1. A group of 5 students - Aagam Shah, CH Nikhil Reddy, CH Pavan, U Phani Abhinav, and Vaishali Das - under the guidance of Dr. B. Satyanarayana are developing a thermoacoustic refrigerator. 2. Thermoacoustic refrigerators use sound waves in a pressurized gas to transfer heat without refrigerants or moving parts. This project aims to design and test a prototype refrigerator. 3. The document outlines the objectives, methodology, literature review, work progress to date including design calculations and modeling, and applications of thermoacoustic refrigeration.

1. Department of
Mechanical Engineering
1. AAGAM SHAH -14071A0361
2. CH NIKHIL REDDY -14071A0365
3. CH PAVAN -14071A0367
4. U PHANI ABHINAV -14071A03A8
5. VAISHALI DAS -14071A03B0
Under the guidance of :
Dr. B. Satyanarayana,
Professor,
Department Of Mechanical Engineering,
VNR VJIET
DEVELOPMENT OF THERMOACOUSTIC
REFRIGERATOR

2. Department of
Mechanical Engineering
Abstract
Introduction
Literature Review
Work Plan
Methodology
Work Progress
Result
Conclusion
Scope of work
Applications
References
LIST OF CONTENTS

3. Department of
Mechanical Engineering
Thermo-acoustics is a phenomenon that deals with the interaction between the
sound and thermal energies. Its recent use is to develop heat Engines and
Pumps/Refrigerators. Thermo-acoustic refrigeration is one such phenomenon
that uses high intensity sound waves in a pressurized gas tube to transfer heat
from one place to other to produce refrigeration effect. In this type of
refrigeration, refrigerants are eliminated, and Sound waves take their place. A
loud speaker and an acoustically insulated tube are used for the purpose. Further,
this system eliminates lubricants and results in 40% less energy consumption.
Hence, in this project, a prototype of low cost environmental friendly
thermoacoustic refrigerator is developed. Thermo-acoustic refrigerator operates
with inert gases and without moving parts, making them highly efficient devices
for environmentally-safe refrigeration with almost zero maintenance cost.
ABSTRACT

4. Department of
Mechanical Engineering
INTRODUCTION
Over the past two decades, 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. These so called 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. Such materials thus can be used, for example, to
generate electricity or to provide refrigeration and air conditioning. Because
Thermo-acoustic devices perform best with inert gases as the working fluid,
they do not produce the harmful environmental effects such as global warming
or stratospheric ozone depletion that have been associated with the engineered
refrigerants such as CFCs and HFCs. Recent advances have boosted efficiencies
to levels that rival what can be obtained from internal combustion engines,
suggesting that commercial Thermo-acoustic devices may soon be a common
place.

5. Department of
Mechanical Engineering
OBJECTIVE
The aim of present work is “To design and develop a model of Standing Wave
Thermoacoustic Refrigerator” (TAR) worked by a sound wave of 385Hz
frequency. The prime objectives of this project are as follows
• To theoretically examine the impact of various working parameters and
working medium on TAR execution.
• To design and construct a TAR model as per the theoretical parameters and to
test the model experimentally.
• To compare theoretical and experimental models of TAR and to estimate the
practical viability of the current research.

6. Department of
Mechanical Engineering
LITERATURE REVIEW
1. Paek I, Braun J.E., Mongeau L., “Evaluation of standing-wave
thermoacoustic cycles for cooling applications”, International Journal
of Refrigeration 30, pp 1059-1071, (2007).
2. Tijani M.E.H., “Loudspeaker Driven Thermoacoustic Refrigeration”, PhD
Dissertation, Technical University of Eindhoven, Netherlands, (2001)
3. Poese M.E., Garrett S.L., “Performance measurements on a thermoacoustic
refrigerator driven at high amplitudes”, Journal of the Acoustical
Society of America 107, pp 2480- 2486, (2000).
4. Hofler T.J., “Thermoacoustic Refrigerator Design and Performance”, Ph.D.
dissertation, Physics Department, University of California, San Diego,
(1986).

7. Department of
Mechanical Engineering
WORK PLAN
Phase-I
• Project Selection and Research
• Feasibility Study and Market Survey
Phase-II
• Project Design and Analysis
• Cost Approximations and Material Procurement
Phase-III
• Fabrication of Demonstrative Prototype
• Testing and Analysis cum Feedback
• Project Report Generation

8. Department of
Mechanical Engineering
METHODOLOGY
1. INITIAL RESEARCH DETERMINING THE CHARACTERISTICS OF THE
COMPONENTS OF THERMOACOUSTIC REFRIGERATOR.
2. DETERMINING THE OPERATIONAL PAREMETERS, DESIGN PARAMETERS
AND MATERIAL PROPERTIES.
3. EXPERIMENTAL FEASIBILITY AND MARKET SURVEY.
4. ARRIVING ON A FINAL THEORITICAL MODEL FOR THE THERMOACOUSTIC
REFRIGERATOR.
5. FABRICATION USING THE THEORITICAL PARAMETERS AND VALUES.
6. TESTING THE THERMOACOUSTIC REFRIGERATOR FOR MAXIMUM
EFFICIENCY.
7. FINDING THE EXPERIMENTAL COP AND COMPARING IT WITH THEORITICAL
COP.

