- 作者: 黃光治
- 作者服務機構: 國立清華大學動力機械研究所
- 中文摘要: 本論文研究水平平行槽內流動空氣熱穩定的問題。軸長方向柱狀渦流之產生是由於空氣受熱浮力的影響造成的。本論文是觀察全展層流在下板加熱之平行槽熱入口區內柱狀渦流之形成,本實驗使用2×30公分,3×30公分及4.5×30公分三種截面之平行槽同時使用煙作直接流體觀測。本論文發表了由下游及上方所照之柱狀渦流之照片,實驗結果顯示柱狀渦流發生後其橫向波長治流體流動方向保持不變;同時顯示由於需要一段距離放大初產生之渦流至某一相當強度之渦流才能觀察,所以用直接觀測法所得之雷利(Rayleigh)數,比線性理論值高1.4至10倍,根據照片渦流波數與平行槽高寬之比的關係也劃出來,同時與線性理論波數值比較,如此發現實驗值,當高寬之比趨向無窮大時實驗值有趨向理論值的傾向。
- 英文摘要: This paper presents results of an experimental investigation on the onsetof longitudinal columnar vortices due to buoyant ;forces in the thermalentrance region of a horizontal parallel-plate channel heated from below.A horizontal parallel-plate channel with width 30 cm and height h=2, 3and 4.5 cm was employed in the experiment. The lower plate of thechannel was heated and maintained at a uniform temperature Tl which ishigher than the upper plate temperature T2.The instability of the conve-ctive motion is caused by the effects of temperature gradients in bothlongitudinal and vertical directions. The onset of longitudinal columnarvortices was observed by a direct flow-visualization technique using smoke.Photographs showing the front view and the top view of the vortex rollsare presented.Experimental results indicate that the wave number of vortexrolls remains constant along the flow direction after the onset of thermalinstability and that due to the distance required for the amplification ofsmall vortex, the critical Rayleigh number from flow visualization is 1.4 to10 times higher than the critical value from a linear theory. Based on theexperimental observation,the wave number of vortex rolls versus channelwidth-height aspect ratio is plotted against the wave number from the lineartheory and the experimental data tends to approach the theoretical valueas the channel width-height aspect ratio increases.
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