Thermoacoustic engines can be generators ( generate electricity) or refrigerators.
Thermoacoustic engines has two basic groups:
-standing waves engines
-traveling waves engines
Core:
-In standing wave engines the core is stack.
-In traveling wave engines the core is usually a regenerator or occasionally a stack also.
The regenerator is dense the stack is rare, transparent.
Standing wave generators:
It is essentially a Sondhauss tube which, in my experiments, has to be placed at 1/3 close to the closed end of the stack.
In the case of professional construction of the stack (or, in the case of traveling wave engines, on both sides of the regenerator), heat exchangers are fitted to help heat to the hot side of the stack and cool the other side. Heat exchangers consist of a sieve made of a material with good thermal conductivity, usually copper (possibly in several layers), or an array of channels, possibly plates, possibly a lump of copper conductor. The thickness of the heat exchangers individually does not exceed that of the stack, nor that of the regenerator.
In a basic experiment, the machine can be easily tested with a test tube. The secret to keeping the stack loose is to keep the light passing through it. It is much easier to start the machine if you extend the test tube with some kind of tube, even a paper tube, and thus use a machine at least 25-30cm long. In this video you can see how to make a stack in two minutes from fine metal wool that can be bought at a paint or DIY store. If this metal sponge is heated from the closed end, a quarter standing sound is obtained. A quarter wave means that the gas springs into the semi-closed tube and into the atmosphere like a piston.
Calculation of the frequency of a standing wave thermoacoustic generator
at atmospheric pressure with air:
The actual efficiency is, of course, significantly lower than the theoretical for all types of engine due to thermal, mechanical and other losses. This does not mean that 20-30% efficiency cannot be achieved with a standing wave. A standing wave engine can be competitive with a good idea, good design. Stupidity is that we do not deal with this, especially that other, more favored, much more expensive, and more complex engines look not much better.
The distance of the between the threads in the stack is named the thermal penetration dept.
It is a kind of ideal heat transfer distance ... In the regenerator used in the stirling cycle, this is approx. 0.1 mm, for quarter-wave machines it can be around 0.4 for atmospheric pressure air, but this is modified by the frequency.
Like any heat engine, this engines is only powerful under pressure, so and because we don’t want to be deaf, our loud tube needs to be closed.
If the loud test tube is simple plugged the work of the tube will stop.
There are several ways to our loud tube closed. In the case of our open-ended tube, our air piston vibrates into the atmosphere, if we close it, we still have to fit some counter-gasspring (resonator).
Thin resonator standing wave thermoacoustic generator:
It seems that the standing wave can be more windy if the resonator is thinner as the stack. Of course, it cannot be thinner than a certain thinness, e.g. maybe it could work up to 6-7mm in diameter. In this case, the proportions of the resonator and the machine are different, the proportions of the resonator are shorter and the rest of the machine is longer. Maybe it’s worth investigating because we can maybe use this geometry to improve on a standing wave machine.
Update: It seems that it is the good if approx. half of the resonator tube is as wide as the engine with the stack.
Videos:
https://odysee.com/@Tibsim:9/standing-wave-thermoacoustic-model:4
https://odysee.com/@Tibsim:9/Standing-wave-thermoacoustic-turbine-generator-2.:7
There is a YouTuber who consistently refers to this design as a Hofler tube. I couldn't find any data that anyone before me had made such a thin air power piston standing wave engine.
It's true, I haven't delved into the subject, but I found a document that mentions Hofler's research and a drawing that looks similar, but it's not the same, and it's very different. This document:
And in it these links:
4. Wheatley, J., Hofler, T., Swift, G.W., Migliori, A. 1985. "Understanding Some Simple Phenomena in Thermoacoustics with
Applications to Acoustical Heat Engines” J. Acoustical Society of America. 74(1).
7. Hofler TJ. "Thermoacoustic refrigerator design and performance". Ph.D. dissertation, Physics Department, University of
California at San Diego, 1986.
8. Garrett SL, Adeff JA, Hofler TJ. Thermoacoustic refrigerator for space applications. J Thermophys Heat Transfer 1993;7:595–9
If I have time and energy, I will try to find them, although I do not have access to such documents.
At the same time, if you look at the photo, you can immediately see that this is a completely different machine!
