The use of a phase adjuster (PA) has been proposed to improve the cooling effect of a loop-tube-type thermoacoustic cooling system. A PA is a device for increasing the particle velocity of sound by narrowing a part of the loop tube. In this experiment, we present a discussion of the efficiency of heat-to-sound energy conversion in a loop-tube-type thermoacoustic prime mover, particularly emphasizing on the inner diameter change of PA. It is found that the sound pressure is higher for larger inner diameter; the particle velocity is higher for larger inner diameter and the phase difference between the sound pressure and the particle velocity is bigger for larger inner diameter. It is also found that sound intensity is different according to the inner diameter, and that it is higher for larger inner diameter. Results obtained confirm that PA improves the efficiency of heat-to-sound energy conversion in the loop-tube-type thermoacoustic prime mover, and that the efficiency depends on the inner diameter of PA.
In this report, we propose a low-temperature driving method for loop-tube-type thermoacoustic cooling systems with a diverging tube. We specifically examine the sound field within a loop tube and the temperature at the top of a prime mover stack when the diverging tube position is changed. Experimental conditions included constant input heat energy and the temperature at the bottom of the stack. The diverging tube position was adjusted to increase the efficiency of energy conversion from heat energy to sound energy. Furthermore, the temperature at the top of the prime mover stack decreased by about 500 C, from 845 to 345 C, compared with that in systems without a diverging tube. The results suggest that the phase difference between the pressure and particle velocity in the prime mover stack improved. The diverging tube system was driven by the low-temperature difference because the energy conversion efficiency was increased.
Experimental investigations were carried out to establish a design method for a thermoacoustic cooling system. When a straight acoustic tube is used, the acoustic power is supplied from the tube end. The ceramic stack, which consists of many narrow channels, is inserted into the tube. By changing the insertion position and the stack channel radius, a temperature decrease at the stack end is observed as the energy conversion parameter. A nondimensional parameter, !, considering the relaxation time is determined from resonance frequency and stack channel radius. The temperature decrease is examined using several values of !. Results show that the insertion position for which the maximum temperature decrease is obtained depends on !. Therefore, the best stack insertion position can be designed according to the given frequency and stack channel radius. For that reason, ! is an important index for thermoacoustic cooling systems.
We investigate the photoresistance of a magnetically confined quantum wire in which microwave-coupled edge channels interfere at two pinning sites in the fashion of a Mach-Zehnder interferometer. The conductance is strongly enhanced by microwave power at B = 0 and develops a complex series of oscillations when the magnetic confinement increases. Both results are quantitatively explained by the activation of forward scattering in a multimode magnetically confined quantum wire. By varying the strength of the magnetic confinement we are able to tune the phase of electrons in the arms of the interferometer. Quantum interferences which develop between pinning sites explain the oscillations of the conductance as a function of the magnetic field. A fit of the data gives the distance between pinning sites as 11 μm. This result suggests that quantum coherence is conserved over a distance three times longer than the electron mean free path.
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