Abstract
本研究乃針對限制平面噴流之衝擊熱流特性作一系列理論與實驗的探討。在此研究中，除對有關噴流雷諾數、噴流出口至衝擊面距離與噴流寬度之比率、噴嘴長度、噴流出口流速分佈、及衝擊板熱傳導等參數對噴流局部流力發展與熱傳特性之影響作了完整的分析外，也對此類噴流之衝擊停滯點邊界層厚度作出一合理的定義。如果在噴流中心線上的最大側向速度梯度已知，則利用二維停滯流的關係式將可準確地預測在本研究中定義之邊界層厚度。研究中發現此最大側向速度梯度與噴流雷諾數成線性正比，與噴流出口流速分佈參數(N)的0.25 次方成正比；與噴流出口至衝擊面距離與噴流寬度之比率(H/W)的0.34 次方成反比。因此，停滯點之邊界層厚度與噴流寬度之比值與噴流雷諾數的0.5 次方成反比；而與H/W的0.17 次方成正比。此外，也針對停滯點與加熱面之局部紐塞數提出新的經驗公式而其預測結果與理論實驗的數據相當吻合。 關於噴嘴出口流速分佈之流力穩定性分析，則使用能量穩定分析法來探討噴流出口流速分佈對噴流組穩定現象之影響。由研究結果顯示，噴嘴出口流速分佈影響噴流組流力穩定性甚鉅。具有變化較劇烈的噴流出口流速分佈情形，其流力穩定區間也比較低。同時亦發現在噴流出口流速為均勻分佈時，沒有任何臨界雷諾數可滿足穩定準則。 關於在限制渠道中受到橫向流影響的平面噴流之衝擊研究，在本文中亦作了詳盡的探討。結果發現在橫向流的影響下，衝擊噴流的流力結構會變得不規則和混亂，而不再是對稱的流場。由於噴流之衝擊，可在噴流與橫向流之合流處的後方與限制渠道的上板間發現一主要渦旋。此外，局部紐塞數與全展區紐塞數之比值(Nux/Nuf) 隨著質量比率之增加而減少；而具最大Nux/Nuf 比值之位置會隨著質量比率的增加而往下游移動。 本文最後也探討了含多發熱源之限制渠道中受到平面噴流之衝擊與橫向流相互作用的熱流特性。在只有橫向流作用時，如同在連續加熱面的情形一樣，局部紐塞數沿著流動方向遞減。由於相臨發熱源的間隔距離造成熱傳特性之不連續，而導致熱邊界層之不連續與再發展。因此在每個發熱源之起始位置產生局部最大的熱傳效果。另外，亦發現局部紐塞數隨著渠道雷諾數與相臨發熱源間隔距離之增加而增加；然而，每一發熱源與最下游處發熱源之平均紐塞數比值則隨著渠道雷諾數與相臨發熱源間隔距離之增加而降低。文中亦對等熱通量和等溫加熱兩種情形，分別提出了相關的經驗公式來預估各發熱源的平均紐塞數。Both theoretical and experimental investigations on fluid flowand heat transfer characteristics in confined channels with aslot slot jet impingement have been systematically performed inthis study. The parametric effects of jet Reynolds number,spacing between the nozzle exit and the target surface, nozzlelength, jet velocity profile at nozzle exit, and wallconduction parameter on local flow development and heattransfer characteristics of the heated target surface areexplored. The organization of the thesis is as follows: theintroduction to the research, including the rationale, papersurvey, and research subtopics and their objectives isdescribed in Chapter 1. The general research theoreticalformulation, including the formulation of the governingequations and the treatment of all possible boundary conditionsused in the study is derived in Chapter 2. In addition, theresults and discussion for the fluid flow and heat transfer ofa confined slot jet impingement are shown in Chapter 3. Arelevant experimental study for a confined slot jet impingementis then conducted in Chapter 4. Furthermore, the effects ofusing an extended nozzle on fluid flow and heat transfercharacteristics are observed in Chapter 5. For exploring theflow stability of jet velocity profile at nozzle exit, anenergy stability method is implemented to investigate theeffect of jet exit velocity profile on the stability of jetarray in Chapter 6. In Chapter 7, the results of slot jetimpingement under the influence of crossflow in a confinedsmooth heating channel are discussed. Next, the heat transferof slot jet impingement in a confined channel with discreteflush-mounted heat sources is studied in Chapter 8. Finally,recommendations are given in Chapter 9 in addition to clusionsdrawn from the present results and discussion.