Experimental Study of Mixed Convection Air Flow over a Heated Wafer in a Horizontal Rectangular Duct and Flow Stabilization by Wafer Tilting
林 清 發
|關鍵字:||矩形管道, 水平化學氣相沉積反應爐, 混合對流, 迴流;Rectangular duct, Horizontal CVD reactor, Mixed convection, Returning flow|
|摘要:||本篇論文利用流場可視化及溫度量測方式, 對於底部鋪設圓形加熱板的水平矩形管道內空氣強制對流在空間和溫度場上所形成的複雜渦流結構和熱力學特性加以探討。以模擬水平CVD反應爐之熱浮力驅動流場。雷諾數 (Reynolds nimber) 從20到200, 雷利數 (Rayleigh number) 則由180000 到 990000, 此範圍內熱浮力所驅動的流場將分別有穩態, 週期及非週期的特性。由結果我們可看出低浮力-慣性力比時在流場中央垂直面附近會有迴流 (returning flow) 產生, 而在兩邊側板附近則看到了兩個較弱的渦流 ( vortex flow ) 結構。當浮力-慣性力比提高時, 迴流結構將朝測試段上游移動, 而兩邊的渦流結構亦將朝上游延伸, 並逐漸變的更為厚實。同時, 當浮力增加後, 有時流場會由穩定轉變為不穩定的狀態。所以我們將熱浮力所形成的流場之暫態溫度歷程整理成流場組織圖後, 我們發現在雷利數等於 810000 而雷諾數為 60 時, 流場呈次臨界過渡狀態。而在穩定流場方面, 底板傾斜的確有助於使不穩定的流場趨向穩定, 我們的傾角是從0°到4°。|
Combined flow visualization and temperature measurement were carried out in the present study to investigate the complex spatial and temporal vortex flow structures and thermal characteristics in a forced air flow through a horizontal rectangular duct with a heated circular copper plate laying on the duct bottom, which intends to model the buoyancy driven flow in a horizontal chemical vapor deposition reactor. Results were obtained for the Reynolds number ranging from 20 to 200 and Rayleigh number ranging from 1.8x105 to 9.9x105 covering the steady, time periodic and nonperiodic flows. The results showed the presence of the returning flow in the entry half of the duct around the central vertical plane at x=b/2 and two weak vortex rolls near the duct sides at a low buoyancy-to-inertia ratios. At a higher buoyancy-to-inertia ratios the returning flow zone is induced in the more upstream region and near the side walls the vortex rolls are stronger. Besides, a downstream flow recirculation is induced. Moreover, at increasing buoyancy flow transition from stable to unstable states was noted. A flow regime map was given to delineate the temporal state of the flow. It is important to note the subcritical flow transition at Ra=8.1x105 and the reverse flow transition at Re=60. Moreover, the temperature oscillation in the unstable flow was strongest in the interboundary between the upstream and downstream flow recirculations near the plane x=b/2. Finally, the inclination of the heated plate was found to produce significant flow stabilization for the inclination angle varied from 0°to 4°.
|Appears in Collections:||Thesis|