Brainstormer: Is this thermo-acoustic laminar flow engine suggestive of solar processes?

Posted: January 22, 2015 by tallbloke in Solar physics, solar system dynamics
Tags: , , ,

As regular readers know, I’m interested in small devices for generating trickle charging solutions for batteries out in the cloudy mountains where the sun rarely shines. We’ve looked at potentially useful stirling engine designs before, but I just found this interesting video on Youtube which differs fundamentally from the stirling design, while retaining some of its thermodynamic features.

 

This type of very simple engine is known by various names such as laminar flow, thermo-acoustic, thermal lag etc, but no-on seems to have a fully developed thermodynamic theory of exactly how it works. Unlike classic stirling engines, there is no ‘displacer’ to shunt the working gas from the hot to the cold end in order to drive a cycle of expansion/contraction which then sucks and pushes a power piston which drives a flywheel (or a linear electric motor). It’s more reminiscent in a way of a pulse-jet engine, but with a closed cycle, rather than an open system generating thrust directly from the explosive expansion of combustible gases.

But besides thinking about the way this engine operates as a collection of glass and aluminium parts heated at one end, it put me in mind of the way the Sun ‘pulses’ every eleven years or so. So this is today’s brainstormer. If objects can be set into oscillation by the application of heat (and let’s not forget thermodynamic theory here, whereby atoms and molecules ‘vibrate’ more vigorously as heat is applied to them), then what if the heavy dense metallic hydrogen core of the Sun is set into oscillation by the heat generated in the fusion process? It wouldn’t oscillate so easily in the X-Y plane, because the Sun is rotating, but it is freer to move in the Z axis.

What evidence exists to suggest this might be happening? Well, we do observe that in successive solar cycles, more/less sunspot activity takes place in the southern/northern hemispheres. We also observe an ~11 year reversal of magnetic polarity between leading and trailing sunspots. If as Nicola Scafetta suggests, the Sun has a natural frequency of oscillation around 10.8 years, and as with our solar-planetary theory, the gas giants and terrestrial planets have interaction periods at 10.38 and 11.86 years, then we have a potential explanation for the beat period at around 11.07 years which characterises the average length of the solar cycle. We should also recall Ray Tomes’ Z axis theory here, which postulates that the gas giants are gravitationally pulling the core of the Sun up and down by a couple of km relative to its envelope as they move above and below the tilted Solar equatorial plane.

Clearly there are many factors which will affect the characteristic oscillation period of a ‘thermoacoustic engine’, as the youtube video says. The same is true of the Sun; the mass of the core, the viscosity of the surrounding fluid, the rate of heat flow from core to surface, and possibly coupled with the harmonic interaction of the planetary gravitational effect too. Simple it ain’t.

Comments
  1. […] recently put up a post on a different Sterling engine see here https://tallbloke.wordpress.com/2015/01/22/brainstromer-is-this-thermo-acoustic-laminar-flow-engine-… I have been interested in the concept of using heated air and been meaning to buy a model for […]

  2. Do not know how to post photos with a comment so have put a post on my blog https://cementafriend.wordpress.com/2015/01/23/sterling-engine/
    I have been meaning to buy the model which is made of brass and as I remember costs about $450.
    Here is a picture of the chap who made it http://www.olds.com.au/ old school hands on engineering which I am sure you would appreciate Roger. ( I have no connection with the Olds company other than admire the skills and innovative thinking -the elevator is interesting in that it turns the screw or augur conveyors on its head. Instead of the screw turning the body rotates and the screw is stationary. For a bit of fun look at the Steam Products page.)

  3. I was a bit low on the price and I find you can order one. Added this to my post http://www.olds.com.au/stirling/index.html

  4. tallbloke says:

    CF: That Olds engine is a conventional stirling engine, with separate displacer and power pistons, phased at 90 degrees. This is something different. A single power piston with no displacer, which works when you get the resonant timings right.

