Simulation of Membrane Distillation for Purifying Water Containing 1,1,1‐Trichloroethane

Vacuum membrane distillation is modeled for the purification of water containing organic matter. The separation medium is a hollow‐fiber membrane contactor that is simplified to a two‐dimensional structure with a single porous membrane wall. The model considers the transport phenomena of a vacuum membrane distillation system in porous media, in which the aqueous volatile organic solution was considered as an incompressible and steady fluid. The numerical simulation of the two‐dimensional model of vacuum membrane distillation for an aqueous solution of 1,1,1‐trichloroethane was established under steady state. The effects of the bulk feed temperature and the feed flow rate on the percentage of 1,1,1‐trichloroethane removal from an aqueous solution are discussed.     

Gas and liquid phase mass transfer within KATAPAK-S structures studied using CFD simulations

The gas phase mass transfer in the empty channels, and the liquid phase mass transfer within the catalyst-packed channels, of the criss-crossing sandwich structures of KATAPAK-S have been studied using computational fluid dynamics. Due to the “upheaval” caused by the flow splitting at the cross-overs, the mass transfer coefficient is significantly larger than that for fully developed flow in a single tube.     

Liquid-phase mass transfer within KATAPAK-S structures studied using computational fluid dynamics simulations

The liquid-phase mass transfer within the catalyst-packed criss-crossing sandwich structures of KATAPAK-S has been studied with the use of computational fluid dynamics. Due to the “upheaval” caused by the flow splitting at the crossovers, the mass transfer coefficient is about 40% times larger than for fully developed laminar flow in a single, packed tube.     

Modelling of heat and mass transfer during the polymerisation of olefins on heterogeneous Ziegler catalysts

The modelling of heat and mass transfer during the gas and slurry phase polymerisation of olefins is examined. It is demonstrated that it might not be necessary in many cases to calculate concentration gradients in the growing catalyst/polymer complex, and that the currently used representation of heat transfer from small, highly active particles using standard chemical engineering correlations might not be accurate.

Close examination of the morphology of catalyst particles shows that it is unlikely that the particles should be treated as a pseudo-homogeneous medium, and in fact the critical length scale for mass transfer is not the particle radius, but is much smaller. Furthermore, computational fluid dynamic simulations of single and interacting particles shows that convection is not the dominant heat transfer mechanism during the critical stages of the reaction.     

有机硅单体合成的气固流化床的三维数值模拟

为了探索有机硅单体合成气固流化床内硅粉颗粒的流化特性,作者利用计算流体力学CFD软件,采用双欧拉气固两相流模型及SIMPLE算法,模拟了三维的气固流化床内硅粉颗粒的流化特性;分析了气泡生成、长大和破裂的过程,及不同床层高度的固体颗粒运动速度矢量图,不同床层高度处横截面颗粒体积分数变化。结果表明:三维模拟能直观的表现颗粒在流化床中的流化状态,为工业生产及应用提供了有效的依据。     

Hollow fiber membrane contactor as a gas-liquid model contactor

Microporous hollow fiber gas-liquid membrane contactors have a fixed and well-defined gas-liquid interfacial area. The liquid flow through the hollow fiber is laminar, thus the liquid side hydrodynamics are well known. This allows the accurate calculation of the fiber side physical mass transfer coefficient from first principles. Moreover, in the case of gas-liquid membrane contactor, the gas-liquid exposure time can be varied easily and independently without disturbing the gas-liquid interfacial area. These features of the hollow fiber membrane contactor make it very suitable as a gas-liquid model contactor and offer numerous advantages over the conventional model contactors. The applicability and the limitations of this novel model contactor for the determination of physico-chemical properties of non-reactive and reactive gas-liquid systems are investigated in the present work. Absorption of CO₂ into water and into aqueous NaOH solutions are chosen as model systems to determine the physico-chemical properties for non-reactive and reactive conditions, respectively. The experimental findings for these systems show that a hollow fiber membrane contactor can be used successfully as a model contactor for the determination of various gas-liquid physico-chemical properties. Moreover, since the membrane contactor facilitates indirect contact between the two phases, the application of hollow fiber model contactor can possibly be extended to liquid-liquid systems and/or heterogeneous catalyzed gas-liquid systems.     

