Thermo acoustic refrigeration

Thermo Acoustic refrigeration is a phenomenon that uses high intensity sound waves in a pressurized gas tube to pump heat from one place to other to produce refrigeration effect. This system completely eliminates the need for lubricants and results in 40% less energy consumption.

1. THERMO ACOUSTIC REFRIGERATION 1 Presented by K.PAVAN KUMAR MECHANICAL DEPT VIGNAN ENGG COLLEGE HYDERABAD.

2. 2 CONTENTS ABSTRACT INTRODUCTION BASICS OF REFRIGERATION DISADVANTAGES OF CONVENTIONAL REFRIGERATOR BASICS OF THERMO ACOUSTIC REFRIGERATION COMPONENTS HOW IT WORKS MERITS OF TAR DEMERITS OF TAR IMPROVEMENTS MADE APPLICATIONS CONCLUSION

3. ABSTRACT 3 Thermo acoustic refrigeration ( TAR ) is a phenomenon that uses high intensity sound waves in a pressurized gas tube to pump heat from one place to other to produce refrigeration effect. This system completely eliminates the need for lubricants and results in 40% less energy consumption.

4. INTRODUCTION Thermo acoustic devices take advantage of sound waves reverberating within them to convert a temperature differential into mechanical energy or mechanical energy into a temperature differential. Thermo acoustic devices perform best with inert gases. They do not produce the harmful environmental effects such as global warming or stratospheric ozone depletion. 4

5. 5 Leading Researcher United Technologies Corporation Professor of Acoustics, The Pennsylvania State University. He invented the thermo acoustic refrigerator in the year 1992 and that TAR was used in the space shuttle Discovery(STS-42). Steven L. Garrett

6. BASICS OF REFRIGERATION 6 In refrigeration heat is not created, it is converted and transferred.

7. 7 The compressor is the heart of the system. It compresses the low pressure refrigerant vapour into high pressure refrigerant vapour. The condenser removes heat from the refrigerant, it changes state into high pressure liquid. Metering devices are small thin copper tubes ( thermal expansion devices ). It regulates the amount of refrigerant going into the evaporator. The evaporator absorbs the heat in the system, the low pressure liquid changes into low pressure gas. The low pressure vapour pulled into the compressor and the cycle starts over….

8. 8 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, and respiratory effects. DISADVANTAGES OF CONVENTIONAL REFRIGERATOR

9. 9 BASICS OF THERMO ACOUSTIC REFRIGERATION Thermo acoustics combines the branches of acoustics and thermodynamics together to move heat by using sound. While acoustics is primarily concerned with the macroscopic effects of sound transfer like coupled pressure and motion oscillations, thermo acoustics focuses on the microscopic temperature oscillations that accompany these pressure changes. Thermo acoustics takes advantage of these pressure oscillations to move heat on a macroscopic level. This results in a large temperature difference between the hot and cold sides of the device and causes refrigeration.

10. 10 THERMO ACOUSTIC REFRIGERATOR

11. 11 COMPONENTS RESONANCE TUBE: The purpose of the resonance tube in a TAR is to contain the working fluid and to cause it to have a desired natural frequency.

12. 12 ACOUSTIC LOUD SPEAKER: A loudspeaker is an electro acoustic transducer that produces sound in response to an electrical audio signal input. It was invented in the mid 1820’s by the scientist Johann Philipp Reis. It is powered by electricity. The magnet or the coil in the speaker vibrates to produce the waves of required frequency.

13. 13 REGENERATOR STACK: The most important piece of a thermo acoustic device is the stack. The stack consists of a large number of closely spaced surfaces that are aligned parallel to the resonator tube. In a usual resonator tube, heat transfer occurs between the walls of cylinder and the gas. However, since the vast majority of the molecules are far from the walls of the chamber, the gas particles cannot exchange heat with the wall and just oscillate in place, causing no net temperature difference. The purpose of the stack is to provide a medium where the walls are close enough so that each time a packet of gas moves, the temperature differential is transferred to the wall of the stack.

14. 14 Most stacks consist of honeycombed plastic spacers that do not conduct heat throughout the stack but rather absorb heat locally. With this property, the stack can temporarily absorb the heat transferred by the sound waves.

15. 15 HEAT EXCHANGER: Heat exchangers are devices used to transfer heat energy from one fluid to another. The media maybe separated by a solid wall, so that they never mix. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants.

16. 16 HOW IT WORKS? Acoustic or sound waves can be utilized to produce cooling. The principle can be imagined as a loud speaker creating high amplitude sound waves that can compress refrigerant allowing heat absorption. The pressure variations in the acoustic wave are accompanied by temperature variations due to compressions and expansions of the gas. For a single medium, the average temperature at a certain location does not change. When a second medium is present in the form of a solid wall, heat is exchanged with the wall. An expanded gas parcel will take heat from the wall, while a compressed parcel will reject heat to the wall.

17. 17 Experimental Setup

18. 18 MERITS OF TAR No moving parts for the process, so very reliable and a long life span . Environmentally friendly working medium (air, noble gas). Use of simple materials with no special requirements, which are commercially available in large quantities and therefore relatively cheap . The technology could represent a major breakthrough using a variety of refrigerants, and save up to 40% in energy. Thermo acoustic refrigeration works best with inert gases such as helium and argon , which are harmless, nonflammable, nontoxic, non-ozone depleting or global warming and is judged inexpensive to manufacture.

19. DEMERITS OF TAR 19 Thermo acoustic refrigeration is currently less efficient than the traditional refrigerators. Lack of suppliers producing customized components. Lack of interest and funding from the industry due to their concentration on developing alternative gases to CFCs.

20. IMPROVEMENTS MADE 20 To overcome the drawbacks, some improvements were made: In order to improve the efficiency, regenerators are used. The function of a regenerator is to store thermal energy during part of the cycle and return it later. This component can increase the thermodynamic efficiency to impressive levels. Increasing the level of temperature gradient setup thereby providing more refrigeration effect.

21. APPLICATIONS OF TAR 21 Liquefaction of natural gas. Chip cooling. Electronic equipment cooling on naval ships. Electricity from sunlight. Upgrading industrial waste heat.

22. CONCLUSION 22 Thermo acoustic engines and refrigerators were already being considered a few years ago for specialized applications. 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 which promise to improve everyone’s standard of living while helping to protect the planet might soon take over other costly, less durable and polluting engines and pumps.

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