复合床反应器中液体停留时间分布模拟研究

在对置式复合床液停留时间分布的实验研究基础上,对2喷嘴对置式复合床液体停留时间分布的三维模型进行了研究。使用压力喷嘴模型,水-氮气系统,用Fluent模拟了气量、液体流量对液体停留时间分布的影响,与实验值进行了比较。结果表明,尽管实验值与模拟值的平均停留时间tm之间存在一定差别,但在整个停留时间分布上,二者吻合较好。通过对模拟结果分析,发现喷嘴撞击区有较强混合,但在撞击区之后较长的空间,气体保持平推流,与实验结果一致。     

Liquid–liquid phase separation and crystallization of polydisperse isotactic polypropylene solutions

Phase diagrams were calculated based on Flory-Huggins solution thermodynamics to investigate the effects of polydispersity of polymer molecules and interaction parameter on the phase equilibria of crystallizable polymer solutions. The polydispersity was modeled with blends of two monodisperse polymers differing in chain lengths as a simplification. It was found that a longer chain length component could be separated easily to a polymer-rich phase by liquid demixing, but a shorter chain length component might exist at relatively constant concentration in each phase on fractionation. The influence of polydispersity on the liquid–solid phase equilibrium was small, and the phase boundary could be moved significantly in the region of low concentration of polymer by a small change of temperature. Liquid–liquid phase separation was more sensitive to the interaction between polymer and solvent than liquid–solid phase transition. Numerical calculations showed that the temperature at which liquid–liquid phase separation was coupled with liquid–solid phase equilibrium increased with a lower concentration of the polymer due to polydispersity of polymer chain lengths, and this phenomenon was observed at a lower temperature with more favorable interaction. The results were consistent with the experimental observations of isotactic polypropylene solutions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 849–857, 1998     

Influence of thermal history on the formation of liquid crystalline phase of hydroxyethyl cellulose acetate

The influence of thermal history on the formation of HECA liquid crystalline phase was studied by DSC. It was found that the degree of ordering in the liquid crystalline phase was heterogeneous, and the multiphase transformation appears when the liquid crystalline phase transformed to the isotropic one. When HECA was annealed in the liquid crystalline state, the parts with the lower degree of ordering could transform to ones with the higher degree of ordering, and the temperature and the enthalpy of the phase transformation from the liquid crystalline phase to the isotropic phase increased. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1137–1142, 1998     

Evaporation characteristics of multi-component fuel

The maximum liquid phase penetration and evaporation behavior was investigated by using simultaneous measurement for mie-scattered light images and shadowgraph ones. The objective of this study was to analyze effect of variant parameters and fuel properties on evaporation behavior, and to investigate liquid phase penetration for the single- and multi-component fuels. The experiments were conducted in a constant-volume vessel with optical access. Fuel was injected into the vessel with electronically controlled common rail injector. It was observed that: liquid phase length is influenced by fuel properties. High-boiling point fuel within the multi-component fuel controls liquid phase length.     

第二液相对气液二相体系传质的影响

以CO2气体-K2CO3/KHCO3水溶液吸收过程为研究体系,用酸解法测量气体被吸收的速率,通过对比试验考察了加入第2液相(有机相)对体系传质速率的影响。经过试验研究证明,第2液相的加入对气液传质过程的影响程度与加入的物质有关,在试验条件下甲苯对体系强化作用高于异辛醇和庚烷对体系的强化作用。当第2液相加入量较小时,随加入量的增加,其对气液传质过程的促进作用增强,但当第2液相加入量较大时,这种作用则不明显。同时第2液相对传质作用的影响与流动场有关,增加流动场的搅动有助于强化气液传质作用。     