    I love them all though.🙂

    By the way, if you just post the image url, wordpress will try to pull in the image, like this:

  5. Andrew McRae says:

    NASA already detected magnetic ripples on the surface, and measured the oblateness of the sun.
    http://science.nasa.gov/science-news/science-at-nasa/2008/02oct_oblatesun/
    To test the z-axis theory of planetary modulation of solar activity, it would be interesting to see if oblateness is itself different between north and south poles and if it slowly changes over the 11 year cycle.

    If the cycle affects vertical energy transport, does this imply the same instrument can measure cycles in the solar diameter?

    Trying to visualise the 3D churning in the sun, as different latitudinal zones rotate at different speeds and slide past each other while some waves of compression and rarefaction spread out from the core cyclically, is all rather dizzying.

  6. Graeme No.3 says:

    The efficiency of this engine is likely to be very low. I suggest you might look at a thermoelectric device. Solid state, light weight and a couple of years ago there was a report of 17% efficiency (at 400℃ temperature difference) from a semiconductor base (lead antimonate doped with silver from memory), but that disappeared from public view (USNavy and GM). But even a simple thermocouple might provide the charge you want, assuming you can make a fire.

  7. tallbloke says:

    G3: Yes, I’ve played with small peltier units, and it can be made to work. Stirling engines have achieved over 50% efficiency, though that’s at the crank rather than the electrical output from the rectifier. The problem with easily available peltiers is they won’t take much more than 150C and the proper TEG’s are expensive. As you say, th really exciting ones aren’t available to the public.

  8. tallbloke says:

    Andrew M: Yes, it makes my head spin too.🙂
    Ray Tomes calculated a 2.8km peak to peak core motion. He points out that this would lead to substantial flows at the surface, where the pressure is much lower. However, these flows would be broad and flat, due to the Sun’s powerful gravity maintaining sphericity. I think the oblateness anomalies you linked to are more a surface magnetism effect than an effect of a theoretical core wobble. The point is the hypothetical core wobble is slow, so the Sun has plenty of time to pull itself back to sphericity it occurs. The flow would still be substantial though.

  9. hunter says:

    Cool toy engine.

  10. p.g.sharrow says:

    Tesla Invented a steam control system that replaced the valves in a reciprocating steam engine by utilizing the the resonate pulses from the engine in a chevron labyrinth to make the steam flow 1 way. pg

  11. E.M.Smith says:

    At the center of the Sun (or the Earth, for that matter) gravity becomes zero. There is equal mass on each side of a point at the dead center, so equal gravity in all directions, net zero.

    Now add a gas giant planet on one side. Suddenly the ‘zero point’ is moving around (even if the mass sits still). Yes, the pressure from gravity is still massive, but things like mass/density fractionation will be much less near the dead center, and much faster away from it.

    So put that point in motion…

    Now you have a nuclear reactor that is making waste products, those will tend to slow reactions. The tendency to diffuse out of an area is driven by things like mass, density, concentration. Those forces are now moving around in a circle.

    The potential for oscillations in the reaction rates as the reactants and products (potential reaction poisons) rates of fractionation change sure looks likely to me. At the ‘dead center’ where pressures are highest, reactions ought to go faster, but then have low density driven diffusion of waste away from that reaction point. Then the point moves away… now the waste products have differential gravity / density driven fractionation increase. Hmmmm…..

    Would be a lot better with actual numbers and reactions, but you get the picture. A slowly moving and steady ‘dead center’ would have a more stable reaction rate with somewhat higher waste / poison levels. A fast moving ‘dead center’ would be moving the center of pressure into ‘cleaner’ areas of fuel that had the poisons migrated out more rapidly (prior to the max density point arriving, when gravity gradients were higher) and would, I think, react more and faster.

    That’s my thesis, for what it’s worth.

    Per the trickle charge: A Sterling engine is likely a bit harder to set up ‘in the rough’ than a simple ordinary miniature steam engine, with a small robust boiler (tea kettle😉 set near the fire and water from the local stream… In the desert I’d likely go with solar.

