本研究利用暫態之數值方法探討水平鰭片熱沉在多通道情形下的自然對流特性，著重探討側向氣流之三維流場對於各通道與整體熱沉散熱量的影響。模擬之鰭片尺寸為L=80 ~254 mm，H=6.4~25 mm，S=6.4 mm、8 mm。全文共分為四個部分，第一部分利用無限通道之模擬結果與實驗數據進行比對以驗證模擬的可靠度；第二部分探討L=127 mm下鰭片高度H對於多通道流場以及散熱效果的影響，結果顯示H=6.4 mm時由於側向氣流會嚴重壓制熱沉外部通道中上浮之氣流，且僅有內側通道能順利產生滑移煙囪流，因此內側通道的散熱效果將優於外側通道；隨著高度增加至H=25 mm，各通道的流場行為會趨近單一煙囪流，側向氣流將無法壓制各通道上浮之氣流，反而還會增加外側通道上方空氣之浮力，因此外側通道的散熱效果反而優於內側通道；第三部分討論L=127 mm時不同型式的側板條件對於側向氣流與整體熱傳效果的影響，結果發現熱沉外側有無添加保護鰭片(guard fin)對於高鰭片(H=25 mm)而言影響不大；然而對於矮鰭片(H=6.4 mm)而言卻能大幅增加外側通道的散熱效果，使得多通道熱沉平均各通道之 h ̅ 接近於無限通道模擬之結果。此外若將矮鰭片(H=6.4 mm)最外側的鰭片增添6.6 mm高的絕熱段或是改為13 mm高之等溫鰭片皆能有效的阻隔側向氣流對於內部通道的壓制行為。其中最外側為13 mm高等溫鰭片的熱沉，平均內部各通道之h ̅可高出標準十六通道之熱沉21.9%；第四部分則探討鰭片長度對於多通道流場之影響，模擬結果發現短鰭片(L=80 mm)熱沉，在任何鰭片高度下各通道之流場型態皆為單一煙囪流，此外側向氣流幾乎不會對內部通道造成影響，因此採用無限通道所求出之h ̅ 與多通道(平均通道1~8)之間差異不超過1.2%；反觀長鰭片(L=254 mm)在三種高度下(H=6.4~25 mm)，側向氣流皆會被引入熱沉中段上方影響內部通道之熱傳效果。即便在H=25 mm之情況下，利用無限通道模擬所求出之h ̅仍會高估11.4%。另外模擬結果還發現矮鰭片(H=6.4 mm)熱沉之側向氣流在z方向上會產生大週期左右振盪行為，這現象導致熱沉部分通道之h ̅甚至會低於穩態解hss。因此多通道長鰭片之熱沉須同時考量長度方向上流場的振盪行為、側向氣流帶來的三維效應還要顧及側向氣流是否會發生左右振盪的情形。

This study investigates the transient natural convection characteristics of horizontal multi-channel plate-fin heat sinks, focusing on the impact of the three-dimensional side flow on the heat dissipation of each individual channel and the overall heat sink. The simulated fin dimensions are L=80~254 mm, H=6.4~25 mm, S=6.4~8 mm. The full text is divided into four parts. The first part compares the simulation results of the infinite channel heat sink with the experimental data to verify the reliability of the simulation. The second part discusses the effect of the fin height H under L=127 mm on the multi-channel flow field and heat dissipation. The results show that when H=6.4 mm, the side flow will seriously suppress the upward airflow in the outer channel of the heat sink, and only the inner channel can smoothly generate the sliding chimney flow. Consequently, the heat dissipation ability of the inner channels is better than that of the outer channels. As the fin height increases to H=25 mm, the flow field behavior of all channels approximates a single chimney flow. The side flow does not suppress the upward airflow, but increase the buoyancy for the outer channels. Therefore, in this case, the heat dissipation of the outer channels is better than of the inner channels. The third part discusses the influence of different types of side plate conditions on the side flow and the overall heat transfer effect at L=127 mm. It is found that whether there are guard fins on the outer sides of the heat sink has little effect on the high-fin heat sink (H=25 mm). But for a short-fin heat sink (H=6.4 mm), the heat dissipation of the outer channels is significantly increased and the h ̅ in each individual channel of the multi-channel heat sink approximates the result of infinite-channel simulation. Besides, if both outermost fins of the short-fin heat sink (H=6.4 mm) are added with a 6.6 mm-high insulation section or are changed to 13 mm-high isothermal fins, the suppression of the side flow to internal channels can be effectively avoided. Also, if the outermost are 13 mm- high elongated isothermal fins, the average of h ̅ in internal channels can be 21.9% higher than the standard 16-channel heat sink. The last part mainly discusses the effect of fin length on the multi-channel flow field. The simulation results indicate that for the short-fin (L=80 mm) heat sink, the flow field pattern of each channel at any fin height is a single chimney flow. The side flow hardly affects the internal channels, so the difference of h ̅ between the infinite channel and multi-channel heat sink (average of channels 1~8) does not exceed 1.2%. In contrast, for the long-fin heat sink (L=254 mm) at three fin heights (H=6.4~25 mm), the side flow will penetrate above the heat sink to affect the heat transfer effect of the internal channels. Even in the case of H=25 mm, the h ̅ obtained by simulation with the infinite channel will still be over-estimated by 11.4%. Also, the simulation results indicate that the side flow of the low fin (H=6.4 mm) heat sink will oscillate left and right in the transverse direction with a larger period, which will cause the h ̅ of part of the heat sink channels to be even lower than the steady-state solution hss. Therefore, the analysis for multi-channel long-fin heat sinks must consider the oscillation behavior of the flow field in the longitudinal direction, the three-dimensional effect brought by the side airflow, and whether the lateral airflow will oscillate.

