PEMFC流道横截面二维两相流数学模型(Ⅱ)流道设计对电池性能影响

利用之前建立的数学模型（across-the-channel model）研究了流道设计对电池性能的影响。结果表明,对不同增湿条件的质子交换膜燃料电池（PEMFC）,其流道设计策略应有所不同：在增湿较差或者不增湿的条件下,电池阴极流场板应当采用较宽的脊以获得较好的保湿效果;在增湿较好的条件下,则应当采用较窄的脊以增强阴极排水功能,从而提高电池性能。     

基于预测电流控制的有源功率滤波器的研究

通过分析APF的数学模型和预测电流理论,推导出了预测电流控制在有源滤波器中的应用.利用预测电流控制的数学推导过程,对反馈调节和最优化处理做了分析,并对控制参数与系统性能之间的关系进行了讨论.     

PEMFC冷却剂循环条件下冷启动数值模拟

质子交换膜燃料电池(PEMFC)具有高能量比、环境友好、工作温度低等优点，可用作未来新能源汽车的能量来源，具有很好的发展前景。然而零下温度启动时，电池内水结冰堵塞通道，严重影响电池启动性能及寿命。提出了PEMFC冷启动三维多物理场数值模型，考虑了冷却剂流动与传热的影响，对冷启动过程组分浓度、电势、温度、含冰量等参数进行了可视化分析。数值模拟结果与试验吻合良好，表明模型可用于预测电池冷启动性能并用于机理研究。     

Observer based nonlinear quadratic dynamic matrix control for state space and input/output models

An observer based nonlinear Quadratic Dynamic Matrix Control (QDMC) algorithm is developed for use with nonlinear input-output (I/O) and state space models. It generalizes and extends previously published nonlinear QDMC algorithms. The extension to I/O models is particularly important due to the increased use of neural networks and other types of nonlinear black box models in the chemical industry. Disturbance rejection and offset free tracking is addressed in a general setting utilizing concepts from filtering theory. Various kinds of disturbance models can be incorporated in the formulation. Even though nonlinear models are utilized for model prediction, the on-line optimization is formulated as a single Quadratic Program, thus preserving the computational advantages of nonlinear QDMC as compared to Model Predictive Control algorithms based on nonlinear programming techniques. The examples illustrate parameter tuning for open-loop unstable and stable processes and point out both benefits and shortcomings of the algorithm.     

Computational fluid dynamics simulation of polymer electrolyte membrane fuel cells operating on reformate

Carbon monoxide (CO) can extremely diminish the polymer electrolyte membrane fuel cell (PEMFC) performance since it is preferentially absorbed on the platinum catalyst layer blocking and reducing the number of catalyst sites available for the hydrogen oxidation reaction. To gain a good insight of CO poisoning characteristics so as to provide a remedial solution for CO-poisoned PEMFCs, a two-dimensional, isothermal, and single phase CO poisoning numerical model taking into account the transport phenomena, electrochemical reactions and multi-component gas mixture transport is developed for such purpose. Linear and bridged-bonded adsorbed CO modes were considered to occur in parallel on the highly dispersed nano-crystalline Pt/C and PtRu/C catalysts. By performing computational fluid dynamics numerical simulations, this study clearly demonstrates the CO poisoning mechanisms and characteristics of PEMFCs. The numerical results obtained are in reasonably good agreement with the experimental data showing the predictive capability of the model.     

Nano-engineered PtVFe catalysts in proton exchange membrane fuel cells: Electrocatalytic performance

Proton exchange membrane fuel cells (PEMFCs) are attractive because of their high conversion efficiency, low pollution, lightweight, and high power density. A major area of challenges is the design and engineering of active, robust, and low-cost electrocatalysts. This report discusses recent findings of our investigations of the design and nano-engineering of platinum-vanadium-iron catalysts for use in PEMFC. The membrane electrode assembly was prepared using nano-engineered PtVFe nanoparticles with controlled composition and size supported on carbon as cathode electrocatalysts. The electrocatalytic activity and stability of the catalysts have been characterized by both rotating disk electrode and membrane electrode assembly measurements. The trimetallic catalysts have been shown to exhibit excellent electrocatalytic performance in PEMFC in comparison with commercial platinum catalysts. The results exhibited a good agreement between obtained these two types of measurements in terms of the dependence on particle size, composition, and thermal treatment condition. The catalysts also showed good stability, which are potentially useful for practical application in PEMFCs.     

