studiot Posted February 4, 2023 Posted February 4, 2023 (edited) 38 minutes ago, Tom Booth said: You are apparently not very well read on the subject of thermodynamics is about the only conclusion I'm able to draw from your above attestation. Thank you for that childish personal remark. Although you know next to nothing about me, you have managed to teach me something. Here it is. I thought I would follow up on your Google remark so I typed in "xxyyzz" and should not have been suprised to find that Google will nearly always return some sort of result - just like a working calculator will always display something, even if it is GIGO. https://www.google.co.uk/search?hl=en-GB&gbv=2&q=xxyyzz&oq=xxyyzz&aqs=heirloom-srp..0l5 Apart from the music hots there appears to be a maths course on the subject and it apparantly has applications in Rheumatology. Sleep Well. Edited February 4, 2023 by studiot spelling correction
Tom Booth Posted February 4, 2023 Author Posted February 4, 2023 (edited) 5 hours ago, swansont said: Yes. So why do you keep bringing it up? Nobody else has used caloric in their explanations. The thing is, while caloric was abandoned, the thermodynamic principles it attempted to explain are still there. Heat is transferred. Some of it can be converted to work. It just isn’t because of caloric moving about. Yes, I just explained that. Physicists do idealized systems all the time when discussing theory. Why? There is no real engine that follows the Carnot cycle. You just agreed to that. Fill up with heat? I would think someone railing against caloric theory would avoid treating heat as a substance. Skip, irrelevant semantic knit picking IMO. 41 minutes ago, studiot said: Thank you for that childish personal remark. Although you know next to nothing about me, you have managed to teach me something. Here it is. I thought I would follow up on your Google remark so I typed in "zxxyzz" and should not have been suprised to find that Google will nearly always return some sort of result - just like a working calculator will always display something, even if it is GIGO. https://www.google.co.uk/search?hl=en-GB&gbv=2&q=xxyyzz&oq=xxyyzz&aqs=heirloom-srp..0l5 Apart from the music hots there appears to be a maths course on the subject and it apparantly has applications in Rheumatology. Sleep Well. A silly argument. "Carnot efficiency limit" is a phrase in common usage in learned papers (Science direct etc.) Not "garbage". I did not invent the term, the phrase or the application. Unlike you I actually read many of the papers that come up with that search. You consider that a "personal" attack or something, well sorry but I told you you are better off if I just ignore such nonsense and move on, but then you have a meltdown and want to go crying to mommy and report me for ignoring you and threaten to have the thread shut down. You asked for it. You got my honest appraisal. Your protestations about my usage of a common phrase in thermodynamic literature speaks to your ignorance of the subject not my misuse of common terminology Time to get some work done. Sorry about additional unanswered posts (from anyone) I haven't read yet, I'll get to them later whenever I find some time. 4 hours ago, swansont said: I recall trying to run my stirling engine on a hot day. I put it on a mug of hot water and it would barely run - too much friction. When I put ice cubes on the top plate, it ran pretty well. Since the source of heat was the same, the only way this could be the case is if I was converting more heat to work - the efficiency increased. Before I go to work, I just want to say that this is a puzzling phenomenon if heat is not actually passing through to the ice, why does the ice cause the engine to run observably much better. It certainly appears that the increased ∆T results in increased efficiency. The conventional, or generally accepted explanation is that the ice increases the temperature "gradient" or slope, allowing the heat to "run downhill" to the ice faster increasing the "flow". Seems reasonable. But after years of observation, taking measurements, doing experiments etc. I've arrived at a different explanation. I don't have time now, but I am very anxious to get back to and address this particular point of interest. Unfortunately, I also have other matters to attend to at the moment. Edited February 4, 2023 by Tom Booth
swansont Posted February 4, 2023 Posted February 4, 2023 2 hours ago, Tom Booth said: Before I go to work, I just want to say that this is a puzzling phenomenon if heat is not actually passing through to the ice, why does the ice cause the engine to run observably much better. Who said heat is not passing through to the ice? Certainly not me. 2 hours ago, Tom Booth said: It certainly appears that the increased ∆T results in increased efficiency. That’s the only variable that changed. And work increased from zero to some nonzero value, so there is no arguing about the increase in efficiency 2 hours ago, Tom Booth said: The conventional, or generally accepted explanation is that the ice increases the temperature "gradient" or slope, allowing the heat to "run downhill" to the ice faster increasing the "flow". Seems reasonable. There is more heat flow. Fourier’s law of conduction, Stefan-Boltzmann law for radiation and the equation for convective heat transfer all depend on temperature differences. Though it’s interesting you continue to describe this in terms of fluid behavior.
