Abstract
In this report, we propose a loop-tube-type thermoacoustic system with a diverging sub-loop tube to control the sound field, specifically the phase difference between sound pressure and particle velocity, in the prime mover of a thermoacoustic system for improvement in energy conversion. The phase difference must become 0° or near 0°. This phase difference contributes to energy conversion through isothermal heat exchange process and makes a thermoacoustic system highly efficient in terms of energy conversion. The sub-loop tube diverges from the main loop tube and rejoins it. Thereby, the sub-loop tube forms a loop. The sub-loop tube position is changed. By diverging the sub-loop tube, the acoustic impedance at the connection position changes and the resonance condition in the thermoacoustic system is changed. As a result, the phase difference in the prime mover is controlled for improvement in energy conversion. Nevertheless, the phase difference in the prime mover cannot be measured. The sound field and ωτ are measured with and without a sub-loop tube. The degree of heat exchange between the working gas and the stack wall is represented as ωτ, which is the product of angular frequency ω and thermal relaxation time τ. Results show that diverging the sub-loop tube and changing its position alter the sound field in the thermoacoustic system, specifically changing the phase difference in the prime mover. The change in the phase difference in the prime mover raises the efficiency of energy conversion from heat to sound.