质子交换膜燃料电池稳态自增湿性能分析

增湿及水管理系统使得燃料电池系统结构复杂,质子交换膜燃料电池（proton exchange membrane fuel cell,PEMFC）自增湿操作在实用化方面逐渐引起研究者的兴趣。提高PEMFC自增湿性能的关键在于对生成水的有效管理,保证质子交换膜的良好水合。实践证实采用自增湿膜电极组件是一个有效途径。本文建立催化层中增加保水层的水传递平衡模型预测膜中水的分布,考察自增湿操作的可行性和稳定性。数值分析表明：只有低于50 mm（如Nafion112）的薄膜能满足电池自增湿膜水合的要求。保证膜水合性能和电池操作稳定性的电池温度为60℃,操作压力为0.15 MPa,阴极气体过量系数可以增大到1.8。在上述操作条件下,电池自增湿性能与饱和增湿有可比性,与饱和增湿最佳条件有差距。因此PEMFC自增湿性能在综合考虑降低成本和费用,简化结构和操作时具有可行性,但不能替代增湿操作。     

Fast distributed MPC based on active set method

Modern chemical plants are characterized by their large-scale, strong interactions and the presence of constraints. With its ability to systematically handle these issues, distributed model predictive control (DMPC) is a promising approach for the control of such systems. However, the problem of how to efficiently solve the resulting distributed optimization problem is still an open question. This paper develops a novel fast DMPC approach based on a distributed active set method and offline inversion of the Hessian matrix to efficiently solve a constrained distributed quadratic program. A dual-mode optimization strategy based on the value of unconstrained optimal solution is developed to accelerate the computation of control action. The proposed method allows for the optimization to be terminated before convergence to cope with the fast sampling periods. Furthermore, a warm-start strategy based on the solution of the previous sampling instant is integrated with the approach to further improve convergence speed. The approach is highly parallelized as constraints can be checked in parallel. The approach is demonstrated using an academic example as well as a chemical process network control.     

The online use of first-principles models in process operations: Review,current status and future needs

The online use of first-principles models (FPMs) to support process operations has been practised in the chemical and petroleum industry for over 40 years. FPMs can encapsulate a large amount of process knowledge and many companies have realized significant value from the use of these models in online model based applications (OMBAs). Such applications include real-time optimization, model predictive control, data reconciliation, virtual sensors, and process performance monitoring to name a few. The sophistication of both the FPM models and applications based on them has increased over time. At some points in the evolution certain applications were not successful due to issues related to sustainability, which includes model complexity, solvability, maintainability and tractability. Also, model development cost can be a factor in considering the type of model used in these applications. Hence many simplified and empirical model-based online applications became preferred in some domains, even though the overall prediction quality of the FPM may be superior. This paper will review the past experiences, current status and future challenges related to FPM based online modeling applications. There are many areas where the issues related to FPMs can be addressed through proper model management, better software tools and improved technical approaches and work processes. It is hoped that this paper can serve as a basis to promote an understanding of the issues for researchers, modeling software vendors, modeling engineers, and application engineers and help to stimulate improvements in this area leading to increased usage and value of FPMs in supporting process operations.     

Modeling the steady-state effects of cationic contamination on polymer electrolyte membranes

When cationic impurities, such as Na⁺, Ca²⁺, or metal cations, are present in a polymer electrolyte membrane fuel cell (PEMFC) the performance of the PEMFC can be significantly reduced. These effects were modeled in a PEM by solving the Nernst-Planck equation for all cationic species in the membrane. The model shows that cationic contaminants will always be more concentrated on the cathode side of the PEM when current is drawn through the PEM. This was attributed to the trade off between diffusion and migration of contaminants in the membrane. It was then theorized that at high currents and contamination levels a maximum current density of protons through the PEM would be encountered. This model allows us to better understand the effects of cationic contamination on PEMFCs. This understanding should lead to development of new modes for diagnosis and better methods to recover fuel cell performance.     