Numerical Investigation of a Ranque–Hilsch Vortex Tube using a Three-Equation Turbulence Model

The thermal separation flow characteristic in a vortex tube using a three-equation turbulence model is discussed in the present research. Flow behavior and energy separation of a vortex tube in different boundary conditions are investigated through a 3D model. The effect of the operating parameters on the turbulent viscosity ratio and the Mach number is also discussed. It was found that strong swirling flows with a high order of tangential velocity in the peripheral flow contributes to the rise in temperature due to viscous heating. Energy separation and cold-end side temperature depend mainly on the ratio of cold and hot-end side mass flow rates and the inlet conditions. Moreover, the effect of back pressure at cold-end side was investigated to determine how it alters the performance of the vortex tube. Finally, the results of the proposed computational fluid dynamics model are validated by the available experimental data.     

微裂缝内液固两相流动特性研究

应用欧拉-拉格朗日模型,对微裂缝中液-固两相流动过程进行数值模拟。在数学模型中,液相采用连续相模型,颗粒当做离散分散在连续相中,并考虑了相间耦合作用。对于物理模型,建立了二维直微裂缝模型,研究裂缝的液相粘度、液相速度和颗粒密度等因素对裂缝中两相流动的影响。模拟得到了微通道内颗粒瞬时分布状态、颗粒运动轨迹、颗粒停留时间、颗粒轴向速度分布、液相轴向速度分布等参数的变化规律,定性的揭示了储层裂缝内液固两相流动过程。     

污水汽提氨精制装置改造及运行效果

比较污水汽提装置改造前后的运行情况,说明改造后装置具有显著的经济、环境、社会效益。提出进一步提高运行效果的建议。     

搅拌槽内固液两相流的数值模拟及功率计算

使用计算流体动力学的方法对搅拌槽中的流场进行模拟,得到搅拌槽中液体的流动状况和体积分数分布。对流场分布规律、固体颗粒体积分数特点加以分析,进而利用模拟出的数据计算搅拌轴的功率,为搅拌器的设计提供参考。     

Numerical Simulation of Uranium Extraction from Nitric Acid Medium Using Hollow-Fiber Contactor

ABSTRACT

A two-dimensional axisymmetric computational fluid dynamics (CFD) model is presented to simulate uranium extraction from nitric acid medium using tri-n-butyl phosphate in n-dodecane in a hollow-fiber membrane contactor operated in non-dispersive solvent extraction mode. CFD model solves continuity and momentum-transport equations for the feed and shell sides and species transport equations for the feed side, shell side, as well as the membrane. Complex boundary conditions of flux continuity and concentration jump are implemented in the CFD model. The estimates of percentage of uranium extraction obtained from CFD simulations for different parametric conditions are compared with the experimental results, and a good agreement is observed. The validated CFD model is used to gain detailed insights into the hydrodynamics and mass transfer.

Abbreviations CFD: Computational fluid dynamics; NDSX: Non-dispersive solvent extraction; TBP: Tri n-butyl phosphate     

Numerical study of a hybrid membrane cell with semi and fully permeable membrane sub-sections

Hybrid membrane cells with up to 128 sections, each one comprising a fully and a semi-permeable membrane sub-section and, the limit case of a cell with an infinite number of membrane sections were studied by numerical methods. These hybrid cells separate a feed stream into two parts: a solvent stream which crosses the semi-permeable membranes and a concentrate stream which crosses the fully permeable membranes. The concentrate stream has a cleaning effect on the mass boundary layer over the semi-permeable membranes. The numerical results show that concentration polarization in hybrid cells is much lower than the polarization in conventional cells. Additionally, a highly concentrated solution is recovered. The cell with an infinite number of membrane sections (n) has the best performance: the lowest polarization and the highest concentration in the concentrate stream. As n increases to infinite, the concentration in the concentrate stream tends to the concentration over the semi-permeable membrane, i.e., to the maximum concentration inside the mass boundary layer. The number of membrane sections needed to achieve a performance similar to that of a cell with an infinite number of sections is very high, greater than 128. The velocity of the concentrate stream also plays an important role. As this velocity is increased (until an upper limit), the cleaning effect of the boundary layer intensifies but the purity of the concentrate stream decreases (dilution effect). An intermediate value for the velocity of the concentrate stream (between the lower and upper limit) should be used to optimize both effects.