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.
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.
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.
[Ed] from Ed’s Systems, aka [Aussie50] took some time to demo his high pressure Frankenstein air compressor he stitched together from two refrigeration compressors. The two Danfoss SC15 compressors can produce upwards of 400psi and can run all day at the 300 psi range without overheating. The dual units may get up to pressure quickly considering the small accumulator “tank”, but high CFM isn’t the goal with this build. [Ed] uses the system to massacre some LCD panels with lead, ball bearings, and other high speed projectiles shot from a modified sandblasting gun. Just a bit of air at 400 psi is all you need for this terminator toy.
Don’t think the destruction is wasteful either; [Ed] strives to repair, rebuild, reuse, repurpose and a few other R’s before carefully separating and sorting all the bits for recycling. This modification included lots of salvaged hardware from older teardowns such as high pressure hoses, connectors, accumulator and pressure cutoff switches.
At first it seems strange to see something engineered for R22 refrigerant working so well compressing air. Morphing refrigeration systems into air compressor service is something [Ed] has been doing for a long time. In older videos, “fail and succeed”, [Ed] shows the ins and outs of building silent air compressors using higher capacity storage tanks. Being no stranger to all variations of domestic and commercial refrigeration systems, [Ed] keeps home built air compressors running safe and problem free for years.
Don’t think this is the only afterlife for old refrigeration compressors, we’ve seen them suck too. You’ll get a few more tidbits, and can watch [Ed’s] video overview of his home built compressor after the break.
As the summer heats up an air conditioning system is a necessity in many climates. [Grayson’s] system suffered some damage over the winter that caused it to vent its refrigerant, avoiding an explosive situation. Before he can chill out inside he’ll need to recharge it and he’s chosen to use propane in his cooling system. According to our friend Google this is not his original idea, but has been done many times before. [Grayson] makes the point that although propane is flammable it’s not necessarily any more dangerous in a fire than Chlorodiflouromethane, or R22, which is the nasty little gas that fled his system for its new home in the upper atmosphere.
The video above includes a brief explanation of recharging the system and the tools needed. We’d need to mill this over for quite a while before working up the gumption to give it a try. For now we’ll stick to [Grayson’s] more pedestrian hacks like making some servo motors sing or easing our yard work woes.
Producing ice without electricity just got a lot easier thanks to these engineering students from San Jose State University. Their system uses solar heat to facilitate evaporation of a coolant. When the sun goes down and the coolant turns back to liquid, its temperature drops drastically due to extreme pressure differences. The unit can produce 14 pounds of ice per day with zero carbon footprint. It has no moving parts and an entirely sealed system, this should mean that the only maintenance necessary would be keeping the unit clean. [via DVICE]