空气自然对流式质子交换膜燃料电池的三维建模和实验分析

在空气自然对流式燃料电池内部,速度、温度、组分浓度及电流分布特性有着极强的耦合作用.氧气质量传输限制引起的浓度过电位是这种燃料电池的主要性能损失.从自然对流、传热传质的角度,建立了三维数学模型.利用三维流体动力学软件和用户建立的子程序,对自然对流下Navier-Stokes 方程,能量方程,电化学动力学方程以及组分、水的传输方程进行了数值求解.通过分析数值计算的结果,结合自然对流的特性,设计了实验系统.对温度分布和电池性能进行了测试.对空气湿度对电池性能的影响进行了分析.数值计算结果与实验结果很好地吻合.模型的建立,对于认识空气自然对流式质子交换膜燃料电池内部的耦合传输现象有极大的意义,可以作为质子交换膜燃料电池的计算机辅助优化设计工具.     

Nanocellulose water treatment membranes and filters: a review

This review covers the use of nanocelluloses in water treatment applications with particular focus on membranes and filters made either entirely from (nano)cellulose or in composite approaches. Nanocelluloses are among the emerging materials of this century, having found an abundance of potential applications in the fields of composites, medicine, functional additives or water treatment. Water treatment applications in particular have received significant academic and commercial attention, with a large variety of approaches developed in order to address arguably one of the largest problems that humanity is confronted with in the 21st century: clean water. In this regard, treatment of both potable water and wastewater is of high importance. The reason for the viability of nanocelluloses as base material relies upon their high specific surface area and abundance of OH groups that already exhibit certain attraction toward pollutants carrying ionic structures or dyes and also can be easily modified to significantly increase the affinity of nanocelluloses toward these pollutants. Nanocelluloses in their various forms (cellulose nanocrystals, cellulose nanofibrils, bacterial cellulose) have been applied in water treatment, with membranes and filters (size exclusion, e.g. for nanoparticle filtration, or affinity membranes) as well as adsorbents (e.g. heavy metal ions, dyes, nitrates) being the most studied. © 2020 The Author. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

微流道气-液两相流研究及其在PEMFC中的应用进展

微流道由于具有比表面积高、传质能力强等优点,已成功地应用于化工领域的多种气-液反应体系中。此外,其在化工领域中的研究成果还可以应用于目前备受关注的燃料电池领域以提高其电化学转化效率。然而,微流道尺度的微小化以及其中气-液两相流规律的复杂性使得微流道内的气-液两相流特性的阐明还需要进一步的研究,才能促使微流道在实际应用中发挥更优异的作用。本文从流型、压降和传质三个关键特征的研究角度来介绍微流道内气-液两相流的研究进展,简述了不同流型的特征及其形成条件,阐明了其对应的压降大小和传质能力的高低,回顾了现有的压降和传质系数的预测模型及其相应的优化措施,并分析了运用这三个关键特征的相关参数来优化质子交换膜燃料电池流场设计方面的研究进展,得到了流场类型、流道尺寸、流道形状、流道表面特性等的优化方案。但是,燃料电池中的精细流道的特殊结构及其特定工况使得其与传统的微流道有显著的区别。由此,本文提出了应当根据燃料电池精细流道的特点探明其中的两相流型、压降和传质的动态变化规律以及构建相应的压降预测模型的建议,以期为流场设计提供更准确的参考依据,进而提高燃料电池性能,加速燃料电池的商用进程。     

质子交换膜燃料电池膜中气态水管理模型

分析质子交换膜燃料电池的膜水含量与运行参数的关系,从工程方法的角度建立水传输模型.模型分析得到,要提高膜的水合程度,需要通过增湿反应气体.过高的增湿反应气体又会引起阴极扩散层水的泛滥,需通过调节反应气体流量来缓解水的泛滥.为保证膜的高水合程度和低的阴极扩散层水的泛滥,建立了膜水含量的神经网络控制模型,为电池水管理奠定了基础.     

