攪拌反應(yīng)器內(nèi)液—液分散特性的CFD-PBM數(shù)值模擬
發(fā)布時間：2019-04-09 17:05
【摘要】：液-液攪拌反應(yīng)器被廣泛應(yīng)用于冶金、化工、制藥等行業(yè)中,是促進相間混合、傳質(zhì)、傳熱,實現(xiàn)萃取、結(jié)晶、分散等過程的重要工業(yè)設(shè)備。計算流體力學(xué)(CFD)在用于研究液-液分散體系的過程中,由于相間耦合及液滴破碎和聚并的復(fù)雜性,現(xiàn)有模型很難對其進行精準(zhǔn)的預(yù)測。為此,本文結(jié)合CFD和群體平衡模型來對攪拌反應(yīng)器內(nèi)的液-液分散體系進行深入研究,研究結(jié)果可為大型液-液攪拌反應(yīng)器的優(yōu)化設(shè)計提供參考和指導(dǎo)。本文對CFD中的可壓縮雙流體模型進行詳細(xì)分析,結(jié)合群體平衡模型求解方法中的積分矩方法(QMOM)和拓展積分矩方法(EQMOM),對控制方程中的壓力泊松方程、矩傳輸方程等進行重構(gòu)優(yōu)化,實現(xiàn)了并行求解穩(wěn)定性、相分?jǐn)?shù)的有界性及守恒性、矩的有界性及可實現(xiàn)性,同時將CFD與群體平衡模型耦合并植入到OpenFOAM中,模擬結(jié)果和實驗數(shù)據(jù)吻合。表面活性劑會直接影響液-液分散體系內(nèi)的液滴破碎和聚并行為。本文選用QMOM求解群體平衡模型并結(jié)合CFD對附加表面活性劑的液-液分散體系進行研究。研究結(jié)果表明表面活性劑使得液滴聚并行為難以發(fā)生,MB和Lehr破碎模型的預(yù)測平均Sauter直徑和實驗數(shù)據(jù)偏離較大,改進后的MF破碎模型預(yù)測的平均Sauter直徑可以和實驗數(shù)據(jù)較好的吻合且優(yōu)于CT和Alopaeus破碎模型的預(yù)測結(jié)果。對于低離散相相含率的液-液分散體系,由于液滴碰撞的可能性較小以致聚并行為很難發(fā)生。本文從文獻中選取不同的實驗數(shù)據(jù),使用不同的破碎模型研究離散相粘度及放大效應(yīng)對液滴破碎的影響。CT破碎模型假定液滴的破碎頻率主要取決于湍流動能耗散率。MF破碎模型認(rèn)為液滴的破碎頻率和湍流動能耗散率、湍流動能、湍流尺度以及其他的流體屬性均相關(guān)。研究結(jié)果表明CT破碎模型不能夠捕獲湍流間歇性以及離散相粘度引起的液滴平均Sauter直徑變化,MF破碎模型可以很好的捕獲這種平均Sauter直徑的差異。當(dāng)離散相相含率增加時,液滴之間的破碎以及聚并過程同時存在。離散相相含率對液滴聚并過程的影響可通過“湍流阻尼因子”來實現(xiàn)。本文選取文獻中不同的中等離散相相含率的液-液分散體系,結(jié)合CT和MF模型對液滴的破碎及聚并過程進行研究。研究結(jié)果表明基于連續(xù)數(shù)量密度函數(shù)的log-normal EQMOM優(yōu)于常規(guī)的QMOM方法,CT模型預(yù)測的破碎和聚并過程較為迅速,MF模型預(yù)測的破碎和聚并過程較為動態(tài)且更好的反映了平均Sauter直徑實驗數(shù)據(jù)的動態(tài)變化過程。湍流阻尼因子的引入也有助于使得模擬結(jié)果更加準(zhǔn)確。
[Abstract]:Liquid-liquid stirred reactor is widely used in metallurgy, chemical industry, pharmaceutical industry and so on. It is an important industrial equipment to promote interphase mixing, mass transfer, heat transfer, extraction, crystallization, dispersion and so on. The computational fluid dynamics (CFD) model is difficult to accurately predict the liquid-liquid dispersion system due to the coupling between phases and the complexity of droplet fragmentation and coalescence in the study of liquid-liquid dispersion system. Based on CFD and population equilibrium model, the liquid-liquid dispersion system in stirred reactor is studied deeply in this paper. The results can provide reference and guidance for the optimization design of large-scale liquid-liquid stirred reactor. In this paper, the compressible two-fluid model in CFD is analyzed in detail. Combined with the integral moment method (QMOM) and the extended integral moment method (EQMOM), the pressure Poisson equation in the governing equation is combined with the integral moment method (QMOM) and the extended integral moment method (EQMOM),). The moment transfer equation is reconstructed and optimized to realize the stability of parallel solution, the boundedness and conservation of phase fraction, the boundedness and realizability of moment. At the same time, the CFD is coupled with the population equilibrium model and implanted into OpenFOAM. The simulation results are in good agreement with the experimental data. Surfactant has a direct effect on droplet fragmentation and coalescence in liquid-liquid dispersion system. In this paper, QMOM is used to solve the population equilibrium model and CFD is used to study the liquid-liquid dispersion system with additional surfactants. The results show that surfactant makes the coalescence of droplets difficult to occur, and the predicted average Sauter diameter and experimental data of MB and Lehr fragmentation models deviate greatly. The average Sauter diameter predicted by the improved MF fragmentation model is in good agreement with the experimental data and is better than that predicted by the CT and Alopaeus fragmentation models. For liquid-liquid dispersion systems with low discrete phase holdup, the coalescence behavior is difficult to occur due to the low probability of droplet collision. In this paper, different experimental data are selected from the literature. Different fragmentation models are used to study the effects of discrete phase viscosity and amplification effects on droplet fragmentation. Ct fragmentation model assumes that the breakup frequency of droplets is mainly dependent on turbulent kinetic energy dissipation rate. MF fragmentation model considers that the breakup frequency of droplets is mainly dependent on turbulent kinetic energy dissipation rate. Rate and dissipation rate of turbulent kinetic energy, Turbulence kinetic energy, turbulence scale and other fluid properties are all related. The results show that the CT fragmentation model can not capture the turbulent intermittency and the variation of the mean Sauter diameter caused by the viscosity of the discrete phase. The MF fragmentation model can capture the difference of the average Sauter diameter well. When the phase holdup of the discrete phase increases, the fragmentation and coalescence process of the droplets exist at the same time. The effect of discrete phase holdup on droplet coalescence can be realized by "turbulent damping factor". In this paper, different liquid-liquid dispersion systems with medium discrete phase holdup are selected in the literature, and the breakup and coalescence process of droplets are studied by means of CT and MF models. The results show that the log-normal EQMOM based on the continuous quantitative density function is superior to the conventional QMOM method, and the fragmentation and coalescence process predicted by the CT model is faster than that based on the continuous quantitative density function. The fragmentation and coalescence process predicted by the MF model is dynamic and better reflects the dynamic change process of the experimental data of the average Sauter diameter. The introduction of turbulent damping factor also helps to make the simulation results more accurate.
