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標題: | 片堆之轉換效率於熱聲管之實驗研究 Experimental study on stack performance in Thermoacoustic engine |
作者: | Yen-Chih Chen 陳彥志 |
指導教授: | 王安邦(An-Bang Wang) |
關鍵字: | 駐波與行波式熱聲管,無因次片堆長度與位置,平均溫度變化率,聲功率,轉換效率,單一平板理論, Thermoacoutic engine,dimensionless stack length and position,the rate of mean temperature of stack,acoustic power,thermal efficiency,single plate theory, |
出版年 : | 2010 |
學位: | 碩士 |
摘要: | 本文對駐波式與行波式熱聲管進行基礎研究,首先,於定性方面,進行保麗龍球於駐波式熱聲管之顯影與軸向聲壓振幅分佈量測,由結果得知,駐波式熱聲管之軸向聲壓振幅與速度分佈與駐波管之分佈型式相同,並且發現無因次片堆長度不影響壓力分佈。同時,利用熱線測速儀量測方型試管之軸向速度分佈,發現越靠近方型共振管出口,速度振幅越大,並利用全像干涉術量測片堆出口之溫度場。
利用LabVIEW進行非穩態加熱過程之標準程序,利用方均根之訊號處理、2階多項式配適曲線與量測誤差值為1%,作為本實驗之量測標準程序。接著,討論無因次片堆長度與位置對發聲時間之影響,由結果可知,隨著無因次片堆長度增加,發聲時間也逐漸增加,由於無因次片堆長度增加,片堆之平均溫度之變化率(T ̇_m)也逐漸變小,因此發聲時間隨無因次片堆長度增加而增加。而無因次片堆位置對發聲時間則無明顯趨勢。 由聲功率結果可以得知,最大聲功率約為90 mW左右之數量級,發生於無因次片堆長度( l_s^* )與位置(l*)分別為0.09與0.25之條件,其平均轉換效率約為0.11%。並將轉換效率之結果除上無因次片堆長度可以發現,當無因次片堆長度為0.01~0.04之範圍時,其轉換效率均非常接近,隨著無因次片堆長度大於0.04,最大轉換效率也逐漸降低。此外,最佳無因次片堆位置(l*)發生於0.2~0.3之範圍,由於受到黏滯項之影響,和單一平板理論所預測之最佳位置(l*=0.5)略有不同。並討論於片堆冷端加入水冷式熱交換器與片堆絕熱之影響,加入水冷式熱交換器可以解決聲壓振幅衰減之情形,並增加聲壓振幅,同樣的片堆絕熱同樣可以使聲壓振幅增加,減少聲壓振幅衰減之情形。 於熱聲理論部分,量測片堆之臨界溫度差與單一平板之理論值進行比較,除了無因次片堆長度為0.17之臨界溫度差大於理論結果,推測為溫度分佈並非線性所造成此結果,而在無因次片堆長度為0.09~0.01之範圍,在趨勢上之預測大致接近,可做為定性方面之參考。 最後,討論環型(行波式)熱聲管之量測與轉換效率之計算,由結果得知,於較高之輸入瓦數下,環型熱聲管之聲壓振幅衰減情形逐漸趨緩,且環型熱聲管之轉換效率(η = 0.28%)比駐波式熱聲管(η = 0.13%)高。 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%). |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/47859 |
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