规整填料波纹结构上的二维两相流模拟方法

规整填料是由规则排列的波纹板组成的。液相是沿着波纹板壁面往下流动,而气相则是在波纹板之间形成的通道内与液相呈并流或逆流的状态。因此,气液两相的水力学特性决定着填料塔的操作弹性和质量传递效率。波纹板上的液膜流动状态因在很多应用领域都发挥作用而备受关注。本文从物理建模、自由界面处理方法、表面张力模型以及湍流模型等方面对规整填料波纹板上的二维液膜数值模拟方法作了详细的陈述,并且对该领域的研究现状作了进一步分析和总结。     

Recovery of Copper Ions from Wastewater by Hollow Fiber Supported Emulsion Liquid Membrane

Recovery of copper ions from wastewater using a hollow fiber supported emulsion liquid membrane (HFSELM) was studied with LIX984N as carrier, kerosene as diluents, and sulfuric acid solution as strippi...     

THE THREE-LIQUID PHASE NONEQUILIBRIUM PROBLEM

This article deals with the development of a non-equilibrium model for solving problems with three liquid phases. The model consists of the material balance equations, the interface material balance equations, the transfer-rate equations and the interface equilibrium equations. First the two liquid phase non-equilibrium solution is obtained. Then rigorous stability analysis in the form of the tangent plane criterion is used on two liquid phase solutions to detect the presence of the third liquid phase. The model equations are then solved to obtain the three liquid phase non-equilibrium solution.     

Effect of Binary/Ternary Fatty Acids Ratio and Glycerin on the Phase Behaviors of Soap Solutions

Phase behaviors of liquid soaps prepared with single myristic acid, binary fatty acid mixtures and ternary fatty acid mixtures (with 30% total fatty acids) are described. The influence of glycerin on the phase behaviors of ternary soaps is discussed. Phase behaviors were characterized by combining pH, viscosity, polarization microscopy, X‐ray scattering and differential scanning calorimetry (DSC) analysis. The results showed that the kind and proportion of fatty acids played key roles in the phase behaviors of soaps. Glycerin had a significant influence on the phase behaviors of soaps. Liquid and Cub + Hex (cubic and hexagonal phase) phase were stable, while Liq + Crystal (liquid micelle and crystal phase), Liq + Lam (liquid micelle and lamellar phase), Liq + Hex + Lam (liquid micelle and hexagonal and lamellar phase) phases displayed separation regions, Glycerin was investigated to improve the stability of separation phases for two weeks, appropriate percentage of the fatty acids in soaps application.     

微通道内离子液体/乙醇混合溶液吸收CO2的传质特性

采用高速摄像仪对微通道内离子液体/乙醇混合溶液吸收CO₂的传质行为进行了实验研究。考察了弹状流型下气液两相流量比和离子液体浓度对液侧体积传质系数k_La和液侧传质系数k_L的影响。当离子液体浓度不变时,k_La、k_L均随气液流量比的升高而增大并逐渐趋于恒定。当液相流量不变时,对于不同浓度的离子液体溶液,液侧体积传质系数k_La和液侧传质系数k_L随气液流量比的变化曲线出现了交叉点。在交叉点之前,k_La和k_L均随着离子液体浓度的增大而减小;在交叉点之后,k_La和k_L均随着离子液体浓度的增大而增大。提出了用于预测液侧体积传质系数k_La的新的量纲1经验关联式,预测效果良好。     

The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior

We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several open questions with respect to the impact of disorder on universal phase and structural behavior could be explored. Main advantages of liquid crystalline materials and different experimental realizations of random field-type disorder imposed on liquid crystal phases are described.     

Effects of floating contactors on oxygen transfer and hydrodynamics in a bubble column

This study investigates the adoption of floating contactors to promote the rate of oxygen transfer from non-uniform air bubbles to liquid in a bubble column with continuous operation. The volumetric oxygen transfer coefficient and axial dispersion coefficient of a liquid phase have been analyzed based on the axial dispersion model. Attention was focused on the effects of the volume fraction of the floating contactors on the volumetric oxygen transfer coefficient, axial dispersion coefficient of a liquid phase, and gas phase hold-up in the bubble column. The results have shown that the volumetric oxygen transfer coefficient and gas phase hold-up can increase by up to 25% and 13%, respectively, while the axial dispersion coefficient of a liquid phase decreases by up to 30% by adding floating contactors in the column.     