摘要 I
Abstract II
誌謝辭 IV
目錄 V
圖表目錄 VIII
符號表 XVIII
第一章 緒論 1
1.1 前言 1
1.2 文獻回顧 2
1.2.1 垂直平行板 2
1.2.2 鰭片熱沉 5
1.2.2.1 垂直鰭片熱沉 5
1.2.2.2 水平鰭片熱沉 6
1.2.2.3 傾斜角對於鰭片熱沉的影響 11
1.3 研究動機 13
第二章 理論基礎與模型建構 28
2.1 數學模型 28
2.1.1 統御方程式 28
2.1.2 邊界條件 29
2.1.3 熱對流數之計算方式 29
2.2 數值方法 30
2.2.1 速度與壓力求解方式 30
2.2.2 方程式離散方法 31
2.2.3 相關參數設定 31
2.2.3.1 鬆弛因子 31
2.2.3.2 收斂條件 31
2.3 模擬參數 31
2.4 計算域大小 32
2.5 網格之測試與選用 32
2.6 時間步大小與區間的選用 33
第三章 結果與討論 39
3.1 無限通道模擬結果 39
3.1.1 改變鰭片尺寸對於散熱效果的影響 40
3.1.2 數值模擬與實驗數據的比對 40
3.2 L=127 mm下多通道熱沉的數值模擬結果 41
3.2.1 L=127 mm；H=6.4 mm；S=6.4 mm十通道鰭片熱沉之模擬結果 42
3.2.2 L=127 mm，H=6.4 mm，S=6.4 mm十六通道鰭片熱沉之模擬結果 43
3.2.3 L=127 mm，H=13 mm，S=6.4 mm 鰭片熱沉之模擬結果 45
3.2.4 L=127 mm，H=25 mm，S=8 mm鰭片熱沉之模擬結果 48
3.2.5 鰭片高度(H)對於L=127 mm之多通道熱沉的影響 49
3.3 不同形式的側板條件對於多通道數值模擬的影響 52
3.3.1 保護鰭片對於多通道熱沉的影響 52
3.3.1.1 L=127 mm，H=6.4 mm，S=6.4 mm含保護鰭片之模擬結果 52
3.3.1.2 L=127 mm，H=25 mm，S=8 mm含保護鰭片之模擬結果 57
3.3.2 L=127 mm，H=6.4 mm，S=6.4 mm增高側板之多通道熱沉模擬結果 58
3.3.2.1 十六通道熱沉外加6.6 mm高絕熱保護段 58
3.3.2.2 十六通道熱沉側板加高為13 mm之鰭片 61
3.3.3 四種側板型式對於矮鰭片(H=6.4 mm)多通道熱沉散熱效果的影響 63
3.4 鰭片長度對於多通道熱沉之影響 64
3.4.1 短鰭片(L=80 mm)熱沉之數值模擬結果 64
3.4.1.1 L=80 mm無限通道模擬結果 64
3.4.1.2 L=80 mm十六通道模擬結果 65
3.4.2 L=254 mm下十六通道熱沉之數值模擬結果 65
3.4.2.1 L=254 mm，H=6.4 mm，S=6.4 mm 65
3.4.2.2 L=254 mm，H=13 mm，S=6.4 mm 67
3.4.2.3 L=254 mm，H=25 mm，S=8 mm 68
3.4.3 鰭片長度對於多通道熱沉三維流場及散熱效果的影響 69
第四章 結論 141
參考文獻 143

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