具高熱通量元件流道內之薄霧流熱傳增強研究

Abstract

近年來因工業上對冷卻技術要求日增，傳統之單相冷卻方式已無法滿足需求。薄霧流冷卻為極具前景之技術，可應用於未來氫能渦輪機及電子系統之散熱。將薄霧流送進發熱元件之通道中，其在表面形成一微細液膜之蒸發現象能大幅移除熱量，冷卻效果遠高於一般常見之強制熱對流冷卻。此方法可應用於相對較低及均勻溫度下移除高熱通量，在較長的通道系統中能覆蓋較大的熱傳面積，和利用噴霧直接衝擊到發熱表面上之噴霧衝擊冷卻方式不同。實際應用上高熱通量元件有不同幾何大小及配置，將引起不同的迴流或流體再接觸等二次流現象，將影響薄霧流冷卻之效果。 本計畫將進行薄霧流之流體特性及熱傳現象之研究。在第一年計畫中，建構同時量測薄霧流液滴大小及速度場之量測裝置，利用較便宜發光二極體照明方式，取得粒子陰影影像來計算流速及粒子大小，此種方法具有結合粒子影像測速儀流場量測與雷射都卜勒粒子大小量測的優點；在第二年中，將研究薄霧流之熱傳，需利用第一年所完成之量測結果，研究薄霧流速度場及形成薄霧之粒子大小對流傳之效應。針對較常見之發熱元件分佈如長方體或圓柱體陣列等之排列方式，研究薄霧流冷卻之效果。研究結果可用於未來的的設計上增進薄霧冷卻的效果，以推廣未來在工業上之應用。

Traditional cooling with the single phase fluid is not sufficient to satisfy the increasing demand of the cooling requirement in industry. Cooling with the mist flow is a promising technology which can be applied to the advanced hydrogen-fueled gas turbine engines and future electronic systems. By circulating the mist flow in the flow channel, a thin liquid film can be formed on the surface and large amount of heat can be removed by the evaporation on the surface of the liquid film. It can be used to remove high heat flux at a relatively low and uniform temperature and achieve better cooling performance than the conventional forced convective cooling. Mist flow can cover large heat transfer area in longer channels and it is fundamentally different from the conventional spray impingement cooling, which cools the target surface by direct liquid drop impingement. Due to geometry characteristics of the high heat flux component arrangements in the real application, the induced secondary flow, such as flow reattachment or circulation, may influence cooling performance by the mist flow. This proposal studies mist flow characteristics and the corresponding heat transfer behavior. In the first year, a device for simultaneously measurement of the liquid drop size and flow velocity of the mist flow will be established. It utilizes the cheaper LED light as the illumination source to obtain the shadow image of the particles, and the particle size and flow velocity can be calculated based on the image. It has the combined advantages of the velocity measurement by the Particle Image Velocimetry (PIV) and the particle size measurement by the Laser Doppler Anemometry (LDA); in the second year, effect of liquid drop size and mist flow velocity on heat transfer will be investigated based on the mist flow characteristics obtained in the first year. Cooling performance will be tested in the channels with high heat flux components fabricated on the surface arranged in rectangular arrays or cylindrical arrays. The results can be used for evaluating better design with the mist flow cooling technology for future applications in industry.