Just a quick fun thing today, a view of my new Stirling engine:
This is a just a simple little toy one that I found on Amazon for $40, but if you look at the related videos on YouTube, you’ll see that many people have built much more sophisticated engines, including many that are capable of useful work.
Stirling engines run on temperature differentials. If there is a source of heat (in this case my wireless router it’s resting atop), then you have warmer air on one side of the driving diaphragm and cooler air on the other. It works equally well whether its on top of a cup of coffee or a cup of ice water. Give it a spin to get the diaphragm and attached piston moving, and thermodynamics takes over from there. The expansion and contraction of the warmer and cooler air, coupled with the moving diaphragm, does all the work.
These engines come in a variety of different configurations and use various working fluids (this one uses air). They can run on pretty much any heat source. Many commercial products have used them, though their adoption has never been widespread. Issues like size, weight, cost, torque, and other factors have limited their use. Interestingly for space geeks, Stirling radioisotope generators using the same plutonium heat sources as the RTGs currently powering Mars Curiosity are several times more efficient. Why aren’t they on Mars? Basically, weight, complexity, and reliability. For such applications, moving parts are always less desirable than the solid state RTGs currently in use.
Before the Segway was made public, rampant speculation suggested it was to be powered by a Stirling engine. It wasn’t, so we don’t know how this would have worked. It would have needed to burn some kind of fuel and would have had major trouble generating enough torque. If the Stirling component was used to generate electricity to drive a high-torque electric motor, you would have gotten only a tiny amount of use for each unit of time the generator ran.
For now, I’m enjoying my little toy. Some graphite will quiet down the friendly little noise it makes, but I might let the noise stay. It’s kind of like a comfortingly tick-tocking grandfather clock in the office.