Basic Idea about Thermocaoustics

1. Aravind N. Badiger
7 ME
USN:2BA09ME012

2.  Introduction
 What is THERMOACOUSTICS?
 History
 Sound Waves and Pressure
 Principle
 Main Components
 How it works?
 What is a Stack?
 Standing wave Thermo acoustic System
 Travelling wave TAR
 Present work
 Merits of the technology
 Demerits
 Applications
 Conclusions
 References
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3.  Thermoacoustics is science of generating or amplifying sound waves with
the help of thermal energy
 Sound waves are simply pressure oscillations; these pressure oscillations
can be amplified with heat
 High pressure sound waves have the capacity to drive a piston
 It can be used as alternative method of refrigeration but this is an
eco-friendly
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4.  Thermoacoustics is a branch of physics which
deals with thermodynamics, acoustics and their
interaction with each other
 The term “Thermoacoustics” was first termed by
Rott in 1980, who described it as rather self
explanatory
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5.  Thermoacoustics is being studied for over the past two centuries.
 In 1777,Bryon Higgins was able to excite pipe oscillations in a
large tube, open at two ends, by suitable placing in hydrogen
flame.
 Later in 1850,Sondhauss experimented with a open-close tube ,
heating it by applying a flame to the bulb at the close end to
produce sound.
 In 1859, Rijke investigated with similar apparatus but with
hydrogen flame replaced by heated mesh wire and also found
that sound was maximum when mesh heater was quarter to tube
length from the bottom.
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6. 66
(c) Illustration of the Sondhauss tube

7.  sound waves propagate through the air via
molecular collisions causing a disturbance in the
air in a closed tube, gets reflected and which in
turn creates constructive and destructive
interference
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8.  constructive interference makes the molecules
compress, and the destructive interference makes
the molecules expand.
 optimal resonant frequency in found to get the
maximum heat transfer rate, using
Where,
n- no of moles, f – frequency, v – velocity of the
wave, L – length of the tube.
f= nv/4L
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9.  Thermoacoustics is based on the principle that sound waves are
pressure waves and they propagate causing compressions and
rarefactions in the medium.
 It is also based on Ideal gas equation, PV=nRT, where P=
pressure in Pascal, V= volume in cubic meter, n= no of moles,
R=Real gas constant (8.314 J/kgK), T= temperature in Kelvin.
 And Clausius statement on second law of thermodynamics i.e.,
Heat flows from body at higher temperature to a body at lower
temperature but reverse is not possible spontaneously.
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10. Driver
• Houses the Loudspeaker
Resonator
 Houses the gas ( Helium)
 The hot and cold heat exchangers
 Houses the Stack
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11. Loudspeaker
 Creates sound waves up to 200 dB!
Resonator—where gas cooling
and compression take place
Uses inert gas, commonly Helium for
refrigeration
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12. Stack
Series of small parallel
channels through which
pressure and velocity of
waves change
In between the heat
exchangers
Heat Exchangers
Hot heat exchanger
Cold heat exchanger
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13.  Closely spaced surfaces aligned parallel to
the resonator tube.
 Purpose: provide a medium for heat transfer.
 Honeycombed plastic spacers used which
absorb heat locally.
 Spacing crucially depends on few times the
thermal penetration depth.
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17.  The Below figure shows a schematic diagram of a
travelling wave thermoacoustic engine. It consists
of resonator tube and a loop containing a
regenerator, three heat exchanger and a bypass
loop.
 A regenerator is a porous medium with high heat
capacity. It is similar to stack but the plate spacing
will be less than thermal penetration depth.
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19. QC =
Wa =
Co-efficient of
performance
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23.  Studies show that for relatively small heat loads, TARS
compares well with VCRS, thus ideal for cooling of
electronic equipments.
 TARS run by a thermo acoustic engine may be prove
useful especially in areas where electricity is not
available.
 Despite its demerits, TARS will continue to be an area of
interest due to:
 no need of lubrication and sliding seals,
simplicity,
use of environmentally harmless working fluids
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24. • Jonathan et al., 2006, Thermo acoustic Refrigeration, GSET
Research Journal .
• R. Starr et al., 1996, The Reality of a Small Household
Thermo acoustic Refrigerator, International refrigeration and
Air Conditioning Conference.Paper 344.
• “Standing Waves.” Rod Nave, Georgia State University.
Available: http://hyperphysics.phyastr
• http://www.youtube.com/watch?v=rep6IyFl-lE
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