT site. Using heat storage leads to the ability to make heat batteries, more or less, and harness what would otherwise be waste energy.

We’ve noticed a lot of interest in drawing power from hot pipes lately. All of them techniques we’ve seen rely on some kind of exotic materials.

Mobile Sauna For On-The-Go Relaxation

While it might be nice to imagine owning a cabin in the woods to escape from society, complete with an outdoor sauna to take in the scenic views of nature, most of us will be satisfied with the occasional vacation to a cabin like that. For those trips, or even for long-term camping trips, [Schitzu] and a group of friends thought it would be nice to be able to ensure access to a sauna. For that, they created this mobile, timber-framed sauna that he can tow behind his car.

The sauna is built out of a combination of spruce and Douglas fir, two types of lumber with weather-resistant properties. For an additional layer of protection, the frame was varnished after assembly. The walls are filled with baked cork for insulation, and heat is provided by a small wood-fired oven placed in the corner of the sauna with a stove pipe plumbed through the roof. Performance of the sauna shows good design too, as it can heat up quickly and performs well in all of the tests so far. The final touch on the mobile sauna was to finish the roof with some solar panels in order to gather some energy for long-term camping trips and also to ensure that the roof was protected from rain and weather.

The sauna is designed for two adults to sit in, but it will also accommodate a single person to lay down and sleep (presumably when not using it as a sauna), so the entire trailer actually makes a fairly capable mobile camper too. With the addition of a panoramic window, anyone can take in the sights as well as someone with their own permanently-located sauna could, which is a win in all of our books. If you’re looking for a mobile sauna that’s a little more discrete though, be sure to check out this one which is built in the back of a white panel van.

Using Heaters To Display Time

We’re always fans of interesting clock builds around here, whether it’s a word clock, marble clock, or in this case a clock using a unique display method. Of course, since this is a build by Hackaday’s own [Moritz v. Sivers] the display that was chosen for this build was a custom thermochromic display. These displays use heat-sensitive material to change color, and his latest build leverages that into one of the more colorful clock builds we’ve seen.

The clock’s display is built around a piece of thermochromic film encased in clear acrylic. The way the film operates is based on an LCD display, but using heat to display the segments. For this build, as opposed to his previous builds using larger displays, he needed to refine the method he used for generating the heat required for the color change. For that he swapped out the Peltier devices for surface mount resistors and completely redesigned the drivers and the PCBs around this new method.

Of course, the actual clock mechanism is worth a mention as well. The device uses an ESP8266 board to handle the operation of the clock, and it is able to use its wireless capabilities to get the current time via NTP. All of the files needed to recreate this are available on the project page as well, including code, CAD files, and PCB layouts. It’s always good to have an interesting clock around your home, but if you’re not a fan of electronic clocks like this we can recommend any number of mechanical clocks as well.

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Heating A Home With Sunlight… And Water

The sun is a tremendous source of energy, and while photovoltaic panels are an easy way to harvest some of that energy especially now that prices for them are incredibly low, there are plenty of other ways to tap into that free energy as well. [Engelbert] was looking for alternative ways to heat his house since traditional methods were prohibitively expensive, and ended up building a heat exchanger using solar-heated water to cover his home heating needs. (Google Translate from Dutch)

The system uses several large roof-mounted hot water heating panels. The heat captured by them is then pumped into an underground pipe network which is able to warm up a large area of earth in the summer. In the winter, that heat is able to be extracted back out of the earth and used to heat his home. The system includes almost three kilometers of pipe which are buried two meters below grade, so this will probably not be a weekend project, but it still cost much less than the €80,000 to install gas heating in his home.

[Engelbert] is able to use this self-built system to keep his home and another smaller building at a constant 23°C all year. He actually overbuilt the system slightly and has since disconnected almost half of the pipes, but we certainly understand the desire to over-engineer things around here. The only problem he has had is with various government entities that are slow to adopt energy-efficient systems like these. Perhaps the Dutch government can take some notes from the Swiss when it comes to installing geothermal systems like these.

Thanks to [Jero] for the tip!