本文選題：中空纖維膜 + 死端過濾��； 參考：《山東大學(xué)》2017年碩士論文

【摘要】：中空纖維膜具有結(jié)構(gòu)簡(jiǎn)單、分離效率高、裝填密度小、成本和操作費(fèi)用低以及應(yīng)用靈活等優(yōu)勢(shì),在污水和飲用水處理領(lǐng)域受到越來越多的關(guān)注。然而膜污染的存在使得中空纖維膜系統(tǒng)過濾性能受到嚴(yán)重影響,膜污染已成為制約中空纖維膜分離技術(shù)發(fā)展的關(guān)鍵因素。數(shù)學(xué)模型是研究中空纖維膜污染、優(yōu)化中空纖維膜系統(tǒng)過濾性能的重要手段�，F(xiàn)有的死端過濾中空纖維膜過濾模型多以Hagen-Poiseuill方程為基礎(chǔ),尚未考慮到中空纖維膜腔內(nèi)流體加速造成的動(dòng)壓損失對(duì)流體流動(dòng)阻力的影響,削弱了模型模擬結(jié)果的準(zhǔn)確度。另外,模型均是基于商業(yè)或開源計(jì)算流體力學(xué)(CFD)軟件進(jìn)行求解,CFD過程復(fù)雜,需要輸入多個(gè)邊界條件才能運(yùn)行,而這些邊界條件一般情況下是未知的,因此使用起來并不方便或誤差較大。本研究以流體力學(xué)和膜過濾理論為基礎(chǔ),構(gòu)建了一個(gè)描述死端過濾中空纖維膜過濾過程的數(shù)學(xué)模型,在模型構(gòu)建時(shí)同時(shí)考慮了膜腔內(nèi)摩擦造成的壓力損失和流體加速造成的動(dòng)壓損失在膜長度方向上的累積,并以此模型為基礎(chǔ)解析死端過濾中空纖維膜系統(tǒng)過濾特征參數(shù)及膜污染的時(shí)空分布規(guī)律,確定影響系統(tǒng)過濾性能的關(guān)鍵因子,為中空纖維膜系統(tǒng)的優(yōu)化提供了科學(xué)依據(jù)。研究發(fā)現(xiàn),模型模擬結(jié)果很好地吻合了實(shí)驗(yàn)結(jié)果,通過增加膜腔內(nèi)動(dòng)壓損失對(duì)流體流動(dòng)阻力的影響,模型模擬結(jié)果與實(shí)驗(yàn)結(jié)果吻合度明顯提高。在進(jìn)行模型求解時(shí),死端處跨膜壓差的確定是模型得以求解的關(guān)鍵。本研究提出了一種以二分法為基礎(chǔ)的死端處跨膜壓差的反向迭代計(jì)算法,該解法效率高,適用范圍廣,對(duì)恒流和恒壓運(yùn)行模式、不同膜污染機(jī)理作用下死端過濾中空纖維膜過濾模型均適用。基于上述死端過濾中空纖維膜過濾模型和數(shù)值解計(jì)算方法,研究模擬了中空纖維膜污染及系統(tǒng)各過濾特征參數(shù)的時(shí)空分布規(guī)律。研究發(fā)現(xiàn),隨著過濾時(shí)間的增加,膜長度方向上各點(diǎn)處膜污染均逐漸加劇;而任意時(shí)間時(shí),膜長度方向上從死端到出水端,膜污染程度均逐漸增加。另外,各過濾參數(shù)跨膜壓差、點(diǎn)通量及軸向流速在膜長度方向上的分布均呈現(xiàn)出從死端到出水端逐漸升高的規(guī)律。隨著過濾時(shí)間的增加,近出水端部分點(diǎn)通量逐漸降低,近死端部分點(diǎn)通量逐漸升高,同時(shí)膜長度方向上存在部分區(qū)域,點(diǎn)通量呈現(xiàn)先升高到達(dá)峰值后再逐漸下降的趨勢(shì)。膜長度方向上不同位置處跨膜壓差均隨過濾時(shí)間的增加而逐漸升高。對(duì)于軸向流速,死端和出水端處在整個(gè)過濾過程保持不變,而其他位置處則隨著過濾時(shí)間的增加逐漸升高。死端過濾中空纖維膜系統(tǒng)運(yùn)行壓力隨過濾時(shí)間的增加而逐漸增加。膜長度越小、膜內(nèi)徑越大、膜固有阻力越低、運(yùn)行通量越低、污染物質(zhì)濃度越低時(shí),系統(tǒng)運(yùn)行壓力越低,能耗越小。另外,隨著過濾時(shí)間的增加,膜內(nèi)徑、運(yùn)行通量及污染物質(zhì)濃度對(duì)運(yùn)行壓力的影響逐漸增大,而膜長度及膜固有阻力對(duì)運(yùn)行壓力的影響程度基本不發(fā)生變化。另外,死端過濾中空纖維膜系統(tǒng)點(diǎn)通量在膜長度方向上的分布均勻度隨過濾時(shí)間的增加而逐漸增加。膜長度越小、膜內(nèi)徑越大、運(yùn)行通量越高、污染物質(zhì)濃度越高,則點(diǎn)通量分布均勻度越高,系統(tǒng)膜污染趨勢(shì)越低。另外,隨著過濾時(shí)間的增加,膜內(nèi)徑、運(yùn)行通量及污染物質(zhì)濃度對(duì)點(diǎn)通量分布均勻度的影響均呈現(xiàn)先增加后減小的趨勢(shì),而膜長度對(duì)點(diǎn)通量分布均勻度的影響逐漸減小。膜固有阻力對(duì)點(diǎn)通量分布均勻度的影響包括兩個(gè)階段,過濾前期膜固有阻力越大,點(diǎn)通量分布均勻度越高,而過濾后期點(diǎn)通量分布均勻度隨膜固有阻力的增加而降低。特別注意的是,膜內(nèi)徑對(duì)死端過濾中空纖維膜系統(tǒng)過濾性能有重要影響,當(dāng)膜內(nèi)徑過低時(shí),系統(tǒng)運(yùn)行壓力顯著升高,點(diǎn)通量在膜長度方向上的分布均勻度大幅降低,系統(tǒng)過濾性能迅速惡化。因此在中空纖維膜系統(tǒng)的實(shí)際應(yīng)用中,應(yīng)注意膜內(nèi)徑的優(yōu)化。
[Abstract]:Hollow fiber membrane has the advantages of simple structure, high separation efficiency, small filling density, low cost, low operating cost and flexible application, and has attracted more and more attention in the field of sewage and drinking water treatment. However, the existence of membrane fouling has made the filtration performance of hollow fiber membrane seriously affected, and membrane pollution has become a restriction of hollow fiber. The key factor in the development of membrane separation technology is that the mathematical model is an important means to study the pollution of hollow fiber membrane and optimize the filtration performance of the hollow fiber membrane system. The existing dead end filter hollow fiber membrane filtration model is based on the Hagen-Poiseuill equation, and the fluid pressure loss caused by the fluid acceleration in the hollow fiber membrane cavity has not been taken into account. The effect of flow resistance weakens the accuracy of model simulation results. In addition, the model is based on commercial or open source computational fluid dynamics (CFD) software to solve the problem. The CFD process is complex and needs to enter multiple boundary conditions to operate, and these boundary conditions are generally unknown, so it is not convenient to use or have large error. Based on the theory of fluid mechanics and membrane filtration, a mathematical model describing the filtration process of hollow fiber membrane in dead end filtration is constructed. In the model construction, the pressure loss caused by the friction in the cavity and the accumulation of dynamic pressure loss caused by fluid acceleration in the direction of the membrane are also taken into account. The filtration characteristic parameters of the end filter hollow fiber membrane system and the temporal and spatial distribution of membrane fouling are used to determine the key factors affecting the filtration performance of the system. It provides a scientific basis for the optimization of the hollow fiber membrane system. The results of the model simulation are well consistent with the experimental results, and the flow resistance of the fluid is