Hysteretic behavior induced by an electroacoustic feedback loop in a thermo-acousto-electric generator

Abstract

An active control method of the spatial distribution of the acoustic field is applied in a thermo-acousto-electric generator. An auxiliary acoustic source is used to force the self-sustained thermoacoustic oscillation in order to control the thermoacoustic amplification. The auxiliary source consists of a loudspeaker, located inside the loop-tube close to the main ambient heat exchanger, and supplied with a delayed signal through an electric feedback loop, comprising a phase-shifter and an amplifier, connected to a reference microphone. Experiments are performed on a prototype engine working with air at a static gauge pressure of 5 bars. Experimental results demonstrate how it is possible to tune the acoustic oscillations in order to increase the global performance of the generator, compared to the case without control, as well as the existence of a hysteretic behavior induced by the electroacoustic feedback loop itself, which leads to a discrepancy between the onset heat input and the offset one.

Simplified modeling of a thermo-acousto-electric engine forced by an external sound source

“…By tuning the properties of this feedback (in terms of amplification gain and phase-shift relative to the reference signal), the efficiency of the transducer can either be reduced down to the death of the auto-oscillations, or increased, thus generating a greater output power for the same heat input. More recently, we have shown on the same device that the electroacoustic feedback loop is also responsible for the occurrence of hysteretic behavior [5] of both the temperature difference across the regenerator and the efficiency versus the heat input. However, at the present time the multiplicity of the involved nonlinear effects and their complexity does not allow to understand why and how the mechanisms at stake in this process of "active control" enable to increase the global efficiency of the thermoacoustic engine.…”

“…Simplified analytical models can help in getting a deeper physical insight about the processes involved, but they are also based on substantial approximations. In this study, we use a simplified modeling of thermoacoustic engines to help understanding recent experimental observations dealing with the external forcing of thermoacoustic oscillations [3][4][5].…”

Multi-physics coupling in thermoacoustic devices: A review

“…Poignand [234]. In Olivier s study [233], an auxiliary sound source is added to the looped tube, connected through a phase-shifter to a reference microphone located at another position on the loop as shown in Figure 27.…”

Theoretical study of a thermo-acousto-electric generator equipped with an electroacoustic feedback loop

“…In this study, we use a simplified modeling of thermoacoustic engines to help understanding recent experimental observations dealing with the external forcing of thermoacoustic oscillations [3,4,5]. Indeed, at the present time the multiplicity of the involved nonlinear effects and their complexity does not allow to understand why and how the mechanisms at stake in this process of active control enable to increase the global efficiency of the thermoacoustic engine.…”