Simple engines that work with just temperature differences
No, this is not a goofy free energy thing like I saw at Gnomedex on Saturday (ugh, it still bugs me). This is real science, real physics, and doesn’t violate the laws of thermodynamics: heck it uses them!
This papercraft engine only needs to sit on a cup of hot coffee to drive its pistons. No, it’s not the precious caffeine that drives the motion, but the Stirling engine design, in which the difference between alternating hot and cold gas pressure is harnessed for power. Source: Cheaper Than Gas: Paper Stirling Engine Runs Off Hot Coffee – Gizmodo
Boing Boing has the best description of what’s going on–but essentially what you’re seeing is the expansion, contraction, and circulation of the air in the little area below the engine will drive it. This strengthens something I was probably boring people to death with later on Saturday evening, there are hundreds, probably thousands of creative ways we can take current technology and improve it or apply it in creative ways. That’s freakin’ open sourcing energy man!
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The problem, though, is that most distributed energy sources have a very low temperature differential. That translates to a very low thermodynamic efficiency. True, you can get some energy out of such systems, but they’re typically very small amounts (which makes the economics of building devices to extract this energy doubtful). I’m reminded that even a nuclear power plant has to run at a lower thermodynamic efficiency than a coal fired plant, due to temperature restrictions on the materials in the reactor itself (and, those things still run pretty hot).
Of course, if the machine extracting the energy from the low temperature differential is cheap enough, then it definitely makes sense to use it. But, that will almost certainly preclude most machined mechanical devices.
On the other hand, one of the items I’d like to find the time to study in a bit more detail (and, it doesn’t look like I’ll have that opportunity in the near future due to work schedules) is a Seebeck cell. These produce electricity directly from a temperature differential. While they don’t produce very much electricity, they are fairly cheap to manufacture.
One of the scenarios I’ve envisioned is a roof covered with water pipes (PVC? Copper? Aluminum?) as sort of a crude solar hot water system. Have this heated flow past a Seebeck cell (with the other side in contact with a heat sink, such as a well, or swimming pool), and you produce electric power. Since the Seebeck cell is relatively cheap, and the solar hot water system is relatively cheap, you end up with almost free electricity.
Anyway, it’s something to think about.
Dave