Exergy-based methodology to develop design guidelines for performance optimization of a coupled co-axial thermoacoustic refrigerator

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Performance of thermoacoustic (TA) systems are very complex, and their performance optimization is a difficult task, and most TA systems have relatively very low efficiencies. The main objective of this study was to develop an exergy analysis to introduce a guide for a designer, how to optimize the performance of a TA system. We have applied this methodology to a coupled thermoacoustic engine and refrigerator with a standing wave in the engine and a traveling wave in the refrigerator. In an optimization procedure, a lumped systems numerical analysis was performed to predict the main parameters of the thermoacoustic system. The numerical method was validated by comparison with numerical and experimental results in the literature. The cost function was the total system coefficient of performance, and design parameters include the refrigerator regenerator length, location, and hydraulic radius. The performance index was decomposed into three main subsystem indices, i.e., the efficiency of the engine, the efficiency of the resonator, and the coefficient of performance of the refrigerator. The optimum point for each component was found, and the total system optimal point which is a result of thermoacoustic interaction of all segments were analyzed. It was illustrated how a change in design parameters could affect the pressure and velocity amplitude and phase distribution in different subsystems, which help the designer deal with the challenge of the optimal parameter selection to enhance the system performance. Finally, an exergy analysis was introduced to assess loss mechanism's contribution to each refrigerator's component. This result in a roadmap for optimization of the system. A new parameter called non-dimensional exergy loss portion (NELP) was introduced, which may significantly show the improvement potential in each system component.