THERMOACOUSTIC REFRIGERATION PPT

Presented By Pawan Kumar Singh 09ME31

CONTENTS  INTRODUCITON  VAPOR COMPRESSION REFRIGERATION  DISADVANTAGES OF VAPOUR COMPRESSION REFRIGERATION  HISTORY OF THERMO ACOUSTIC REFRIGERATION(TAR)  WHAT IS THERMO ACOUSTIC?  THERMOACOUSTIC EFFECT

 COMPONENTS AND SETUP  THERMOACOUSTIC CYCLE  MERITS AND DEMERITS OF TAR  APPLICATION  CONCLUSION  REFERENCES

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 EFFECT  Consider 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.

Fig.03

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

COMPONENTS  Acoustic 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

Stack

Resonator tube

Fig.04

Heat Exchanger

SETUP  First 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

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

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

Fig.07

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.

THERMOACOUSTIC CYCLE (cont.)

Fig.08

Fig.09

MERITS  No 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.

CONCLUSION  Thermo 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.

REFERENCE  G. W. Swift, “Thermoacoustic engines and refrigerators,”  

 

Phys. Today 48, 22-28 (1995). http://en.wikipedia.org/wiki/thermoacousticengine http://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

THANK YOU

ANY QUERIES ?