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Study and Development of Thermoacoustic Devices

Hadi Babaei

Supervised by : Dr. Kamran Siddiqui

April 6, 2009

PhD Seminar

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What is thermoacoustics ?Heat energy Sound energy

Fundamentals of Thermoacoustics

Engine

Refrigerator

Main components of a thermoacoustic device:

Resonator tube

Stack

Heat exchangers

Acoustic source (e.g. loud speaker)

Thermoacoustic engines: converting heat energy to sound energy

Thermoacoustic refrigerators: Utilizing sound energy to transfer heat

Schematic of a thermoacoustic device

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Thermoacoustic Engine

Schematic of a thermoacoustic engine

-Thermoacoustic Engines convert heat energy (Qh) to sound energy (E2).

-Heat energy (Qh) is provided through the hot heat exchanger (HXh).

-Conversion of heat energy (Qh) to sound energy (E2) takes place inside the stack.

-The remaining heat energy (Qa,eng) is transferred to the outside environment

throughout the ambient heat exchanger (HXa,eng).

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Schematic of a acoustically-driven thermoacoustic refrigerator

Acoustically-Driven Thermoacoustic Refrigerator

-Acoustically-driven thermoacoustic refrigerators transfer heat (Qc) from a

low temp. reservoir (HXc) to a high temp. reservoir (HXa,ref) by using

acoustic power provided by a loudspeaker (E2) .

-The heat transfer from a cold medium to a warm medium takes place inside

the stack.

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Thermoacoustically-driven thermoacoustic refrigerator (TADTAR) :

Engine Refrigerator

Schematic of a thermoacoustically-driven thermoacoustic refrigerator

-Heat energy is converted to sound energy by a thermoacoustic engine.

-The produced sound energy is used to run a thermoacoustic refrigerator.

Heat energy Sound energy Cooling power

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(i) At most one moving part (a loudspeaker) with no sliding seals

(ii) Nontoxic and environmentally friendly working gases

(iii) Low fabrication and maintenance cost

(iv) Utilizing any source of heat energy for cooling purposes (in a TADTAR)

(v) Generating electricity via a linear alternator or other electroacoustic power transducer

(vi) Flexible dimensions

Advantages of thermoacoustic devices

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From a miniature thermoacoustic refrigerator with the length of about an inch, to

a thermoacoustic refrigerator for natural gas liquefaction with the capacity of 7 kw of

cooling power.

The thermoacoustic natural gas liquefier developed in Los Alamos National Laboratory

by Swift et el.(2002)

Applications

Covering a broad range of application:

The solar-powered TADTAR developed in Naval Postgraduate School by Adeff and Hofler (2000)

Thermoacoustic device, Symko et al. (2006)

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My Research Work:

1. Theoretical StudiesI. Designing and optimizing of thermoacoustic devices

II. Modifying the theoretical model of thermoacoustic couples

2. Experimental InvestigationsI. Measuring and studying acoustic and streaming velocity fields

using synchronized PIV technique in thermoacoustic couples

II. Measuring and studying the developed temperature fields at the two

sides of a thermoacoustic couple using thermocouples

3. Developing a prototypeI. Designing, developing and testing a unique thermoacoustic device

9Flow chart showing the design and optimization procedure for thermoacoustic devices

Input data such as:

-Working gas-Desired temperaturesof the heat exchangers-Desired cooling power

Optimized output data:

-Ref. stack length and position-Eng. stack length and position -Required heat input for the hotheat exchanger

-Cross sectional area of the tube

1. Theoretical StudiesI. Designing and optimizing of thermoacoustic devices

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Sustainable thermoacoustic refrigerator(Operating on the waste heat of the tri-generation gas turbine engine)

• Working Fluid: Helium (high sound velocity and high thermal conductivity)• Mean Pressure: 10 atm• Acoustic frequency: 400 Hz

1. Theoretical StudiesI. Designing and optimizing of thermoacoustic devices

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Sustainable thermoacoustic refrigerator(Operating on the waste heat of an automobile engine)

Working gas Helium

Mean pressure (kPa) 700

Frequency (Hz) 400

Cooling power (W) 30

Cooling temperature (˚C) 2

Ambient heat exchangers temperature (˚C) 27

Drive ratio (%) 3

Estimated required waste heat for engine (W) 159

Hot heat exchanger temperature (˚C) 260

Overall efficiency (%) 18.8

1. Theoretical StudiesI. Designing and optimizing of thermoacoustic devices

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1. Theoretical StudiesII. Modifying the theoretical model of thermoacoustic couples

Steady-state temperature difference between the hot and cold ends of the stack versus stack position along the resonator at the pressure amplitude of 460 Pa, RVC is the stack material, comparing previous theoretical models, the present model and experimental results

Wheatley et al. model

Atchley et al. model

Developed model

Triangles: experimental results

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2. Experimental InvestigationsI. Measuring and studying acoustic and streaming velocity fields using

synchronized PIV technique in thermoacoustic couples

Schematic of the experimental set-up for acoustic and streaming investigations Plexigalss stack

30-ppi RVC stack

14Simultaneously obtained velocity fields in the presence of the plexiglass stack at the peak pressure amplitude

of 628 Pa and the frequency of 146 Hz, (a) acoustic velocity field (b) streaming velocity field

(a) (b)

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Resonator tube, 30-ppi RVC stack and heat exchangers

Air heater, control cube, flow switch and heat exchanger of the device

Air heater

Flow switch

Resonator tube RVC stackHeat exchangers

Developing a prototypeI. Designing, developing and testing a unique thermoacoustic device

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1. Developed a comprehensive and systematic procedure to design and optimize

thermoacoustic device.

2. Modified the available theoretical model predicting the stack temperature

difference and validated the model by conducting experiments.

3. Investigation of the acoustic and streaming velocity fields using a novel

synchronization technique.

4. Design, development and performance testing of a sustainable thermoacoustic

device.

Conclusions:

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Thank you

18Basic principles of thermoacoustic heat engines and refrigerators

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Thermoacoustic couples (stacks):

Primary device that thermoacoustic phenomenon can be examined

Removing heat exchangers from a thermoacoustic refrigerator

Schematic of a thermoacoustic couple

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Acoustic Streaming:

The streaming velocity is a second order flow induced by and superimposed on thedominant first-order acoustic velocity. The streaming patterns are almost stationary andtime invariant.

Schematic of the acoustic and streaming velocity fields

-In thermoacoustic engines and refrigerators, streaming generates mean motions

that result in an unwanted heat convection within the device.

-Streaming adds a heat load to the cold heat exchanger in a refrigerator or drives

away heat from the hot heat exchanger in an engine (causing a reduction in thermal

efficiency).

Schematic of the inner and outer streaming fields

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Synchronized PIV technique:

-The measured velocity field inside a standing-wave resonator is the superposition ofacoustic and streaming velocities.

-Synchronized PIV technique allows us to measure streaming velocities in any spatialregion along the resonator

Acoustic and streaming velocity fields captured at a particular phase of the excitation signal, Nabavi et al. (2007)

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Energy saving by TADTAR(theoretical prediction)

TADTARs have the potential to reduce the fuel consumption and

reduce the emission of harmful CFC refrigerants.

If all the industrial waste heat above 140ºC in the Netherlands can be

used in TADTARs, this would save 16 PJ yearly. This corresponds to

more than 5 billion m3 of natural gas (http://www.ecn.nl/en/).