Aravind N. Badiger7 ME

USN:2BA09ME012

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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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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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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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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(c) Illustration of the Sondhauss tube

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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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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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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Driver• Houses the Loudspeaker

Resonator

Houses the gas ( Helium)

The hot and cold heat exchangers

Houses the Stack

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Loudspeaker Creates sound waves up to 200 dB!

Resonator—where gas cooling and compression take placeUses inert gas, commonly Helium for

refrigeration

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StackSeries of small parallel channels through which pressure and velocity of waves changeIn between the heat exchangers

Heat ExchangersHot heat exchangerCold heat exchanger

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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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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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QC =

Wa =

Co-eff icient of performance

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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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• 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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