Ghideon Posted February 4, 2023 Posted February 4, 2023 (edited) 9 hours ago, studiot said: the Carnot formula is not hogwash if used for the purpose for which it was intended. @Tom Booth here is an example where the scientists probe at the limits of applicability: Quote The Carnot cycle imposes a fundamental upper limit to the efficiency of a macroscopic motor operating between two thermal baths. However, this bound needs to be reinterpreted at microscopic scales. ... Quote an experimental realization of a Carnot engine with a single optically trapped Brownian particle as the working substance Source: https://www.nature.com/articles/nphys3518.pdf (I do not wish to take the discussion off topic, we discuss the case of Carnot limit for macroscopic engines. Just wanted to share in case there is any interest in papers discussing limits of applicability in the context of Studiots comment.) Edited February 4, 2023 by Ghideon 1
sethoflagos Posted February 5, 2023 Posted February 5, 2023 10 hours ago, joigus said: Perhaps "upper bound" are the words to look for here? It definitely sets a theoretical upper bound in terms of energy obtained to energy invested ratio ... I personally would prefer some more neutral phrase like 'Carnot coefficient'. Or just 'eta'. Remember that it is a standin for (QH - QC) / QH = W / QH for an isentropic process, and its inverse is the maximum theoretical amount of heat that can be transferred to a hot reservoir by a heat pump with a work input of W. Clearly, this inverse can be far greater than 1 for low temperature differentials and tends to be called the Coefficient of Performance (COP). Another neutral phrase. It's absolutely clear that COP is not an 'efficiency' in any normal scientific sense, but how should we express the actual real world efficiency of these machines? For a heat engine I think it ends up being actual work output divided by the closed path integral of TdS. A simplification (!) of this may be: Isentropic efficiency ~ Wact / (- THdSH - TCdSC ) evaluated for the reservoirs (SH & SC are numerically equal for the reversible case so conveniently cancel out). More than a bit of a challenge to measure accurately, though not so difficult to estimate fairly closely I think. 1
joigus Posted February 5, 2023 Posted February 5, 2023 1 hour ago, sethoflagos said: I personally would prefer some more neutral phrase like 'Carnot coefficient'. Or just 'eta'. Remember that it is a standin for (QH - QC) / QH = W / QH for an isentropic process, and its inverse is the maximum theoretical amount of heat that can be transferred to a hot reservoir by a heat pump with a work input of W. Clearly, this inverse can be far greater than 1 for low temperature differentials and tends to be called the Coefficient of Performance (COP). Another neutral phrase. It's absolutely clear that COP is not an 'efficiency' in any normal scientific sense, but how should we express the actual real world efficiency of these machines? For a heat engine I think it ends up being actual work output divided by the closed path integral of TdS. A simplification (!) of this may be: Isentropic efficiency ~ Wact / (- THdSH - TCdSC ) evaluated for the reservoirs (SH & SC are numerically equal for the reversible case so conveniently cancel out). More than a bit of a challenge to measure accurately, though not so difficult to estimate fairly closely I think. Yes. Thank you. I remember that definitions of efficiency also depend on whether it's an engine, or a refrigerator, --inverse Carnot cycle-- or a heat pump. In the end, it's a definition based on our particular interest.
Tom Booth Posted February 5, 2023 Author Posted February 5, 2023 On 2/3/2023 at 5:17 PM, sethoflagos said: Compare with Wikipedia Same thing. I didn't mention the Carnot cycle in that post. Given the nature of the remainder of your post, let's close with a proverb. Again, I apologize for jumping to conclusions in that I assumed you were talking about the "Ideal Carnot Cycle" I've taken some time to revisit this post and review what you wrote compared with the Wikipedia article. Unfortunately, IMO, the description in the Wikipedia article is also wrong as far as having any relevance to how a real Stirling engine operates. Is it an accurate description of an "Ideal" Stirling engine? Maybe, I don't really know. Out of who's imagination was this "Ideal" concocted? I did some perusing through the original patents of Robert Stirling. Maybe I missed something but I didn't find anything I could put my finger on that related to this "Ideal" mode of operation. What is generally agreed upon by "experts" I've known on the Stirling engine forums for years, some passed on now, is that so called "Isothermal" processes in a REAL engine are not possible. The portion of the Wiki article cited also does not include any description of the action of the displacer, normally advanced 90° ahead of the piston (in a real engine with a crankshaft) etc. I have no particular interest in debating the issue at length to prove anybody right or wrong, I could really care less. I'm interested in Real engines I can build not imaginary theoretical "ideal" engines based on impossible cycles arising from some pipe dream. Anyway taking one leg of the cycle (your description): Quote For an ideal Stirling engine maximum compression occurs at the end of the cooling cycle with the working fluid at cold reservoir temperature TC. This is simply false. Well, is it an accurate description of an "Ideal" Stirling Engine, backed up with references? Probably, I'll grant you that, but it has no correspondence with how a REAL Stirling engine operates. In a real Stirling engine, during compression, which is