Experimental study of dynamic performance of defective cell within a PEMFC stack

Defective cell in a PEMFC stack may reduce durability and reliability of the stack and even damage the stack. However, the dynamic performance of defective cell within a PEMFC stack is not clear. In this paper, the dynamic characteristics of the defective cell under different load conditions are analyzed. The results reveal that the defective cell has slower dynamic response rate than other single fuel cells, and the defective cell causes a poor voltage uniformity of the stack. The increased frequency of load change makes the voltage change rate of defective cell higher. The increased amplitude of load change has a more negative impact than the increased frequency of load change, and makes the defective cell more prone to flooding. Furthermore, impedance spectrum shows that these load conditions have greater negative effect for the defective cell than other cells. Finally, according to the experimental results and practical application, recommends related to control strategy of PEMFC stack are proposed to extend lifetime.     

Review on current research of materials,fabrication and application for bipolar plate in proton exchange membrane fuel cell

Bipolar plate (BP) in proton exchange membrane (PEM) fuel cells provides conducting paths for electrons between cells, distributes and blocks the reactant gases, removes waste heat, and provides stack structural integrity. It is a key component to ensure the aforementioned functions while maintaining a low cost of fuel cell stack. This paper presents a comprehensive review about the BP materials (metallic, non-porous graphite and composite materials) and the corresponding fabrication methods, flow field layouts, and PEM fuel cells applications. Among the materials, the metallic BP has attracted high attention in automotive application due to its superior mechanical and physical properties, competitive cost compared with non-porous graphite and composite materials, but the fabrication technology and corrosion resistance are the major concerns for metallic bipolar plates. In recent studies, the protective coatings reported such as the conductive polymer, metal nitride/carbide and noble coatings have become the hot topics. They have been widely applied in different kinds of metallic bipolar plates, and the metal nitride coatings exhibit relatively low corrosion current and moderate interfacial contact resistance in comparison to other coatings. In future, developing excellent corrosion resistance and electrical conductivity coatings or novel metallic materials for bipolar plates will greatly enhance PEM fuel cells application in transportation field.     

Fault diagnosis in gears operating under non-stationary rotational speed using polar wavelet amplitude maps

This paper will attempt to analyse the effectiveness of the Continuous Wavelet Transform in vibro-acoustical diagnostics of gearboxes operating under non-stationary rotational speed. For this, a simple PC-software program for signal processing and extraction of diagnostic features was developed and tested. The objective of the program test is fault-detection, localisation, and assessment at helical spur gears. This includes improvements of the visual estimation of the WT-plots, especially by the task-specific balance of time- and frequency-resolution and by the display of the wavelet amplitude versus the rotational angle in polar coordinates. The following examples demonstrate the improvements in the detection of gear faults.     

Scale and material effects on flame characteristics in small heat recirculation combustors of a counter-current channel type

Small energy sources have been interested with the recent development of small-scale mechanical systems. With the purpose of developing a basic model of micro-combustors of heat recirculation, small combustors of a counter-current channel type were fabricated, and the premixed flame stabilization characteristics were investigated experimentally. Each combustor consists of a combustion space and a pair of counter-current channels for heat recirculation. The channel gap was less than the ordinary quenching distance of a stoichiometric methane-air premixed flame. Depending on the flame locations and structures, flame stabilization was classified into four modes: an ordinary mode, a channel mode, a radiation mode, and a well-stirred reaction mode. Base-scale combustors of stainless steel were initially examined. Additional half-scale combustors of stainless steel and quartz were fabricated and their flame stabilization conditions were compared. Consequently, a change of the material of the combustor significantly affected the flame stabilization compared to the effects of a scale-down design. A half-scale quartz combustor had a wide range of flame stabilization conditions. Surface temperatures and the composition of the emission gas were measured. At a higher flow rate, the combustor temperature increases and the light emission from the middle wall is enhanced to extend the flame stabilization conditions. The combustion efficiency and the composition of emitted gas were feasible. These results provide useful information for the design of small-scale combustors.     

