本研究利用一基於 VOF 的 CISIT 之介面追蹤法模擬一薄膜沸騰現 象。使用單一流體模型以一組質量、動量與能量守恆方程式的統御方程組 來描述此雙流體系統。由介面追蹤法所得之介面位置進一步求出介面處用 以驅動相變化產生之熱傳通量，並將相變化造成之質量變化量加入連續方 程式之源項，藉以滿足兩相間之跳躍條件。先以具理論解的相變化問題驗 證相變化之處理，可以發現溫度分佈之準確性與計算熱傳通量時所用之定 長
n
影響相變化結果甚鉅。若選擇適當長度作為 n
之設定，本研究之計 算結果(介面位置、介面速度)接近理論解。最後模擬了一薄膜沸騰現象，除了可以觀察到氣泡的生成過程，此外同時計算底部某一定點的
Nu
，藉 此研究氣泡的生成情形與氣相內的熱傳性質變化的變化關係。可以發現每 當有氣泡在底部成形時，此時Nu
會處於相對極小值；而當氣泡逐漸上升Nu
也隨之變大，到了氣泡正要脫離氣體薄層時，Nu
將會達到相對極大值。因此得知也可從
Nu
的變化趨勢推測此時氣泡的成長情況。參考文獻
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50
表四、薄膜沸騰測試所用之流體性質(Psat 1.0135 10 5 Pa)
kg m/ 3
N s m / 2
vc
J kg K/
k
W m K/
hfg
J kg K/
液體 200 0.1 400 400 10000氣體 5 0.005 200 1
52
圖 2.1 通用傳輸方程式示意圖
圖 2.2 流體分布及曲率符號之示意圖
圖 3.1 控制體積及其鄰格點之關係示意圖
54
圖 3.3 一介面前端跨越過一計算網格之示意圖
圖 3.4 一介面尾端跨越過一計算網格之示意圖
圖 3.5 計算主格點與鄰格點和計算面之示意圖
56
圖 3.6 介面處熱傳量計算之示意圖
圖 3.7 介面處熱傳量計算之示意圖
圖 4.1 Stefan 1st 問題之示意圖
58
圖 4.5 網格(50x5) 計算時間 t=10s 之溫度分佈圖
60
圖 4.10 Stefan’s 2nd 問題之示意圖
62
圖 4.14 網格(50x5)不同混合熱傳係數計算時間 t=2s 之溫度分佈圖
64
圖 4.19 液相流體之熱傳係數搭配不同
n
計算結果之介面位置圖66
圖 4.23 薄膜沸騰模擬所給的初始介面分佈圖
圖 4.24 薄膜沸騰模擬在不同網格之第一顆氣泡升起情況
t=0.35s red=16x48 blue=32x96 green=64x192
t=0.36s red=16x48 blue=32x96 green=64x192
t=0.37s red=16x48 blue=32x96 green=64x192
68
0.1
70
0.1
72
圖 4.30 不同網格在底部一定點之
Nu
隨時間變化圖t (s)
Nu
0 0.2 0.4 0.6
2 4 6 8 10 12 14
mesh=16x48 mesh=32x96 mesh=64x192 berenson correlation