Abstract
Linear alternators convert acoustic power into an electric output and thus are integral parts of thermoacoustic power converters. Their performance is significantly affected by their matching with the thermoacoustic engine and their matching with the electric load. This critical operation may cause any slight change in the design or operating conditions to induce a significant effect on the linear alternator performance. In this work, this performance is monitored by examining the acoustic-to electric conversion efficiency, the mechanical stroke, the mechanical-motion loss, the fluid-seal loss and the Ohmic loss. A reference experiment is carried-out to document the performance of the linear alternator under certain operating conditions typical in thermoacoustic power conversion conditions at the linear alternator's mechanical resonance frequency. Then, using the methodologies of design-of-experiments and sensitivity analysis, a scheme of experiments is designed and implemented to analyse the changes in the alternator performance indices to 10% changes in four selected operating conditions, namely the helium molar fraction in the gas mixture composition, the mean gas pressure, the electric load resistance and the pressure ratio. The results reveal how variations in each of these operating variables as well as variations in their combined interactions affect the linear alternator's performance indices with respect to the results obtained in the reference experiment. For example, the mechanical stroke is mostly affected by the pressure ratio, followed by the mean gas pressure and then by the load resistance. The most significant combined interaction arises from the product of the mean gas pressure and the helium molar fraction.