速溶茶中试冻干过程模拟研究

目的 采用数值模拟方法预测和优化冻干速溶绿茶粉的中试试验生产工艺。方法 通过有限元法建立二维传热传质相变模型, 模型模拟茶粉冻干过程中温度场、压力场、水分迁移的变化过程。结果 利用模型优化的生产工艺为: 物料铺盘厚度调整为15 mm, 采用阶段升温方法, 在升华干燥0~2 h、2~4 h、4~6 h、6~8 h及8~26.5 h五个时间段中, 调整环境辐射温度为0、10、30、50、60℃。按上述工艺生产所得的速溶绿茶粉的水分含量(质量分数)是(3.9±0.19)%, 各项理化指标符合国家产品标准要求。结论 该模型的预测结果与试验结果相吻合, 采用数值模拟方法可以用于预测和优化冻干速溶茶粉的中试试验生产工艺, 为今后进一步的产业化生产提供参考与借鉴。     

A three-dimensional numerical model of a single-chamber solid oxide fuel cell

The aim of this work is to analyze the hydrodynamic/electrochemical performance of a solid oxide fuel cell operating on nitrogen diluted hydrogen/oxygen mixture. In this respect, a three-dimensional numerical model of a single-chamber solid oxide fuel cell (SC-SOFC) is developed. The model incorporates the coupled effects of fluid flow in a rectangular duct with mass transport in porous electrodes, selective electrochemical reactions (i.e. hydrogen oxidation on anode and oxygen reduction on cathode) on individual electrodes while operating on nitrogen diluted hydrogen–oxygen mixture. Results show the effect of depletion of gaseous mixture due to hydrogen and oxygen consumption along the flow direction. The model can predict hydrodynamic/electrochemical effects by varying the porosity of the gas diffusion electrodes/catalyst layers. The model is formulated in COMSOL Multiphysics 3.4, a commercial Finite Element Method (FEM) based software package.     

基于Comsol Multiphysics无限长圆柱载流导线产生的磁场分布研究

介绍一种基于Comsol Multiphysics软件的工程电磁场仿真方法。以无限长圆柱载流导线产生的磁场分布为例,在理论计算的基础之上,给出了基于Comsol Multiphysics软件的仿真过程。并对比分析了理论计算值和仿真结果。证明了Comsol Multiphysics软件是一款功能强大,操作简单,计算精度高的工程电磁场仿真软件。     

一种新型开放式旋转磁场磁系分析与仿真

旋转磁场作为开放式磁场的一种新型磁场形式,目前应用逐步广泛,对于该类磁系的深入研究与分析可为相关的磁路优化、工艺流程优化以及相关工程设备的选型提供依据。借助于COMSOL Multiphysics软件,仿真并分析了旋转磁系的磁场特性,根据磁场分布特性与动力学相关理论,从微观角度研究了不同转向条件下的磁性颗粒在磁场中的运动状态,并通过试验确立了最佳的磁系转向方案,最后对旋转磁系的磁系固定方法进行了讨论。     

硅基氮化镓波长可调DFB激光器的模拟分析

基于严格耦合波以及介质平板波导理论,构建了硅基氮化镓分布反馈激光器的二维稳态物理模型。且利用多物理场直接耦合分析软件Comsol Multiphysics求解波动方程,得到了分布反馈激光器在可见光各波段形成单模输出的电场模一维、二维图谱,以及相对应的入射波长与电场模关系曲线。结合硅基光微机电系统技术和微加工技术,本文提出利用悬空的自支撑氮化镓周期可调光子光栅实现分布反馈激光器波长可调。数值模拟表明,在光栅的格子数目、光栅厚度、光栅宽度以及有源层厚度一定的情况下,改变光栅周期可以实现分布反馈激光器输出不同波长激光。理论分析与仿真结果基本一致,证明所建立激光器模型具有一定的合理性,得出的仿真数据为实现分布反馈激光器波长可调提供了有意义的参考。     

3D multiphysics modeling aided APU development for vehicle applications: A thermo-structural investigation

