Open cycle traveling wave thermoacoustics: Energy fluxes and thermodynamics

Abstract

In an open cycle traveling wave thermoacoustic engine, hot gas steadily flows into the hot side of the regenerator, replacing the hot heat exchanger as the primary energy source for the engine. In such an engine, interactions between the acoustic, convective, conductive and thermoacoustic energy fluxes facilitate conversion of the input thermal energy into acoustic energy. This study describes the energy flux interactions throughout the engine, thus clarifying the important role of the mean temperature difference that exists between the mean flow of hot gas and the hot-side regenerator interface in the open cycle engine. Furthermore, this study derives an optimal regenerator interface temperature that maximizes the acoustic power output of the engine for a given thermal energy input. The acoustic power output and thermal efficiency of the open cycle engine are compared to those in a closed cycle engine in which a crossflow heat exchanger is used to supply the required heat input. By accounting for the effectiveness of the heat exchanger, it is shown that the open cycle has the potential to achieve higher efficiencies than the closed cycle in converting the thermal energy in a stream of gas into acoustic energy.