absorption

4 Articles

A clear plastic block is shown on a workbench. The plastic block has channels running through it, with liquid flowing through the channels. A pressure gauge is mounted to the top of the block, and an alcohol burner is placed near the base.

3D Printed Einstein-Szilard Refrigerator Cools With Fire

October 31, 2026 by 16 Comments

They may not deliver the highest efficiency, but absorption refrigerators have earned a persistent place in camper vans and industrial plants thanks to a few distinct advantages: they can operate using waste heat alone as an energy source, and they can be quite reliable due to their lack of moving parts. It can be a bit hard to understand their working principles, though, which is why [Ben Krasnow] built a transparent Einstein-Szilard refrigerator.

Most absorption refrigerators use ammonia and water as their working fluids; since the ammonia gas needs to condense at room temperature, the refrigerator requires pressures above what can be comfortably held in a glass or plastic enclosure. The Einstein-Szilard design, by contrast, uses a third liquid as its refrigerant. A strong solution of ammonia in water is separated by boiling, and the ammonia gas induces the refrigerant to evaporate by decreasing its partial pressure. The refrigerant and ammonia gasses then mix with water, in which the ammonia dissolves, leaving the refrigerant vapor to condense and start the cycle again. The newly reformed water-ammonia solution flows back into the boiler.

The refrigerant is usually butane, but since [Ben] was powering this pressurized system with an open flame, he opted instead for nonflammable perfluoropentane. The refrigerator body itself was 3D printed in clear resin, with a copper block transferring heat from the flame to the boiler chamber; ammonia solutions do dissolve copper, so this isn’t a long-term solution, but it works for a demonstration. The single internal path of the refrigerator presented some difficulties: since almost no pressure builds up between different parts of the system, a bubble in the wrong place can easily airlock it. In the end, [Ben] managed to get it working well enough to reach five degrees Celsius below the ambient temperature. Conveniently, he notes that, for alcohol at a sufficiently high concentration, you could cool your drink by burning a portion of it.

Ammonia-based refrigerators are a tough build for most hackers, but we have seen a salt-water-based absorption refrigerator before. For more less-known refrigerators, check out our article on strange cooling methods.

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Homebrew Optical Sensor Helps Your Diesel Pass The Smoke Test

June 27, 2022 by 50 Comments

We’ve all heard of the smoke test, and we know that it’s the lowest possible bar for performance of an electronic device. If it doesn’t burst into flames when power is applied, you’re good to go for more functional testing. But the smoke test means something else for cars, especially those powered by diesel fuel. And passing diesel exhaust tests can become something of a chore.

To make passing these tests a little easier, [Janis Alnis] came up with this diesel exhaust monitor that measures the opacity of his car’s emissions. The sensor itself is quite simple, and mimics what commercial exhaust analyzers use: a LED and a photodiode at opposite ends of a tube of a specified length. Soot particles in exhaust passing through the tube will scatter light in a predictable way, and the numbers work out that a passing grade is anything greater than 53% transmission.

The sensor body is cobbled together from brass pipe fittings with glass windows epoxied into each end. Exhaust enters via a tee fitting attached to a hose and sampling tube, and exits through another tee. One window of the sensor has a cheap battery-powered flashlight as a light source, while the other end has a Texas Instruments OPT101 photodiode sensor. The sensor is connected to one of the analog inputs of an Arduino, which also runs a 128×64 pixel LCD display — inspired by this air quality meter — to show the current smokiness both graphically and as a percentage. The video below shows the sensor at work.

While there were some issues with soot buildup and water vapor condensation, using the sensor [Janis] discovered that a little bit of a warm-up drive got things hot enough to clear up his ride’s tendency to smoke a bit, allowing him to pass his inspection. Continue reading “Homebrew Optical Sensor Helps Your Diesel Pass The Smoke Test” →

Build Your Own Anechoic Chamber

December 14, 2018 by 16 Comments

For professional-level sound recording, you’ll need professional-level equipment. Microphones and mixing gear are the obvious necessities, as well as a good computer with the right software on it. But once you have those things covered, you’ll also need a place to record. Without a good acoustic space, you’ll have all kinds of reflections and artefacts in your sound recordings, and if you can’t rent a studio you can always build your anechoic chamber.

While it is possible to carpet the walls of a room or randomly glue egg crate foam to your walls, [Tech Ingredients] tests some homemade panels of various shapes, sizes, and materials against commercially available solutions. To do this he uses a special enclosed speaker pointed at the material, and a microphone to measure the sound reflections. The tests show promising results for the homemade acoustic-absorbing panels, at a fraction of the cost of ready-made panels.

From there, we are shown how to make and assemble these panels in order to get the best performance from them. When dealing with acoustics, even the glue used to hold everything together can change the properties of the materials. We also see a few other cost saving methods in construction that can help when building the panels themselves as well. And, while this build focuses on acoustic anechoic chambers, don’t forget that there are anechoic chambers for electromagnetic radiation that use the same principles as well.

Thanks to [jafinch78] for the tip!

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Feeling The Heat Of High-Frequency Trading

August 6, 2018 by 45 Comments

It’s high summer here in North America, and for a lot of us, this one has been a scorcher. Media reports have been filled with coverage of heat wave after heat wave, with temperature records falling like dominoes.

But as they say, it’s not the heat, it’s the humidity, and that was painfully true in the first week of July as a slug of tropical air settled into the northeast United States. With dewpoints well into the 70s (25°C plus) and air temperatures pushing the century-mark (38°C), people suffered and systems from transportation to the electrical grid strained under the load. But as punishing as such soupy conditions are for people, there are other effects that are less well known but of critical importance to financial markets, where increased humidity can lead to billion-dollar losses for markets. Welcome to the weird world of high-frequency trading.

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