Development of co-continuous structure in liquid crystalline polyester

We investigated liquid crystallization of liquid crystalline polyester BB-5 during isothermal annealing by digital high-fidelity microscope and light scattering. A liquid crystalline spherical domain having a radius of micrometers appeared by annealing at around 180 °C. The domain grew dendritically in all directions. Neighboring liquid crystalline regions coalesced and then interconnected. The interconnected structure changed to a co-continuous two-phase structure with increasing ordering of the liquid crystalline phase, and the interface between the liquid crystalline phase and the isotropic phase became smoother over time. Liquid crystallization stopped before volume filling the whole space, and the liquid crystalline phase and isotropic phase coexisted. The liquid crystalline region became narrower with an increase in the temperature of the liquid crystallization. Such structural development is different from the liquid-liquid phase separation via spinodal decomposition, and it may be attributed to the segregation of non-liquid crystallizable low molecular weight molecules from the growth front by fractionation of the molecular weight distribution during the liquid crystallization in terms of the instability of the diffusion-controlled interface.     

Models for fuel droplet heating and evaporation: Comparative analysis

The results of comparative analysis of liquid and gas phase models for fuel droplets heating and evaporation, suitable for implementation into computational fluid dynamics (CFD) codes, are presented. Among liquid phase models, the analysis is focused on the model based on the assumption that the liquid thermal conductivity is infinitely large, and the so-called effective thermal conductivity model. Seven gas phase models are compared. These are six semi-theoretical models based on various assumptions and a model based merely on the approximation of experimental data. It is pointed out that the gas phase model, taking into account the finite thickness of the thermal boundary layer around the droplet, predicts the evaporation time closest to the one based on the approximation of experimental data. In most cases, the droplet evaporation time depends strongly on the choice of the gas phase model. The droplet surface temperature at the initial stage of heating and evaporation does not practically depend on the choice of the gas phase model, while the dependence of this temperature on the choice of the liquid phase model is strong. The direct comparison of the predictions of various gas models, with available experimental data referring to droplet heating and evaporation without break-up, leads to inconclusive results. The comparison of predictions of various liquid and gas phase models with the experimentally observed total ignition delay of n-heptane droplets without break-up, has shown that this delay depends strongly on the choice of the liquid phase model, but practically does not depend on the choice of the gas phase model. In the presence of droplet break-up processes, the evaporation time and the total ignition delay depend strongly on the choice of both gas and liquid phase models.     

Modelling intra-particle phenomena of biomass pyrolysis

The characteristic times of the main intra particle phenomena of wood pyrolysis are discussed to develop a new model of biomass pyrolysis. The model accounts for a simplified multi-step chemical decomposition with the formation of tars at liquid phase inside the particle. The tars at liquid phase are then competitively converted into a secondary char and gases and evaporated following a Clausius–Clapeyron law. To our knowledge, a tar evaporation law had so far never been coupled with cellulose pyrolysis kinetics. The convective mass transport of all the volatile species through the porous particle is modelled by a Darcy's law. This model offers a first approach to simulate the tar (at liquid phase) life time and its intra-particle conversion. The Clausius–Clapeyron evaporation parameters are reviewed and modified if levoglucosan or cellobiosan are supposed as the main tar compounds at liquid phase. The effects of these parameters on cellulose pyrolysis mass loss rate are modelled and discussed. Mass transfer limitations can lead to a high intra-particle over-pressure and can control the life time of tar at liquid phase and the subsequent “secondary” char formation from the liquid tar conversion.     

浆态床甲醇合成反应过程数学模拟

在固定床等温积分反应器中回归了LP201催化剂上的甲醇合成反应动力学参数,在液固拟均相、全混流、气相流动形式分别为全混流、平推流的基础上建立了浆态床搅拌反应器中甲醇合成反应的数学模型. 模拟结果显示,根据所得动力学参数,计算结果与实验结果吻合良好;气相甲醇合成过程中气相流动形式明显影响反应效率;在液相甲醇合成过程中,气相的流动形式对反应影响不大;气液传质阻力对反应有较显著的影响,必须与反应过程同时加以考虑.     

