We discuss the stack which is the key device of the thermoacoustic system. We elucidate the stack mechanism to realize further energy conversion efficiency improvement. We propose installing a heater inside the stack. This heater adjusts the internal temperature of the stack and controls the heat flow in the stack. Controlling the heat flow in the stack can also affect the mutual conversion of the heat flow and the work flow. In this report, the effect of the resonance frequency with the standing-wave thermoacoustic-system and the internal temperature of the stack on the heat flow in the stack was experimentally investigated. The resonance frequency was changed with the total length of the system. As a result, the lower the frequency, the larger the amount of the work flow generated in the stack. This can be influenced by the increase and decrease of the dissipation with changing the resonance frequency. Also, at any resonance frequency, the amount of the work flow generation increased with controlling the heat flow in the stack. The heat flow can be controlled by adjusting the internal temperature of the stack at any resonance frequency.

In this study, we prepared single-walled carbon nanotube electrodes for lithium–air batteries (LABs) to investigate the structural changes of the electrodes during the discharge–charge cycle coupled with the precipitation and decomposition of Li oxide. Wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) were used for the structural analysis. A new test cell was designed and fabricated to perform these measurements under operando conditions. From the results of the WAXS measurements during discharge tests, diffraction peaks indicating crystalline oxides and a broad peak indicating amorphous components were observed. The intensities of these peaks increased rapidly in the later stages of the discharge. Moreover, the WAXS measurements showed that the peak of the amorphous component preferentially disappears during the charging process. Furthermore, the nanoscale structural changes associated with the precipitation and decomposition of Li oxide were analyzed using SAXS. The results suggest that the electrode expansion caused electrolyte depletion in the electrode. The post-test electrode thickness was also analyzed, and the results support interpreting the data obtained from WAXS and SAXS. We think that the structural analysis approach and the pore formation discovered in this study will enable LABs to be used more effectively in the future.

To effectively use the whole area in a stack for energy conversion, the formation of a uniform temperature gradient over the whole area in the stack is necessary. For the temperature gradient formation, a method to heat the intermediate positions in the stack with heaters is proposed. In this paper, the relation between the heating position of the stack and the quantity of the work flow generation is experimentally investigated. As a result, the work flow generation increased and the energy conversion efficiency improved due to the effect of heating the intermediate position in the stack. In addition, the work flow generation increases most significantly in the case where the whole area of the stack has a uniform temperature gradient. Therefore, it is assumed to be preferable for stack design that the temperature gradient is uniform over the whole area in the stack.