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The thermoacoustic effect provides a means to convert acoustic energy to heat and vice versa without the need for moving parts. This enables the realization of mechanically robust, noise mitigating energy harvesters, although there are limitations to the power-to-volume ratio achievable. The mechanical, thermal, and geometric properties of the porous stack that forms a set of acoustic waveguides in thermoacoustic devices are key to its performance. In this feasibility study, first, various 4-in. diameter ceramic and polymeric stack designs are evaluated using a custom-built thermoacoustic test rig. Influence of stack parameters such as material, length, location, porosity, and pore geometry are correlated to simulations using DeltaEC, a software tool based on Rott’s linear approximation. An acousto-thermo-electric transduction scheme is employed to harvest useable electrical power using the best performing stack. Steady-state peak voltage generated was 33.5 mV for a temperature difference of 34 °C between thehot and cold sides of the stack at an acoustic excitation frequency of 117.5 Hz. Further investigations are underway to establish structure-performance relationships by extracting scaling laws for power-to-volume ratio and frequency-thermal gradient dependencies.
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Temperature-Dependent Acoustic Properties of Magnetostrictive Iron-Gallium Alloys
Abstract The precise and continuous measurement of reactor core temperature is crucial for the safe and efficient operation of light water reactors. Current sensor technologies are limited in their capabilities for continuous monitoring, linearity, and multilocation detection. Magnetostrictive materials, which deform in response to magnetic fields or exhibit magnetization variation when stressed, offer a promising solution through ultrasonic waveguide thermometers. This study prototyped a high-temperature and radiation-tolerant UT consisting of a solenoid and a Galfenol waveguide, and quantified its performance as a thermometer up to 300 °C. The impact of waveguide diameter, ambient temperature, and thermal treatment on UT performance was then thoroughly assessed. Galfenol waveguides with diameters of 0.5 mm, 0.8 mm, and 1.0 mm showed uniform temperature-dependent behavior with minimal hysteresis error when cycled between RT and 300 °C. The acoustic attenuation coefficient decreased with increasing wire diameter, likely due to the combined effects of eddy currents and magneto-mechanical energy conversion. Although thermal annealing at 900 °C for an hour in a nitrogen environment caused significant surface damage to the waveguides, it effectively relieved internal stress, thus minimizing the nonlinearity in the acoustic attenuation coefficient.
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- Award ID(s):
- 2216310
- PAR ID:
- 10555546
- Publisher / Repository:
- American Society of Mechanical Engineers
- Date Published:
- ISBN:
- 978-0-7918-8832-2
- Format(s):
- Medium: X
- Location:
- Atlanta, Georgia, USA
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1115/SMASIS2024-140156
