• 作者： 洪儒珍; 龍瀛天
• 作者服務機構： 美國阿拉巴馬大學機械與航空太空工程學系
• 中文摘要： 在法向及斜向重力加速度影響下，熱對流在極低壓力下，由原始材料經蒸汽沈澱處理之數學模式作了研討：在法向重力加速度作用時，熱對流所推動的蒸汽沈澱可在複雜的回流流動模型下完成。在此種複雜的回流及非均勻溫度分佈的模型下，顯然無法達成處理均勻精細的結晶狀薄膜。在斜向作用時，重力加速度可分解成垂直減弱加速度及水平分量加速度。沿重力加速度垂直的剖面上可看出，減弱重力加速度可促進簡單向上流動及均勻溫度分佈。此種流體運動及均勻溫度分佈可形成有利造成良好光學材料之晶體成長的環境。但因有水平分量加速度的存在，總體上斜向重力加速度仍無法推動勻質晶體的成長。因此，要造成勻質晶體成長的環境，恐怕仍有賴於在微重力太空環境下，來推動晶體的成長。
• 英文摘要： A set of mathematical formulations is adopted to study vapor deposition from source materialsdriven by a heat transfer process under normal and oblique directions of gravitational acceleration withan extremely low pressure environment of mmHg. A time step animation series of the initiationand development of flow and temperature profiles during the course of vapor deposition has beenobtained through the numerical computation. Computations show that the process of vapor depositionis accomplished by the transfer of vapor though a fairly complicated flow pattern of recirculationunder normal direction gravitational acceleration. It is obvious that there is no way to produce ahomogeneous thin crystalline film with fine grains under such a complicated flow pattern of recirculationwith a non-uniform temperature distribution under normal direction gravitational acceleration. There isno vapor deposition due to a stably stratified medium without convection for reverse normal directiongravitational acceleration. Vapor deposition under oblique direction gravitational acceleration in the vertialdirection is favorable for production of a homogeneous thin crystalline film. However, oblique directiongravitational acceleration also induces an unfavorable gravitational acceleration along the horizontaldirection, which is responsible for initiation of a complicated flow pattern of recirculation. In other words,it will be necessary to carry out vapor deposition under a reduced gravity in future space shuttle experimentswith an extremely low pressure environment so as to process vapor deposition with a homogeneouscrystalline film with fine grains. Fluid mechanics simulation can be used as a tool to suggest the mostoptimistic experimental method with the best setup to achieve the goal of processing the best nonlinearoptical materials.
• 中文關鍵字： material processing; convection driven flow; flow field; temperature distribution
• 英文關鍵字： --