基于改进回声状态网络的游离氧化钙预测控制

在非线性时延水泥烧成系统中,针对传统预测控制方法调节时间长、控制精度不高的问题,提出一种改进的在线型回声状态网络预测控制模型。首先将带有L1范数约束项的递归最小二乘法与回声状态网络相结合构建在线型预测模型,解决传统预测控制模型辨识精度较低、无法进行实时预测的问题;然后基于改进的回声状态网络预测模型,构建预测控制模型结构,并采用具有全局优化能力的粒子群算法进行滚动优化,保证实际输出量快速、准确、平稳地跟随被控量的设定值;最后利用改进的预测控制模型对水泥烧成系统中的游离氧化钙含量进行预测控制仿真实验,结果表明改进的预测控制模型具有良好的性能和应用前景。     

Application of Gas Permeation in Fuel Cell Powered Vehicles

Main motivation for the use of a polymer electrolyte membrane fuel cell (PEMFC) in traffic applications is its significant higher vehicle efficiency compared to internal combustion engines (ICE) especially under low‐load operation. Hydrogen is the ideal fuel for PEMFCs as it yields the highest level of fuel cell performance. Three different applications for gas permeation inside a fuel cell system have been investigated: water recovery, hydrogen purification, and oxygen enrichment. The focus was on the analysis of the technical feasibility and the availability of capable membranes on the pilot‐scale size for each application.     

质子交换膜燃料电池电堆的动态热模型及其温度控制

A dynamic thermal transfer model of a proton exchange membrane fuel cell (PEMFC) stack is developed based on energy conservation in order to reach better temperature control of PEMFC stack. Considering its uncertain parameters and disturbance, we propose a robust adaptive controller based on backstepping algorithm of Lyaponov function. Numerical simulations indicate the validity of the proposed controller.     

Polymer Electrolyte Membranes Containing Functionalized Organic/Inorganic Composite for Polymer Electrolyte Membrane Fuel Cell Applications

To mitigate the dependence on fossil fuels and the associated global warming issues, numerous studies have focused on the development of eco-friendly energy conversion devices such as polymer electrolyte membrane fuel cells (PEMFCs) that directly convert chemical energy into electrical energy. As one of the key components in PEMFCs, polymer electrolyte membranes (PEMs) should have high proton conductivity and outstanding physicochemical stability during operation. Although the perfluorinated sulfonic acid (PFSA)-based PEMs and some of the hydrocarbon-based PEMs composed of rationally designed polymer structures are found to meet these criteria, there is an ongoing and pressing need to improve and fine-tune these further, to be useful in practical PEMFC operation. Incorporation of organic/inorganic fillers into the polymer matrix is one of the methods shown to be effective for controlling target PEM properties including thermal stability, mechanical properties, and physical stability, as well as proton conductivity. Functionalization of organic/inorganic fillers is critical to optimize the filler efficiency and dispersion, thus resulting in significant improvements to PEM properties. This review focused on the structural engineering of functionalized carbon and silica-based fillers and comparisons of the resulting PEM properties. Newly constructed composite membranes were compared to composite membrane containing non-functionalized fillers or pure polymer matrix membrane without fillers.     

分布式预测控制全局协调及稳定性分析

实际的化工过程系统维数都较高,对系统进行关联分解并使各子系统进行协调来实现整个大系统全局最优是必要的。对于关联作用存在反馈的化工过程大系统,分散式预测控制算法和基于串联过程推导的邻域优化分布式预测控制算法都不适用,因此在这两个算法的基础上推导出约束条件下基于全局协调的分布式预测控制算法。针对分解后得到的子系统,假设子系统间关联信息的传递存在一个采样时间的滞后,建立每个子系统的预测模型时考虑滞后的关联信息;建立子系统的目标函数时,综合考虑所有关联子系统的输入和输出对本子系统的关联作用;每个子系统滚动优化并行求解各自的最优控制作用。然后,在一定条件下分析了基于全局协调的分布式预测控制算法与集中预测控制算法的一致性,并说明了闭环系统的全局稳定性。最后,通过对Shell公司重油分馏塔和TE过程两个例子进行仿真并与其他算法进行比较,验证了本文提出算法的可行性和有效性。