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    Title: 渠道型式對直接接觸式薄膜蒸餾效能影響之研究
    Other Titles: Effect of channel design on the performance of direct contact membrane distillation
    Authors: 簡文洋;Chien, Wen-Yang
    Contributors: 淡江大學化學工程與材料工程學系碩士班
    鄭東文;Cheng, Tung-Wen
    Keywords: 薄膜蒸餾;流動型態;極化現象;渠道;Direct contact membrane distillation;Flow Pattern;Polarization phenomena;Channel
    Date: 2011
    Issue Date: 2011-12-28 18:50:05 (UTC+8)
    Abstract: 本研究為利用疏水性聚四氟乙烯薄膜(PTFE)來進行直接接觸式薄膜蒸餾,主要研究目標將改良模組進料側渠道型式對於直接接觸式薄膜蒸餾效能之影響。實驗將以兩種不同渠道型式(Concaves、Convexs)下改變進料溫度、進料流量、膜組傾斜角、曝氣來探討其對於滲透通量之提昇。並利用估算理論薄膜蒸餾海水滲透通量與實驗值作一比較,與計算流體力學(CFD)來模擬流體於進料側通道內之速度分佈與膜面上之剪應力。
    實驗結果可以發現,提高進料溫度能明顯的增加滲透通量,但極化現象也最嚴重。而增加進料流量與曝氣則可以減輕極化現象,但對於滲透通量的提昇較有限。改變膜組傾斜角則是由於不穩定自然對流關係使滲透通量提昇,其中又以傾斜角45o時之滲透通量為最高。凹槽模組(Concaves)則是造成進料流體產生亂流流動,使得滲透通量大幅度的提高;而凸出模組(Convexs)增加了對膜面造成之剪應力,也就有效的減緩了膜面上之極化現象而使滲透通量提昇。
    藉由Dusty-Gas model並假設海水相當為3.4%之NaCl溶液所估算出薄膜蒸餾海水之理論滲透通量,其理論計算的結果與實驗趨勢非常符合。結果顯示出溫度極化係數介於0.5~0.65之間;濃度極化係數隨著溫度差或進料流速減少而有明顯的增加,故濃度極化現象為影響滲透通量的主要影響因素。由計算流體力學(CFD)模擬出凹槽模組會使通道內之流體形成擾流進而提昇滲透通量,而凸出模組則大幅的提昇膜面之剪應力,也減緩了膜面上的極化現象。
    The effects of flow patterns on the permeate flux in a modified direct contact membrane distillation (DCMD) module, in that there were some concaves or convexes cross the flow direction, was studied in this work. The operating parameters included temperature difference, feed flow rate, module inclination angle, gas flow rate. The DCMD experiment was conducted in a flat sheet module with using 0.2 µm pore size polytetrafluoroethylene (PTFE) membrane. The flow patterns was Simulated by computational fluid dynamics(CFD) software.
    The experimental results show that increasing the temperature difference will increase the permeate flux, but also heighten the polarization phenomena. Increasing the feed flow rate and the gas flow rate can reduced the polarization phenomena. As the membrane of inclination was changed from the horizontal (flow below membrane), the permeate flux increased, and reached a maximum at about 45°, and the enhancement in flux is significant in the two-phase flow system.
    The results of modified DCMD show that the concaves in the feed channel can cause turbulence to feed stream and enhance flux significantly. And the convexes in the feed channel will increase the shear stress on the membrane, thus, effectively reduce the polarization phenomena and increase the permeate flux.
    The distillate fluxes of DCMD were well predicted by adopting the Knudsen-molecular diffusion in series based on Dusty-Gas model for in desalination of seawater in which the seawater was assumed to be equivalent to 3.4wt% of NaCl solution. The theoretical calculations showed that the temperature polarization coefficients were in the range of 0.5 to 0.65 that was reasonable for DCMD operation; and the concentration polarization coefficients increased significantly as the temperature difference increased or the flow rate decreased. The simulated of CFD results shows that the modified modules with concaves can cause turbulence to feed stream, and the convexes in the feed channel will increase the shear stress on the membrane surface, and thus effectively reduce the polarization phenomena.
    Appears in Collections:[化學工程與材料工程學系暨研究所] 學位論文

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