JoeOlivaresThermoacousticsx

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Nov 16, 2013 (3 years and 4 months ago)

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THERMOACOUSTICS

Energy and Work from Sound

By Joe Olivares ME 258

Fall 2012

Multiple Regenerator Thermoacoustic Generator


I. Fundamentals

Getting Work from Sound


What is Sound?
-

Its
mechanical
radiant energy that is transmitted by
longitudinal pressure waves in a material medium (as air) and is the
objective cause of
hearing


How are Heat and Sound/Pressure Related?

Thermodynamics, Fluid
Mechanics, Heat Transfer


How do I make WORK?
-

Drive a Speaker
in Reverse and Make Electricity OR
Transfer the Heat! Drive a
Stirling

Engine?


Thermoacoustic

Generators are a Basis of
a Bigger Thermodynamic Cycle.

Waves

The two types of waves dealt with in
thermoacoustics are the standing wave
and the traveling wave. The standing
wave looks like it’s standing still
because it is vibrating at the resonant
frequency, or mode, of the tube.


The traveling wave is a moving wave,
when it hits one end it is reflected back.
This reflection can either weaken or
strengthen its amplitude.


Air travels in a compression wave and
as air is heated it wants to move in
accordance with natural laws.

Waves

Standing waves have nodes and anti
nodes. In the case of air these nodes
are representative of the pressure they
have along the dimensional axis.


With the variations in pressure there is
a variation in temperature and normally
it is negligible, unless you talk very
loudly and right in
-
front of someone.


With resonance the temperature and
pressure effects are no longer
dismissed and you get a great effect.


Reijke and Sondhauss Tubes

Making Noise


The Sondhauss effect was noted by glassblowers and explained and
replicated in
1850
by the German physicist Karl Friedrich Julius
Sondhauss

The effect is a standing sound wave in a tube with one open end and one
closed end



In
1859 physicist PL Rijke

discovered
a way
to
sustain a sound in a
cylindrical
tube open at both
ends using heat by moving the heat source
around in the tube.

The sound comes from a
standing wave whose
wavelength
is about twice the length of the tube, giving the
fundamental
frequency.


1877

John William Strutt,
“Lord Rayleigh” writes the
Theory of Sound
the
definitive book on acoustics relating pressure and sound waves, and
creating the basis for thermoacoustics. The field is silent for almost 90
years


Robert Carter (1960’s) of
Atomics
International Division of North American
Aviation,
Inc.,

Gregory Swift (1980’s) at
LANLab
, Thermal Physics Group,
Nicolas Rott (1980) lay the mathematical and modern basis using a system
of linearized Navier
-
Stokes equations coupled with acoustical energy
balances to describe the dynamics of a modern system



Reijke Tube Basics

Making Noise

Reijke and Sondhauss Tube

Power of Resonance

1850
-
1880

Closed End
-
Sondhauss

Open Ends
-
Reijke

The Modern System

Building on the Noisy Tube

Why such a long time?


Modern methods of
controlling the waveform
have led to increases in
pressure and heat
transfer rates that can
no longer be ignored but
harvested as energy
sources.


Modern computing has
led to numerical analysis
that can solve the
multiphysics

problem



The Modern System

Building on the Noisy Tube

The major
improvement to
modern systems was
how do you get the
heat exchangers to
work like efficiently to
get closer to Carnot

The Modern System

Building on the Noisy Tube

• Each ‘simple’ system is comprised of a Resonator, Stack, Working
Fluid/gas


The resonator is designed to at a ¼, ½ wavelength of the standing
frequency to maximize heat transfer into the stack elements


The stack is a porous plug. It’s design and placement along the tube is
the fundamental design issue in all systems. Some stacks are parallel
plates of thermally conducting material or ceramic insulators. The distance
between the plates and or holes is defined as
𝛿
𝑘
=
𝑘

𝑓
𝑐
𝑝

, called the
thermal penetration depth and is roughly the distance heat can diffuse
through the gas during the time 1/
f
𝜋

• The
working fluid is chosen for its dynamic property values. Air and other
inert gasses are most common. Most working mean pressures in ‘simple’
systems are 3atm or less.