9. Department of
Mechanical Engineering
INITIAL RESEARCH DETERMINING THE CHARACTERISTICS OF
THE COMPONENTS OF THERMOACOUSTIC REFRIGERATOR
1. Working Medium
2. Acoustic driver
3. Resonator
4. Stack
5. Heat exchanger

10. Department of
Mechanical Engineering
DETERMINING THE OPERATIONAL PAREMETERS,
DESIGN PARAMETERS AND MATERIAL PROPERTIES.

11. Department of
Mechanical Engineering
WORK PROGRESS
 FEASIBILITY STUDY
We can summarize that the theory of standing wave thermoacoustics is well
established, stating back over a century. Recent developments are encouraging
in the field with the improving efficiency starting from 12% of Carnot COP by
Tom Hofler in 20th century, yet many aspects of the thermoacoustic refrigerator
are not known like gas behavior inside the resonating column. Also, the low
efficiency of the acoustic driver results in overall low efficiency of the system.

12. Department of
Mechanical Engineering
WORK PROGRESS
 PROJECT STUDY
Various parts of the thermoacoustic refrigerator, namely, acoustic
driver, resonator, stack, gas & their characteristics were studied as
stated in methodology.
1. ACOUSTIC DRIVER
• In order to create an acoustic standing wave in the gas at the
fundamental resonant frequency of the resonator.
• The acoustic driver converts electric power to the acoustic power.
• The range of operating frequency of the acoustic device is between
350-450Hz depending on the working fluid medium employed in the
resonator and is driven by a power amplifier.
.

13. Department of
Mechanical Engineering
WORK PROGRESS
2. RESONATOR
• Shape, weight, length are important parameters for designing the resonator
• Length of the resonator is decided by the frequency of the resonator and
minimal losses at the wall of the resonator
• For an acoustic device of 385Hz frequency a resonator of 474mm length and
dia 52.3mm is selected for air medium.
• Due to easy availability, strength as well as design considerations Nylon rod
was used for resonator.
• A rod of 90mm Dia was used and a bore of 52.3mm was machined inside.

14. Department of
Mechanical Engineering
WORK PROGRESS
3. STACK
• The stack forms the heart of the refrigerator where the process of heat
pumping takes place and it is thus an important element which determines
the performance of the refrigerator
• The stack material must have a low thermal conductivity (Ks) and a heat
capacity (Cs) must be larger than the heat capacity of working gas in order
that the temperature of the stack plate remains steady.
• The distance b/w the stack plates is determined using thermal penetration
depth.
• Stack used for the initial prototype is a spiral stack made by using Teflon
sheets with Nylon rod(6mm) at the core. Alternatively, Mylar sheets can be
used.

15. Department of
Mechanical Engineering
WORK PROGRESS
BLOCK DIAGRAM FOLLOWED IN DETERMINING THE DESIGN
CALCULATIONS

16. Department of
Mechanical Engineering
WORK PROGRESS
GRAPHICAL CALCULATIONS FOR AIR AND HELIUM GASES

17. Department of
Mechanical Engineering
WORK PROGRESS
COP (Vs) Lsn for He-Xe gaseous mixture

18. Department of
Mechanical Engineering
WORK PROGRESS
4. HEAT EXCHANGER
• Heat exchanger plays an important role in cooling the hot end of the stack.
• Heat exchangers can be of convective air flow type or conductive water flow
type.
• Copper H.E. can be effectively used to dissipate heat from the resonator.

19. Department of
Mechanical Engineering
WORK PROGRESS
5. WORKING MEDIUM
• The working medium should have high sound speed
• The gas must have low thermal conductivity so that loss of cooling due to
axial conduction is low
• High specific heat capacity
• Low viscosity
• Gas must be safe, cheap, easily available.
• Air is chosen as the working medium for the initial prototype purpose.
• An operating pressure of 10Bar is to be maintained inside the resonator
column for the drive ratio to be ‘0.02’.

20. Department of
Mechanical Engineering
WORK PROGRESS
THERMOACOUSTIC CYCLE

21. Department of
Mechanical Engineering
WORK PROGRESS
THE MODEL
• Resonator
• Stack
• Driver
• Heat exchanger

22. Department of
Mechanical Engineering
WORK PROGRESS
FINAL MODEL

23. Department of
Mechanical Engineering
VALUES OF PARAMETRES
1. Medium – Air
2. Velocity of Medium – 351.9m/s
3. Frequency – 385Hz
4. Stack Length – 50mm
5. Distance of centre of stack from speaker - 44mm
6. Cooling Power – 10Watts
7. Acoustic Power – 9.75 Watts
8. Pressure - 10Bar
9. Length of resonator – 457mm
10. Radius of Resonator – 26.48mm
11. Length of Cold HE – 17.132mm
12. Length of Hot HE – 34.265mm

