以熱聲效應提升熱堆散熱效率之研發

Abstract

熱聲效應在兩百多年前，經由玻璃工人工作時所聽到的高音而發現，這兩百年來，經過前人的努力研究，我們目前已經對此一效應有了相當完整的定性解釋，除此之外，整合熱力學、流體力學、熱傳學、再加上聲學理論，此一領域的理論架構業已進展成為一套名為「熱聲學」的數學模型。熱聲效應顧名思義便是熱能與聲能的互相轉換，利用一定溫差可以在共振管內產生駐波聲波以及聲流現象，一般稱此為熱機模式。反之，利用輸入的聲波能量，也可以在共振管內產生一溫差，此一現象稱為冷機模式。冷機模式目前已經被利用於開發熱聲冰箱，且已獲得相當不錯的卡諾冷機效率。本論文則將從熱機模式出發，探討熱力學、流體力學、聲學、以及熱聲學，並將應用面著眼於散熱，試圖了解影響熱聲效應的所有重要參數。最後還將利用本論文所提及之各種理論，配合上實驗數據的佐證，確認了熱聲效應發生時的熱滯後效應以及影響熱聲效應的因子，大致上可以歸納為：臨界溫度梯度、共振管長度、工作流體、片堆材料、厚度與孔隙等。本論文同時還將藉由前述參數來找尋熱聲散熱裝置的最佳化設計。

Thermoacoustic effect has already been discovered by glassmakers for more than 200 years. Through many scholars’ research effort, detailed qualitative analysis of thermoacoustic effect has been developed over the years. The theory of thermoacoustic and its mathematic model were developed by integrating thermodynamics, fluid mechanics, heat transfer, and acoustics. As implied by the name, thermoacoustic effect is the transformation between heat energy and acoustical energy. Thermoacoustic heat engine can generate acoustic standing waves and acoustic streaming by a temperature difference located between heated side and cool side of a stack in a resonance tube. On the contrary, acoustic standing waves in a resonance tube can generate a temperature difference between heated side and cool side of stack. While thermoacoustic refrigerant was well developed, thermoacoustic heat engine remains within the development stage. This thesis discusses the thoughts behind the intention to integrate thermodynamics, fluid mechanics, heat transfer, acoustics, and thermoacoustics to examine cooling efficiency improvement in heat piles. In addition, it transforms thermoacoustic heat engine system to thermoacoustic cooling system. Utilizing the theory of thermoacoustic and experimental investigation, it identifies a hysteretic loop of onset and termination of thermoacoustic effect and it concludes by identifying some factors which may influence the behaviors of thermoacoustic effect. These newly identified factors include critical temperature difference, length of the resonance tube, working fluid and stack’s material, thickness, and porosity. By means of these factors, it tries to optimize the design of thermoacoustic cooling system.