Jump to content
Science Forums


  • Content Count

  • Joined

  • Last visited

  • Days Won


Everything posted by TomBooth

  1. Something else Tesla mentioned in his 1900 article, that he viewed as a potential contradiction of the second law of thermodynamics, as then stated by Carnot and others as applied to heat engines: "I came to the conclusion that it was possible to construct a machine which would do the same. "As the first step toward this realization I conceived the following mechanism. Imagine a thermopile consisting of a number of bars of metal extending from the earth to the outer space beyond the atmosphere. The heat from below, conducted upward along these metal bars, would cool the earth or the sea
  2. "Believe me when I say, it's not entirely hypothetical since we have observed analogue radiation from analogue black holes." Who is "we" anyway? Just curious.
  3. You are talking about such things as this, presumably?: "Hawking radiation, stimulated by quantum vacuum fluctuations, emanating from an analogue black hole in an atomic Bose-Einstein condensate is reported (references)" source: https://www.sciencedirect.com/science/article/pii/S2405844019361572 I was joking about Bose-Einstein condensates in connection with heat engines and Carnot efficiency, about 7 years ago: https://www.physicsforums.com/threads/assumed-violation-of-physics-heat-vs-work.667129/post-4247322 My threads were locked, and I was banned from that forum. For what? questionin
  4. Congratulations if you do not consider Carnot efficiency a hard limit. I don't think I do either, but it is supposed to be the second law of thermodynamics. Or one of the legitimate ways of expressing it. As appears in the link posted earlier by Dubbelosix: "The second law of thermodynamics has a third form: "A Carnot engine operating between two given temperatures has the greatest possible efficiency of any heat engine operating between these two temperatures." So, according to that, assuming my Stirling engine is in the category of a heat engine 19.6 % is a hard limit, according to t
  5. I thought the epoxy piston seemed a little too loose in the cylinder, I also wanted to check the actual diameter of the original piston, so picked up some calipers, which I've needed, and will come in handy anyway. The epoxy piston is about 5 thousandths of an inch too small. I did lap it in with some fine grinding compound, but I didn't think that much. Apparently, over time, as it dried, the epoxy shrunk. I'm guessing. It was a really snug fit to begin with, but it had only dried overnight.
  6. I don't think there is anything wrong with sticking with 20%. That is what we have been working with. That is the theoretical "Carnot efficiency" of my model engines when running on hot water (approximately), and I don't have a problem with the fact that there are loses, so that all of the 20% of the theoretically "available heat" cannot be utilized, because of friction, conduction of heat through the engine body, etc. What I have an issue with, that I think needs ironing out, if possible, is the seemingly universal assumption that the remaining 80% of "heat" that cannot be used passes throu
  7. The thermometer seems fairly accurate, as far as I can tell, out of the box, with all four probes plugged in and just measuring ambient room temperature. There is some fluctuation, within 0.5 degrees F, possibly due to drafts, body heat? But close enough for the purpose at hand I think. It is factory calibrated, so I don't think I'll need to recalibrate or anything. The three photos were taken a few seconds apart. The probes are just dangling off the edge of the table in the open air
  8. https://youtu.be/LRtvGABJC2Q If nothing else, I find it very interesting that a virtual particle pair can be separated, so that 1/2 of the virtual particle pair becomes a real particle in our universe.. So I learned something new today, And, black holes are "evaporating". That's two things.
  9. Regarding the highlighted statement. This is ultimately true, of course, but, suppose the engine is coupled to an electric generator, connected to the grid, sending current across the country to power someone's electric range. The heat reappears in the stoves heating element to cook someones food, miles away. If the engine was running on ice, that heat is not really going to the "sink" (the ice), it is far far away from the sink. With a little Stirling engine running on a cup of ice, this is mostly also true of heat from friction. The engine is running in the open air above the ice and hea
  10. I'm going to go out and buy some 9 volt batteries for the thermometer. I'll be trying different experiments and different readings and probably making various modifications. Dubbelosix's posts, I tend to agree, seem to be self promotion of his paper, which contributes little to the discussion, as far as I can see, so far, other than the fact? that a black hole is a heat engine (I guess). But I know next to nothing on the subject (of black holes), so I'll reserve judgement. I very much value your input, so I do hope you will continue to contribute to the thread.
  11. I"m just trying to get across that the "Carnot efficiency" IS THE SAME THING as the temperature difference. Not, in this example, 18.9% of the temperature difference. Which would be 18.9% of 18.9% which is like 3.6% or something? But "Carnot efficiency" generally is supposed to mean that the 81% down to absolute zero goes through the engine to the sink, not 15.3% (18.9 - 3.6) or whatever. I know it is an unusual way of measuring on the Fahrenheit scale (but not that unusual), but I'm just trying to reverse obfuscate the fact that Carnot efficiency is really nothing more than the temperatu
  12. As the graph apparently does not render consistently on different computers/browsers, I took a screenshot: LOL But seriously, what temperature is a black hole anyway? Also, air is no longer air, but condenses into a liquid, or various liquids, at very low temperatures, so in a "Hot air engine" does efficiency below about 80K have any meaning?
