Analysis of the small-angle X-ray scattering of linear polyethylene by a paracrystalline lattice model

Three paracrystalline lattice models for the interpretation of the small angle scattering of polyethylene are discussed: The “lattice model”, the “stapel model” (often referred to as the lamellar stack model) and the “proportional model”. While the applicability of the first model is restricted, the latter models differ in the statistical assumptions of lamellar and interlamellar thickness distributions. The principal advantage of the proportional model over the stapel model is its applicability through the adjustment of only three parameters: long period, crystallinity and one statistical parameter. Small angle X-ray curves of linear polyethylene are interpreted by the proportional model. The results are in good agreement with stapel model calculations.     

Kinetic modeling of industrial steam cracker

A comprehensive mathematical model is a very useful tool for the selection of feedstock, optimized cracker product mix, downstream production planning, and optimized plant performance. As a part of achieving this prime objective, a mathematical model has been developed for the simulation of the radiation section of a steam cracker unit. The model involves solving differential component, energy, and momentum balance equations numerically to generate temperature, concentration, and pressure profiles along the length of the reactor tube. The model has been developed in FORTRAN using the lSODE solver. The model considers 19 free radicals and 35 molecules connected over 433 reactions. The model was used to simulate the performance of propane and ethane cracking. The model predicted propane conversion is 95.55 against the plant data of 95% at a coil outlet temperature of 845 ​°C and the corresponding predicted ethylene and propylene yield is 34.49 and 11.53% respectively. The model has been validated for ethane cracking performance. The model predicted ethylene yield is in good agreement with that of plant values for ethane cracking. The model provides a basis for the optimization of process parameters for the given geometry. The model is useful to answer what-if questions and to investigate operational strategies.     

(Liquid + liquid) equilibria of binary polymer solutions using a free-volume UNIQUAC-NRF model

In this work, a modified free-volume (FV) model based on the UNIQUAC-Nonrandom factor (UNIQUAC-NRF) model developed by Haghtalab and Asadollahi was proposed. While the combinatorial part of the proposed model for activity coefficient takes the same form as that of the entropic free-volume (entropic-FV) model, the residual part is similar to that of the UNIQUAC-NRF model. The proposed model, i.e., the FV-UNIQUAC-NRF model overcomes the main shortcoming of the original UNIQUAC-NRF model in predicting the lower critical solution temperature (LCST) for polymer solutions. The appearance of the LCST is believed to be attributed to the existence of the free volume differences between polymer and solvent molecules. Thus, the models without considering such differences fail to predict the LCST behavior of polymer solutions. The proposed model was applied to correlate the experimental data of (liquid + liquid) equilibria (LLE) for a number of binary polymer solutions at various temperatures. The values for the binary characteristic energy parameters for the proposed model and the FV-UNIQUAC model along with their average relative deviations from the experimental data were reported. It should be stated that the binary polymer solutions studied in this work were considered as monodisperse. The results obtained from the FV-UNIQUAC-NRF model were compared with those obtained from the FV-UNIQUAC model. The results of the proposed model show that the FV-UNIQUAC-NRF model can accurately correlate the experimental data for LLE of polymer solutions studied in this work. Also the error produced from the FV-UNIQUAC-NRF model show the slightly better accuracy in comparison with that from the FV-UNIQUAC model. The clear advantage of the proposed model, contrary to the original UNIQUAC-NRF model, is its capability in predicting the LCST for binary polymer solutions.     

分子动力学模拟苯和萘在超临界二氧化碳中的无限稀释扩散系数

采用球型模型和点位-点位模型对超临界二氧化碳的自扩散系数及苯或萘在超临界二氧化碳中的无限稀释扩散系数进行了分子动力学模拟。结果表明,球型模型及点位-点位模型均可较准确地预测二氧化碳的自扩散系数,球型模型因形式简单,准确度相对较差;点位-点位模型准确度虽高,但需较长的模拟机时。两种位能模型所获得的准确度相当,但点位-点位模型可以更精细地反映体系的微观结构。     

CFD-PBM approach for the gas-liquid flow in a nanobubble generator with honeycomb structure

In recent years, nanobubble technologies have drawn great attention due to their wide applications in many fields of science and technology. From previous studies, a kind of honeycomb structure for high efficiency nanobubble generation has been proposed. In this paper, the numerical simulations of bubbly flow in the honeycomb structure were performed by using a computational fluid dynamics–population balance model (CFD-PBM) coupled model. The numerical model was based on the Eulerian multiphase model and the population balance model (PBM) was used to calculate the bubble size distribution. The bubble size distributions in the honeycomb structure under different work conditions were predicted. Two different drag force models (Schiller-Naumann model and Tomiyama model) and two different aggregation models (Luo model and turbulent aggregation model) were investigated. Both two drag models gave similar prediction of bubble number density distribution at the outlet. The results obtained from Luo model had better reflection of the trend of number density distribution. The turbulence dissipation rate ε can be used to evaluate the nanobubble generating ability. The water tank was not included in the CFD model in this work. The bubbles in the water tank should be studied in the future.     