really neither isothermal nor adiabatic but something else that I don't think any thermodynamic terminology could describe, but let's just go with adiabatic for the moment. The gas, during "compression" is really contracting. Well what actually causes Air to expand and contract? I mean actually? Heat is added to a gas and it expands, or if confined, tries to, creating pressure. We know what it does, it expands, but how? Do the electrons orbiting the nucleus move to a higher orbit? Does anyone actually know? Any quantum physicists in here? Let's just say that for whatever reason the gas needs more room. But pushing the piston out the energy previously added is used up 100% so the gas then drops back down to the original lower energy state. It no longer requires the extra room. The piston gets sucked back down the cylinder (or if anyone prefers, atmospheric pressure pushes the piston back.) This collapse back to a lower energy state looks like isothermal compression with "heat rejection" but it isn't. Remember the graph, at BDC, full expansion the gas experiences a sharp drop in temperature. So a cold gas is contracting while continuing to collapse back to a lower energy state. This may look isothermal "with heat rejection" but that is not possible. A cold contracting gas cannot "reject heat" to any adjoining hotter body. It's colder than both the hot and the cold heat exchangers so how can it transfer any heat to either? When "compression" (contraction) is about half way completed the displacer shifts the gas over into contact with the hot heat input heat exchanger. Compression continues as more heat is being introduced simultaneously. So does this really make sense: "For an ideal Stirling engine maximum compression occurs at the end of the cooling cycle with the working fluid at cold reservoir temperature TC." No, it is actually closer to the temperature of the hot "reservoir" due to the displacer shifting the working gas over into contact with the hot heat input plate. With the added heat of compression. Remember the ACTUAL READINGS? the temperature exceeds the temperature of the hot heat exchanger at full compression. This, in actuality resembles an Ideal Carnot cycle more closely than this so-called "ideal Stirling cycle" in the Wiki article dreamed up by whom, I have no real idea. You can take it or leave it, but this is very hard won information distilled from years of careful observation. All this "ideal" nonsense, in my mind, goes straight in the "circular file". As far as I'm concerned, any talk about "Ideal" anything in here is "off topic". We are looking at REAL engines, actual experiments, real measurements. Not that I'm going to report anybody or anything of that sort. The question is, does this Carnot fantasy "efficiency limit" or "upper bound", whatever you want to call it actually mean anything at all in the real world? Does an engine that utilized just 21% of the heat supplied to it, instead of the 20% predicted by the "Carnot coefficient" 😆 Or that "rejects" just 79% of the heat supplied REALLY overturning some physical "LAW" of the universe ? That's a pretty big number (80%) Seems like a lot of heat that is just "unavailable" for no good reason whatsoever. I think I'd like to check on that. Do some actual tests/experiments. That the 80% on the absolute scale below TC is unavailable I can live with but 80% of the heat I actually put into the engine? No Way. "Extraordinary claims require extraordinary proof" and 80% of the heat supplied being whisked away without explanation, for no good reason seems like an extraordinary claims to me, especially when such a supposed large proportion of "waste heat" is apparently undetectable. Are we supposed to just swallow all this 1800's archaic steam engine theorizing without actual proof? I mean is this really "accepted science"? I still haven't seen any historical account of who originally verified any of this experimentally. So, maybe it works for steam turbines? I don't know. People actually use it? I doubt it. But even if they do, how does that prove anything conclusively? 19 hours ago, joigus said: Perhaps "upper bound" are the words to look for here? It definitely sets a theoretical upper bound in terms of energy obtained to energy invested ratio, having nothing to do with time --how long the machine is running, as you pointed out before--, or with whether the machine will eventually stop or keeps going forever --as Swansont pointed out. Because the Carnot cycle is defined in terms of state variables --due to all intermediate states beeing equilibrium ones-- and because an ideal gas has no internal mechanism to hide energy other that its pressure, volume, and temperature, no matter how many contraptions or intermediate complications we introduce, this upper bound cannot be overcome. The dynamics of this discussion does remind me of that of a Carnot engine, with a reservoir full of an inexhaustible resource, and the corresponding sink that can take any amount of such resource without in any way changing its state. Quote or with whether the machine will eventually stop or keeps going forever --as Swansont pointed out. Did he? I must have missed that. Quote and because an ideal gas has no internal mechanism to hide energy other than its pressure, volume, and temperature I took the liberty to correct a minor typo ("that" to than, if that's not ok let me know) That is a good point I think, but not for the reasons you follow up that with. Quote this upper bound cannot be overcome. How does that follow? Besides, a gas DOES hide it's "internal energy" I think, if that's the right term for it. I mean it has been heated up from ABSOLUTE ZERO or thereabouts. Right?