  13. 459 + 212+1(for zero) = 672 (F measuring units) 672 X 0.189 = 127 F measuring units 672 X 0.811 = 545 F measuring units 545+127=672 So-called "Carnot efficiency" is exactly nothing more and nothing less than the temperature difference. In other words the "available heat" above equilibrium, or above the ambient baseline. Carnot efficiency is really just a measure of the amount of heat available for conversion to work. In this case 18.9% of the imagined total "caloric" (contained in the steam).
  14. Maybe redo that scale comparison a bit: 0 _ 10 _ 20 .... 300 _ 310 _ 320 _ 330 _ 340 _ 350 _ 360 _ 370 _ 380..(Kelvin) ^ ^ 302K 373K -459F 85F 212F <------81.1%-------><------------------------18.9%---------------------> <---------------------------------100%------------------------------------->
  15. I think your argument contains a logical inconsistency. You start out with "if one cup of water at 373 K cools down to ambient 300 K, it releases about 72,500 Joules of heat energy." <--- That is the 20% The 80% is all the remaining potential "heat" from 300K down to absolute zero that is supposed to be rejected to the sink. In a steam engine, I suppose this makes some sense because all that "latent heat" if it can be called that, is actually contained in the molecules of H2O that actually do pass through the engine. The unused "heat" or internal molecular kinetic energy IS carried alon
  16. Absolute zero on the fahrenheit scale is −459.67 °F not zero.
  17. Carnot considered heat a substance. an actual thing. a fluid. Add a cup of "caloric" to zero and you have one cup of caloric..... all the way up to ambient ->302K, call that 302 cups of fluid caloric. My heat engine can only utilize a mere 18.9% of that body of fluid, that volume of "Caloric" substance that is somehow burned up or destroyed by my engine like firewood. Carnot efficiency is nothing other than the temperature difference, or the actual heat available. But the remaining unused "Caloric" does not flow through the engine!
  18. As an example. Take boiling water at 212 Fahrenheit and apply it to an engine in a room at 85 Fahrenheit. That is a 127 degree temperature difference. To get Carnot efficiency that has to be changed to Kelvin on an absolute scale. Why? 212 = 373.15 85 = 302.594 373.15 - 302.594 = 70.556 70.556 / 373.15 = 0.189 X 100 = 18.9% That 18.9% "Carnot efficiency" on the absolute scale, is exactly the same thing as the 127 degree Fahrenheit temperature difference. 0 _ 10 _ 20 _ 30 _ 40 _ 50....... 300 _ 310 _ 320 _ 330 _ 340 _ 350 _ 360 _ 370 _ 380 _ 390 _ 400 _ 410 ...Kelvin
  19. You are welcome. I don't think I'm challenging ‘Heat flows spontaneously from a substance at a higher temperature to a substance at a lower temperature and does not flow spontaneously in the reverse direction’ at all though. An engine is not "spontaneous", it is a carefully crafted work of engineering. Even a refrigerator or heat pump operates on the same principle. I think Carnot efficiency is also generally true, most of the time, though I think it has been widely misinterpreted. I think at any "Carnot efficiency" is the theoretical maximum efficiency between any two temperatures, at wh
  20. With the epoxy piston, I wasn't really doing an experiment yet. My only real intention was to see if the piston worked at all. It didn't, until I gave it a little oil. Just feeling the epoxy piston between the fingers, it had that grabby feel, like plastic "cling wrap". very different than the silky slick feel of the graphite. Also, in testing the engine on hot water, I did not use any insulation whatsoever. When I switched to running it on ice, I wasn't using any insulation to start with, but I couldn't keep the engine on top of the cup of ice, it kept sliding off. Finally, I put the cup
  21. This is probably nothing, and not really worth reporting, but It seems rather strange to me. Over the years, several times in various forums on this topic, I posted this video, because it looks like, when the engine is picked up, that it is frozen to the ice. https://youtu.be/L6Jmdve1JK8 I speculated, that, because that engine comes as a kit, there are a lot of ways to put it together. I had one or these engines (before I destroyed it, experimenting with it) and the piston pushes onto the connecting rod and is retained by a retaining clip by pressure. There is a lot of leeway in terms
  22. BTW, I'm working on making that epoxy piston: Update: The epoxy has set, but I failed to get out all the air pockets. I may try to make it work anyway, while another one is setting. Epoxy may not work very well after all, some forum posts on the subject say it has problems similar to Teflon or other plastics. Too much drag.
  23. Not if it is efficiently dissipating the heat to the greater ambient surroundings. If the sink gets as hot as the source, the machine will not work. Hopefully with that thermometer you now have, you can take some T data and clear up some of these questions. Yes, though I don't have the thermometer yet. Mail order is agonizingly slow these days. I really appreciate your input. It is very encouraging. "If the sink gets as hot as the source, the machine will not work", That is absolutely true, as far as anyone who has ever worked with these engines, model builders and such, has ever known.
  24. Epoxy filler might be better, for practical reasons, it's easy to form or set in a mold, right inside the cylinder for a perfect fit. I also know model builders have had success using it to form pistons. Conductivity is 0.5 or so compared to 168 for graphite. That aluminum heat exchanger (top plate) is about 230 compared with graphite 168. Compared with the 5 inch diameter aluminum top of the engine, the 1/4 inch diameter piston, attached to a thin rod, is probably carrying a negligible amount of heat by comparison. But I think it's worth trying to eliminate anyway, so we shall see
  25. This discussion suggests Teflon may not work well, as it swells with frictional heat. https://www.homemodelenginemachinist.com/threads/teflon-as-a-piston.30440/ Glass, according to this forum, is almost as good as graphite: "A polished glass piston works almost as well as graphite." and glass has a very low heat conductivity. I have some glass test tubes that, well, probably won't fit. But a glass piston might be the way to go.
  • Create New...