- 學位論文
薄膜蒸餾傳輸特性之計算流體力學研究
CFD study of transport characteristics of membrane distillation
摘要
本研究利用計算流體力學(Computational Fluid Dynamics, CFD)模擬探討薄膜蒸餾模組內之流力與熱傳特性。本研究使用FLUENT軟體模擬了操作於層流範圍的三種模組，包括使用具粗糙面與具間隔物通道的直接接觸式模組，以及真空式模組。透膜熱質傳是利用使用者定義函數納入模式中。 流力方面，具粗糙面通道之摩擦因子與使用受限水力直徑之關聯式預測值接近；具間隔物通道之各重複單元具有類似流場，且壓損隨間隔物空隙率減小而增大；真空式模組液體側壓損較關聯式預測值低。在熱傳方面，具粗糙面通道與真空式模組均有明顯的入口熱發展區，其熱傳通量與質傳通量均顯著地高出後段穩定區。有無介面質傳對熱傳係數之影響不大。具間隔物通道之熱傳係數隨圓柱物之配置位置呈上下震盪變化。
並列摘要
In this study, the fluid flow and heat transfer in the membrane distillation (MD) modules are investigated by the computational fluid dynamics (CFD) simulation. The FLUENT software is used to simulate three laminar flow MD modules, including the direct contact type MD (DCMD) modules with roughened-surface and spacer-filled channels as well as the vacuum type MD (VMD). The trans-membrane heat and mass transfer are taken into account using the user-defined-functions in FLUENT. In fluid flow, the simulated friction factors of the roughened-surface channels are close to the correlation predictions using constricted hydraulic diameters. For the spacer-filled channels, the flow fields of individual repeated units are similar and the pressure drop increases with the reduction of spacer voidage. For VMD, the fluid side pressure drops are lower than that predicted from correlations. In heat transfer, the entrance thermal developing section, which gives higher heat and mass transfer rates, is observed in both roughened-surface channels and the VMD channels. The trans-membrane mass transfer does significantly affect the heat transfer coefficient. For the spacer-filled channels, the local heat transfer coefficients fluctuate with the layout of the spacer filaments.