Our research activity focuses on experimental investigations of thermoacoustics, which include experimental understanding of thermoacoustic phenomena, proposal of acoustic devices working as heat engines, and development of novel experimental techniques.
About thermoacoustic phenomena
A rich variety of thermoacoustic phenomena arises from thermal interactions between acoustic waves and a channel wall. When a steep temperature gradient is made along a flow channel, a gas column spontaneously begins to oscillate at natural frequencies. Furthermore, when the acoustic wave runs through differentially heated channels, the acoustic intensity, power flux delivered by the acoustic wave, is thermally amplified and damped depending on the sign of the temperature gradient. On the other hand, acoustic waves not only enhance the heat transport from hot to cold, but also pump heat from cold to hot.
Since acoustic intensity in ordinary conversation is only on the order of 10-4 W/m2, one might think that acoustic waves could not carry a large amount of energy. However, acoustic intensity can become significantly large when the channel is filled with pressurized gas. In fact, acoustic intensities exceeding 100 kW/m2 have been generated in acoustic resonators.
Recently, a large number of new acoustic devices has been developed based on these thermoacoustic phenomena, which can produce acoustic power from heat and vice versa inherently without using moving parts such as pistons. Such devices are called pistonless Stirling prime movers and coolers, since acoustic waves execute thermodynamic cycles similar to the Stirling cycle. Innovation of energy conversion devices has begun. Thermoacoustic technology makes heat engines consisting of a few parts possible.
Book of thermoacoustic phenomenaTetsushi Biwa
「Introduction to Thermoacoustic Devices」, World Scientific (2021)