Oil-Immersed Raspberry Pi Keeps Its Cool Under Heavy Loads

As a general rule, liquids and electronics don’t mix. One liquid bucks that trend, though, and can contribute greatly to the longevity of certain circuits: oil. Dielectric oil cools and insulates everything from the big mains transformers on the pole to switchgear in the substation. But what about oil for smaller circuits?

[Lord_of_Bone] was curious to see if an oil-cooled Raspberry Pi is possible, and the short answer is: for the most part, yes. The experimental setup seen in the video below is somewhat crude — just a Pi running Quake 3 for an hour to really run up the CPU temperature, which is monitored remotely. With or without heatsinks mounted, in free air the Pi ranges from about 50°C at idle to almost 70°C under load, which is pretty darn hot. Dunking the Pi in a bath of plain vegetable oil, which he admits was a poor choice, changes those numbers dramatically: 37°C at idle and an only warmish 48°C after an hour of gaming. He also tested the Pi post-cleaning, which is where he hit a minor hiccup. The clean machine started fine but suffered from a series of reboots shortly thereafter. Twelve hours later the Pi was fine, though, so he figures a few stray drops of water that hadn’t yet evaporated were to blame.

Is oil immersion a practical way to cool a Pi? Probably not. It doesn’t mean people haven’t tried it before, of course, but we applaud the effort and the careful experimentation.

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Computers May Someday Need A Drink

“We want to put water right into your processor.” If that statement makes you sweat, that is good. Sweating is what we’re talking about, but it’s more involved than adding some water like a potted plant. Sweating works naturally by allowing liquid to evaporate, and that phase change is endothermic which is why it feels cool. Evaporative coolers that work in this way, also known as swamp coolers, haven’t been put into computers before because they are full of sloshy water. Researchers in South Korea and the United States of America have been working on an evaporative cooling system mimicking the way some insects keep themselves cool by breathing through their exoskeletons while living in damp soil.

Springtails are little bugs that have to keep the water and air separate, so they don’t drown in the wet dirt where they live. Mother Nature’s solution was for them to evolve to do this with columns that have sharp edges at the exit. Imagine you slowly add water to a test tube, it won’t spill as soon as you reach the top, it will form a dome. This is the meniscus. At a large scale, say a river dam, as soon as you get over the dam you would expect spillage, but at the test tube level you can see a curve. At the scale of the springtail, exuded water will form a globe and resist water pressure. That resistance to water pressure allows this type of water cooling to self-regulate. Those globes provide a lot of surface area, and as they evaporate, they allow more water to replenish the globe. Of course, excessive pressure will turn them into the smallest squirt guns.

We have invented a lot by copying Mother Nature. Velcro was inspired by burrs, and some of our most clever robots copy insects. We can also be jerks about it.

16-Cylinder Stirling Engine Gets a Tune Up

Tiny catapults, kinetic sculptures, a Newton’s Cradle — all kinds of nifty toys can adorn the desk of the executive in your life. On the high end of the scale, a 16-cylinder butane-powered Stirling engine makes a nice statement, but when it comes equipped with a propeller that looks ready for finger-chopping, some mods might be in order before bestowing the gift.

We don’t knock [JohnnyQ90] for buying a rotary Stirling engine from one of the usual sources rather than building, of course. With his micro Tesla turbine and various nitro-powered tools, he’s proven that he has the machining chops to scratch-build one of these engines. And it wasn’t just the digit dicing potential of the OEM engine that inspired him. There was a little too much slop in the bearings for his liking, so he machined a new bearing block and shaft extension. With a 3D-printed shroud, a small computer fan, and snappy brass nose cone, the engine started looking more like a small jet engine. And the addition of a pulley and a small generator gave the engine something interesting to do. What’s more, the increased airflow over the cold end of the engine boosted performance.

Need the basics of Stirling engines? Here’s a quick look at the 200-year history of these remarkable devices.

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Aluminum Foil Heatsink Keeps LEDs in Check

In your kitchen is very likely a roll of aluminum foil, like most people you probably use it to line pans or wrap food for baking. If you heard somebody used aluminum foil in the cooling of items, you could be forgiven for thinking they were referring to wrapping leftovers and tossing them in the refrigerator. But rather than preserving Mom’s famous meatloaf, [Michael Dunn] is using that classic kitchen staple to protect his LED strips.

Cheap LED strips are becoming extremely popular and have been popping up in more and more projects, but they have a pretty serious flaw: heat dissipation. Left on their own they can get hot enough to cook themselves, which is sort of a problem when you’re looking to replace as much of your home lighting with them like [Michael] is.