基于不同燃料PAH特性改进的适用于多组分燃料的碳烟模型

将多环芳烃(PAH)骨架模型与甲苯参比燃料(TRF)氧化模型耦合,构建了一个新的TRF-PAH骨架模型.以新的TRF-PAH骨架模型作为燃料燃烧的气相化学反应模型,基于不同分子结构的燃料氧化过程中生成PAHs和碳烟的路径也不同的研究结论,本文进一步优化了以PAHs为碳烟前驱生成物的碳烟半经验模型.通过甲苯在流动反应器、搅拌反应器和激波管中的氧化/裂解实验验证发现,新的TRF-PAH骨架模型可以相对准确地预测小分子PAHs和重要中间组分的浓度.通过对比烷烃和芳香烃氧化过程中生成苯的计算值可以发现,燃料的分子结构对PAHs的生成路径影响很大.另外,改进后的碳烟模型利用甲苯、正庚烷/甲苯及异辛烷/甲苯混合物为燃料的激波管中裂解和氧化实验验证,结果表明在较宽的工况内碳烟模拟值与实验值吻合较好.最后,将新的碳烟模型应用于KIVA程序,模拟以TRF20为燃料的柴油机碳烟排放,结果表明TRF-PAH骨架模型和碳烟模型能重现缸内燃烧和排放的特性.     

A comparison of three polymer network models in current use

The relationship between three theories of polymer network deformation is explored. The theories are: the eight-chain model of Arruda and Boyce; the full network model of Wu and van der Giessen; and the crosslink–sliplink model of Edwards and Vilgis. All have a history of use as the network component in theories of solid polymer deformation. Given results from either the eight-chain or full network models, least-squares fitting of the stresses is used to derive optimal parameters of the Edwards–Vilgis model. Both the eight-chain and the full network models can be closely approximated by an Edwards–Vilgis model, provided the finite chain extensibility limit is not approached too closely. The eight-chain model is found to be equivalent to an Edwards–Vilgis model with a small number of sliplinks, whereas the full network model corresponds to an Edwards–Vilgis model with no sliplinks. The physical interpretation of these findings is discussed.     

Extension of the Wilson-NRF Gibbs Energy Model in Correlating Vapor-Liquid and Liquid-Liquid Phase Behavior of Polymer-Polymer Aqueous Two-Phase Systems

In this work, the proposed model by Pazuki et al. based on the Local Composition Concept (LCC), has been used in correlating the vapor-liquid phase behavior of polymer solutions and the liquid-liquid phase behavior of aqueous two-phase systems. The Flory-Huggins model has been used as the combinatorial part of the proposed model, as well as the model proposed by Pazuki et al. was considered as the residual term. The proposed model has been used in correlating the vapor-liquid phase behavior for a number of PEG-Water systems at constant temperature. The results obtained from the proposed model have been compared with those obtained from the Poly-NRTL and the Poly-Wilson models. The results showed that the proposed model can accurately correlate the VLE data for PEG-Water systems. Also, the proposed model has been used to obtain phase behavior of aqueous two-phase systems for PEG-DEX-Water systems. The results obtained from the proposed model have been compared with those obtained from the UNIQUAC and the UNIQUAC-NRF models. The results showed that the proposed model can accurately correlate liquid-liquid phase behavior of aqueous two-phase systems than the UNIQUAC and the UNIQUAC-NRF models.     

橡胶贮存寿命预测方法研究进展与思考建议

概述了用数学模型法预测橡胶贮存寿命的方法,包括阿伦尼斯模型,用ASTM D412评估橡胶拉伸性能,应力应变老化模型,压缩永久变形的预测方法,橡胶疲劳寿命损伤模型,用有限元法考核橡胶的裂纹长度与抗裂能之间的关系,基于叠加原理的寿命预测模型等,针对上述模型预测研究结果提出了相关思考建议。认为以老化动力学为基础预测材料寿命的数学模型法发展非常迅速,建议深入研究并拓宽应用;在透彻了解和掌握必需的分子结构参数的基础上,如果结合计算机技术模拟长期贮存或使用条件,对橡胶老化反应机理的研究可能是一个有前景的发展方向。     

Heterogeneous modeling for the alcoholic fermentation process

In this paper a heterogeneous model is developed for the alcoholic fermentation process. The model is expressed in terms of intracellular and extracellular concentrations of ethanol and sugar as well as biomass concentration as state variables. The model takes into consideration the floc size and the mass transfer rates of both ethanol and sugar. The intrinsic kinetics of the process used in the model was developed from published data which includes the inhibitory effects of ethanol and cells. The model development is achieved through comparison with one set of experimental results given by Novak et al. (1). The model is then checked against two other sets of experimental results. The developed model is also used to simulate an industrial fed-batch fermentar.     