Tom Booth Posted February 5, 2023 Author Posted February 5, 2023 18 hours ago, studiot said: Of course it does. I am not saying that invalid means useless (see hogwash). But my development is to show that it forms an upper bound. Lots of posters here have offered various parts of the thinking development of this, including yourself. Since Tom rejects the whole caboodle, I am trying to offer these parts in a logical step by step order. Sadly everyone but Tom seems to understand that. And if he is genuinely doing all that work over decades then it is a shame for him it will ultimately be to no avail. I have not yet got into state variables, reversibility or the quasi-static concept and their implications for the discussion. Skip
Tom Booth Posted February 5, 2023 Author Posted February 5, 2023 (edited) 19 hours ago, swansont said: Yes. So why do you keep bringing it up? Nobody else has used caloric in their explanations. The thing is, while caloric was abandoned, the thermodynamic principles it attempted to explain are still there. Heat is transferred. Some of it can be converted to work. It just isn’t because of caloric moving about. Yes, I just explained that. Physicists do idealized systems all the time when discussing theory. Why? There is no real engine that follows the Carnot cycle. You just agreed to that. Fill up with heat? I would think someone railing against caloric theory would avoid treating heat as a substance. The word "flow" (aside from other thermodynamics terms we could talk about) among other possible meanings/applications can refer to the flow of water down a hillside in a stream or river, or a flow of traffic on the highway. I have no issue with the word itself just how it is associated with heat and the implications on a subliminal level of all this archaic terminology: flow, reservoir, etc. Directly relating the "flow" of heat through a heat engine to the flow of water over a mill wheel and so forth. A flow of water from a height is caused by gravity. The flow of cars on the highway, or people down a sidewalk or corridor is self motivated. Maybe "self motivated" is not the best way of putting it, but cars are not pulled along by an outside "gravitational" force, they have their own motive force or kinetic energy or motion, they are self propelled. Why is that an important distinction to make? Well, gravity holds water down to earth in a "reservoir". And gravity causes water to flow in one general direction: down. Gas particles sealed inside a Stirling engine aren't going anywhere. If they are zipping around or vibrating or expanding and contracting it is all due to the energy they are carrying around with them, not something somewhere else compelling them to "flow" anywhere. So there is a general dispersal of kinetic energy in a quantity of gas from the more energetic particles to the less energetic particles, setting aside infrared waves or other possible quantum phenomenon for the moment. In his unpublished papers Carnot wrote; paraphrasing, that if heat is actually motion, that would explain everything, the action of Joules calorimeter etc. But if that is rely the case, to quote (in translation): Quote But it would be difficult to explain why, in the development of motive power by heat a cold body is necessary; why in consuming the best of a warm body, motion cannot be produced. Difficult indeed. If we have a gas enclosed in a sealed container with one piston and cylinder, all at thermal equilibrium, then introduce some additional heat into the gas, there will be billions upon billions of collisions per second, some of which contact the piston causing it to move in the cylinder. The gas has no need for a "cold reservoir" outside this container anywhere to "flow" to like water down a hill to a lower "reservoir" I keep repeating the language so as to bring it into awareness and point out the influence it has and it's origin. Edited February 5, 2023 by Tom Booth
Ghideon Posted February 5, 2023 Posted February 5, 2023 2 hours ago, Tom Booth said: Or that "rejects" just 79% of the heat supplied REALLY overturning some physical "LAW" of the universe ? Based on personal experience from my garage; the second law of thermodynamics can be compared to the contents of a spilled assortment box. The contents of the box tend to end up in a disorganized mess. The probability of the contents of the box becoming sorted is low. (Side note: Here is a video describing the statistical aspect of thermodynamics; the description does not rely upon archaic steam engines: https://www.khanacademy.org/test-prep/mcat/chemical-processes/thermodynamics-mcat/v/second-law-of-thermodynamics)
sethoflagos Posted February 5, 2023 Posted February 5, 2023 3 hours ago, Tom Booth said: Again, I apologize for jumping to conclusions in that I assumed you were talking about the "Ideal Carnot Cycle" I've taken some time to revisit this post and review what you wrote compared with the Wikipedia article. Unfortunately, IMO, the description in the Wikipedia article is also wrong as far as having any relevance to how a real Stirling engine operates. Is it an accurate description of an "Ideal" Stirling engine? Maybe, I don't really know. Out of who's imagination was this "Ideal" concocted? I did some perusing through the original patents of Robert Stirling. Maybe I missed something but I didn't find anything I could put my finger on that related to this "Ideal" mode of operation. What is generally agreed upon by "experts" I've known on the Stirling engine forums for years, some passed on now, is that so called "Isothermal" processes in a REAL engine are not possible. The portion of the Wiki article cited also does not include any description of the action of the displacer, normally advanced 90° ahead of the piston (in a real engine with a crankshaft) etc. I have no particular interest in debating the issue at length to prove anybody right or wrong, I could really care less. I'm interested in Real engines I can build not imaginary theoretical "ideal" engines based on impossible cycles arising from some pipe dream. Anyway taking one leg of the cycle (your description): This is simply false. Well, is it an accurate description of an "Ideal" Stirling Engine, backed up with references? Probably, I'll grant you that, but it has no correspondence with how a REAL Stirling engine operates. In a real Stirling engine, during compression, which is really neither isothermal nor adiabatic but something else that I don't think any thermodynamic terminology could describe, but let's just go with adiabatic for the moment. The gas, during "compression" is really contracting. Well what actually causes Air to expand and contract? I mean actually? Heat is added to a gas and it expands, or if confined, tries to, creating pressure. We know what it does, it expands, but how? Do the electrons orbiting the nucleus move to a higher orbit? Does anyone actually know? Any quantum physicists in here? Let's just say that for whatever