The Hofler-tube is a totally different engine. Hofler-tube is a thermoacoustic cooling design that cannot be used as a generator because it is a Pusle tube. These are differences:
1. The driver, i.e. the power piston, is not the thin tube, but the mechanical piston or speaker on the other side of the machine.
2. Therefore, the thin tube has a completely different role, it is a Pulse tube. In my tube, the gas in the thin tube is the power piston, in the Hofler tube it is the displacer.
3. The pulse tube Hofler-tube is not a standing wave machine, it does not have a stack, but a regenerator in it.
There are others who show a Hofler tube as a generator on the internet, but that tube looks just the other way around. The air power piston is not thin, but expands like a funnel:
https://www.youtube.com/watch?v=7WHTaRdIugA&t=32s
Hofler was certainly a great man and not a Nazi, but there is no evidence that he did this design, especially that he did not know the thermoacoustic turbine at the time, which could possibly be used if it is really good which is not certain.
other:
Similar engine:
https://en.wikipedia.org/wiki/Pop_pop_boat
Standing wave generator model with mechanical rezonator:
https://odysee.com/@Tibsim:9/simple-standing-wave-thermoacoustic-engine-3.:1
How do you do it?
https://odysee.com/@Tibsim:9/simple-standing-wave-thermoacoustic-engine-1.:f
Half-wave resonator:
For example, after the buzzing Sondhauss tube (machine), an identical Sondhauss tube must be fitted as a resonator without leakage so that the machine can be shut down without any problems. Below is a video of it, but here the position of the stack is really very important, if it is 5mm away from where it should be, it can no longer work. It is best to adjust the pipe length so that the stack is set in the right place. This experiment is also good for observing exactly where the stack is best, as it will only work on the machine almost if it is in the right place. But it’s a lot easier to use a tube longer than the test tube, because then you don’t have to position the stack so accurately anymore. In the video below, there is a piezo chip at the end of the tube that vibrates and produces power for the LEDs. It is very important if you want to reproduce this experiment that it does not work with one LED (two LEDs must be connected in parallel and in opposite directions) and that high-gloss red LEDs are worth using.
There is already a half-wave in this tube, i.e. a half-wave machine, because we put two Sondhauss tubes together. This means that it has "two gas pistons" that rest on each other in the middle of the machine, and the pistons spring to and fro between the two ends of the closed tube. But you can also imagine imagining a piston in the middle of a closed tube, where one is to compress or thin out the gas on the other side. At the quarter-wave, an imaginary piston pushed into and out of the machine from the atmosphere ...
https://odysee.com/@Tibsim:9/DIY-thermoacoustic-toy-5-minits:d
Half-wave machines can be grouped in two. . In one, the pressure ide-ode bounces at a lower frequency, equal to when half the length of this half-wave machine is taken and counted as a quarter-wave.
The other is when the two ends of the tube vibrate opposite to each other. The pressure point is then in the middle of the pipe. The frequency is twice that of the previous half.
Kovács-tube:
Tandem:
One of the interesting ways of closing stationary wave machines, which BladeAttila christened tandem. The point is to fit two heated standing wave machines of the same size opposite each other, which gives us a very stable and reliable construction.
http://www.youtube.com/watch?v=cgGu49H1h0k
All you have to do is make sure that the stacks are at the same distance from the ends of the test tubes, so that the two machines you are assembling have the same dimensions. An additional advantage of this design is the higher performance as it has double heating and double stack cross section. If the machine is bent in a U-shape, it can also be heated with only one heat source.
https://www.mdpi.com/2076-3417/8/2/287/htm#
Quarter wave (Helmholtz) resonator:
The most common closure is to connect the tube to a larger container (resonator) (Helmholtz resonator). This is better than a half-wave tube resonator because the location of the stack does not need to be determined as precisely for a successful experiment. With the tank, the machine behaves as if the tube is open to the atmosphere. The tank, or cavity, acts as an atmosphere.
The generator (or piezo) is usually placed on the cold side of the stack. This is usually used in professional solutions. In this case, even when the machine is open, the LEDs light up during the experiment.
Our generator, piezo (or any membrane, balloon) can also be placed in place of the closed end.
