具氣體渦漩腔之微噴嘴設計與性能測試

Design and Performance Analysis of Novel Micro-Atomizers Assisted with Air Swirler

郭敦詠(Duen-Yung Kuo)

指導教授 ： 陳理定 ； 楊鏡堂

國立清華大學/工學院/動力機械工程學系/碩士(2006年)

https://doi.org/10.6843/NTHU.2006.00322

摘要

本文主旨為設計及製作具渦漩氣流之氣助式噴嘴，透過壓力渦漩式微噴嘴與氣體渦漩腔之結合，以渦漩氣流衝擊液相渦漩流場，形成雙渦漩作用，增加液氣介面間之剝離能力，以提昇噴嘴之霧化效果。應用微機電製程技術製作具高深寬比結構之微噴嘴，達到縮小幾何尺寸及降低霧化粒徑之目的。實驗部分包括噴嘴性能測試及流場觀測，透過流量量測可計算噴嘴流數(flow number)及噴射係數(discharge coefficient)，藉此參數推估噴嘴之性能，流場觀測則利用雷射系統及光學鏡組產生雷射光頁使流場可視化，高速攝影機記錄影像，分析流場結構及變化；運用粒子顯像測速儀(Particle Imaging Velocimetry, PIV)計算霧化液滴之速度向量。結果顯示：渦漩氣流作用前後流場結構差異在於噴霧錐角及中空結構的改變，氣體流速之增加拓展噴霧之錐角，且流場中心可觀察到低壓核心之生成，核心結構隨氣流之加速愈顯清晰完整，表示流場之渦漩強度增強，液氣間之相對速度提高，有利於液體碎化。此外，流場之縱切面速度分佈呈“W”形，邊界層上具最大速度峰值，隨氣體流速之增加，軸向速度亦增強；橫截面之速度向量場顯示流場有反轉現象，推斷液相流場之切線速度介於1.7~3.4 m/s。以上實驗結果說明氣體渦漩腔之設計對液體霧化有顯著之成效，證實壓力渦漩式噴嘴結合氣體渦漩腔之設計理念可提昇噴嘴之霧化能力。

關鍵字

微噴嘴 ； 微機電製程 ； 氣體渦漩腔 ； PIV

並列摘要

The objective of this study is to design and fabricate the micro-atomizers assisted with the air swirler. By combining the pressure-swirl type atomizer and the air swirler, the swirling air makes great impact on the liquid swirl of spray. Double-swirl interaction is active to enhance the ability of disintegration between air and liquid, achieving the goal of fine atomization. MEMS technique is applied to fabricate the micro-atomizer characterized by high-aspect ratio structure which scales down the size of geometry and subsequently reduces the mean droplet size. In experiments, the performance test of the micro-atomizer and flow visualization have been carried out. Through measuring the flow rate of injection, performance of the micro-atomizer is evaluated via flow number and discharge coefficient. For analyzing the structure and the development of flow field, the spray is visualized by laser sheet illumination and high-speed camera recording; particle imaging velocimetry (PIV) is also manipulated to study the velocity field. The results show that the flow field caused variation in spray angle and hollow cone structure before and after the swirling air acts on spray. Spray angle expanded with increasing the air velocity. Also, vortex core was observed in the center of flow field and the vorticity increased with increasing the air velocity. It means that the strength of liquid swirl and the relative velocity between liquid and air increased and, therefore, are beneficial to atomize liquid. In addition, the velocity field across spray on the vertical face has “w” profile distribution, and the peak value occurs on the boundary layer. Accelerating the air velocity raises the axial velocity of spray as well; the vector plot of flow field indicates that the flow reversal occurred, indicating that the tangential velocity of spray is between 1.7 to 3.4 m/s. The experimental results show that the air swirler indeed has great effects on liquid atomization, and it proves the design concept of combining the pressure-swirl atomizer and the air swirler for better quality of atomization.

並列關鍵字

micro-atomizer ； MEMS fabrication ； air swirler ； PIV

參考文獻

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