Study On Resonance Control By Locally Expanding The Outer Tube In A Coaxial Thermoacoustic System

Toward the enhancement of the cooling ability of a coaxial-type thermoacoustic system, the control of the sound field in the tube, in particular that of the resonance mode, is investigated. The coaxial type thermoacoustic system consisting of two tubes with different radii is capable of forming a sound field of traveling wave with a high energy conversion efficiency similar to a loop-tube type thermoacoustic system. In addition, because of the linear shape, this system is advantageous for downsizing. However, the setting position of the prime mover (PM) is different from that for the loop-tube type. When the setting position is moved to closer to the tube end, the sound pressure of the fundamental mode is enhanced and the cooling ability increases in the range not too close to the tube end. However, when the position is too close to the end, the sound pressure of the second mode increases instead of the fundamental mode and the cooling ability is degraded. Therefore, assuming the shift to the second mode is the cause to lower the cooling ability, in order to make the input heat concentrate to the fundamental mode the radius of the tube is locally enlarged at the position of the antinode in the second mode. As the result, the decrease of the second mode sound pressure and the increase of the fundamental mode sound pressure are confirmed. The lowered temperature at the high temperature end and the promotion of the energy conversion from sound to heat are also confirmed.