Heat was of particular concern as he was looking to retrofit a delicate shade with his beloved LED strips. Since he wanted a column of LEDs inside the unique shape of the shade, he reasoned that some kind of heat-conductive tubular structure could be used as both a mandrel to wrap the LEDs around and a way to dissipate heat. Like most of us, his first thought was copper pipe. But unfortunately the only copper pipe he had handy was of too small a diameter.

The tube of foil on the other hand was the perfect diameter, and while aluminum isn’t as good a conductor of heat as copper, it’s certainly no slouch either. Early tests weren’t that great when the tube was laying on the bench, but once it stood vertically convection got the air moving and cooled the LEDs down to where [Michael] was comfortable enough to put them inside the shade. Though he does have some lingering doubts about leaving the cardboard tube in such a toasty environment.

Going back through the archives, we’ve seen some absolutely fantastic projects utilizing LED strips in the past, some of which have come up with their own creative ways of beating the heat.

Fluid Simulations in the Kitchen Sink

In an age of ultra-powerful GPUs and cheap processors, computational techniques which were once only available to those with a government-sized R&D budgets are now available to the everyday hacker. An example of industry buzzword turned desktop software is the field of “computational fluid dynamics”, which put simply allow modeling how gasses or liquids will behave when moving through a cavity under specific conditions. Extensive utilization of these fluid simulations are often cited as one of breakthrough techniques which allowed SpaceX to develop their engine technology so rapidly when compared to Apollo and Shuttle era methods.

But just because anyone with a decent computer has access to the technology used for developing rocket engines doesn’t mean they have to use it. What if you prefer to do things the old-fashioned way? Or what if, let’s me honest, you just can’t figure out how to use software like Autodesk CFD and OpenFOAM? That’s exactly where [Desi Quintans] found himself when developing GUST, his cooling duct for i3-type 3D printers.

[Desi] tried to get the big name fluid simulation projects working with his prototype designs for an improved cooling duct, but had no end of trouble. Either the learning curve was too steep, or the simulation wasn’t accurate enough to give him any useful data. But remembering that air is itself a fluid, [Desi] took his simulation from the computer to the sink in order to better visualize what his cooling duct was doing to the airflow.

[Desi] printed up a box with a hole in the bottom that would connect up to his nozzles under test. As the volume of water in the box would be a constant between tests, he reasoned that this would allow him to evaluate the different nozzles at the same pressure. Sure enough, he found that the original nozzle design he was using caused chaotic water flow, which backed up what he was seeing in his experiments when mounted onto the printer.

After several iterations he was able to tame the flow of water by using internal baffles and fins, which when tested in water created something of a laminar flow effect. When he tried this version on the printer, he saw a clear improvement in part cooling, verifying that the behavior of the air and water was close enough for his purposes.

We’ve seen other projects that successfully used fluid simulations in their design before, but the quick and dirty test procedure [Desi] came up with certainly has its charms.

The Silence of the Fans

The good thing about using a server-grade machine as your desktop is having raw computing power at your fingertips. The downside is living next to a machine that sounds like a fleet of quadcopters taking off. Luckily, loud server fans can be replaced with quieter units if you know what you’re doing.

Servers are a breed apart from desktop-grade machines, and are designed around the fact that they’ll be installed in some kind of controlled environment. [Juan] made his Dell PowerEdge T710 tower server a better neighbor by probing the PWM signals to and from the stock Dell fans; he found that the motherboard is happy to just receive a fixed PWM signal that indicates the fans are running at top speed. Knowing this, [Juan] was able to spoof the feedback signal with an ATtiny85 and a single line of code. The noisy fans could then be swapped for desktop-grade fans; even running full-tilt, the new fans are quieter by far and still keep things cool inside.

But what to do with all those extra fans? Why not team them up with some lasers for a musical light show?

Make Mulled Wine With A Processor Heatsink!

Now, over the holiday season there seems to be a predilection towards making merry and bright. As many an engineer and otherwise are sure to note, fine alcohols will facilitate this process. One such warm holiday beverage is mulled wine; there are many traditions on how to make it, but a singular approach to preparing the beverage would be to re-purpose an old PC and a CPU liquid cooling unit into a mulled wine heating station.

Four years ago, [Adam] found himself staring at a pile of mostly obsolete PCs in his IT office and pondering how they could be better used. He selected one that used a power-hungry Pentium 4 — for its high heat output — strapped a liquid cooling block to the CPU and pumped it full of the holiday drink. It takes a few hours to heat three liters of wine up to an ideal 60 Celsius, but that’s just in time for lunch! The Christmastime aroma wafting through the office is nice too.

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