  12. tallbloke says:

    EM: Thanks for your thoughts. I agree the conditions are present which make oscillation likely.

    Regarding miniature steam engines. Don’t. There’s a reason Mamod went out of business. Apart from the severe scalding and shrapnel wounds, small steam piston engines are fiddly and small steam turbines are inefficient. They’re both bloody noisy too.

    I have found a quiet free piston stirling engine with miniaturisation potential though:

    The main problem is getting heat to the working gas in the displacer cylinder fast enough. Hence the big blowtorches prototypers use. Making a hot-end cup with sufficient energy transfer potential is hard. You need rigidity, fast heat transfer and large surgface area. I have some ideas for using corrugated copper sweated with brazing alloy to the inside of a thin stainless steel cup.

    I want to make an engine which will run on a quiet old US army white-gasoline cookstove I own, and make enough power for simultaneous lighting, smartphone charging, running a pocket MP3/radio and running the water pump for cooling the cold end of the engine; about 4 watts at the rectifier output.

  13. suricat says:

    TB.

    Why not separate the gas system’s ‘expander’ from the ‘compressor’? The same element used for both processes is too thermodynamically inefficient!

    For example, two mechanically linked ‘vane pumps’ with interconnecting pipework from the ‘compressor’ to the ‘expander’, where the ‘pipework’ is heated!

    NB. The ‘effective area/pumping volume’ of the ‘expander’ needs to be greater than that of the ‘compressor’ to permit a flow of gas through the ‘pipework’.

    This would be a ‘non-turbo’ ‘jet’!🙂

    Best regards, Ray.

  14. suricat says:

    suricat says: January 24, 2015 at 2:05 am

    Wot! Still no response to a low powered efficient electricity generator TB?

    Okay. Going back to the ‘op’, I doubt the applicability of this form of energy transport at the densities within Sol. I would favour ‘barry centre variation’ within Sol’s mass.

    Best regards, Ray.

  15. tallbloke says:

    Ray: I’ve been on the campaign trail over the weekend, and haven’t had time to respond, sorry.
    I’m not able to visualise your proposal from your description, but it’s worth noting that there are various configurations of stirling engines which have the power piston in a separate cylinder remote from the displacer cylinder.

    I’m not saying that this form of energy transport is working in the Sun, but possibly an analogous process is. It’s the general principle of the generation and movement of heat setting up an oscillation I’m trying to consider.

  16. suricat says:

    tallbloke says: January 26, 2015 at 9:36 am

    “I’ve been on the campaign trail over the weekend, and haven’t had time to respond, sorry.”

    We ‘prioritise’ as we must TB.

    “I’m not able to visualise your proposal from your description, but it’s worth noting that there are various configurations of stirling engines which have the power piston in a separate cylinder remote from the displacer cylinder.”

    Um, I find your explications a bit obtuse TB. IIRC, a ‘Stirling’ engine is a ‘4 stroke engine’ that runs on ‘petrol’, or ‘alcohol’, in its modern form (two revolutions of the crankshaft = a cycle [induction = ~180 degrees of crank rotation, compression ~180, power ~180 and exhaust ~180]).

    However, history indicates that the root source for this type of engine is a ‘two stroke’ ‘externally heated’ type of engine. These earlier engine configurations have given way to the more thermodynamically efficient configurations of modern Stirling cycle engines.

    TB. All ‘pistons’ ‘displace’! What do you mean by “there are various configurations of stirling engines which have the power piston in a separate cylinder remote from the displacer cylinder.”??? Did you mean ‘compressor’???

    “I’m not saying that this form of energy transport is working in the Sun, but possibly an analogous process is.”

    There are many ‘analogies’ that try to describe convection, but this process may well provide some insight. IMHO when the energy transport outstrips the rate that the initial energy can be realised. IOW, the rate that energy can be introduced into the system is less than the energy can be transported.

    This would be a ‘gradual leak’ of energy in a ‘stable system’, but where a ‘barrier’ exists to the ‘source of energy’, the hysteresis of the ‘barrier’ is augmented in the ‘energy flow’.

    “It’s the general principle of the generation and movement of heat setting up an oscillation I’m trying to consider.”

    I appreciate this TB, but a ‘hysteresis’ needs to be introduced that can show this.🙂

    BTW. The ‘brightening’ and ‘dimming’ of the lights in your linked vid aren’t due to ‘piston rotation’. Look at the ‘piston travel’, it lengthens and shortens. The speed that the piston cuts the EM coils alters the voltage generated.

    Best regards, Ray.

  17. “TB. All ‘pistons’ ‘displace’! What do you mean by “there are various configurations of stirling engines which have the power piston in a separate cylinder remote from the displacer cylinder.”??? Did you mean ‘compressor’???”

    Look up Split cycle cryogenic refrigerator! The displacer can be off by 90 degrees via t timing delay.

  18. tallbloke says:

    Ray: Um, I find your explications a bit obtuse TB. IIRC, a ‘Stirling’ engine is a ‘4 stroke engine’ that runs on ‘petrol’, or ‘alcohol’, in its modern form (two revolutions of the crankshaft = a cycle [induction = ~180 degrees of crank rotation, compression ~180, power ~180 and exhaust ~180]).

    However, history indicates that the root source for this type of engine is a ‘two stroke’ ‘externally heated’ type of engine. These earlier engine configurations have given way to the more thermodynamically efficient configurations of modern Stirling cycle engines.

    TB. All ‘pistons’ ‘displace’! What do you mean by “there are various configurations of stirling engines which have the power piston in a separate cylinder remote from the displacer cylinder.”??? Did you mean ‘compressor’???

    The displacer piston doesn’t compress anything. It fits loosely in the cylinder and simply displaces the working gas from the hot end of the system to the cold end, which causes alternate expansion and shrinkage of the working gas volume. This alternately pushes and pulls the tight fitting power piston to and fro, driving the flywheel. The connecting rod from the flywheel to the displacer is phased at 90 degrees to the power piston’s motion.

    So when supplying heat it’s a four stroke external combustion engine with no ‘exhaust’, which can be fired by any heat source capable of being directed at the hod end of the closed system.

    Here’s one possible configuration

    If instead you drive the crank, the engine can work as a very efficient cooler, which is used in cryogenic applications.

  19. suricat says:

    tallbloke says: January 27, 2015 at 6:54 am

    Thanx. Yes! I blame my confusion on my elder ‘bruv” Bryan (RIP). Although he loved the Vincent HRD and insisted that the ‘four stroke cycle’ was a ‘Stirling cycle’ he was wrong! The ‘four stroke cycle’, as ‘historically understood’, is the ‘Otto cycle’ (I’m now thinking back to the days when I received instruction from my College Tutors)!

    However, the ‘animation’ in your post can only be ‘analogised’ as a ‘two stroke’ engine. It requires ‘two passages’ of the ‘power piston’ through the ‘cylinder volume’ to achieve a ‘power stroke’!

    You may well argue that ‘vacuum power’ is involved, but this would require ‘two systems’. One that provides ‘pressure’, and another that provides ‘vacuum’.

    Where do you want to go with this?

    The ‘power stroke’ is implied by the ‘sweep’ (the piston’s traverse through the entire cylinder) that ‘adds’ to the systems ‘entropic state’. The number or ‘sweeps’ of the piston that imply a ‘power stroke’ determines the ‘numerical cycle’ (degrees of crankshaft rotation [TDC (top dead centre) to BDC (bottom dead centre)]). Thus, for an internal combustion engine, the ‘power stroke’ is the determinant for the ‘class of engine’ indicated by the ‘degrees of rotation’ of the ‘crankshaft’, or the ‘sweeps’ of the cylinder by the ‘powering’ piston.