Solid oxide fuel cells (SOFC) are suitable for on-board electricity generation as Auxiliary Power Unit (APU) to support the electric power supply in heavy-duty vehicles. In order to satisfy the requirements of a lightweight fuel cell stack for mobile applications, thin-walled components must be used for the stack structure. This necessity is associated with material, process and design difficulties that must be solved in order to achieve a successful utilization. In this work a novel lightweight SOFC stack design with metal-supported cell was studied both numerically and experimentally. The metallic components are made from the Intermediate Temperature Metal (ITM), a high performance, high chromium ferritic stainless steels alloy. The multiphysics modeling approach (fluid dynamics, heat transfer, structural mechanics) was utilized in this work to predict the temperature distribution and the thermo-structural behavior of the new developed design. Geometric details of the fuel cell stack components as well as appropriate nonlinear, temperature and time-dependent constitutive models were developed to describe the material behavior. Experimental data were used to determine the material model parameters and validated the simulation results. The three-dimensional stress and deformation distributions in the individual stack components were evaluated and their maximum values for elements at risk were identified. Thus, the developed model enables the investigation of sustainability and serviceability of the structural elements to ensure a reliable operation of the stack. The developed computational model can be used as a design tool for parametric studies and optimization analysis to investigate the effects of process boundary conditions, material properties as well as geometrical design parameters and their variation on the induced thermal stresses.     

固结灌浆深度对丹巴水电站深厚覆盖层坝基中流固耦合的影响

中国西南地区水利工程多建于有明显强弱相间结构的河谷深厚覆盖层上,此类大坝通常采用垂直防渗墙或帷幕灌浆等防渗措施,但这些措施不能有效提高坝基承载力,坝基不均匀沉降反而会造成防渗体的破坏和失效。因此,引入多孔介质存储系数S_α,采用有限元软件Comsol Multiphysics建立双场耦合模型,探寻固结灌浆联合垂直防渗墙条件下深厚覆盖层渗流场和应力场演化规律。研究发现,层状深厚覆盖层中,上部弱透水层、弹性模量较小而厚度较大的强透水层是固结灌浆的控制层。当上部关键层固结灌浆后,且灌浆深度达到总坝基深度50%以上时,再增加灌浆深度意义不大。研究成果可为类似工程提供参考。     

基于COMSOL-MULTIPHYSICS的金属套管穿孔检测

针对金属套管由于各种原因而造成的腐蚀穿孔,提出了基于恒流源场分布扫描法的金属套管检测方法,论述了用有限元软件COMSOL-Multiphysics建立套管穿孔模型,借助点电极对套管内壁注入恒定电流,从而仿真出套管内电流与电场的分布情况来定性地反映套管穿孔的方位与程度,着重阐述了电流强度、电极系分布与检测分辨率之间的关系。     

基于COMSOL Multiphysics的金枪鱼罐头热杀菌过程数值模拟

以COMSOL Multiphysics软件为基础,建立纯传导和固液混合两种模型来模拟金枪鱼罐头的热杀菌过程。通过无线温度传感器检测热杀菌过程中130 g金枪鱼与55 g,4%Na Cl卤水罐头中心温度的变化,结果发现:固液混合模型的预测结果与试验数据十分吻合,而纯传导模型明显低估了罐内温度传递。在此基础上,用固液混合模型模拟工业杀菌条件(10 min-60 min-10 min/116℃)下金枪鱼罐头内的温度分布、速度分布及致死率值,结果发现最慢加热区(SHZ)位于罐高的22.9%~50%之间,最慢冷却区(SCZ)位于罐高的50%~81%处。在升温和降温阶段,罐内液体流速可达4.41 mm/s。杀菌结束时罐内最大与最小致死率值相差4.93 min,而中心点致死率与最小致死率相差很小。本文建立的模型可为金枪鱼罐头的热杀菌优化提供参考。     

Spatiotemporal evolution of thermo-hydro-mechanical-chemical processes in cemented paste backfill under interfacial loading

Cemented paste backfill (CPB) and rock interface interaction causes the formation of an interfacial loading and affects the thermal, hydraulic, mechanical, and chemical processes in bulk CPB and thus its in-situ behavior. In this study, a new meter-sized column model is developed to systematically investigate the multiphysics processes in CPB under interfacial loading. The obtained results discover that for the mechanical process, the interfacial loading leads to a reduced settlement and a weakened stress level in CPB. For the hydraulic process, lower matric suction and smaller moisture content coexist in CPB under interfacial loading. For the thermal process, the interfacial loading weakens the porosity-dependent thermal conduction and causes retardation in temperature variation relative to the ambient temperature. For the chemical process, weakened cement hydration with smaller electrical conductivity was observed in CPB under interfacial loading. Therefore, the obtained results reveal the linkage between the interfacial loading and multiphysics processes in CPB and thus contribute to an in-depth understanding of the multiphysics behavior of CPB in underground mines.