Experimental study on stack performance in Thermoacoustic engine
Date Issued
2010
Date
2010
Author(s)
Chen, Yen-Chih
Abstract
The study was a series of fundamental research of thermoacoustic engine (TAE). At first, the qualitative experiment was focused on the styrofoam ball visualization in the quarter wave TAE and the measurement of axial sound amplitude distribution in the TAE. The results showed that the axial velocity and sound amplitude distribution were the same with the quarter wave resonator. The axial velocity distribution in the quarter wave rectangular resonator was also measured by the hot wire anemometry. The Michelson type of interferometer was also applied to measure the temperature field inside the TAE (above the stack).
In the quantitative experiment, the criteria of sound pressure measurement should be established before starting the experiment. In order to reach the peak value of the sound amplitude, the study used the second order polynomial curve fitting to present the sound amplitude. Besides, the signal processing of sound amplitude and defining the measurement error were achieved by the LabVIEW.
The study had put emphasis on the influence of dimensionless stack length and position in the TAE. First, the time of sound emission was increased as increasing the dimensionless stack length. As the increasing the dimensionless stack length, the rate of mean temperature(T ̇_m) of stack will become smaller. It caused that the time of sound emission was longer for large dimensionless stack length. However, the dimensionless stack position made not much difference in the time of sound emission.
Second, the maximum acoustic power was reached to the scale of 90 mW under the dimensionless stack length and position are 0.09 and 0.25 respectively. The maximum averaged thermal efficiency is around 0.11%. Besides, dividing the thermal efficiency by the dimensionless stack length and the result showed that when the dimensionless stack lengths lower than 0.04, the thermal efficiency per unit dimensionless stack length was almost the same. As the dimensionless stack length increasing, the thermal efficiency of unit length was become lower. And the optimal dimensionless stack position was ranged from 0.2 to 0.3. The difference in optimal stack position between the experimental results and single plate theory (optimal dimensionless stack position is 0.5) was caused by the viscous effect. By the way, the influence of water-cooled heat exchanger and thermal insulation was also discussed in this study.
The study also compared the critical temperature difference in quarter wave TAE between experimental results and single plate approximation. The result was reasonable for estimating the critical temperature difference; except for the dimensionless stack length is equal to 0.17. There was still large error (around 40%) between the experimental results and single plate theory, but the single plate theory is still valuable as the basic approximation.
Finally, the traveling type TAE was constructed and measured the thermal efficiency. As the result showed, in high input power, the sound amplitude decayed slowly in traveling wave TAE than in the quarter wave TAE and the traveling wave TAE (η = 0.28%) has better thermal efficiency than quarter wave TAE (η = 0.13%).
Subjects
Thermoacoutic engine
dimensionless stack length and position
the rate of mean temperature of stack
acoustic power
thermal efficiency
single plate theory
Type
thesis
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