Impedance matching for investigating operational conditions in thermoacoustic Stirling fluidyne

This study investigates acoustic impedance matching between a thermoacoustic Stirling heat engine and a branch liquid column, using multiple regenerators. We characterize acoustic impedances at both the engine and liquid column load ends using thermoacoustic theory, expressed as functions of frequency and temperature differences across regenerators. The intersection points of these functions indicate matched impedances, critical for evaluating the engine’s operating points. Notably, this study emphasizes the impact of a vibrating membrane on the system’s acoustic impedance, highlighting its significant role in modulating acoustic states and facilitating self-sustained oscillations. To verify our theoretical models, we conducted experiments with the proposed fluidyne engine under various liquid column volumes. The verifications confirmed our simple calibrations for characterizing a vibrating membrane clamped in the engine and the oscillating liquid columns. Significantly, the acoustic compliance and inertance effects respectively introduced by the membrane and liquid columns enable us to modulate the engine’s acoustic states. The proposed configuration is named a thermoacoustic Stirling fluidyne. This fluidyne, a heat engine that outputs work power using a liquid piston, achieves a markedly higher acoustic impedance than the pure gas case while maintaining traveling wave phasing for the regenerators.