reason the gas needs more room. But pushing the piston out the energy previously added is used up 100% so the gas then drops back down to the original lower energy state. It no longer requires the extra room. The piston gets sucked back down the cylinder (or if anyone prefers, atmospheric pressure pushes the piston back.) This collapse back to a lower energy state looks like isothermal compression with "heat rejection" but it isn't. Remember the graph, at BDC, full expansion the gas experiences a sharp drop in temperature. So a cold gas is contracting while continuing to collapse back to a lower energy state. This may look isothermal "with heat rejection" but that is not possible. A cold contracting gas cannot "reject heat" to any adjoining hotter body. It's colder than both the hot and the cold heat exchangers so how can it transfer any heat to either? When "compression" (contraction) is about half way completed the displacer shifts the gas over into contact with the hot heat input heat exchanger. Compression continues as more heat is being introduced simultaneously. So does this really make sense: "For an ideal Stirling engine maximum compression occurs at the end of the cooling cycle with the working fluid at cold reservoir temperature TC." No, it is actually closer to the temperature of the hot "reservoir" due to the displacer shifting the working gas over into contact with the hot heat input plate. With the added heat of compression. Remember the ACTUAL READINGS? the temperature exceeds the temperature of the hot heat exchanger at full compression. This, in actuality resembles an Ideal Carnot cycle more closely than this so-called "ideal Stirling cycle" in the Wiki article dreamed up by whom, I have no real idea. You can take it or leave it, but this is very hard won information distilled from years of careful observation. All this "ideal" nonsense, in my mind, goes straight in the "circular file". As far as I'm concerned, any talk about "Ideal" anything in here is "off topic". We are looking at REAL engines, actual experiments, real measurements. Not that I'm going to report anybody or anything of that sort. The question is, does this Carnot fantasy "efficiency limit" or "upper bound", whatever you want to call it actually mean anything at all in the real world? Does an engine that utilized just 21% of the heat supplied to it, instead of the 20% predicted by the "Carnot coefficient" 😆 Or that "rejects" just 79% of the heat supplied REALLY overturning some physical "LAW" of the universe ? That's a pretty big number (80%) Seems like a lot of heat that is just "unavailable" for no good reason whatsoever. I think I'd like to check on that. Do some actual tests/experiments. That the 80% on the absolute scale below TC is unavailable I can live with but 80% of the heat I actually put into the engine? No Way. "Extraordinary claims require extraordinary proof" and 80% of the heat supplied being whisked away without explanation, for no good reason seems like an extraordinary claims to me, especially when such a supposed large proportion of "waste heat" is apparently undetectable. Are we supposed to just swallow all this 1800's archaic steam engine theorizing without actual proof? I mean is this really "accepted science"? I still haven't seen any historical account of who originally verified any of this experimentally. So, maybe it works for steam turbines? I don't know. People actually use it? I doubt it. But even if they do, how does that prove anything conclusively? Did he? I must have missed that. I took the liberty to correct a minor typo ("that" to than, if that's not ok let me know) That is a good point I think, but not for the reasons you follow up that with. How does that follow? Besides, a gas DOES hide it's "internal energy" I think, if that's the right term for it. I mean it has been heated up from ABSOLUTE ZERO or thereabouts. Right? TLDR. This stuff is beyond you. Flick the switch on your tin foil hat from transmit to receive. You might learn something. 2
exchemist Posted February 5, 2023 Posted February 5, 2023 3 hours ago, Tom Booth said: Bla, bla, bla.... ....[snip]... Well what actually causes Air to expand and contract? I mean actually? Heat is added to a gas and it expands, or if confined, tries to, creating pressure. We know what it does, it expands, but how? Do the electrons orbiting the nucleus move to a higher orbit? Does anyone actually know? Any quantum physicists in here? Let's just say that for whatever reason the gas needs more room. .....[snip]..... The question is, does this Carnot fantasy "efficiency limit" or "upper bound", whatever you want to call it actually mean anything at all in the real world? Does an engine that utilized just 21% of the heat supplied to it, instead of the 20% predicted by the "Carnot coefficient" 😆 Or that "rejects" just 79% of the heat supplied REALLY overturning some physical "LAW" of the universe ? That's a pretty big number (80%) Seems like a lot of heat that is just "unavailable" for no good reason whatsoever. Yes of course, we have known exactly why raising the temperature makes a gas (at constant pressure) expand, or alternatively why (at constant volume) its pressure goes up, for almost 200 years. Look up the kinetic theory of gases: https://en.wikipedia.org/wiki/Kinetic_theory_of_gases . And yes, an engine rejecting less waste heat than the prediction of the Carnot efficiency limit would violate a physical "law" of the universe. This law arises from the statistics of large numbers of molecules, which again has been well understood for about 150 years, Maxwell and Boltzmann being the founding fathers, but subsequently further built on with the advent of quantum theory. Look up statistical thermodynamics (or statistical mechanics, of which statistical thermodynamics is a subset). To think that by tinkering in your garage you are going to overturn 200 years of well established physics, which you have not even bothered to find out about, is solipsistic and idiotic. (I blame the modern popular disease of suspicion of expertise and deference to stupidity - as reflected in modern US politics for instance. 😁)
studiot Posted February 5, 2023 Posted February 5, 2023 1 hour ago, Tom Booth said: In his unpublished papers Carnot wrote; paraphrasing, that if heat is actually motion, that would explain everything, the action of Joules calorimeter etc. But if that is rely the case, to quote (in translation): Quote But it would be difficult to explain why, in the development of motive power by heat a cold body is necessary; why in consuming the best of a warm body, motion cannot be produced. Difficult indeed. Yes difficult indeed. Which is why it is such a shame that you threw your toys out of the pram at a critcal moment when I had just posted the diagram showing how Carnot overcame that difficulty. Again a pity that you did not complete the translation of his works, putting that hugely insightful statement into its proper context.
joigus Posted February 5, 2023 Posted February 5, 2023 4 hours ago, Tom Booth said: Did he? I must have missed that. Quote Here: On 2/1/2023 at 11:53 PM, swansont said: Mechanical devices getting stuck violate NO principles of known science. And then --not 'than', nor 'that' --, 4 hours ago, Tom Booth said: How does that follow? Because there's nowhere else for any form of energy to go but the state variables P, V, T. And, interestingly enough an ideal gas provides you with a better gauge for entropy than any other system has. It's, in a manner of speaking, a natural dipstik for entropy. It provides you with the zero and with the slope entropy/temperature. The exception to this is, as we well know, 1) Phase transitions: As the temperature goes down, the ideal gas (P, V, T) temperature must be replaced by another relation that contemplates the finite size of the molecules and their mutual short-range repulsive/long-range attractive force --Van Der Walls gas. And, 2) Quantum mechanics has to replace classical Newtonian mechanics when we get close to absolute zero of temperature. But point 2) should be of no concern to you. Point 1) should.
exchemist Posted February 5, 2023 Posted February 5, 2023 2 hours ago, Tom Booth said: The word "flow" (aside from other thermodynamics terms we could talk about) among other possible meanings/applications can refer to the flow of water down a hillside in a stream or river, or a flow of traffic on the highway. I have no issue with the word itself just how it is associated with heat and the implications on a subliminal level of all this archaic terminology: flow, reservoir, etc. Directly relating the "flow" of heat through a heat engine to the flow of water over a mill wheel and so forth. A flow of water from a height is caused by gravity. The flow of cars on the highway, or people down a sidewalk or corridor is self motivated. Maybe "self motivated" is not the best way of putting it, but cars are not pulled along by an outside "gravitational" force, they have their own motive force or kinetic energy or motion, they are self propelled. Why is that an important distinction to make? Well, gravity holds water down to earth in a "reservoir". And gravity causes water to flow in one general direction: down. Gas particles sealed inside a Stirling engine aren't going anywhere. If they are zipping around or vibrating or expanding and contracting it is all due to the energy they are carrying around with them, not something somewhere else compelling them to "flow" anywhere. So there is a general dispersal of kinetic energy in a quantity of gas from the more energetic particles to the less energetic particles, setting aside infrared waves or other possible quantum phenomenon for the moment. In his unpublished papers Carnot wrote; paraphrasing, that if heat is actually motion, that would explain everything, the action of Joules calorimeter etc. But if that is rely the case, to quote (in translation): Difficult indeed. If we have a gas enclosed in a sealed container with one piston and cylinder, all at thermal equilibrium, then introduce some additional heat into the gas, there will be billions upon billions of collisions per second, some of which contact the piston causing it to move in the cylinder. The gas has no need for a "cold reservoir" outside this container anywhere to "flow" to like water down a hill to a lower "reservoir" I keep repeating the language so as to bring it into awareness and point out the influence it has and it's origin. This passage of Carnot's that you are paraphrasing is very interesting. Can you provide a link to it so I can read what else he says?
Tom Booth Posted February 5, 2023 Author Posted February 5, 2023 (edited) 20 hours ago, swansont said: I recall trying to run my stirling engine on a hot day. I put it on a mug of hot water and it would barely run - too much friction. When I put ice cubes on the top plate, it ran pretty well. Since the source of heat was the same, the only way this could be the case is if I was converting more heat to work - the efficiency increased. Ah, finally worked my way down to the question I was really looking forward to addressing. Same question Carnot asked in his unpublished notes. If heat is just another form of kinetic energy that can be directly transfered, why should cold be necessary? Why does lowering the temperature of the cold side improve performance of the engine? Why do we need a temperature difference at all? My tentative theory stated somewhat figuratively or by analogy would be that making the working fluid colder gives it more room to expand. The container volume is fixed, so at any given temperature expansion is limited to the distance the piston can travel, restrained by being connected to a crankshaft. (Excluding "free piston" type engines from the discussion for the moment). Cooling the gas causes it to contract more, increasing it's potential to expand. Does that require an outside source of cooling? Certainly, initially. But once a new baseline is established and the engine can start producing more rotational force, more work output, then the cold side only provides a kind of stability or thermal buffer of a sort, but the engine no longer transfers heat to it, and it runs the same as before the ice was added, transforming all the heat supplied into work again. This is why load balancing is important. The gas expansion is limited to the distance the piston is designed to travel, once that limit is reached, if too much heat was supplied that cannot be converted to work output, the bottom dead center is reached too early so instead of having room to convert all the heat into work output, the engine WILL certainly begin to build up excess heat In other words the extra cold being present does indeed help the engine run better, but the ice placed on top doesn't constitute a lower temperature sink for the heat to "flow into faster" it doesn't "increase the gradient" or "downhill slope". The cold or a temperature difference generally just provides a starting point for expansion, and adding ice just provides more leeway for expansion and contraction generally, it doesn't mean that the ice is continually taking in more of the heat, or taking away the heat faster. I sometimes use the analogy of a trampoline. If you have a low ceiling you can't bounce very high. But also if the trampoline is not raised high enough off the floor, you can't bounce very much either. There will not be enough room under the trampoline to bounce without hitting the floor. The throw of the piston creates a ceiling on how far the piston can travel out and so also how much the gas can expand, and the cold is the floor which has to be low enough to provide room to bounce also. What keeps the engine going is "adiabatic bounce". An oscillation, that just needs enough heat to match the work output and loses to friction and other parasitic heat loses, but NOT losses to the "cold reservoir". If you notice, I always put these archaic terms in Air Quotes to basically shorthand saying so-called (in quotes) "reservoir" etc. Possibly some new terminology IS in order, so rather than in quotes so-called "cold reservoir" we could just call it floor or something. I've been calling it the ambient baseline but that is not accurate when ice is added and the floor or starting point for expansion is lowered below ambient. Thanks for asking a most pertinent question. Edited February 5, 2023 by Tom Booth
