Modeling of Caked Contacts in DEMs

When modeling the caking properties of bulk solids, it is not only necessary to incorporate the yield properties of individual particle contacts, but also to extend them to a many‐particle system. To accomplish this by means of Distinct Element Method (DEM) simulations a contact model for (spherical) particles, including a yield criterion for combined load is proposed. An application to the simulation of a caking test is presented and compared to experiments.     

Role of Water and Selected Minor Components on Association Colloid Formation and Lipid Oxidation in Bulk Oil

This study investigated the influence of water content in combination with selected minor components including oleic acid, stigmasterol, α‐tocopherol, and Trolox on their association colloid formation as well as their impact on lipid oxidation in bulk corn oil. First, surface activity of each minor component was evaluated by determining the ability of these components to lower the interfacial tension between bulk oil and water. All components but α‐tocopherol were able to decrease interfacial tension of stripped oil. Second, the critical micelle concentration (CMC) of each minor component was determined in bulk oil with no water added and in the presence of 1000 ppm of water. In the bulk oil without extraneous water, we could not determine the CMC of minor components in the range of concentrations studied. However, in the presence of 1000 ppm of water, only stigmasterol could form association colloids at the CMC of 20 mmol/kg oil. Last, the effect of water content (400 and 1000 ppm) and minor components on lipid oxidation in bulk oil was studied by following the lipid hydroperoxides and hexanal formation during storage at 55 °C. Different water content did not significantly impact the lag time of lipid oxidation compared with the control. Interestingly, water caused prooxidant by decreasing the lag time of lipid hydroperoxides and hexanal formation in bulk oil containing oleic acid, stigmasterol, and Trolox compared with the control of each system. On the other hand, there was not significant impact of water on the antioxidant activity of α‐tocopherol, a lipid soluble antioxidant in bulk oil. This study highlights the impact of water content on the surface activity of minor components as well as on the oxidative stability in bulk oil.     

The Linear Thermal Expansion of Bulk Nanocrystalline Ingot Iron from Liquid Nitrogen to 300 K

The linear thermal expansions (LTE) of bulk nanocrystalline ingot iron (BNII) at six directions on rolling plane and conventional polycrystalline ingot iron (CPII) at one direction were measured from liquid nitrogen temperature to 300 K. Although the volume fraction of grain boundary and residual strain of BNII are larger than those of CPII, LTE of BNII at the six measurement directions were less than those of CPII. This phenomenon could be explained with Morse potential function and the crystalline structure of metals. Our LTE results ruled out that the grain boundary and residual strain of BNII did much contribution to its thermal expansion. The higher interaction potential energy of atoms, the less partial derivative of interaction potential energy with respect to temperature T and the porosity free at the grain boundary of BNII resulted in less LTE in comparison with CPII from liquid nitrogen temperature to 300 K. The higher LTE of many bulk nanocrystalline materials resulted from the porosity at their grain boundaries. However, many authors attributed the higher LTE of many nanocrystalline metal materials to their higher volume fraction of grain boundaries.     

Impact of Free Fatty Acids and Phospholipids on Reverse Micelles Formation and Lipid Oxidation in Bulk Oil

Association colloids such as phospholipid reverse micelles could increase the rate of lipid oxidation in bulk oils. In addition to phospholipids, other surface active minor components in commercial oils such as free fatty acids may impact lipid oxidation rates and the physical properties of reverse micelles. In this study, the effects of free fatty acids on changes in the critical micelle concentration (CMC) of 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) in stripped corn oil (SCO) were determined by using the 7,7,8,8-tetracyanoquinodimethane solubilization technique. Different free fatty acids including myristoleic, oleic, elaidic, linoleic and eicosenoic were added at 0.5 % by wt along with the DOPC into the bulk oils. There was no significant effect of free fatty acids with different chain length, configuration and number of double bonds on the CMC value for DOPC in bulk oil. However, increasing concentrations of oleic acid (0.5 to 5 % by wt) caused the CMC value for DOPC in bulk oils to increase from 400 to 1,000 μmol/kg oil. Physical properties of DOPC reverse micelles in the presence of free fatty acids in bulk oils were also investigated by the small angle X-ray scattering technique. Results showed that free fatty acids could impact on the reverse micelle structure of DOPC in bulk oils. Moreover, free fatty acid decreased pH inside reverse micelle as confirmed by the NMR studies. The oxidation studies done by monitoring the lipid hydroperoxide and hexanal formation revealed that free fatty acids exhibited pro-oxidative activity in the presence and absence of DOPC. Different types of free fatty acids had similar pro-oxidative activity in bulk oil.     

