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Prandtl number and thermoacoustic refrigerators
M E H Tijani1, J C H Zeegers, A T A M de Waele
1Department of Applied Physics, Eindhoven University of Technology, The Netherlands.
The Journal of the Acoustical Society of America
|July 27, 2002
Summary
Lowering the Prandtl number using monatomic gas mixtures significantly enhances thermoacoustic refrigerator performance. A mixture with 30% xenon achieved a 70% higher relative Carnot coefficient of performance.
Area of Science:
- Thermodynamics
- Acoustics
- Fluid Dynamics
Background:
- Kinetic gas theory establishes the Prandtl number for hard-sphere monatomic gases as 2/3.
- Lower Prandtl numbers are achievable with gas mixtures of heavy and light monatomic gases.
- Previous studies indicate potential for Prandtl numbers between 0.2 and 0.67 using helium-based mixtures.
Purpose of the Study:
- To experimentally investigate the impact of Prandtl number on thermoacoustic refrigerator performance.
- To evaluate the effectiveness of various helium-argon, helium-krypton, and helium-xenon gas mixtures.
Main Methods:
- Experimental setup for a thermoacoustic refrigerator.
- Systematic variation of gas mixture composition to achieve a range of Prandtl numbers (0.2–0.67).
- Measurement of refrigerator performance, including the coefficient of performance relative to Carnot.
Main Results:
- Thermoacoustic refrigerator performance improves as the Prandtl number decreases.
- A helium-xenon mixture (30% xenon) yielded the lowest Prandtl number (0.2).
- This mixture resulted in a 70% increase in the relative Carnot coefficient of performance compared to pure helium.
Conclusions:
- Reducing the Prandtl number is a viable strategy for enhancing thermoacoustic refrigerator efficiency.
- Helium-xenon mixtures show particular promise for achieving low Prandtl numbers and high performance.
- The findings support the use of tailored gas mixtures in optimizing thermoacoustic cooling technologies.