Presented ByPawan Kumar Singh 09ME31

CONTENTSINTRODUCITONVAPOR COMPRESSION REFRIGERATIONDISADVANTAGES OF VAPOUR COMPRESSION REFRIGERATIONHISTORY OF THERMO ACOUSTIC REFRIGERATION(TAR)WHAT IS THERMO ACOUSTIC?THERMOACOUSTIC EFFECTCOMPONENTS AND SETUPTHERMOACOUSTIC CYCLEMERITS AND DEMERITS OF TARAPPLICATIONCONCLUSIONREFERENCES

INTRODUCTION

Physicists and engineers have been working on a class of heat

engines and compression-driven refrigerators that use no

oscillating pistons, oil seals or lubricants.

Thermo acoustic devices take advantage of sound waves to

convert a temperature differential into mechanical energy or

mechanical energy into a temperature differential.

Thermo acoustic devices perform best with inert gases as the

working fluid and don’t produce harmful environment .

VAPOR COMPRESSION REFRIGERATION

The compressor compresses the ammonia gas and heats up.

In condenser the hot ammonia gas dissipate its heat and

condenses into ammonia liquid at high pressure.

The high-pressure ammonia liquid flows through the expansion

valve and its pressure dropped.

The liquid ammonia boils and vaporizes its temperature

dropping to -23 C. This makes the inside of the refrigerator cold.

The cold ammonia gas is sucked up by the compressor, and the

cycle repeats.

VAPOR-COMPRESSION REFRIGERATION CYCLE

Fig.01

DISADVANTAGES OF VAPOUR COMPRESSION REFRIGERATION

Uses harmful refrigerants like ammonia, CFC’s and HFC’s.

Refrigerants if leaked causes the depletion in the ozone layers.

Refrigerants are costly.

The moving parts like the compressors require lubrication.

Leakage of refrigerant may result in adverse human health effects including cancers, immune system deficits.

HISTORY OF THERMO ACOUSTIC REFRIGERATION

Lord Rayleigh discussed the possibility of pumping heat with

sound in 1887.

S. L. Garrett , Leading Researcher United Technologies

Corporation Professor of Acoustics, The Pennsylvania State

University.

He invented the thermo acoustic refrigerator in the year 1992.

University of Utah began a research project in 2005 called

Thermo Acoustic Piezo Energy Conversion.

WHAT IS THERMO ACOUSTIC?Thermo acoustics is a science that is concerned with the

interactions between heat(thermo) and pressure oscillation in

gases(acoustics).

This field can be broken into two subcategories.

The first is the forward effect which is concerned with the

generation of pressure oscillation from heat, is primarily used to

create engines known as thermo acoustic engines.

The second subcategory is reversed of using acoustic waves to

pump heat, creates thermo acoustic refrigerators.

THERMO ACOUSTIC EFFECTConsider a loudspeaker generate sound waves in a resonator tube close

at both ends. Interference can occur between two waves travelling in

opposite direction at certain frequencies.

The interference causes resonance creates a standing or acoustic wave.

Resonance occurs at resonance frequencies.

In the acoustic wave, parcels of gas adiabatically compress & expand.

Variation of temperature and pressure due to compression and

expansion of the gas.

Expanded and compressed gas parcels can take or reject heat on wall.

Fig.03

COMPONENTSAcoustic Loudspeaker, is an electro acoustic transducer that

produces sound in response to an electrical audio signal input.

Resonance tube, long hollow tube filled with gas( 97% helium

and 3 % xenon) at high pressure.

Stack, consist of honeycombed plastic spacers that do not conduct

heat but temporarily absorb heat & transferred by the sound

waves.

Heat Exchangers, are the devices used to transfer heat energy

from one fluid to another.

COMPONENTS(cont.)

Loudspeaker Resonator tube

Stack Heat ExchangerFig.04

SETUPFirst take a resonator tube.

Customized loudspeaker are attached to the resonator tube.

Filled it with inert, pressurized gases such as xenon and helium.

Placing the stack at certain position.

Placing heat exchanger

at each side of the stack.

Fig.05

THERMOACOUSTIC CYCLE (cont.) When the loud speaker blast sound at 180 decibels, an acoustic wave

resonate in the resonance tube.

Adiabatic compression of the gas: In stack, a gas parcel is adiabatic

compressed from the right to left position and thus the temperature

increases. Now parcel has a higher temperature than stack plate.

Isobaric heat transfer: Due to higher

temperature of gas parcel, causing it to transfer

heat to the stack plate at constant pressure losing temperature.Fig.06

THERMOACOUSTIC CYCLE (cont.)Adiabatic expansion of the gas: Gas parcel is displaced back from

the left to right position and due to adiabatic expansion, the gas is

cooled to a temperature lower than stack plate.

Isobaric heat transfer: The parcel's temperature

is now lower than the plate and heat transferred

from the plate to the gas at a constant pressure, increasing the

parcel's temperature back to its original value.

Heat is moved by placing heat exchangers at each side of the stack.

Fig.07

THERMOACOUSTIC CYCLE (cont.)

Fig.08 Fig.09

MERITSNo moving parts, so very reliable and a long life span.

The harmful refrigerant gases are removed.

Thermo acoustic refrigeration works best with inert gases such as

helium and argon, which are harmless, nonflammable, nontoxic,

non-ozone depleting and is judged inexpensive to manufacture.

Use of simple materials, which are commercially available in large

quantities and therefore relatively cheap.

Saved energy up to 40% .

DEMERITS

Efficiency of thermo acoustic refrigeration is currently less than the

traditional refrigerators.

Lack of suppliers producing customized components.

Lack of interest because industry concentration on developing

alternative gases to CFCs.

There are not enough people who have expertise in this discipline.

APPLICATIONS

Space-Exploration-Mission: It was launched with the Space

Shuttle Discovery (STS-42) on January 22, 1992.

Liquefaction of natural gas.

Electronic chip cooling.

Electricity from sunlight.

Upgrading industrial waste heat.

Food merchandising where toxicity is an important issue.

CONCLUSIONThermo acoustic engines and refrigerators were already being

considered a few years ago for specialized applications, where

their simplicity, lack of lubrication and sliding seals, and their use

of environmentally harmless working fluids were adequate

compensation for their lower efficiencies.

In future let us hope these thermo acoustic devices help to protect

the planet might soon take over other costly, less durable and

polluting engines and pumps.

REFERENCEG. W. Swift, “Thermoacoustic engines and refrigerators,”

Phys. Today 48, 22-28 (1995).http://en.wikipedia.org/wiki/thermoacousticenginehttp://www.thermoacousticscorp.com/news/index.cfm/ID/

4.htm. 17 July 2006.S. L. Garrett and S. Backhaus, ‘‘The power of sound,’’ Am.

Sci. 88, 516–525 (2000).www.arl.psu.edu/capabilities/uss_acou_tre.html

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