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 Aaron Beckendorf 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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Turning Fruits Into Ethylene And Ethane Refrigerant

August 2, 2026 by Maya Posch 11 Comments

One of the best parts about DIY chemistry and physics projects is that you get to decide how early in the supply chain you want to begin, such as with [Hyperspace Pirate]’s adventures in ethanol production from sugar fermentation. Although you can certainly just buy packs of sugar and yeast from the store and pretend that this will be helpful once the world embraces its Mad Max era, you may as well start with the stuff that actually grows on trees, like fruit.

While you could use the ethanol produced this way as ethanol fuel in combustion engines and the like, you can also turn the ethanol into ethylene and ethane. That way you can fill up your refrigerator, freezer, and air conditioner to keep your perishable foods and yourself fresh as the outside world descends into highly questionable fashion choices.

Even outside such a scenario it makes sense to generate your own ethane and ethylene, due to how much these refrigerants cost. Once you have the ethanol, some aluminium oxide catalyst at 350°C is enough to produce ethylene and water. Producing ethane is admittedly a bit more involved, requiring acetobacter bacteria to produce acetic acid, along with baking soda, a platinum anode and a few more odds and ends.

Producing butene and even longer chains from ethylene is also possible as a next step, but this gets even hairier than producing ethane from ethanol, so we’re likely to see this in a future update after all the low-hanging fruit has been harvested.

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Strange Ways To Make Cold

May 4, 2026 by Maya Posch 15 Comments

Making stuff cool and keeping it that way has been a pretty essential part of human civilization for thousands of years, with only in the past few hundred years man-made methods having become available that remove the reliance on the whims of nature and lugging around massive blocks of ice. The most important cooling method is undoubtedly that of vapor-compression refrigeration, but this is hardly the only method to transfer thermal energy from one location to another.

For example, we recently covered an elastocaloric cooling project by a group of scientists that uses strips of NiTi metal. By flexing these they induce a cooling effect which when put in a number of stages serves to transfer a significant amount of thermal energy between both sides, much like a vapor-compression system but without the gases and compressor. Meanwhile the Seebeck effect is relatively well-known from Peltier thermocouple devices, and features heavily in portable refrigerators and kin where these solid-state devices can also transfer thermal energy.

Of course, along with how they function the major question with all of these cooling technologies is how efficient they are, as this determines when you’d want to even consider them for a specific application.

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Testing Refrigerants And Capillary Tubes To Find Peak Performance

April 11, 2026 by Maya Posch 11 Comments

Heat lift graphs. (Credit: Hyperspace Pirate, YouTube)

Although vapor-compression refrigeration is a simple concept, there are still a lot of details in the implementation of such a system that determines exactly how efficient it is. After making a few of such systems, [Hyperspace Pirate] decided to sit down and create a testing system that allows for testing of many of these parameters.

Some of the major components that determine the coefficient of performance (COP) of a heat pump or similar system include the used refrigerant, as well as the capillary tube diameter or expansion valve design. For the testing in the video three refrigerants are used: R600 (N-Butane), R134a (tetrafluoroethene, AKA Freon) and R290 (propane), with R134a being decidedly illegal in places like the EU. The use of R600 instead of R600A is due to the former allowing for a lower pressure system, which is nice for low-power portable systems.

The test rig has the typical fresh-from-the-scrap-heap look that we’re used to and love from [Hyperspace Pirate], but does exactly what it says on the tin, and is easy for any DIY enthusiast to replicate. Which compressor to pick for a specific refrigerant is also covered in the video, along with oil type and more.

For basic systems you’d use a simple capillary tube, whereas an airconditioner or similarly more complex system would use an adjustable valve design. With the rig you can test the efficiency of different tube diameters, with three sizes available in this version. Unfortunately the electronic expansion valve (EEV) that was going to be used didn’t get a chance to shine due to unforeseen events.

With the R134a and butane a COP of 2.0 – 2.5 was achieved when taking power factor into account, which was reasonable considering a compressor was used that targets R134a. Regardless, if you have ever felt like repurposing that old compressor from a fridge or AC unit, this might be a fun afternoon project.

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Helium Recovery System Saves Costs

June 13, 2022 by Bryan Cockfield 31 Comments

Helium is the most common element in the universe besides hydrogen, but despite this universal abundance it is surprisingly difficult to come across on Earth. Part of the problem is that it is non-renewable, so unless it is specifically captured during mining its low density means that it simply escapes the atmosphere. For that reason [Meow] maintains a helium recovery system for a lab which is detailed in this build.

