The relationship between the viscosity boundary layer and the resonance frequency of the generated sound in a loop-tube-type thermoacoustic cooling system is investigated. The frequency of the sound has been observed for various loop-tube lengths, inner pressures and working fluids, and the influence of the viscosity boundary layer upon the resonance frequency is discussed. It was generally considered that the sound generated in the loop-tube was usually resonated with the tube length by 1 wavelength. Under certain conditions, however, the resonant wavelength is 2. This results from the influence of the viscosity boundary layer. It is found that the loop-tube determines the resonance frequency so that the thickness of the viscosity boundary layer is smaller than the stack channel radius. As a result, the resonant wavelength is 2 under certain conditions. The frequency is an important parameter for the thermoacoustic cooling system. From obtained results, one of the factors for selecting the frequency is found.
2006 by The Acoustical Society of Japan