24. Department of
Mechanical Engineering
RESULTS
1.TEST-I Involved testing without heat exchangers installed. The result obtained was not satisfactory.
2.TEST-II Theoretically, a temperature drop of 15.69 degrees can be achieved considering all the other
parameters constant, but a temperature of 29 degrees from the hot end temperature of 33degrees
(drop of 4degrees) could be achieved, the reason is because the theoretical calculations were done at
10 bar and the experiment was conducted at 1 bar pressure.
Time(mi
n)
5 15 25 35 45 55
Temperat
ure cold
end(oC)
32 31 30.5 30 29.5 29

25. Department of
Mechanical Engineering
RESULTS
Temperature of cold end vs Time
26.5
27
27.5
28
28.5
29
29.5
30
30.5
0 10 20 30 40 50 60
Temperature
Time(min)
Temperature vs Time

26. Department of
Mechanical Engineering
CONCLUSION
• A standing-wave TAR was designed by using the dimensionless parameter approach as
suggested by Tijani.
• The detailed theoretical discussion of various design parameters influencing thermoacoustic
refrigerator's COP and efficiency are discussed.
• Operating air at maximum pressure sustainable by the setup (1.5bar) resulted in efficiency of
3K over a span of 60minutes, which indicated that the efficiency of the system is very low.
• Efect of working pressure is immense on the temperature difference of the system as
working pressure is directly proportional to the power density. With increase in the
working pressures, the thermal penetration depth decreases which makes the stack
fabrication more difficult.

27. Department of
Mechanical Engineering
SCOPE OF WORK
This promising “green technology” leaves immense scope of improvement. We have, in our
design analysis chapter, theoretically shown the increase in COP of the system with the improvement
in the following areas of the thermoacoustic refrigerator system:
• A TEST-3 is desired to be conducted at elevated pressures of up to 10bar inside the resonator.
• Improving the driver efficiency by matching it to the natural frequency of the gas parcel.
• Using more efficient materials like Delrin for resonator and Mylar sheets for stack.
• To achieve the efficient driver construction, magnetic materials with higher strength and pole
piece material having high permeability shall be employed.
• Using rubber material for the speaker diaphragm instead of a paper-type diaphragm.
• Better and efficient heat exchanger design.
• Using lighter gases, especially Helium. This gas provides superior sound velocity and results in
better COP of the thermoacoustic system.
• Using noble gas mixture, preferably, He-Xe mixture with roughly 70% weightage of the lighter gas
(He) results in a 60-70% increase in efficiency of the system.
• Employing an open-ended buffer volume at the opposite side of the driver on the resonator
column. It results in better output as they are void of non-linear effects. Using the buffer volume
decreases the power consumption because of lesser surface area and reduces the probability of
gas and pressure leakages in the system.

28. Department of
Mechanical Engineering
APPLICATIONS
Existing:
• Ben and Jerry’s Ice-cream parlor in USA.
• NASA: Preserve blood and urine samples
• US NAVY: Cool radar electronics onboard warships
Potential:
• Liquefication of natural gas: combustion of natural gas in thermoacoustic engine generates sound
energy. This acoustic energy is utilized in a thermoacoustic heat pump to compress and liquidity
natural gas.
• Chip cooling: In this case a piezoelectric element generates a sound wave. A thermoacoustic heat
pump cools the chip.
• Space applications as spacecraft cryocooler.
• Electronic equipment cooling on naval ships.
• Electricity from sunlight.
• Food preservation on naval ships.
• To cool domestic use products vis-à-vis a general refrigerator.
• Upgrading industrial waste heat.
• Cooling of highly reactive metals like sodium, potassium.

29. Department of
Mechanical Engineering
REFERENCES
[1] N. Rott, Thermoacoustics, Advances in Applied Mechanics, 20:135-175, 1980.
[2] J. Wheatley, T. Hofler, G. W. Swift, and A. Migliori, Understanding some simple phenomena in
thermoacoustics with applications to acoustical heat engines, Am. J. Phys. 53 (2), February 1985
[3] B. Higgins, Nicholson’s Journal I, 130 (1802)
[4] P. L. Rijke, Notiz uber einen neue Art, die bieden ende offenen Rohre enthaltene Luft in
Schwingungen zu versetzen, Ann. Phys. (Leipzig) [2] 107,339 (1859)
[5] C. Sondhauss, Ueber die Schallschwingungen der Luft in erhitzten Glas-Rohren und in gedeckten
Pfeifen von ungleicher Weite, Ann. Phys. (Leipzig) [2] 79, 1(1850)
[6] G.W. Swift, Thermo acoustics: A unifying perspective for some engines and refrigerators., short
course, March 1999, Berlin.
[7] Ram Chandrashekhar Dhuley, "Investigations on a thermoacoustic refrigerator.", Master of
technology project. ;2010 (IIT-B).
[8] Tijani M.E.H., Zeegers J.C.H., and De Waele A.T.A.M. “Construction and performance of a
thermoacoustic refrigerator.” Cryogenics, 42(1):59-66, 2001.