The universal gas law states that when heated, things will expand in proportion to their change in absolute temperature (K vs. F or C). In other words, doubling the temp will double the absolute pressure. Note in there that I didn't mention the starting pressure. If you start with 10 PSIA, you could double it to 20. If you start with 2,000, then doubling will get you to 4,000 PSIA. That's quite a bit of work available in any cylinder. As you increase that starting pressure, you're only increasing the density by the same ratio so your efficiency soars because heat transfer is proportional to density.
If you were to include a phase change, then you could certainly get a higher specific output but since there's no free lunch, you can't get your efficiency to keep up with it. In short, it becomes too hard to transfer the heat in one or both directions. With a steam turbine, you certainly get a high output but efficiency tops out at ~30%. A Stirling, running at similar temps could double that but you would need 1,000 of currently available ones to do make the same power. It's this low specific power output that has plagued Stirling designers to date. It's also one problem I have solved. (You did ask what I do for a living.) The past tense was regarding the struggle to increase specific power output, not the engine's use.
A quick note on steam turbines... People think they use the phase change to get their specific power up but there's no phase change happening in them unless they condense in the cycle. I'm not aware of any in existence that don't simply waste all that energy. Heat pumps and vapor compression chillers, otoh, do use phase changes.
"Powerful" may have been the wrong word for the HHO torch. I meant that it is a very hot torch and that it has water vapor as its only exhaust. Sure, this temp can be scaled up with volume to make it powerful (as in to heat large masses) but I was referring to the opportunities of using it in confined human environments like indoors. That alone makes things like furnaces or indoor Stirling heaters much cheaper. Wouldn't you agree? In the powerful category, I've seen it cut steel much easier than an acetylene torch, leaving a cleaner cut with less tempering nearby.
Sure, it's not as high efficacy as a standard heat pump in producing 'cool' temps but for really cold stuff, it sure is. (Keep in mind that efficacy includes external energy while efficiency does not.) If you search YouTube for "The Stirling Cycle part 1 (Stirling Cryogenics)" and watch both parts, you'll see one cooling the air so much that it liquefies nitrogen right out of the air. As with any example of 'ectropy', this is not a case of getting something for nothing, but adding something external to a system to raise the energy value of a closed system.
The rail-gun wasn't the relevant piece in that suggestion. I was giving the only example I had off the top of my head for using plasma as a replacement for a solid, electromagnetic, conductive material. I thought that was your interest regarding plasma, so I suggested it.
My day job is an automation engineer (current project is boilers and chillers) and I'm also co-founder of a renewable start-up that's still in development. In the past, I've been "the serviceman" (from your sig) for many industries and the designer for a few, so my focus is on eliminating the 'primary function' that you cite. ;)
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