臺灣博碩士論文加值系統

本研究旨在探討滴淋式蒸發器內部流場變化，避免液滴被冷媒蒸氣所夾帶，並避免大量的液滴被帶入壓縮機，進而延長壓縮機的壽命。本研究以工作流體為冷媒R-134a 的100冷凍噸冰水機之滴淋式蒸發器為研究對象，於蒸發器內設置一百葉型液滴攔阻裝置，防止壓縮機液壓縮。以計算流體力學分析軟體(ANSYS FLUENT)進行數值模擬分析，研究蒸發器及百葉裝置之冷媒氣流與液滴的流場，並找出造成液滴飛濺特性和百葉攔阻裝置的可行性。模擬結果顯示加入百葉可降低液滴夾卷率；當流場最窄小處之最大速度為5m/s時，原蒸發器的液滴夾卷率在液滴粒徑1mm時為17.8%；液滴粒徑2mm時為13.6%；粒徑3mm時為8.4%。蒸發器在加入三種葉型中的最佳百葉後，三種液滴粒徑在同樣的速度下之液滴夾卷率分別下降為：7.15%、3.5%和0.33%。當蒸發器加入百葉時壓損值約增加了78~972Pa，而此壓損所造成飽和溫度下降僅約0.0065~0.081℃，對蒸發器的整體性能影響不大。由此可見百葉型液滴攔阻裝置具有可行性。

In this study, the flow distribution inside a falling film evaporator is studied. The purpose of this study is to avoid liquid droplets from entering the compressor, and to extend the life of the compressor. Numerical simulation by computational fluid dynamics (CFD) analysis software (ANSYS FLUENT) is used to study the liquid and vapor flow in a falling film evaporator of 100 refrigeration tons, and the working fluid is refrigerant R-134a. Feasibility of a louver-type liquid droplet blocking device is evaluated. The Simulation results show that the original droplet entrainment rate is 17.8%, 13.6% and 8.4%, for droplets diameter of 1mm, 2mm and 3mm, respectively, when the maximum velocity at the flow field narrowest area is 5m/s. By adding the louver-type droplet blocking device, the droplet entrainment rate decreases. Among the three louver types in this study, the best louver yields 7.15%, 3.5% and 0.33% entrainment rate for 1, 2, 3 mm diameter droplet, respectively.
 
The pressure drop increases by 78 ~ 972 Pa when the louver is added in the evaporator, and this results in saturation temperature drop of only 0.0065 ~ 0.081℃ in the evaporator. Hence, the louver-type droplet blocking device is considered as a feasible device for falling film evaporators.

摘要 I
ABSTRACT II
誌謝 IV
目錄 V
表目錄 VIII
圖目錄 IX
第一章 緒論 1
1.1研究背景 1
1.2研究目的 3
第二章 文獻回顧 5
2.1滴淋式蒸發器之特性 5
2.2滴淋薄膜蒸發流場型態 7
2.3氣流夾卷液滴之現象 11
2.4百葉型液滴攔阻裝置 14
2.4.1百葉測定規範 14
2.4.2百葉相關研究 15
2.5液滴運動相關研究 23
2.5.1液滴之二次噴濺 23
2.5.2液滴飛濺損失機制 24
2.5.3顆粒運動方程式 27
2.5.4顆粒之阻力分析 27
2.5.5液滴碰撞模型 31
第三章 數值模擬 33
3.1數值模擬方法 33
3.1.1基本假設 33
3.1.2連續相模型 34
3.1.3 Realizable k-ε 模型 36
3.1.4離散相模型(Discrete Phase Model) 37
3.1.5離散相模型的使用限制 38
3.1.6離散相模型求解過程 39
3.1.7顆粒軌跡計算 39
3.1.8 SIMPLEC演算法 41
3.1.9模擬軟體計算流程 43
3.2滴淋式蒸發器設計 44
3.2.1冷媒分配盤 46
3.2.2蒸發管陣配置 47
3.2.3冷媒蒸氣出口端 48
3.3百葉型液滴攔阻裝置設計 49
3.3.1單一百葉型液滴攔阻裝置 51
3.3.2納入百葉型液滴攔阻裝置之蒸發器 52
3.4模型之基本結構解析 53
3.4.1滴淋式蒸發器 53
3.4.2百葉型液滴攔阻裝置 58
3.5蒸發器之氣流與液滴研究方法 60
3.6物理模型及邊界條件設定 61
3.7鬆弛因數及收斂條件 65
3.8格點獨立分析 67
第四章 模擬結果與討論分析 72
4.1滴淋式蒸發器之流場分析 72
4.1.1滴淋式蒸發器在不同負載下之內部流場變化 72
4.1.2冷媒出口端內徑對蒸發器流場之影響性 80
4.1.3冷媒分配盤高度對蒸發器流場之影響性 85
4.2納入百葉之滴淋式蒸發器流場分析 91
4.2.1氣流模擬結果之流場比較分析 91
4.2.2液滴模擬結果之流場比較分析 98
4.3蒸發器之流場最大速度與液滴粒徑分析 108
第五章 結論與未來展望 112
5.1結論 112
5.2未來展望 114
參考文獻 115
符號彙編 119

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