TA basics

Thermoacoustic generator basics:

The essence of the engines:
These engines make a very loud sound (gas oscillation) from heat energy and this sound makes vibrating a linear generator, which produces electricity.

Standing wave thermoacoustic engine has available efficiency approx around 8-20%, and the traveling wave (Stirling cycle) engine is 1.5-2 times better efficiency. Thus those have 30-40% efficiency!

When we build these engines we strive to provide so hot-air engines which are from less material and parts, and are simpler structure.
We could see at the free piston stirling engines that we were able to leave the crank structures (flywheel etc) even  we presented pistons from membranes, and water too.

Thermoacoustic engine = gas piston:
When we build thermoacoustic engines we make piston from air or other gas.
It is not too difficult because the gas has mass and flexibility in a pipe.
So when we take a tube we immediately created a geometrically gas piston in it.
We need not exactly the roller turning, gas piston does not wear out, does not corrode,  not expensive, but it is durable!
We use the gas in the thermoacoustic engines for a piston!

About he sound (interesting):

Normal conversation is 40-65dB from 1m  distance
65dB at pressure changes in the value of: 0.05 Pa
(The displacement: 0.2 microns
The temperature changes: 40 μK)

Urban transport 85dB
Jackhammer 1m from 100db
Vuvuzela horn from 1m 120dB
Pain threshold 120-130dB
At 30,000 times higher in intensity
165db, (your hair will burn down)

(180db at pressure changes in the value of 0.3 bar
The gas displacement: 10 cm
The changes in temperature: 24 K)
Theoretical max. approximately at atmospheric pressure. 194dB

We can use the thermoacoustic generators:
-solar energy
-progress energy (waste heat)
-geothermal energy
-the exhaust heat (re-use)
-general generator, which can be heated any heat source (heat difference)

Other areas of the thermoacoustics:
- Gas Liquefaction
- Refrigerators
- Imaging device (for doctors)
- Pulse Jet engine
- In flying jet engines, missiles, chimneys and other internal-combustion "pipes"  it can occur  that thermoacoustic phenomenon is so strong, which can damage the engine or structure.  One branches of the thermoacoustic deals to prevent these adverse events.

Thermoacoustics history: 

Japan in 1568:
Buddhist monk reported the loud tone generated by a ceremonial rice-cooker in 1568

Then Byron Higgins in 1777  and the others:

History of the development :

The sites of the main developers:

-standing waves engines (rijke-tube, Soundhauss- tube, steam thermoacoustic engines)
-traveling waves engines (TASHE- with bypass, loop contruction, alpha, engine with displacer piston,  D+P, DTE, etc.
-cascad (mix.) engines
-thermal lag (Peter L. Tailor)
-pulse tubes
-lamina flow engine
-Lee Fellows engines (?)
Engines with machanical resonator


Sondhauss tube:

The standing wave engines are actually a Sondhauss-tube.
According to my experiments we must put the stack 1/3 in the tube near the end. The stack MUST be very loose. Dense stack does not work!
You must use longer tube about 25-30cm. Longer tube works easily.
Standing wave engine produces some electrics:
Standing wave engine produces some electrics with mechanical resonator:

How does this engine work? 
There are two basic phenomenon, we need to focus to understanding.
The first thermodynamics, that is, if the gas heats up, the pressure increases, which encourages expansion, and contraction is when it cools down.
The second is that the gas in the tube is so as a spring and piston.
When air piston goes in the tube more gas is heated so it expands.
In this time the gas piston bounce out, and reverse.
The heating and cooling is done with a small time delay because the stack is loose.

The standing thermoacoustic engine has a brayton cycle, not stirling:

What is the difference between the stack and regenerator?
Stack is loose and we use it in the standing wave thermoacoustic engine.
Regenerator is dense and we use it in the traveling wave thermoacoustic engine.
The air is heated and cooled in the stack with a delay because is it loose.
Standing wave engine makes a 90 degrees phase shift difference the between pressure and heat exchange with a delay in the heat exchanger (brayton cycle).
The air is fast heated and cooled in the regenerator because it is dense.
Traveling wave engine makes a 90 degrees phase shift difference the between pressure and heat exchange with a air displacer piston (stirling cycle).
In the lamina flow engine restrictor is same as stack.
Restrictor can be replaced with stack and visa versa.
First trial:

Steam thermoacoustic engines:


Mechanical resonator:

How does regenerator work? :
When the gas goes through the regenerator or stack from the warm side to the cold side  the air cools and contracts on the porous surface.
The air goes out from the hot porous material to the wider tube (where cool is far away), so gas can not be fast cool. Air stays warm and expanded.
Standing wave thermoacoustic engines has a stack (loose).
Traveling wave thermoacoustic engines has a regenerator (more dense).

Biggest loss is the length of the pipe. The longer the pipe, the greater the "friction" (viscosity) of the air :
This is very significant, greater than the  friction of the conventional piston.
This engine has a brayton cycle, not stirling...

Traveling wave thermoacoustic engines:

Tashe with bypass:
This engine has stirling cycle!

This engine works similarly as a fluidyne Stirling.
The gas piston has a greater momentum in the longer branch.
It goes through the regenerator with a phase delay.

Aster  loop contruction:
Frequency  of the loop equal a four times shorter the frequency of the sondhauss tube. In other words, a full-wave engine.


Cascade engines:
I seem it is not improved. A standing wave and a traveling grade.

Alpha engine:
We can use this only a fridge as a free piston thermoacoustic generator does not working.

Engine with displacer piston 1:
My first experiment:
I have more and better experiment with this, maybe I will upload once.

M+P engine:


Engine displace piston 2 (metronome engine):

Lee Fellows engines:
This engine reality? We do not know.  We don't know how does it work.

Thermal lag - Peter L. Tailor 1995 patent:

Lamina Flow:

The reducer separates the hot and cold side, and makes a turbulence . The heat exchange so happens on the tube wall. and it is so slow, that we can use a crank mechanism. Probably the regenerator save the heat from end of the pipe so it  improves up the engine. At the standing-wave engine I did not realize that the regeneratorl would improve on it rather it will be worse.


continuation soon