    Best regards, Ray.

  20. tallbloke says:

    Hi Ray,
    I think on balance I agree that it looks more like a two stroke system than four. Arguably you could say four because the to and fro motions of the displacer and piston are out of phase. I suppose it depends on how you want to try to explain it.

    You may well argue that ‘vacuum power’ is involved, but this would require ‘two systems’. One that provides ‘pressure’, and another that provides ‘vacuum’.

    Anywhere that has a lower pressure than ambient is a ‘partial vacuum’. Closed and pressurized stirling engines do achieve suck as well as blow on the power piston, and this is one of the reasons they produce more power; the other being greater molecular density in the working gas.

  21. tallbloke says: January 29, 2015 at 7:16 am

    “Hi Ray, I think on balance I agree that it looks more like a two stroke system than four. Arguably you could say four because the to and fro motions of the displacer and piston are out of phase. I suppose it depends on how you want to try to explain it.”

    This is a heat or temperature difference machine, not internal combustion. The sterling cycle is much more efficient than a piston steam engine, not as efficient as a turbo bypass engine that produces only thrust (force). That puppy can be within 0.5% of the Carnot cycle efficiency!

    “You may well argue that ‘vacuum power’ is involved, but this would require ‘two systems’. One that provides ‘pressure’, and another that provides ‘vacuum’.”

    “Anywhere that has a lower pressure than ambient is a ‘partial vacuum’. Closed and pressurized sterling engines do achieve suck as well as blow on the power piston, and this is one of the reasons they produce more power; the other being greater molecular density in the working gas.”

    Wow yes! The inverse cryo-cycle only moves heat uphill to something that can dissipate both that heat and all inefficiency! A 30 watt power can move 0.25 watt from 60 Kelvin to 300 Kelvin easy!
    the details will blow your mind. All is done with a single pipe that transfers the AC power from a sinusoidal free piston compressor 300 psi helium plus minus 25 psi. Everything at the other end is powered by this pressure wave. No computer no wires. Just watch that puppy make ice from atmosphere at the cold end.

  22. suricat says:

    tallbloke says: January 29, 2015 at 7:16 am

    “Anywhere that has a lower pressure than ambient is a ‘partial vacuum’. Closed and pressurized stirling engines do achieve suck as well as blow on the power piston, and this is one of the reasons they produce more power; the other being greater molecular density in the working gas.”

    You didn’t mention the pressure of the ‘working gas’ before TB. This is a ‘game changer’.

    Best regards, Ray.

  23. suricat says:

    Will Janoschkas says: January 29, 2015 at 3:05 pm

    “This is a heat or temperature difference machine, not internal combustion. The sterling cycle is much more efficient than a piston steam engine, not as efficient as a turbo bypass engine that produces only thrust (force). That puppy can be within 0.5% of the Carnot cycle efficiency!”

    “That puppy” can also be made to deliver ‘torque’ into a mechanical system, such as the RR genny. Don’t ‘write off’ turbo-jets so quickly Will. They can also be made into ‘external combustion engines’!

    As an aside. In my youth, I remember taking the guts out of a ‘spark plug’ and brazing a copper tube on to the metal remains. Don’t try this at home because the copper tube may explode, but, after fitting the modified ‘spark plug’ into a 50cc ‘two stroke’ engine without fuel, the engine achieved ‘tick-over’ when I heated the copper tube with a blow torch. I’m sure that there’s a lot more efficiency that can be gained from that scenario.

    Best regards, Ray.

  24. suricat says: January 31, 2015 at 7:26 am

    “That puppy” can also be made to deliver ‘torque’ into a mechanical system, such as the RR genny. Don’t ‘write off’ turbo-jets so quickly Will. They can also be made into ‘external combustion engines’!”

    No writing off, In am amazed that the fan of the turbo-bypass can turn almost all waste heat into thrust.
    Only the shuttle engines in space are more efficient.