在室温下铝酸锌尖晶石大量结晶的生长

铝酸锌ZnAl2O4是被用于紫外线装置、宇宙飞船、抗热涂层和陶瓷及催化剂材料一种有名的宽带间隔混合物半导体。描述了单阶段工艺合成的发展及在低温下生长的ZnAl2O4尖晶石,报道了三元氧化材料新型、经济及自然生长的大量结晶。ZnAl2O4结晶在室温(30℃)下生长。与金属结合的单晶生成的材料被做为初级粒子并被放入作为反应加速试剂(催化剂)及有金属薄片的溶液(阳离子清除剂)及含有酸性物的中性溶池中。铝酸锌结晶在平均周期15天内,在最佳条件下,采用化学溶池在单幅工序下生长。结晶和六方晶面一起生长并且采用XRD测量确认单晶的生长。元素(Zn、Al、O)和化学成份的性能采用EDAX来进行检测。人们发现此项技术对于三元氧化材料大量单晶的生长是有益的低成本技术。     

Comparison of Moving Bed Dryers of Solids Operating in Parallel and Counterflow Modes

The drying rates in moving bed dryers are compared. The gas and the solids to be dried are in parallel flow or counterflow. A new simplified method to simulate the drying in parallel and counterflow moving beds is developed. This model is based on the solution of arbitrary experimental or theoretical drying rate Equations of single solid particles (or thin-layer drying rate equation) coupled with heat and mass conservation Equations of the dryer. The solution is presented in an integral form of the drying equation showing the relation between time or location in the dryer and degree of drying. The method allows rapid calculation of the moisture, vapor mass fraction, and temperature distributions along the dryer in drying with moist air or steam. The model is demonstrated by using a result based on the receding front evaporation model as the specific thin-layer drying equation in the moving bed model. Wood chips are chosen as an example of the substance to be dried, but the method applies also for other medium, if the dependence of the drying rate on moisture and ambient temperature and humidity (thin layer drying rate) is known. The size of the dryer needed to reach the same degree of drying operating in the parallel mode is much greater than that of counterflow type, when the drying medium is air or flue gases. The reason for the poorer drying in parallel flow is mainly the unfavorable distribution of the evaporation temperature. In steam drying, the difference in the size is not so great, since the evaporation takes place approximately at constant temperature.     

Construction of Three-Dimensional Pore Network in Bulk Grain

In order to construct a 3D pore network reflecting the real pore structure of bulk grain, a series of 2D section images are obtained and used to reconstruct 3D images using MATLAB. The parameters of the 3D pore network are extracted by the maximal ball method. A stochastic 3D pore network with a random size is generated, but some throats are lost in generation. The parameter deviation between the original model and the generated model decreases with an increase in volume. There is almost no deviation when the space size is up to meter level. The image resolution of 0.5 mm is enough to extract parameters of the bulk grain.     

Comparison of Moving Bed Dryers of Solids Operating in Parallel and Counterflow Modes

Abstract

The drying rates in moving bed dryers are compared. The gas and the solids to be dried are in parallel flow or counterflow. A new simplified method to simulate the drying in parallel and counterflow moving beds is developed. This model is based on the solution of arbitrary experimental or theoretical drying rate Equations of single solid particles (or thin-layer drying rate equation) coupled with heat and mass conservation Equations of the dryer. The solution is presented in an integral form of the drying equation showing the relation between time or location in the dryer and degree of drying. The method allows rapid calculation of the moisture, vapor mass fraction, and temperature distributions along the dryer in drying with moist air or steam. The model is demonstrated by using a result based on the receding front evaporation model as the specific thin-layer drying equation in the moving bed model. Wood chips are chosen as an example of the substance to be dried, but the method applies also for other medium, if the dependence of the drying rate on moisture and ambient temperature and humidity (thin layer drying rate) is known. The size of the dryer needed to reach the same degree of drying operating in the parallel mode is much greater than that of counterflow type, when the drying medium is air or flue gases. The reason for the poorer drying in parallel flow is mainly the unfavorable distribution of the evaporation temperature. In steam drying, the difference in the size is not so great, since the evaporation takes place approximately at constant temperature.     

