本文以數值方法探討電腦機箱內流量分佈不均與溫度分佈不均
之問題。以泛用熱流軟體FLUENT 來做模擬運算。機箱頂部且/或底
部裝一個風扇時風扇直徑設定為60mm。裝有兩風扇時風扇直徑改成
各為30mm。風扇之總質率皆為0.01732 kg s 。電路板分成串聯和並
聯兩種排列方式，並聯是將12 片電路板排在同一平面上，串聯為12
片電路板分為上下兩部份來排列。(一)從並聯的排列方式中我們發
現：(1)比較頂面兩風扇放置位置時，發現風扇間距與風扇至邊壁距
離一樣時，機箱內部溫度分佈比較均勻；比較兩個風扇皆裝於頂面與頂、底面各裝一個風扇時，我們發現兩風扇皆裝置於頂面時，機箱內流量分佈與溫度分佈比較均勻。當機箱頂部和底部各裝一個風扇時，底部風扇主導了機箱內部的流場，而且空氣室高度愈大，機箱內流量分佈與溫度分佈愈均勻。(2)比較側通風口設立位置時，側通風口開在電路板最底部時，電路板溫度最均勻，而且側通風口位置往上移動會使電路板高溫熱塊縮小，但電路板平均溫度卻會比較高。比較側通風口大小為5mm、10mm、20mm 時發現，側通風口的大小取10mm時，溫度分佈最均勻。(3)風扇正常運轉時，機箱內部溫度約為50℃，風扇損壞後，流動為自然對流，總質量流率還不到風扇正常運轉時的十分之一，電路板的最高溫度高達150℃，且每一電路板上的高低溫差近100℃，但各片電路板之溫度分佈幾乎相同。我們也發現裝設直徑較大之風扇(例如：直徑120mm)，可提高風扇損壞後的總質量流率，電路板的溫度分佈會比較均勻。(二)探討串聯的排列方式時我們發現：(1)風扇裝於頂面，在上、下兩單元之間開側通風口可降低上單元電路板的溫度，而且機箱內部溫度比較均勻；風扇若裝於底部時，部份流體還未流至上單元電路板便由側通風口流出機箱，造成上單元電路板溫度升高。(2)改變上單元其中一片電路板之發熱量，我們發現只有此電路板和左右相鄰的電路板溫度受影響。(3)比較上、下單元內各種電路板片數，我們發現下單元設置較少的電路板且電路板彼此間距較大時，各電路板溫度比較均勻。(4)風扇損壞後，存在側通風口可使串聯排列之電路板溫度比較均勻。

Numerical method is used in this paper to investigate the problem of uneven flow and uneven temperature in a computer chassis. The universal heat flow software, FLUENT, is used to perform simulations. When a fan
is installed at the top and/or bottom of the chassis, the diameter of the fan is set to 60mm; while two fans are installed, the diameter of the fan is changed to 30mm each. The total mass flow rate of the fan is set to
0.01732 kg/s . The arrangement of circuit boards is divided into two kinds:serial and parallel arrangement. Parallel is to arrange all the 12 circuit boards on the same plane while serial is to arrange the 12 circuit boards
into top and bottom two units. (I) We find from the parallel arrangement: (1) Comparing under the situation of placing two fans on top: we find that the temperature
inside chassis distributes more evenly when the distance between the two fans is the same as the distance from the fan to the side wall; Comparing the situation of two fans on top to the situation of one fan each for top and bottom, we find that both the flow distribution and the
temperature distribution inside the chassis are more evenly when both fans are placed on top. While one fan each is placed on top and bottom of the chassis, the bottom fan dominates the flow field inside the chassis and
the higher the air chamber is, the more evenly the flow distribution and the temperature distribution inside the chassis. (2) Comparing the locations of the side vents, the temperature of the circuit board distributes the most evenly when the side vents are located at the bottom of the
circuit board; also, the high temperature heat block on the circuit boards will tend to shrink if the locations of the side vents are moved upward, but the average temperature of the circuit boards will tend to rise higher.
Comparing the side vent size of 5mm, 10mm, and 20mm, we find that the temperature distribution become the most evenly when the side vent size is taken as 10mm. (3) The temperature inside the chassis is about 50℃ under the normal operation of the fan. After the fan is damaged, the flow depends on natural convection only and the total mass flow rate is reduced to less than not even one tenth of that under the normal operation of the fan; the highest temperature of the circuit board can reach up to 150℃. Also the high low temperature differences on each circuit board can be close to 100℃, but the temperature istribution for each circuit board is almost exactly the same. We also find that installing fans with larger diameter (such as 120mm) can raise the total mass flow rate once the fan is damaged and the temperature rate distribution of the circuit board will become more evenly.
(II) We find from the serial arrangement: (1) Under the situation of placing fans on top, the temperature of the circuit boards on the upper unit can be reduced if side vents are installed between the upper and bottom units and the temperature inside the chassis will become more evenly; while placing fans at the bottom, some fluid may flow out of the chassis from the side vents before it reaches the circuit boards on the upper unit and results in the rise of temperature on the circuit boards on the upper unit. (2) We find that if the heat release rate of one circuit board in the upper unit changes, only the temperature of that circuit board and its left and right neighboring boards will be affected. (3) Comparing the
number of circuit boards on the upper and bottom units, we find that the temperature of each circuit board will become more evenly when the bottom unit contains fewer circuit boards and the spacing between them is larger. (4) Once the fan is damaged, the temperature on the circuit
boards in serial arrangement will become more evenly if there exist side vents.

中文摘要 I
英文摘要 III
目錄 V
表目錄 VIII
圖目錄 IX
符號說明 XVII
第一章 序論 1
1-1 前言 1
1-2 文獻回顧 2
1-3 研究動機與目的 4
第二章 理論分析 5
2-1 物理模型與基本假設 5
2-2 統御方程式 6
2-3 紊流模式 7
2-4 邊界條件 9
2-5 標準壁面函數法 10
第三章 數值模擬方法 16
3-1 數值方法概述 16
3-2 求解程序 16
3-3 收斂條件 18
3-4 鬆弛因子19
3-5 數值模擬流程 19
3-6 網格設置 20
第四章 結果與討論 23
4-1 機箱裝有兩風扇且12 片電路板皆並排配置下 26
4-1-1 兩風扇裝於頂面探討風扇位置和空氣室高度 26
4-1-2 探討在機箱兩側各開一側通風口之影響43
4-1-3 探討機箱頂部和底部各裝一風扇 56
4-1-4 探討風扇損壞之影響 63
4-2 機箱內電路板分上下兩單元串聯配置 74
4-2-1 機箱內上下兩單元間距和側通風口的位置 74
4-2-2 風扇改裝於機箱底部改變側通風口的位置 86
4-2-3 改變上單元其中一片的發熱量 93
4-2-4 改變上下單元電路板片數各為三片和九片 101
4-2-5 風扇損壞的情況下 113
第五章 結論與建議 126
參考文獻 129

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