加压下填料塔中液相轴向反混的研究

Liquid phase axial mixing was measured with the tracer technique in a packed column with inner diameter of 0.15m,in which the structured packing,Mellapak 350Y,was installed.Tap water as the liquid phase flowed down through the column and stagnant gas was at elevated pressure ranging from atmospheric to 2.0MPa.The model parameters of Bo andθwere estimated with the least square method in the time domain.As liquid flow rate was increased,the liquid axial mixing decreased.under our experimental conditions,the effect of pressure on Bo number on single liquid phase was negligible,and eddy diffusion was believed to be the primary cause of axial mixing in liquid phase.     

Formation of a High-Temperature Liquid Phase During the Sintering of PbFe2/3W1/3O3

A high-temperature liquid phase (rather than a low-temperature liquid phase at 690°C as reported recently) has been demonstrated to form at 860°C on heating and to solidify at 840°C on cooling in PbFe_2/3O₃. This liquid phase not only promotes densification, but also induces the formation of rounded PbFe_2/3W_1/3O₃ grains during sintering at 870°C. Through slow cooling at a rate of 25°C/h after sintering, platelike grains, designated G phase, are found to form in a thin surface layer of specimens. This formation of platelike G phase is considered to be related to the solidification and recrystallization of the liquid phase exuded from the interior. The amount of the G phase on the surfaces decreases with the increase of cooling rates, indicating that fast cooling will lead the liquid phase to be solidified in the bulk of specimens. These results reveal that the microstructure of PbFe_2/3W_1/3O₃ is greatly affected by the high-temperature liquid phase; additionally, the slow cooling treatment seems to be a direct and effective method for removing the residual liquid phase from PbFe_2/3W_1/3O₃.     

射流鼓泡反应器中液相体积传质系数的测定

羰基合成反应一般采用射流鼓泡反应器,该类反应器气液混合的方式采用射流而非机械搅拌,其主要优点是结构简单、制作简便、维护费用低。研究该类型反应器的传质系数对于其设计、优化及放大操作均具有重要意义。本研究采用缩颈式圆形喷嘴,以动态溶氧法对射流鼓泡反应器内的液相体积传质系数进行测定,考察了表观气速、射流雷诺数对液相体积传质系数的影响。研究发现,随气速增大液相体积传质系数的变化规律为先增大而后保持不变。维持表观气速不变,随雷诺数增加液相体积传质系数增大,但当表观气速小于0.0012 m/s时,雷诺数对传质改善较小。建立了液相体积传质系数的经验关联式,当气体输入功率占总功率56%时,液相体积传质系数最大,气体鼓泡和液体射流的协同作用最强。     

Catalytic behavior of vanadium substituted mesoporous molecular sieves

A series of V-MCM-41 samples with different pore sizes has been systematically investigated with both gas and liquid phase reactions. Methanol oxidation has been performed in the gas phase on these catalysts. Turnover frequencies are normalized by oxygen uptake measured under reaction conditions. A strong effect of pore size on the catalytic activity was observed in the form of a “volcano curve” and may be correlated with a variation in the local bond angle of Si–O–V. Considering this effect, the catalytic activity may be ‘tuned' to maximum by varying the pore size. As expected, the same effect was observed in the liquid phase oxidation of cyclohexene. In order to interpret the pore size effect, the reaction rates of both the gas phase and liquid phase oxidation were then correlated with the variation of edge energies of V K-edge XANES on these MCM-41 catalysts. Additional reactions were performed in the liquid phase to compare the activity of V-MCM-41 with that of crystalline vanadium and titanium silicalite zeolites. The possible causes of the difference in the catalytic behaviors of these materials is also discussed.