Mesure de flux de chaleur dans un réfrigérateur thermoacoustique miniature.

Dans le cadre de la miniaturisation de systèmes thermoacoustiques réfrigérants, un démonstrateur de dimension réduite, muni d'un couple stack-échangeurs de chaleur, qui vise à refroidir un liquide jusqu'à son changement de phase, a été construit. L'évolution temporelle de la température et le flux de chaleur transverse sont mesurés à l'aide de microcapteurs spécifiquement développés. Les premiers résultats expérimentaux sont présentés

Systèmes thermo-acoustiques de transfert de chaleur : répartition interne de température en régime transitoire

L'objet des travaux présentés ici porte sur l'étude théorique et expérimentale de l'évolution en régime transitoire de la distribution de température au cœur d'un réfrigérateur thermoacoustique. Un modèle analytique de ce comportement est présenté, dans le cadre d'une théorie linéaire. Il prend en compte les effets des différents flux de chaleur présents dans l'empilement. Ce modèle analytique permet d'interpréter de façon quantitative, après ajustement réaliste de paramètres inconnus, le comportement transitoire d'un prototype expérimental de réfrigérateur thermoacoustique

Nonreciprocal and even Willis couplings in periodic thermoacoustic amplifiers

hermoacoustic amplifiers are analyzed in the framework of nonreciprocal Willis coupling. The closed form expressions of the effective properties are derived, showing that an applied temperature gradient causes the appearance of a nonreciprocal Willis coupling. Even and nonreciprocal Willis couplings are exhibited already in the first-order Taylor expansion of the solution and are of equal modulus but opposite sign, thus suggesting that the even Willis coupling is a reaction to the nonreciprocity introduced by the temperature gradients. These Willis couplings cause a coalescence point in the k space, which deviates from Re(k) = 0 (with k the wave number) and is thus a zero-group-velocity point, as well as the opening of an amplification gap at low frequency. Effective parameters and scattering properties are found in excellent agreement with experimental results. This article paves the way to further control the acoustic waves at very low frequencies with nonreciprocal systems

Thermacoustics: an overview

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To predict a thermoacoustic engine's limit cycle from its impedance measurement

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Test-bench for the experimental characterization of porous material used in thermoacoustic cooler

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Prediction of limit cycle amplitudes in thermoacoustic engines by means of impedance measurements

International audienceThis paper deals with the prediction of the frequency and the amplitude of self-sustained oscillations generated in thermoacoustic prime movers, which are compared to measurements. A specially designed, high amplitude, acoustic impedance sensor was developed to perform measurements of the input impedance of a thermoacoustic core, as a function of the heating power supplied to the device, of the frequency, and of the amplitude of acoustic forcing. Those measurements can then be used to predict the spontaneous generation of acoustic oscillations and their saturation up to a steady-state. Those predictions were successful for various acoustic loads connected to the thermoacoustic core. Moreover, the measurements of acoustic impedance as a function of the amplitude of acoustic oscillations are compared to a model based on the linear thermoacoustic theory, and this comparison provides insights into the processes controlling the saturation of acoustic oscillations. The experimental procedure described in this paper can also have practical value, since it provides an empirical way, in principle, to optimize the coupling between the thermoacoustic core and the load, so that the potential eciency of thermoacoustic energy conversion is maximized. a) Electroni

Thermoacoustic, Small Cavity Excitation to Achieve Optimal Performance

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Active control of thermoacoustic amplification in a thermo-acousto-electric engine

International audienceIn this paper, a new approach is proposed to control the operation of a thermoacoustic Stirling electricity generator. This control basically consists in adding an additional acoustic source to the device, connected through a feedback loop to a reference microphone, a phase-shifter, and an audio amplifier. Experiments are performed to characterize the impact of the feedback loop (and especially that of the controlled phase-shift) on the overall efficiency of the thermal to electric energy conversion performed by the engine. It is demonstrated that this external forcing of thermoacoustic self-sustained oscillations strongly impacts the performance of the engine, and that it is possible under some circumstances to improve the efficiency of the thermo-electric transduction, compared to the one reached without active control. Applicability and further directions of investigation are also discussed

Design, manufacturing and testing of a compact thermoacoustic refrigerator

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