22-03-2010, 08:55 PM
please read http://p2paysref/22/21165.pdf
The thermoacoustic heat pumping cycle is the youngest technology that will be presented at this workshop. Although the reverse process - the generation of sound by an imposed temperature gradient - had been observed for several centuries by glassblowersl~al nd for decades by cryogenic researchersP1; the recognition that useful amounts of heat could be pumped against a substantial temperature gradient with a coefficient-of-performance which is a significant fraction of the Camot limit was only made ten years agoU1, with the first demonstration, including efficiency measurements, being made in 1986141. This discovery was made even more significant by the recognition that the thermoacoustic heat pumping cycle was intrinsically irreversible. Traditional heat engine cycles, such as the Camot Cycle typically studied in elementary thermodynamics courses, assume that the individual steps in the cycle are reversible. In thermoacoustic engines, the irreversibility due to the imperfect (diffusive) thermal contact between the acoustically oscillating working fluid and a stationary second thermodynamic medium (the "stack") provides the required phasing. This "natural phasing"[41 has produced heat engines which require no moving parts other than the selfmaintained oscillations of the working fluid. During this relatively short period, several refrigerators and prime movers have been fabricated and tested at Los Alamos National Laboratories[3-5] and two refrigerators for spacecraft applications were built at the Naval Postgraduate School.
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An Introduction to Thermoacoustic Refrigeration
Presented By:
Mark McCarty
School of Mechanical and Aerospace Engineering
Outline
I. Thermoacoustics
II. Thermodynamics of Cooling
III. Thermoacoustic Components
IV. Thermoacoustic Theory
V. Applications and Research
VI. Environmental Benefits
VII. Summary
A. Background
1. Uses sound to create cooling
2. No moving parts inside device
B. Tremendous Opportunities
1. Saves energy
2. Economic potential
3. Good for the environment
II. Thermodynamics of Cooling
A. Power Cycles versus Heat Pump Cycles
1. Power generation
2. Cooling
B. Energy balance equation
W l = Q t - Q
cycle ^ out ^ in
COLD
(a) Power cycle (b) Refrigeration and heat pump cycle
Figure 1. Thermodynamics (Adapted from Moran and Shapiro, 2000, p. 70)
A. Resonance Tube
1. Length related to sound
2. Fundamental frequency
L = nâ€, n = 1,2,3,... 2
where L is the length of the resonance tube n is the number of the harmonic †is the wavelength
B. Regenerator Stack
1. Heart of thermoacoustic device
2. Ceramic material
a. Low thermal conductivity
b. Refrigeration
C. Acoustic Loudspeaker
1. Least efficient component
2. Gas spring system
- Improves efficiency
D. Heat Exchangers
- Least understood component
E. Working Gases
- Air versus noble gases
Hot Heat Exchanger
Regenerator Stack
Resonato r Tube
Working Gas (inside tube)
Cold Heat Exchanger
Figure 2. Simple thermoacoustic device (Adapted from Garrett and Backhaus, 2000, p. 517)
A. Acoustic Wave
1. Standing wave
2. Fundamental - Sinusoidal
B. Pressure
C. Temperature
1. Stack gradient
2. Heat exchange
A. Los Alamos National Laboratory
1. Energy industry
- Cryogenics
- Liquifaction of natural gas
2. Spacecraft power (deep space)
(IV. Applications and Research, continued)
B. Penn State University
1. Ben and Jerry's
2. Defense industry refrigeration
(http://acs.psu.edu/, 2005)
(IV. Applications and Research, continued)
C. Interesting Patents
1. Production of potable water from humid air
2. Cooling dock for laptop computers
3. Baby formula/breast-milk cooler/warmer
4. Automatic ice maker
5. Acoustic cooling of automotive electronics
6. Energy recovery system
A. Reduce Greenhouse Gas Emissions
1. Carbon dioxide
2. Refrigerant gases
B. Lower Energy Consumption
A. Simple Device
1. No moving parts
2. Inexpensive to make
B. Applications in Many Areas
1. Food industry
2. Energy sector
3. Consumer products
C. Environmentally Friendly
Questions