  25. oldbrew says:

    Try making one of these?

    ‘Tesla’s oscillator is a reciprocating electricity generator. Steam would be forced into the oscillator, and exit through a series of ports, pushing a piston up and down that was attached to an armature, causing it to vibrate up and down at high speed, producing electricity.’

    http://en.wikipedia.org/wiki/Tesla%27s_oscillator

    If you like tall stories:

    ‘Tesla said the oscillator was around 7 inches (18 cm) long, and weighing one or two pounds; something “you could put in your overcoat pocket”. At one point while experimenting with the oscillator, he alleged it generated a resonance in several buildings causing complaints to the police. As the speed grew he said that the machine oscillated at the resonance frequency of his own building and, belatedly realizing the danger, he was forced to use a sledge hammer to terminate the experiment, just as the police arrived.’

    He told the police it must have been an earthquake – so the story goes.

  26. Most things have two much loss (dispersion) to make resonance useful. As for an accumulation of power, a tool steel tuning fork will destroy itself with magneto-motive coupling of milliwatts within, in my case less than two minutes. Yes such can be dangerous. The Cheyenne mountain bolt hole is on springs but with both friction and hydraulic dampers. How about Tacoma Narrows?

  27. tallbloke says:

    I don’t know what conditions are like in the interior of the Sun, but it seems to be a reasonable hypothesis that there are strong magnetic fields permeating it. I remember bing fascinated as a kid when I set up a magnet on a steel plate and stood a pin on it. When I nudged the pin, it oscillated in the magnetic field for several minutes before air resistance brought it to a standstill again.

  28. oldbrew says:

    Will J says: ‘How about Tacoma Narrows?’

    That was aeroelastic flutter:

    ‘The dramatic, rhythmic twisting that resulted in the 1940 collapse of “Galloping Gertie”, the original Tacoma Narrows Bridge, is sometimes characterized in physics textbooks as a classic example of resonance. The catastrophic vibrations that destroyed the bridge were due to an oscillation caused by interactions between the bridge and the winds passing through its structure — a phenomenon known as aeroelastic flutter.’

    http://en.wikipedia.org/wiki/Mechanical_resonance#Failure_of_the_original_Tacoma_Narrows_Bridge

  29. suricat says:

    Yes OB.

    “‘The dramatic, rhythmic twisting that resulted in the 1940 collapse of “Galloping Gertie”, the original Tacoma Narrows Bridge, is sometimes characterized in physics textbooks as a classic example of resonance. The catastrophic vibrations that destroyed the bridge were due to an oscillation caused by interactions between the bridge and the winds passing through its structure — a phenomenon known as aeroelastic flutter.’”

    This phenomenon is resurgent throughout the spectra of ‘concurrence’. When will someone, besides myself, declare that ‘concurrence’, per se, becomes a ‘resonant entity’?

    Best regards, Ray.

  30. “This phenomenon is resurgent throughout the spectra of ‘concurrence.”

    Huh! What could such a stand alone statement possibly mean, to mortals?

    For destructive resonance that would mean force concurrence at periodic intervals or synchronicity.

  31. suricat says:

    Will Janoschka says: February 6, 2015 at 4:59 am

    Correct Will. However, ‘periodic intervals/synchronicity’ can also be productive!

    It all depends upon ‘what you want to do’. If you ‘want it’ (its part of the system), its enthalpy, but if you don’t want it (its part of the system’s loss), its entropy. You choose in accordance with your ‘system’s’ need.🙂

    best regards, Ray.

  32. suricat says:

    I correct myself Will.

    “if you don’t want it (its part of the system’s loss), its entropy.”

    This is more like. If your system can’t ‘entrap/hold’ the energy, the ‘energy’ is absorbed by ‘other’ systems. It becomes ‘entropy to your system’ (the system under observation) and ‘adds’ to the chaos of ‘other attractors’ that want to ‘rob’ your system of energy.

    Clear as mud?

    Best regards, Ray.