Efficient fault diagnosis method of PEMFC thermal management system for various current densities

The temperature of a fuel cell has a considerable impact on the saturation of a membrane, electrochemical reaction speed, and durability. So thermal management is considered one of the critical issues in polymer electrolyte membrane fuel cells. Therefore, the reliability of the thermal management system is also crucial for the performance and durability of a fuel cell system. In this work, a methodology for component-level fault diagnosis of polymer electrolyte membrane fuel cell thermal management system for various current densities is proposed. Specifically, this study suggests fault diagnosis using limited data, based on an experimental approach. Normal and five component-level fault states are diagnosed with a support vector machine model using temperature, pressure, and fan control signal data. The effects of training data at different operating current densities on fault diagnosis are analyzed. The effects of data preprocessing method are investigated, and the cause of misdiagnosis is analyzed. On this basis, diagnosis results show that the proposed methodology can realize efficient component-level fault diagnosis using limited data. The diagnosis accuracy is over 92% when the residual basis scaling method is used, and data at the highest operating current density is used to train the support vector machine.     

Data-driven parameterization of polymer electrolyte membrane fuel cell models via simultaneous local linear structured state space identification

In order to mitigate the degradation and prolong the lifetime of polymer electrolyte membrane fuel cells, advanced, model-based control strategies are becoming indispensable. Thereby, the availability of accurate yet computationally efficient fuel cell models is of crucial importance. Associated with this is the need to efficiently parameterize a given model to a concise and cost-effective experimental data set. A challenging task due to the large number of unknown parameters and the resulting complex optimization problem. In this work, a parameterization scheme based on the simultaneous estimation of multiple structured state space models, obtained by analytic linearization of a candidate fuel cell stack model, is proposed. These local linear models have the advantage of high computational efficiency, regaining the desired flexibility required for the typically iterative task of model parameterization. Due to the analytic derivation of the local linear models, the relation to the original parameters of the non-linear model is retained. Furthermore, the local linear models enable a straight-forward parameter significance and identifiability analysis with respect to experimental data. The proposed method is demonstrated using experimental data from a 30 kW commercial polymer electrolyte membrane fuel cell stack.     

基于伏安型离子选择性电极的pH检测研究

将含有电活性物质的离子选择性膜直接滴涂在玻碳电极上,制成一种新型伏安型离子选择性电极(VISE)。通过在电极上施加循环伏安信号,提取电活性物质的还原峰电位可实现待测离子的定量分析。将这种VISE应用于pH检测,分别考察VISE的pH响应特性、离子选择性、实际样检测能力以及对积累电荷的抗干扰能力。结果表明:基于循环伏安法的VISE在pH检测中具有较好的准确性、灵敏度、重复性和离子选择性,可用于实际样品的检测。相比于基于电位分析法的传统离子选择性电极(ISE),可不受电荷积累的影响,在水质的实时在线监测中具有较好的应用前景。     

Preparation,characterization, and performance evaluation of LTA zeolite–ceramic composite membrane by separation of BSA from aqueous solution

Using low-cost clay supports as substrates, ceramic–LTA zeolite composite membranes (Z1–Z4) were fabricated with hydrothermal crystallization. The composite membranes were achieved with variations in the sequential zeolite depositional steps. For Z1–Z4 membranes, various characterization techniques such as thermogravimetric (TG), particle size distribution (PSD), X-ray diffraction (XRD), and field emission scanning electron microscopic (FE-SEM) analysis were applied. For the Z1–Z4 membranes, the pure water permeability, porosity, and average pore size varied from 1.22 × 10^?7 to 1.19 × 10^?8 m³/m²s kPa, 30–23%, and 215–76 nm, respectively. For the Z4 membrane, ultrafiltration experiments were conducted at a pH of 2.5 and transmembrane pressure differential of 207 kPa using aqueous bovine serum albumin (BSA) solutions. The optimal flux and rejection correspond to 4.54 × 10^?7 m³/m²s and 80%, respectively.     

内压式中空超滤膜组件的流场分布分析

利用水力学的相似原理,建立了内压式中空超滤膜组件死端过滤时的简化模型,运用流体力学Fluent软件模拟了该组件的内部流态,分析了组件内部总压和径向速度沿流程的分布,讨论了组件不同产水位置内部的流场分布,得出了膜组件的较优产水位置为产水位置1。     

毛毛虫形粗旦仿毛锦纶6纤维的生产工艺

对毛毛虫形粗旦仿毛锦纶6的生产工艺进行了研究分析,发现合理控制纺丝速度、纺丝温度、侧吹风、热辊温度和拉伸比等工艺参数,改进上油方式,可以生产出物性指标良好,并具有较好仿毛手感的粗旦仿毛锦纶6FDY。试验表明:纺速在4000~4300m/min,拉伸比1.1~1.3,热拉伸温度150~170℃,侧吹风速0.10~0.18m/s,下调上油位置,延缓上油时间,可以生产出外观好、染色均匀、性能指标好、仿毛手感好的粗旦仿毛锦纶6全拉伸丝。     

非饱和土大气张力通用公式与库仑土压力

推出大气张力库仑土压力的近似计算方法：假设临界破裂角为已知,可以考虑多层粘性土、坡面任意荷载、水和气压力。提出粘性土的结合水膜可靠连接面积率修正系数等于粘粒含量。推出大气张力库仑抗剪强度公式的Cm 形式,Cm 是膜的抗剪强度贡献。     

Closed-loop control of extracorporeal oxygen and carbon dioxide gas transfer

Additional extracorporeal gas transfer facilitates ultra-protective mechanical ventilation during treatment of severe lung disease. The proposed automation contributes to both patient safety and therapeutic success. A decentralized control system set the oxygen and carbon dioxide gas transfer rates. The controlled variables are estimated using standard measurement devices without direct blood contact. To reduce patient stress, an outer-loop integral controller adjusts the extracorporeal blood flow. The control system was first evaluated in silico and then in vivo using an animal model. Finally, the method is shown to be feasible and its response time is sufficient to meet patients' clinical needs.     

Improving proton exchange membrane fuel cell performance with carbon nanotubes as the material of cathode microporous layer

The cathode microporous layer (MPL) is fabricated by various multiwall carbon nanotubes (CNTs), and its influence on the performance of a proton exchange membrane fuel cell (PEMFC) is evaluated. Three types of CNT with different dimensions are employed in the experiments, and the conventional MPL made by acetylene black (AB) is also considered for the purpose of comparison. The results show that the employment of CNT as MPL composition indeed may improve fuel cell performance significantly in comparison with the case of AB. The type of CNT with the largest tube diameter and straight cylinder in shape exhibits the highest cell performance. The corresponding optimal CNT loading and polytetrafluoroethylene (PTFE) content in the MPL are also evaluated. Results show that the case of cathode MPL composed of 1.5 mg cm^?2 CNT and 20 wt% PTFE exhibits the best performance in all the experimental cases. The present data reveal that the application of CNT for MPL fabrication is beneficial to promote PEMFC performance. Copyright © 2015 John Wiley & Sons, Ltd.     

Temperature dependent coercivity of randomly assembled acicular Fe3O4 particles

Abstract

The Stoner‐Wohlfarth model and the chain‐of‐spheres fanning model are used to calculate temperature dependence of the coercivity of acicular single‐domain particles by taking thermal effect into consideration. Coercivity of the particles is evaluated by summing up the contributions of shape anisotropy, magnetocrystalline anisotropy and magnetostrictive anisotropy. The coercivities of randomly assembled Fe₃O₄ particles above the transition point (119°K) and below room temperature are calculated and compared with the published experimental data.