A novel dynamic constitutive micromechanical model to predict the strain rate dependent mechanical behavior of glass/epoxy laminated composites

In the present research, a novel dynamic constitutive micromechanical (DCM) model was developed to predict the strain rate dependent mechanical behavior of laminated glass/epoxy composites. The present model is an integration of the generalized strain rate dependent constitutive model as a constitutive model for the neat polymer, the plasticity model of Huang as a micromechanical model, and dynamic progressive failure criteria. This model is able to predict the longitudinal and transverse tensile and in-plane shear behaviors of unidirectional glass/epoxy composites with arbitrary fiber volume fractions at arbitrary strain rates. The present model can also predict the stress-strain behavior of laminated composites with different layups and fiber volume fractions at arbitrary strain rates. A comparison between the results predicted by the present model and the available experimental data showed that the model predicts the strain rate dependent mechanical behavior of glass/epoxy composites with very good accuracy.     

CHARACTERIZATIONS ON THE THIXOTROPY-LOOP TESTS USING UCM MODEL WITH A RATE-TYPE KINETIC EQUATION

The theoretical characterizations on the triangular-form thixotropy-loop tests of an LDPE melt (PE-FSB-23D022/Q200) were conducted in the present paper by using a new thixotropy model, which is constituted by the upper convected Maxwell model and a rate-type kinetic equation. The new thixotropic Maxwell model can partially describe well three reported thixotropy-loop experiments by comparison with the previous calculations of the variant form of the thixotropy-type Huang model. It is noted that the stress deviations between the experiments and the predictions of the new thixotropic Maxwell model are much slighter than those deviations obtained by using the variant Huang model at the same condition, although both models include five parameters. The constitution of the new thixotropic Maxwell model is more reasonable than that of the variant Huang model.     

Crystallographic B-factors highlight energetic frustration in aldolase folding

Kinetic simulations of the folding and unfolding of the mammalian TIM barrel protein aldolase were conducted to determine if a minimalist monomeric Gō model, using the native structure to determine attractive energies in the protein chain, could capture the experimentally determined folding pathway. The folding order, that is, the order in which different secondary structures fold, between the Gō model simulations and that from hydrogen-deuterium exchange experiments, did not agree. To explain this discrepancy, two alternate variant of the basic Gō model were simulated: (1) a monomer Gō model with native contact energies weighted by a statistical potential (SP model) and (2) a monomer Gō model with native contact energies inversely weighted by crystallographic B factors (B model). The B model demonstrated the best agreement between simulation and experiments. The success of the B model is attributed to the ability of B factors to highlight local energetic frustration in the aldolase structure which results in weaker native contacts in these frustrated regions. The predictive success of the B model also reveals the potential use of B factor information for energetic weighting in general protein modeling.     

费托合成鼓泡浆态床反应器模型化研究

建立了费托合成鼓泡浆态床反应器双泡模型,通过模型对比的方法模拟讨论了多个反应器模型,双泡模型、全混模型以及多级串联模型,对比模拟讨论了费托合成反应各模型的适用性。模拟结果说明,全混模型适用于费托合成动力学行为的考察模拟;多级串联模型在一定的级数下能够近似模拟鼓泡浆态床中费托合成反应结果,更适用于探讨返混对费托合成反应行为的影响;双泡模型能够描述鼓泡浆态床中流体力学对反应的影响。     

Characteristic heats of adsorption for slit pore and defected pore models

The characteristics of the heat of adsorption from a slit pore model of carbon are presented. This is shown to have a few key features that are always present, regardless of the pore size distribution used, as long as there is a reasonable range of pore sizes considered. The adsorption in a slit pore model is compared against the adsorption for a defected pore model. The isotherms of the defected pore model are qualitatively different from those of the slit pore and similar to those of amorphous carbon models presented in the literature. The heat of adsorption of the defected pore model is qualitatively different from the slit pore model, and its behavior falls between those of the slit pore model and the amorphous carbon models in the literature.     

聚合动力学研究方法进展

从构造聚合动力学模型所采用的数学方法出发 ,对聚合动力学模型———概率统计模型、机理模型及基于MonteCarlo模拟模型等的进展进行了综述。     

动力学方程控制表面反应的模拟模型和方法

提出了动力学方程控制表面反应的模拟模型和方法.该模型从最基本的质量作用定律出发,获得表面反应的动力学方程.而表面反应通过格子模拟反应器进行.通过表面催化样板反应"CO表面催化氧化"检验了该模拟模型和方法,与实验结果吻合.该模型可在其它复杂的表面催化反应体系中推广应用.     

Unified model to predict self-assembly of nonionic surfactants in solution and adsorption on solid or fluid hydrophobic surfaces: effect of molecular structure

We have developed a pseudo-phase model to predict the self-assembly of nonionic surfactants on hydrophobic solid or fluid interfaces and in bulk solution. The uniqueness of this model is that it provides the relationship between molecular structure and self-assembly in solution and on interfaces. This model requires the input of minimal new experimental data. The remaining model parameters may be calculated on the basis of the surfactant molecular structure. The validity of the model has been established by comparing predictions with a wide array of experimental data for nonionic surfactant adsorption at the hydrophobic solid-water interface and at the air-water interface. The same model is then used to predict the self-assembly in bulk solution. The model predictions for critical aggregation concentration, aggregate shapes, and adsorption isotherms of various surfactants are in good agreement with the experimental data available in the literature.