Of course, be careful not to leave a small leak and use a longer tube to keep the generator away from the heat. However, if we use a diaphragm instead of a closed end, we soften the air spring (since the machine is an air spring, the end of which is not fixed now, but to a also flexible diaphragm), as if we had extended the closed end of the machine, so the open end is it should be extended to an ideal location for the heating location. This way, the stack will not be less than 1/3 from the closed end, but less than 1/4 or 1/5 (if the membrane is very soft)! This means that the diaphragm at the closed end will not make the machine worse if its dimensions or proportions are changed accordingly! Moreover, since the membrane has less loss than the tube, it must be even better. Unbelievable, but the flow of gas in the pipe is more lossy than friction or a well-made solid piston due to friction with the pipe, more precisely its viscosity, this is one of the big problems with thermoacoustic machines!
Speaker generator in the Helmholtz resonator:
There were times when the generator was placed in front of the Helmholtz resonator, and below is an example of when it was built into it.
The picture shows one of the older standing wave ideas of the Score, which were designed for simple stoves and stoves. The "test tube" was widened sideways so that the size of the machine became larger, it could deliver more power, but because the machine remained thin, heat exchange of the stack was still provided. A speaker resonates on the side of the resonator box, generating electrical energy.
As can be seen from the flattened machine, larger thermoacoustic machines have problems with heat input and cooling, as they are externally heated machines and the gas flows evenly in the regenerator and heat exchangers. In a thicker machine, heat exchange is difficult.
Here is one of the implemented versions:
The food is cooked on top of the table, while the engine produces electricity...
Losses:
In standing wave engines, the most significant losses are the "air resistance" of the stack and the friction of the resonator tube. In this study, an attempt was made to reduce the loss with a cone widensing.
https://www.sciencedirect.com/science/article/abs/pii/S0011227506000804
Mechanical resonator:
The developers reduces have been made the friction of the tube by simply using a solid piston instead of a gas piston, which is tuned to the resonance of the engine with a weight and spring system. This is called a mechanical resonator. This system at once is also a linear electric generator.
https://www.youtube.com/watch?v=u8VG9AODNbo
https://odysee.com/@Tibsim:9/simple-standing-wave-thermoacoustic-engine-1.:f
Thermal lag, Lamina flow Thermoacoustic engines:
According to Robert Sier, there are patents and descriptions similar to the lamina flow motor since the 1950s!
Here is a plan of a 1984 heat pump:
Thermal lag:
1995 Patent by Peter L. Szabó under the name Thermal Lag.
 |
https://www.youtube.com/watch?v=3zOLZTvNnjY
https://www.google.com/patents/US5414997
Interestingly, its cycle is said to be somewhere between the Stirling and Otto cycles. Better than Otto, but worse than stirling.
Lamina flow engine:
At a conference in the U.S., Jim Senft pointed out that he has a U.S. lamina flow patent. And Robert Sier experimented with the Lamina Flow machine. It is not yet clear whether this is the same as the US patent or whether the lamina flow machine is named after him. Here he writes about the case:
http://www.stirlingengines.org.uk/thermo/lamina.html
There are several places on the World Wide Web that the name Laminar Flow would be correct, but the name without r is prevalent.
This video helps you to understand the lamina:
https://odysee.com/@Tibsim:9/Old-thermoacoustic-experiment:d
The lamina flow is an extremely simple structure, containing only one moving part, a working piston.
It also has a constrictor, or nozzle, and some metal sponge. Video about the lamina flow engine:
Detailed drawing of a machine with dimensions:
Types of Lamina Flow:
-The classic mid-heated type of the Lamina Flow engine:
-The end-heated lamina, often also referred to as Thermal lag, is actually a lamina and not the same as Tailor's machine. It's just called that because it has to be heated in the end.
-Resonator when there is no flywheel:
-The liquid piston version
The reducer separates the cold and hot sides and creates turbulence. The heat exchange thus takes place on the wall of the tube and at the front of the regenerator and is so slow that a crank structure can be used. It also works without a regenerator. In fact, it’s nothing more than a slow-motion quarter-wave machine, it’s just not a stack, it’s a constrictor is in it.
The motor is likely to improve from the regenerator because it reuses some of the heat that travels toward the end of the tube.
https://odysee.com/@Tibsim:9/Standing-Wave-thermoacoustic-experiment-with-can-1.:e
This lamina flow engine is heated at the bottom. This motor is called often thermal leg engine also:
