Experimental Investigation of Heat Transfer Enhancement of Jet Impingement on a Plate Attached by a Porous Medium with a
謝佳佑、吳佩學
E-mail: [email protected]
ABSTRACT
Jet impinging is an important cooling heat transfer technique in the industries, such as industrial drying, metal and glass annealing, secondary cooling in iron casting, laser cooling, plasma cutting cooling, gas turbine blade cooling, and cooling of microelectronics.
Nowadays, enhancement techniques for jet impingement heat transfer are still under intense investigation by academic researchers.
In this study, the jet impingement heat transfer on a target plate covered with porous medium with or without a center hole is experimentally investigated using the transient liquid crystal technique. Based on the results from jet impingement on a bare flat plate, the enhancement in heat transfer due to the addition of porous material is evaluated. The validity of the experimental system constructed for this research was confirmed first by comparing the experimental data of impingement on a flat plate at similar conditions in the literature. The system and the data reduction procedure were then applied to the experimental cases with the flat plate covered with a thick layer of porous medium. Experimental results show that the addition of the porous material with a center hole can effectively enhance the jet impingement heat transfer over a flat plate. The addition of the thick porous layer without a center hole, however, gave rise to adverse effect in jet impingement heat transfer. In addition, the geometry of the center hole of the porous layer has deterministic influence on heat transfer performance. An optimal center-hole geometry will allow fluid to effectively penetrate into the porous medium for heat exchange.
Keywords : jet impingement heat transfer, heat transfer enhancement, porous Material, center hole Table of Contents
目錄 封面內頁 簽名頁 授權書 iii 中文摘要 v 英文摘要 vi 誌謝 viii 目錄 ix 圖目錄 ix 表目錄 xv 符號說明 xvi 第一章 導論 1 1.1 研究背景 1 1.2研究目的 3 1.3文獻回顧 4 1.3.1噴射衝擊流研究 4 1.3.2多孔介研究 9 1.3.3加裝多孔介質或凸塊噴射衝擊 10 第 二章 實驗相關理論及校正 12 2.1數據化約的基本理論 12 2.2雷諾數之計算 13 2.3噴嘴出口速度 14 2.3.1熱線風速儀 14 2.3.2 微差壓計 15 2.3.3熱線校正與速度量測結果 16 2.4熱偶校正與量測 16 2.5液晶校正 17 第三章 實驗設備與實驗步驟 19 3.1 影 像處理系統 19 3.2 實驗系統 19 3.2.1噴嘴設計 19 3.2.2實驗平台 20 3.2.3測試段 20 3.3實驗方法及步驟 21 第四章 結果與討論 23 4.1平板衝擊熱傳之紐賽數結果 23 4.1.1雷諾數的影響 23 4.1.2平板與噴嘴之間距的影響 25 4.1.3噴嘴直徑的影響 25 4.2平 板加裝無中心孔多孔材料之衝擊熱傳 26 4.3平板加裝有中心孔多孔材料之衝擊熱傳 27 4.3.1有中心孔深度30mm 27 4.3.2有 中心孔深度40mm 28 4.3.3挖穿之中心孔 29 4.3.4挖穿之中心孔多孔材四周有包覆 30 第五章 結論 31 參考文獻 33 圖目錄 圖1.1 噴射衝擊流之示意圖 42 圖1.2 噴嘴ILJ(in-line-jet)【10】 42 圖1.3 噴嘴RJR(radial jet reattach)【10】 43 圖1.4 噴嘴、多 孔介質與衝擊底板之組合【32】 43 圖2.1 量測速度分佈熱線頭校正後電壓與速度之取線回歸圖 44 圖2.2 校正熱線頭支小型 風洞噴嘴出口速度場品質 44 圖2.3 H/dj=2,6,10位置量測的速度分佈情形 45 圖2.4 熱偶數據擷取流程圖 45 圖2.5 T型熱偶校 正曲線 46 圖2.6 T型熱偶校正曲線 46 圖2.7 T型熱偶校正曲線較 47 圖2.8 T型熱偶校正曲線 47 圖2.9 T型熱偶校正曲線 48 圖2.10 K型熱偶校正曲線 48 圖2.11液晶校正方式示意圖 49 圖2.12 液晶校正曲線 49 圖3.1 影像處理系統之流程圖 50 圖3.2 直徑10mm的噴嘴 51 圖3.3 實驗平台的架設之示意圖 51 圖3.4 實驗之測試段 52 圖3.5 固定測試段架構圖 52 圖3.6 實驗系統 圖 53 圖3.7 實驗步驟的流程圖 54 圖4.1 平板衝擊熱傳之紐賽數分(case1dj=10mm,H/dj=2,Re=17900,無多孔材) 55 圖4.2 平板 衝擊熱傳之紐賽數分(case2dj=10mm,H/dj=2,Re=12400,無多孔材) 55 圖4.3 平板衝擊熱傳之紐賽數分
佈(casedj=10mm,H/dj=2,Re=8500,無多孔材) 56 圖4.4 平板衝擊熱傳之紐賽數分佈(case1：dj=10mm,H/dj=2,Re=17900) 56 圖4.5 平板衝擊熱傳之紐賽數分佈(case2：dj=10mm,H/dj=2,Re=12400,無多孔材) 57 圖4.6 平板衝擊熱傳之紐賽
數(case3dj=10mm,H/dj=2,Re=8500,無多孔材) 57 圖4.7 平板衝射熱傳之紐賽數受噴柱雷諾數之影響 58 圖4.8 平板衝射熱傳 之紐賽數受噴柱雷諾數之影響 58 圖4.9 平板衝擊熱傳之紐賽數分佈受平板到噴嘴間距影響情形 59 圖4.10 噴嘴直徑對平板 衝擊熱傳之影響 59 圖4.11 平板加裝多孔材之衝擊熱傳紐賽數分佈(case10：dj=10mm,Re=17900,H/dj=6) 60 圖4.12 噴射雷諾 數對平板加裝多孔材之衝擊熱傳的影響情形 60 圖4.13 噴射雷諾數對平板加裝中心挖孔30mm多孔材之衝擊熱傳的影響情形 61 圖4.14 平板加裝多孔材有無挖中心孔30mm之衝擊熱傳的影響情形 61 圖4.15 噴射雷諾數對平板加裝中心挖孔40mm多孔 材之衝擊熱傳的影響情形 62 圖4.16 噴射雷諾數對平板加裝有不同中心孔多孔材之衝擊熱傳的影響情形 62 圖4.17 平板加裝 中心挖孔40mm多孔材之衝擊熱傳的紐賽數分佈受平板到噴嘴間距之影響情形 63 圖4.18 噴嘴直徑對平板加裝中心挖 孔40mm多孔材之衝擊熱傳的影響 63 圖4.19 噴射雷諾數對平板加裝中心挖孔50mm多孔材之衝擊熱傳的影響情形 64 圖4.20
噴射雷諾數對平板加裝有不同中心孔多孔材之衝擊熱傳的影響情形 64 圖4.21 噴射雷諾數對平板加裝挖穿中心孔多孔材並 將多孔材四周包覆之衝擊熱傳的影響情形 65 圖4.22 噴射雷諾數對平板加裝挖穿中心孔多孔材有無在多孔材四周包覆之衝 擊熱傳的影響情形 65 表目錄 表1.T型熱偶校正不準度 39 表2.平板衝擊噴射實驗組數 39 表3.平板加裝多孔材料噴射衝擊實 驗組數 39 表4.平板加裝有中心孔多孔材料噴射衝擊實驗組數 40 表5.實驗所有案例停滯點紐賽數與平均紐賽數比較 41 REFERENCES
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