A typical system consists of a resonator, a “Stack” of
plates or fins connected to the outside world, and a
driver/driven object like a speaker that can create
sound or electricity from vibrations.


The two main versions of engines are the Standing
Wave and Traveling Wave type. The multiple
combinations of regenerators and heat exchangers
creates combined cycle analysis and a much more
complex analysis

The Generator
Vs

Refrigerator

To Pump or to Push

• In 1980 Gregory Swift (
LANLab
) wrote the fundamental paper explaining
to other researchers the simplicity of a complex problem.


In his paper he stressed that not only could you use a TA device as a
generator but if you drove the engine in reverse you could create a
refrigerator

• Q in, Sound Out (Heat Engine) OR Sound In, Q out (Refrigeration) was
the result and two branches of research were developed. The major
difference is that you can’t get as large a gradient from cooling as heat
pumping but you can still get very cool.

The Half Wave Generator

Getting Work
from Sound

I. Fundamentals

Getting Work
from Sound

The Refrigerator

Here the speaker is the driving
force and the heat pump is
turned into a refrigerator. Once
the gas reaches the “cold end” it
readily absorbs heat. Some
researchers have modeled this
as a reverse
Stirling

Cycle.

II. Current Research

Solar Powered Electricity Generation

In May 2012 alternative researchers in China
designed a Traveling Wave TA engine that used a
parabolic array of mirrors as it’s heating source.
They focused the mirrors on a “Sodium” based
liquid base that conducted heat into the TA’s stack.
This method allows for a high heat input. It
produced a thermal to electric efficiency of 15%
and an output of 481 Watts, using 3.5MPa
pressurized helium. Although the effectiveness was
small this research allowed others to see that higher
pressure systems are realizable but more research
needs to be used into the “stack” transfer. The
problem is in funneling of heat and overcoming the
lag associated with conductive heating.



II. Current Research

Experimentally Identifying the Faults in Efficiency

Because the simulated flow of such a system is extremely complex some
asian

researchers feel that the system inefficiencies are characterized by “incomplete”
data and have begun to take thermal time lapse studies of the TA’s temperature
gradients as a function of frequency of oscillation and physical characteristics like
diameter, fluid density, etc. Their conclusions were that the first resonant frequency
is the most effective working frequency for refrigerators and that the velocity
distributions become non
-
uniform the larger the temperature difference at the stack
ends. Lastly, they saw that the addition of sound automatically shifted the problem to
that of a forced convection one.

II. Current Research

Power Refrigeration With No Moving parts

Although not as recent, 1980
-
Current, power
refrigeration has been at the forefront of US research
at the Los Alamos National Laboratory under the
guidance of G. Swift. The use of refrigeration without
moving parts is of particular interest to the US with
regards to HE physics.
t
hey easily been able to reach
temperatures of
-
70
C
elsius

Older Refrigeration Charts

References

Backhaus, Scott., Swift, Greg. “New Varieties of Thermoacoustic Engines”
9
th

International Congress on Sound and Vibration

(
2002): LA
-
UR
-
02
-
2721.


Swift
,
Gregory. “Thermoacoustic Engines and Refrigerators”
Physics Today
(July 1995): Pg. 22
-
28.


Wu, Z., Dai, Wei., Man, Man.,
Luo
,
E
rcang

“A Solar Powered Traveling Wave
Thermoacoustic Electricity Generator ”
Solar Energy #86
-
Elsevier
(May 2012):
Pg.
2376
-
2382.


Swift, Gregory. “Thermoacoustic Engines and Refrigerators”
Physics Today
(July 1995): Pg. 22
-
28.


Pan, Na., Wang, S.,
Shen
, Chao “Visualization Investigation of the Flow and
Heat Transfer in Thermoacoustic Engine Driven by Loudspeaker”
International
Journal of Heat and Mass Transfer #55
(July 2012):
Pg.
7737
-
7746