The purpose of the system is to supply a refrigerant to other projects in the lab. Liquid helium is around 4 Kelvin and is useful across a wide variety of lab tests, but it is extremely expensive to come across. [Meow]’s recovery system is given gaseous helium recovered from these tests, and the equipment turns it back into extremely cold liquid helium in a closed-cycle process. The post outlines the system as a whole plus goes over some troubleshooting that they recently had to do, and shows off a lot of the specialized tools needed as well.

Low-weight gasses like these can be particularly difficult to deal with as well because their small atomic size means they can escape fittings, plumbing, and equipment quite easily compared to other gasses. As a result, this equipment is very specialized and worth a look. For a less lab-based helium project, though, head on over to this helium-filled guitar instead.

Recharged Dehumidifier Put Back Into Service

September 19, 2021 by Tom Nardi 39 Comments

For the average consumer, repairing relatively low-cost home devices such as microwaves and TVs just isn’t economically viable. You can hardly blame them when the repair bill could easily be higher than the cost of just buying a new model. Luckily for folks like us, that means you can often find cheap or even free appliances on the second hand market that can be brought back online with a bit of troubleshooting and some spare parts.

Take for example the non-functional dehumidifier [HowToLou] recently came across. You probably couldn’t find a professional repair shop that would be willing to bother with one of these things if you tried, but as he shows in the video below, that doesn’t mean the DIY’er can’t run through some probable failure modes and get the unit back up and running. As a bonus, he also walks viewers through how your typical compressor-based dehumidifier operates.

Beyond the lack of water in the collection compartment, the first sign that something was wrong with this dehumidifier was that the compressor wasn’t running. Upon closer inspection, [HowToLou] determined that the thermal cut-off switch had failed and was stuck open. Luckily it had a visible part number so he could order a replacement, and in the meantime, all he had to do was cut the switch out of the circuit and wire up the compressor’s power directly.

Unfortunately, even with the compressor running, no water was being collected. Noticing that the evaporator coils weren’t getting very cold, [HowToLou] thought the unit might be low on refrigerant. Usually these systems aren’t meant to be recharged, but with a clever piercing tap valve, you can add a quick-connect port to the low pressure side. This particular dehumidifier happened to be filled with the same R134a used in automotive A/C systems, so a quick trip to the auto parts store got him a can of refrigerant complete with a handy pressure gauge.

After getting juiced up, [HowToLou] shows ice forming on the coils and plenty of water getting dumped into the tank. Automotive A/C refill cans usually include some substance to stop or reduce leaks in the system, so hopefully this will end up being a long-term fix. It might not be the most elaborate dehumidifier repair we’ve ever seen, but it’s certainly the most approachable. If you ever see one of these things laying on the side of the road, maybe you should pick it up and see what ails it.

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A Refrigerator Cooled By Rubber Bands

August 25, 2016 by Adam Fabio 35 Comments

Ever noticed that a rubber band gets warmer when it’s stretched? The bands also get cooler when allowed to snap back to relaxed length? [Ben Krasnow] noticed, and he built a rubber band cooled refrigerator to demonstrate the concept. The idea of stretching a rubber band to make it hotter, then releasing it to make it cooler seems a bit counter intuitive. Normally when things get smaller (like a gas being compressed) they get hotter. When pressure is released the gas gets cooler. Rubber bands do the exact opposite. Stretching a rubber band makes it hot. Releasing the stretched band causes it to get cooler.

No, the second law of thermodynamics isn’t in jeopardy. The secret is in the molecular structure of rubber bands. The bands are made of long polymer chains. A relaxed rubber band’s chains are a tangled mess. Stretching the band causes the chains to untangle and line up in an orderly fashion. By stretching the band you are decreasing its entropy. The energy of the molecules in the band don’t change, but entropy does. All the work one does to stretch the band has to go somewhere, and that somewhere is heat. This is all an example of entropic force. For a physics model of what’s going on, check out ideal chains. If you’re confused, watch the video. [Ben] does a better job of explaining entropic force visually than we can with text.

To test this phenomenon out, [Ben] first built a wheel with rubber bands as spokes. Placing the wheel in front of a heater caused it to slowly rotate. [Ben] then reversed the process by building a refrigerator. He modeled his parts in solidworks, then cut parts with his Shaper handheld CNC. The fridge itself consists of an offset wheel of rubber bands. The bands are stretched outside the fridge, and released inside. Two fans help transfer the thermal energy from the bands to the air. The whole thing is hand cranked, so this would make a perfect museum or educational demonstration. Cranking the fridge for 5 minutes did get the air inside a couple of degrees cooler. Rubber is never going to displace standard refrigerants, but this is a great demo of the principles of entropic force.

For more thermodynamic fun, check out [Al Williams] recent article about building a DIY heat pipe.

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