落膜系統之計算流體力學模擬

CFD simulation of a falling film system

張家蓓(Chia-Pei Chang)

指導教授 ： 張煖

淡江大學/工學院/化學工程與材料工程學系碩士班/碩士(2009年)

https://doi.org/10.6846/TKU.2009.01094

摘要

本研究利用計算流體力學軟體(Computational fluid dynamics，CFD)，模擬微結構落膜系統內之流力與熱傳特性。本研究採用FLUENT內之流體體積(Volume of fluid, VOF)模式，氣液界面間之熱傳面積與熱傳量則利用使用者定義函數(UDF，User defined function)計算。本研究限於層流範圍。
透過模擬建立了微結構落膜系統內部之特性分佈，包括速度、溫度、液膜與氣液界面熱傳量，並一一分析了系統條件參數之影響，包含表面張力、流體流量、液體黏度、液體密度、氣液溫度差、傾斜角度等。
分析結果顯示，雖然是在層流範圍內，因各項條件參數之不同，液膜波動程度與液膜厚度會有差異。針對液膜厚度與熱傳係數，比較模擬結果與理論值亦發現只有在液體雷諾數很小時較接近，當雷諾數增大時，偏差程度即會加大。因此，使用CFD模擬落膜系統以確實掌握其流力與熱傳特性是有必要的。

關鍵字

計算流體力學 ； 微結構反應器 ； 落膜 ； 流體體積模式 ； 兩相流 ； 層流

並列摘要

The thesis studies the hydrodynamics and heat transfer for a microstructure falling film device by CFD simulation using FLUENT. VOF (Volume of Fluid) model is adopted. For calculating gas-liquid interface heat transfer, a User Defined Functions (UDF) is developed. The study is limited to laminar flow region.
Grid independent study is conducted to determine the acceptable grid size. The model is used to simulate the profiles in the system, including velocity, pressure, phase and temperature. The model is further used to investigate the effects of system parameters, including surface tension, fluid flow rates, liquid density and viscosity, angle of inclination and temperature difference.
Even for the laminar flow system, the simulation results indicate that the liquid film characteristics, such as the eddy, the wave, and the film thickness, are affected by the condition parameters studied. Regarding the film thickness and heat transfer coefficient, comparisons between simulated results and theoretical predictions also indicate discrepancies and the difference is larger for higher liquid Reynolds number. All these conclude that using CFD simulation to obtain the hydrodynamics and heat transfer characteristics for laminar falling film is necessary.

並列關鍵字

Computational Fluid Dynamics ； Microreactors ； Falling film ； VOF model ； Two-phase flow ； Laminar flow

參考文獻

蔡孟樵. (2008). 氣體吸收薄膜接觸器之計算流體力學研究. 淡江大學碩士論文.

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Gao, D., Morley, N. B., & Dhir, V. (2003). Numerical simulation of wavy falling film flow using VOF method. Journal of Computational Physics, 192(2), 624-642.

Gu, F., Liu, C. J., Yuan, X. G., & Yu, G. C. (2004). CFD simulation of liquid film flow on inclined plates. Chemical Engineering and Technology, 27(10), 1099-1104.

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