【學(xué)位授予單位】：北京化工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TQ052.5
本文編號：2455371
[Abstract]:Liquid-liquid stirred reactor is widely used in metallurgy, chemical industry, pharmaceutical industry and so on. It is an important industrial equipment to promote interphase mixing, mass transfer, heat transfer, extraction, crystallization, dispersion and so on. The computational fluid dynamics (CFD) model is difficult to accurately predict the liquid-liquid dispersion system due to the coupling between phases and the complexity of droplet fragmentation and coalescence in the study of liquid-liquid dispersion system. Based on CFD and population equilibrium model, the liquid-liquid dispersion system in stirred reactor is studied deeply in this paper. The results can provide reference and guidance for the optimization design of large-scale liquid-liquid stirred reactor. In this paper, the compressible two-fluid model in CFD is analyzed in detail. Combined with the integral moment method (QMOM) and the extended integral moment method (EQMOM), the pressure Poisson equation in the governing equation is combined with the integral moment method (QMOM) and the extended integral moment method (EQMOM),). The moment transfer equation is reconstructed and optimized to realize the stability of parallel solution, the boundedness and conservation of phase fraction, the boundedness and realizability of moment. At the same time, the CFD is coupled with the population equilibrium model and implanted into OpenFOAM. The simulation results are in good agreement with the experimental data. Surfactant has a direct effect on droplet fragmentation and coalescence in liquid-liquid dispersion system. In this paper, QMOM is used to solve the population equilibrium model and CFD is used to study the liquid-liquid dispersion system with additional surfactants. The results show that surfactant makes the coalescence of droplets difficult to occur, and the predicted average Sauter diameter and experimental data of MB and Lehr fragmentation models deviate greatly. The average Sauter diameter predicted by the improved MF fragmentation model is in good agreement with the experimental data and is better than that predicted by the CT and Alopaeus fragmentation models. For liquid-liquid dispersion systems with low discrete phase holdup, the coalescence behavior is difficult to occur due to the low probability of droplet collision. In this paper, different experimental data are selected from the literature. Different fragmentation models are used to study the effects of discrete phase viscosity and amplification effects on droplet fragmentation. Ct fragmentation model assumes that the breakup frequency of droplets is mainly dependent on turbulent kinetic energy dissipation rate. MF fragmentation model considers that the breakup frequency of droplets is mainly dependent on turbulent kinetic energy dissipation rate. Rate and dissipation rate of turbulent kinetic energy, Turbulence kinetic energy, turbulence scale and other fluid properties are all related. The results show that the CT fragmentation model can not capture the turbulent intermittency and the variation of the mean Sauter diameter caused by the viscosity of the discrete phase. The MF fragmentation model can capture the difference of the average Sauter diameter well. When the phase holdup of the discrete phase increases, the fragmentation and coalescence process of the droplets exist at the same time. The effect of discrete phase holdup on droplet coalescence can be realized by "turbulent damping factor". In this paper, different liquid-liquid dispersion systems with medium discrete phase holdup are selected in the literature, and the breakup and coalescence process of droplets are studied by means of CT and MF models. The results show that the log-normal EQMOM based on the continuous quantitative density function is superior to the conventional QMOM method, and the fragmentation and coalescence process predicted by the CT model is faster than that based on the continuous quantitative density function. The fragmentation and coalescence process predicted by the MF model is dynamic and better reflects the dynamic change process of the experimental data of the average Sauter diameter. The introduction of turbulent damping factor also helps to make the simulation results more accurate.
【學(xué)位授予單位】：北京化工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TQ052.5
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