joigus Posted February 5, 2023 Posted February 5, 2023 I have to make some qualitications to what I said about ideal gases not having internal degrees of freedom --energy has nowhere to go... That's not true. They have. But only complication is Cv, Cp (specific heat) which just sets the scale for the relation entropy/temperature I was talking about. No time now. Sorry
swansont Posted February 5, 2023 Posted February 5, 2023 2 hours ago, Tom Booth said: Ah, finally worked my way down to the question I was really looking forward to addressing. Same question Carnot asked in his unpublished notes. If heat is just another form of kinetic energy that can be directly transfered, why should cold be necessary? Why does lowering the temperature of the cold side improve performance of the engine? Why do we need a temperature difference at all? Thermodynamics addresses this. Heat is not simply a form of kinetic energy 2 hours ago, Tom Booth said: My tentative theory stated somewhat figuratively or by analogy would be that making the working fluid colder gives it more room to expand. The container volume is fixed, so at any given temperature expansion is limited to the distance the piston can travel, restrained by being connected to a crankshaft. (Excluding "free piston" type engines from the discussion for the moment). Cooling the gas causes it to contract more, increasing it's potential to expand. You have to realize that heat transfer covers more than heat engines. You can have heat transfer under a number if different situations; whatever analysis you do has to work in general - not just for the one situation. 2 hours ago, Tom Booth said: Does that require an outside source of cooling? Certainly, initially. But once a new baseline is established and the engine can start producing more rotational force, more work output, then the cold side only provides a kind of stability or thermal buffer of a sort, but the engine no longer transfers heat to it, and it runs the same as before the ice was added, transforming all the heat supplied into work again. If you’re extracting all of the heat being supplied into work, why does the engine not run without the cold reservoir? Why does the heat supplied increase as you drop the cold reservoir temperature? Have ever actually measured the heat supplied and the work done? 5 hours ago, Tom Booth said: have no issue with the word itself just how it is associated with heat and the implications on a subliminal level of all this archaic terminology: flow, reservoir, etc. Directly relating the "flow" of heat through a heat engine to the flow of water over a mill wheel and so forth. A flow of water from a height is caused by gravity. The flow of cars on the highway, or people down a sidewalk or corridor is self motivated. Maybe "self motivated" is not the best way of putting it, but cars are not pulled along by an outside "gravitational" force, they have their own motive force or kinetic energy or motion, they are self propelled. Why is that an important distinction to make? Well, gravity holds water down to earth in a "reservoir". And gravity causes water to flow in one general direction: down. Gas particles sealed inside a Stirling engine aren't going anywhere. If they are zipping around or vibrating or expanding and contracting it is all due to the energy they are carrying around with them, not something somewhere else compelling them to "flow" anywhere. So there is a general dispersal of kinetic energy in a quantity of gas from the more energetic particles to the less energetic particles, setting aside infrared waves or other possible quantum phenomenon for the moment. You persist in this strawman. Nobody today is claiming that heat is a substance that moves around - that was abandoned long ago. The heat flow is not due to that atoms moving anywhere. It’s the energy that moves around. One can look at a system where there is no liquid or gas, so there should be no temptation to appeal to that notion. Two solid blocks at different temperatures. The can touch and the temperatures will equalize from conduction, or even if not touching, they will radiate, even in a vacuum. No gas molecules. No flow to invoke. 5 hours ago, Tom Booth said: In his unpublished papers Carnot wrote; paraphrasing, that if heat is actually motion, that would explain everything, the action of Joules calorimeter etc And there isn’t, so why do you keep beating this dead horse? Energy is transferred. Heat is the transfer of energy. That’s what is “flowing”
Tom Booth Posted February 5, 2023 Author Posted February 5, 2023 3 hours ago, swansont said: The heat flow is not due to that atoms moving anywhere. It’s the energy that moves around. Well, I think the idea ( kinetic theory of heat) is that the atoms (let's say helium or perhaps hydrogen, commonly used in a Stirling engine as working fluid) each atom has a center of mass (translational kinetic energy) and are moving and colliding with each other, with the chamber walls and in an engine, with the piston. There is a 1:1 ratio between Joules (heat) and Newton meters (motion) So heat (transfer of energy) on an atomic level is a transfer of motion. There are other kinds of motion of the atoms, rotational etc. But these are relatively static or tend to cancel out on the whole. The only significant conversion (joules to newton meters) taking place at the gas/piston interface where the gas collides with something that can actually move and respond to the impact allowing a transfer of motion (kinetic energy) between the gas particles and the piston. One can imagine the billions and billions of impacts required per second in order for the infinitesimally small gas atoms to displace the gargantuan mass of the piston. I still have some additional comments I need to backtrack and answer in sequence.