团状模塑料注塑成型花斑缺陷分析

本文从材料性能、注塑工艺、模具结构以及真空设备等方面分析了团状模塑料（Bulk Molding Composite简称BMC）注塑成型制品的“花斑”缺陷产生的原因与机理。     

Silo Discharge: Measurement and Simulation of Dynamic Behavior in Bulk Solids

This paper deals with the experimental investigation and the numerical simulation of silo discharge processes, including dynamic interactions between the silo filling and the elastic silo walls. The discharge process is described by a system of nonlinear differential equations. Via the Finite Element Method (FEM) based on an EULERian reference frame, the deformation rate, the velocity field, the porosity, and the stress distribution can be calculated without the need of re‐meshing the FE‐grid. To compare simulation results with measured data, the numerical simulation examples are chosen to be similar to an experimental test‐silo of the Institute of Mechanical Process Engineering at the Technical University of Braunschweig. Optical measurement techniques are applied to investigate the flow profile, and load cells on the silo walls register the stress evolution, e.g., a stress peak (switch) moving from the outlet to the transition from hopper to shaft.     

影响块状模塑料均匀流动的主要因素

采用Brabender转矩流变仪,并结合同心圆取样测定块状模塑料（BMC）中玻纤质量分数的方法,讨论了预混料在模压中的流动性能;研究了温度、玻纤的质量分数及长度、填料粒度、增稠剂用量等因素对BMC预混料的流动粘度和玻纤在BMC材料中分布的影响。     

Habits of Grains in Dense Polycrystalline Solids

We show here that the boundaries of individual grains in dense polycrystals prefer certain crystallographic habit planes, almost as if they were independent of the neighboring crystals. In MgO, SrTiO₃, MgAl₂O₄, TiO₂, and aluminum, the specific habit planes within the polycrystal correspond to the same planes that dominate the external growth forms and equilibrium shapes of isolated crystals of the same phase. The observations decrease the apparent complexity of interfacial networks and suggest that the mechanisms of solid-state grain growth may be analogous to conventional crystal growth. The results also indicate that a model for grain-boundary energy and structure based on grain surface relationships is more appropriate than the widely accepted models based on lattice orientation relationships.     

Bulk polymerization of vinyl chloride with half-titanocene/MAO catalyst

Bulk polymerization of vinyl chloride (VC) with Cp^∗Ti(OPh)₃/MAO catalyst was investigated. The bulk polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst proceeded to give poly(vinyl chloride) (PVC) with high molecular weight in good yields. The M_n of the polymer increased in direct proportion to polymer yields and the line passed through the origin. The M_w/M_n of the polymer decreased with an increase of polymer yield. The GPC elution curves were unimodal and the whole curves shifted clearly to the higher molecular weight as a function of reaction time. This indicates that the control of molecular weight can be achieved in the polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst even in bulk. The structure of PVC obtained from the bulk polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst consists of a regular structure. The thermal stability of the polymer obtained with Cp^∗Ti(OPh)/MAO catalyst was higher than that of PVC obtained from radical polymerization and depended on the molecular weight of the polymer. In contrast to that, the initial decomposition temperature of the polymer obtained from a radical polymerization did not depend on the molecular weight. We presumed that the decomposition of the polymer obtained with Cp^∗Ti(OPh)₃/MAO catalyst initiated at the chain end.     

本体法SAN树脂生产工艺研究

针对国内外本体法SAN树脂生产工艺进行研究,讨论了本体法SAN树脂生产工艺的影响因素和技术关键,对本体法SAN树脂生产工艺的发展方向进行了展望。     

The Relation of Viscosity, Nuclei Formation, and Crystal Growth in Titania-Opacified Enamel

This investigation shows that there is a relationship between viscosity, number of nuclei, and crystal growth during the firing of titania-opacified enamels. This agrees with a similar relationship which Tammann found in his experiments with organic glasses. The history of the development of the size, shape, and relative number of particles per unit area of titanium dioxide crystals was traced from 650° to 1300°C. As the temperature increased from 700° to 1100°C., the color of the specimens viewed under reflected light changed from light blue to white and then to cream-white. The methods used in this investigation were the measurement of viscosity, X-ray analysis, differential thermal analysis, and the study by light microscopy and electron microscopy of very thin heat-treated films which had been produced by blowing bubbles from high-temperature melts.