Similar extrusion and mapping optimization of die cavity modeling for special-shaped products

1 Introduction For special-shaped products, similar extrusion is defined as the extruding deformation process which can make geometrical profile of metal arbitrary cross-section in deforming region be mutually similar to that of its original billet. Duri…     

砂带磨削接触压强模型分析与实验

为验证赫兹接触模型在砂带磨削中应用的准确性,利用ABAQUS软件建立砂带磨削接触有限元模型,分析厚度比、橡胶硬度、接触压力和工件的曲率半径等因素对接触压强和接触参数的影响,以橡胶接触轮与平面和曲面工件的接触实验验证模型的合理性。分析和实验结果表明:忽略影响较小的因素,砂带磨削接触状态基本符合赫兹接触理论。当圆柱接触轮与曲面工件接触时,接触应力分布呈半椭球型,有限元分析与实验结果验证其准确性;当厚度比为20%,橡胶的肖氏硬度为70 HS时,橡胶接触轮的力学性能与赫兹接触理论误差最小。      

Prediction of individual cell performance in a long-string lead/acid peak-shaving battery: application of artificial neural networks

This work represents the culmination of several years of study of an operating large energy storage battery with the purpose of determining if computerized pattern recognition of maintenance data (and/or available fabrication data) could be used for the early detection of poorly performing cells. Also investigated was the possible identification of cells with predicted high performance. Previous studies using k-nearest neighbor pattern recognition have been augmented with the investigation of artificial neural network analysis. Both methods have achieved practical levels of prediction, but the neural network prediction results are somewhat better. It was possible to select 70% of the high-performing cells, without any false selections from the low-performing cells; it was possible to identify nearly 96% of the poor-performance cells, with none of the high-performance cells mis-selected. These results suggest the feasibility of the routine application of neural networks for performance prediction as part of a maintenance strategy for long-string energy storage systems.     

Sensitivity of diesel engine thermodynamic cycle calculation to measurement errors and estimated parameters

The use of thermodynamic models for the calculation of the heat release law from the experimental in-cylinder pressure signal has been a common practice as a way to study the combustion process of internal combustion engines. However, the results of this procedure depend mainly on two factors: the validity of the assumed hypothesis and the quality of the measurement of the experimental parameters (both mean and instantaneous ones) used as input data. In this work a sensitivity study of a thermodynamic diagnostic model is presented, with the objective of evaluating the influence of errors in the measuring techniques or in the estimation of parameters on the main results, such as mean gas temperature, heat release and rate of heat release. In order to eliminate the effect of the uncertainty associated with the combustion process itself, the study focused on motored engine conditions. Otherwise, the effect of the inadequacy of the assumed hypothesis was eliminated by using as input in the diagnostic thermodynamic model the results from a predictive thermodynamic model with the same hypothesis as the diagnostic one, instead of an experimental pressure signal.     

Acoustic emission study of impact-damaged GRP pipes

Acoustic emission monitoring techniques have been used to investigate the effects of external damage on the structural integrity of GRP pipes. The pipes were 100 mm bore and 5.5 mm wall thickness, and were of wrapped chopped strand mat glass/polyester construction. Damage caused by severe impacts, of net energies up to 43 J, exerted a marked influence on the observed acoustic emissions from pipes subsequently pressurized to failure, but even though severe microstructural damage was caused by these impacts, they did not reduce the load-bearing capacity of the pipes in any way. The presence of stress concentrators in the form of axial saw-cuts resulted in a changing response to loading roughly in accordance with fracture mechanics predictions, and the results help to explain to some extent the apparently conflicting conclusions from the impact damage studies. Thus, although AE analysis was, for these materials, able to provide a clear indication of the presence of microstructural damage, it is clear that such indications can only be of value in detecting loss of structural integrity (load-bearing ability) when considered in conjunction with other information about the materials involved. Filament-wound pipes, for example, do not behave in the same manner. Amplitude analysis of the AE signals does not appear to be of significant value in giving indications of the nature of the impact damage.     

Systematic generation of manufacturing changes for safety-critical components

Every time a component’s design is changed, the corresponding manufacturing has to be changed as well. Due to several recent developments such as increasing market dynamics or ever-shorter product life cycles, the amount of component changes is rising sharply. Therefore, the number of manufacturing changes is increasing at a fast pace. Particularly for safety-critical components, the implementation of component changes within manufacturing poses a significant challenge. The reason for this is the high planning reliability required to implement a component change via a manufacturing change. This implementation has to be performed without endangering the component’s functionality, by causing any other change than the intended one. An approach for the systematic generation of manufacturing changes was developed as a contribution to increasing planning reliability and efficiency. The approach systematically enables technology planners to identify alternative manufacturing changes, to analyze the propagation of these changes, and to evaluate the alternatives to form a basis for decision-making. Its practical applicability is validated using a case study from medical technology.