Recovery of thermal energy losses in a traveling wave thermoacoustic engine with mean flow

The use of mean flow in a traveling wave thermoacoustic engine can be used to eliminate the hot heat exchanger in traditional traveling wave engines, which can lead to improved efficiency and reductions in cost, size, complexity, and thermal expansion stresses. In one form of this engine, a mean flow of hot gas provides heat input to the engine by flowing from hot to cold through the regenerator. Previous work has shown that an inherent loss mechanism in this type of engine converts much of the thermal energy input into conductive and entropy flux losses in the regenerator. The present work describes a means to recover much of this lost thermal energy by preheating the mean flow before it undergoes its primary heat addition process. This reduces the heat input required to reach a desired hot temperature, or equivalently, allows higher temperatures to be attained in the engine, thus increasing the engine's efficiency. Appropriate modeling of the preheat process is shown to yield analytic solutions for the regenerator temperature profile and the mean flow preheat temperature. The relevant parameters and design considerations influencing the effectiveness of the preheating process are also explored.