本研究以數值模擬的方法探討定風量及變風量情況下蒸發器中霜層厚度對熱傳量的影響，水蒸汽凝結成霜之質傳效應及凝結產生之潛熱所造成之影響在文中亦有探討，熱交換器型式為四管排交錯排列的平板型鰭管式熱交換器。由於在熱交換器出口強大的尾流作用，本研究在熱流場的分析中採用Low-Reynolds number k-ε turbulent model，並考量鰭片與霜層的固體熱傳導與流體熱質傳效應，網格的建立採用非結構性網格方式。霜層的熱傳導係數參考以前的相關研究選定參數的範圍。定風速或定風量的分析結果顯示，在霜厚度很薄時熱傳量會略高於無霜時，霜持續增厚時熱傳量在大鰭片間距會呈上升趨勢，在小鰭片間距呈下降趨勢。變風量的情況是以典型的風扇性能曲線搭配熱交換器的阻抗曲線來決定風量，結果顯示在此情況下，熱傳量基本上隨著霜層厚度的增加而下降，鰭片間距較小的總熱傳量會高於鰭片間距較大者，當霜阻塞約一半流道截面積時，鰭片間距較小的總熱傳量逐漸不如鰭片間距較大者，這應可做為設計蒸發器除霜時機的重要參考。在水蒸汽熱質傳分析的結果顯示，空氣與霜表面的水蒸汽質傳主要發生在熱交換器的前段，水蒸汽沉積所產生的凝結與凝固熱隨霜厚度而增加，但對整體熱傳的增進效果卻是隨霜厚度而減少。

This study is concerned with the effect of frost thickness on heat transfer rate of the evaporators in constant and variable airflow rate. Numerical computation is used to simulate the flow and heat transfer behaviors. The vapor deposition and the generation of latent heat between air and frost are also included in this study. The heat exchanger simulated here is four tubes stagger fin-tube plate type. Due to a strong wake at the trail of heat exchanger, this study use Low-Reynolds number k-ε turbulent model to calculate the heat and flow fields. The heat conduction is considered in fin and frost. The unstructured grid is adapted in grid establishment. The physical properties of frost are referred to the previous researching work. The results from the analysis of constant airflow rate show that heat transfer rate at thin frost are slightly better than that without frost. However, the heat transfer rate decreases for large fin pitch and increases for small one as the frost thickness increases. In the variable airflow rate, the airflow rate is determined from the combination of fan and resistance curve. The results show that heat transfer rate decreases as frost thickness increases. Generally, total heat transfer rate of small fin-pitch heat exchanger is higher than big one. Nevertheless, the situation is reverse as half of flow channel is blocked by frost. This phenomenon could be treated as criteria of timing for defrost. The analysis of heat mass transfer shows that the vapor mass transfer between air and frost occurs mostly at region near inlet of heat exchanger. When frost thickness increases, the latent heat due to frost deposition increases but the enhancement of overall heat transfer rate decreases.

摘要 i
ABSTRACT ii
誌 謝 iii
目錄 iv
表目錄 vi
圖目錄 vii
符號說明 ix
第一章、緒 論 1
1-1 前言 1
1-2 文獻回顧 1
1-3 研究目的 3
第二章、物理模式與方程式 4
2-1物理模式 4
2-2方程式 7
第三章、數值解法與網格建立 15
3-1關於Star-CD 15
3-1-1 STAR-CD 簡介 15
3-1-2 Star-CD 功能設定 15
3-2 數值解法 16
3-3 網格建立 17
第四章、結果與討論 22
4-1 網格測試與實驗比對 22
4-2 定風速無質傳分析 23
4-2-1 一英吋六鰭片分析 24
4-2-2 一英吋四鰭片分析 25
4-2-3 一英吋二鰭片分析 27
4-2-4 一英吋一鰭片分析 29
4-3 變風速無質傳分析 30
4-3-1 不同霜層厚度阻抗曲線與風扇性能曲線 30
4-3-2 一英吋六鰭片與風扇整合分析 33
4-3-3 一英吋四鰭片與風扇整合分析 34
4-3-4 一英吋二鰭片與風扇整合分析 35
4-3-5 一英吋一鰭片與風扇整合分析 36
4-3-6 不同鰭片間距熱交換器與軸流扇搭配 37
4-4 定風量質傳分析 40
4-4-1定風量時的質傳分析 40
4-4-2 定風量下水汽凝結熱與霜凝固熱對熱交換器熱傳的影響 43
4-5 變風速質傳分析 45
4-5-1 與軸流風扇搭配時的熱質傳分析 45
4-5-2 與離心風扇搭配時的熱質傳分析 49
第五章、結論 53
參考文獻 54
附錄一、飽和蒸汽表 57
附錄二、飽和蒸汽表(續) 58
附錄三、定風速下不同霜熱傳係數隨霜厚對熱傳的影響圖 59
附錄四、Star-CD體發熱副程式 60

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