exchemist Posted February 5, 2023 Posted February 5, 2023 (edited) 25 minutes ago, Tom Booth said: Well, I think the idea ( kinetic theory of heat) is that the atoms (let's say helium or perhaps hydrogen, commonly used in a Stirling engine as working fluid) each atom has a center of mass (translational kinetic energy) and are moving and colliding with each other, with the chamber walls and in an engine, with the piston. There is a 1:1 ratio between Joules (heat) and Newton meters (motion) So heat (transfer of energy) on an atomic level is a transfer of motion. There are other kinds of motion of the atoms, rotational etc. But these are relatively static or tend to cancel out on the whole. The only significant conversion (joules to newton meters) taking place at the gas/piston interface where the gas collides with something that can actually move and respond to the impact allowing a transfer of motion (kinetic energy) between the gas particles and the piston. One can imagine the billions and billions of impacts required per second in order for the infinitesimally small gas atoms to displace the gargantuan mass of the piston. Heat flow is caused by the natural spreading out - diffusion - of energy of random motion from areas with more (higher temperature) to areas with less(lower temperature). This is why it behaves in some respects like a fluid. Temperature is proportional to the average kinetic energy of the molecules in the body (E = 1/2 kT for each degree of freedom the molecule has, k being Boltzmann's constant). Because the motion is random, it cannot all be directed in one direction. We have already been through this. That is why there has to be waste heat. You actually agreed with this earlier in the thread. So, given that there has to be waste heat, it is not unreasonable to suppose there may be a minimum amount of it for a given situation. That is what Carnot's formula tells us. Edited February 5, 2023 by exchemist
Tom Booth Posted February 5, 2023 Author Posted February 5, 2023 (edited) 14 minutes ago, exchemist said: That is why there has to be waste heat. You actually agreed with this earlier in the thread Context? I agree that generally speaking there are known and to one degree or another controllable loses, friction, vibration, conduction. General unwanted dispersal. Disappearance of some 80% or 90% to some specific place (the "cold reservoir) aside from all that (ignoring friction etc.) each cycle is completely ludicrous. Instead of the 1:1 ratio experimentally verified the Carnot ratio is 1:8 or 1:9 in our little heat engine experiments. A glaring discrepancy that I think needs some verification. Edited February 5, 2023 by Tom Booth
swansont Posted February 5, 2023 Posted February 5, 2023 59 minutes ago, Tom Booth said: Well, I think the idea ( kinetic theory of heat) is that the atoms (let's say helium or perhaps hydrogen, commonly used in a Stirling engine as working fluid) each atom has a center of mass (translational kinetic energy) and are moving and colliding with each other, with the chamber walls and in an engine, with the piston. There is a 1:1 ratio between Joules (heat) and Newton meters (motion) So heat (transfer of energy) on an atomic level is a transfer of motion. The center of mass of the object, or collection of atoms, doesn’t move (or doesn’t have to). We all agree on this. So why are you railing against the notion of the atoms going somewhere, when nobody is saying that this happens?
exchemist Posted February 5, 2023 Posted February 5, 2023 1 hour ago, Tom Booth said: Context? I agree that generally speaking there are known and to one degree or another controllable loses, friction, vibration, conduction. General unwanted dispersal. Disappearance of some 80% or 90% to some specific place (the "cold reservoir) aside from all that (ignoring friction etc.) each cycle is completely ludicrous. Instead of the 1:1 ratio experimentally verified the Carnot ratio is 1:8 or 1:9 in our little heat engine experiments. A glaring discrepancy that I think needs some verification. What about the link to your translation from Carnot that I asked you for?
swansont Posted February 5, 2023 Posted February 5, 2023 It would be nice to clarify if you’ve ever measured the heat inflow and work done by the engine. And the pressure and volume values.
Tom Booth Posted February 5, 2023 Author Posted February 5, 2023 45 minutes ago, exchemist said: What about the link to your translation from Carnot that I asked you for? I did not see that request, as I said I have some backtracking to do. Anyway it's in the public domain. Copies can be downloaded from any of dozens of sites. Wikipedia has an online text which is useful for reference and searchable: https://en.m.wikisource.org/wiki/Reflections_on_the_Motive_Power_of_Heat What I referenced is in the appendix A. "extracts from unpublished writings of Carnot". (My apologies to everyone for any other comments I haven't gotten to yet.)
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