An Introduction to Thermoacoustic Refrigeration

Mark McCarty

School of Mechanical and Aerospace Engineering

Cornell University

April 29, 2005

Outline

I. ThermoacousticsII. Thermodynamics of CoolingIII. Thermoacoustic ComponentsIV. Thermoacoustic TheoryV. Applications and ResearchVI. Environmental BenefitsVII. Summary

I. Thermoacoustics

A. Background1. Uses sound to create cooling2. No moving parts inside device

B. Tremendous Opportunities1. Saves energy2. Economic potential3. Good for the environment

II. Thermodynamics of Cooling

A. Power Cycles versus Heat Pump Cycles1. Power generation2. Cooling

B. Energy balance equation

inoutcycle QQW −=

SYSTEM

HOT

COLD

WORKOUT

Qin

Qout

SYSTEM

HOT

COLD

WORKINQin

Qout

(a) Power cycle (b) Refrigeration and heat pump cycle

Figure 1. Thermodynamics (Adapted from Moran and Shapiro, 2000, p. 70)

III. Thermoacoustic Components

A. Resonance Tube1. Length related to sound2. Fundamental frequency

,...3,2,1,2

== nnL nλ

wavelengththeisharmonictheofnumbertheisn

tuberesonancetheoflengththeisLwhere

λ

(III. Thermoacoustic Components, continued)

B. Regenerator Stack1. Heart of thermoacoustic device2. Ceramic material

a. Low thermal conductivityb. Refrigeration

(III. Thermoacoustic Components, continued)

C. Acoustic Loudspeaker1. Least efficient component2. Gas spring system

- Improves efficiencyD. Heat Exchangers

- Least understood componentE. Working Gases

- Air versus noble gases

Loudspeaker

Resonator Tube

Hot HeatExchanger

Cold HeatExchanger

RegeneratorStack

Working Gas (inside tube)

Figure 2. Simple thermoacoustic device(Adapted from Garrett and Backhaus, 2000, p. 517)

IV. Thermoacoustic Theory

A. Acoustic Wave1. Standing wave2. Fundamental

- SinusoidalB. PressureC. Temperature

1. Stack gradient2. Heat exchange

Figure 3. Effect of sound on gas flow moving through the stack

stack

gas flow

hot

cold

V. Applications and Research

A. Los Alamos National Laboratory1. Energy industry

- Cryogenics- Liquifaction of natural gas

2. Spacecraft power (deep space)

Figure 4. The first Thermoacoustic Sterling Heat Engine (TASHE)(Wollan et al., 2002)

(a) 500 gpd prototype (b) 10,000 gpd design

Figure 5. Thermoacoustic Sterling Heat Engine (TASHE)(www.lanl.gov/thermoacoustics/, 2005)

Figure 6. Thermoacoustic radioisotope deep space power system

(www.lanl.gov/thermoacoustics/, 2005)

(IV. Applications and Research, continued)

B. Penn State University1. Ben and Jerry’s2. Defense industry

refrigeration

Figure 7. The Ben and Jerry’s Project Team

(http://www.acs.psu.edu/, 2005)

Figure 8. SETAC being tested(SETAC Project…, 2005)

a) Simple thermoacoustic engine b) Solar powered engine

Figure 9. Demonstration model of thermoacoustic engine(Garrett and Backhaus, 2000, p. 518, photo courtesy of Reh-lin Chen)

(IV. Applications and Research, continued)

C. Interesting Patents 1. Production of potable water from humid air2. Cooling dock for laptop computers3. Baby formula/breast-milk cooler/warmer4. Automatic ice maker5. Acoustic cooling of automotive electronics6. Energy recovery system

VI. Environmental Benefits

A. Reduce Greenhouse Gas Emissions1. Carbon dioxide2. Refrigerant gases

B. Lower Energy Consumption

Figure 10. Global per capita carbon dioxide emissions(Andres et al., 1999)

VII. Summary

A. Simple Device1. No moving parts2. Inexpensive to make

B. Applications in Many Areas1. Food industry2. Energy sector3. Consumer products

C. Environmentally Friendly

Questions