increased by increasing the dynamic pressure loss in the cavity. The simulation results of the model and the experimental results are obviously improved. When the model is solved, the key of the model is to determine the transmembrane pressure difference at the dead end. A reverse iteration calculation method based on the dichotomy method is proposed. This method has high efficiency, wide application range, and constant current and constant pressure. The hollow fiber membrane filtration model of dead end filtration under the action of different membrane fouling mechanism is all suitable. Based on the above dead end filter hollow fiber membrane filtration model and numerical solution calculation method, the spatial and temporal distribution of the hollow fiber membrane pollution and the characteristic parameters of the system are simulated. The membrane fouling at each point in the length direction of the membrane increased gradually, and the membrane fouling degree increased gradually from the dead end to the effluent end at any time. In addition, the distribution of the filtration parameters across the membrane and the axial flow velocity in the film length showed a gradual increase from the dead end to the effluent end. With the increase of time, the passage amount in the near end of the water end gradually decreases, the passage amount in the near dead end increases gradually, and there is a partial region in the direction of the membrane. At the flow rate, the dead end and the outlet end are kept unchanged throughout the filtration process, while the other positions increase gradually with the increase of the filtration time. The operating pressure of the dead end filter hollow fiber membrane system increases gradually with the increase of the filtration time. The smaller the length of the membrane, the larger the inner diameter of the membrane, the lower the inherent resistance of the membrane, the lower the flux, the thicker the contaminant material. At the lower degree, the lower the system operating pressure and the smaller the energy consumption. In addition, with the increasing of the filtration time, the influence of the inner diameter of the membrane, the flux and the concentration of the contaminant on the operating pressure gradually increases, and the influence degree of the membrane length and the inherent resistance of the membrane to the operating pressure is basically not changed. The uniformity of distribution in the length of the membrane increases with the increase of the filtration time. The smaller the membrane length, the larger the inner diameter of the membrane, the higher the flux, the higher the concentration of the pollutants, the higher the uniformity of the distribution of the dots, the lower the pollution trend of the system membrane. In addition, the inner diameter, the flux and the concentration of the contaminant material are increased with the increasing of the filtration time. The influence of the uniformity of the distribution uniformity is increased first and then decreased, while the influence of the film length on the uniformity of the point distribution is gradually reduced. The influence of the inherent resistance of the membrane on the uniformity of the point distribution is two stages. The greater the inherent resistance of the membrane, the higher the uniformity of the point distribution is, and the distribution of the late point distribution of the filtration is all The uniformity of the film decreases with the increase of the intrinsic resistance of the membrane. Especially, the inner diameter of the membrane has an important effect on the filtration performance of the hollow fiber membrane system. When the inner diameter of the membrane is too low, the system operating pressure rises significantly, the distribution uniformity of the flow rate in the film length is greatly reduced and the system filtration performance deteriorates rapidly. Therefore, the filtration performance of the system is rapidly deteriorated. Therefore, the filtration performance of the system is rapidly deteriorated. Therefore, the filtration performance of the system is rapidly deteriorated. Therefore, the filtration performance of the system is rapidly deteriorated. Therefore, the filtration performance of the system is rapidly deteriorated. In the practical application of the membrane system, we should pay attention to the optimization of the inner diameter of the membrane.

【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ051.893;X505

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