Manufacturing catalyst-coated membranes by ultrasonic spray deposition for PEMFC: Identification of key parameters and their impact on PEMFC performance

This study deals with the manufacturing of catalyst-coated membranes (CCMs) for newcomers in the field of coating. Although there are many studies on electrode ink composition for improving the performance of proton-exchange membrane fuel cells (PEMFCs), there are few papers dealing with electrode coating itself. Usually, it is a know-how that often remains secret and constitutes the added value of scientific teams or the business of industrialists. In this paper, we identify and clarify the role of key parameters to improve coating quality and also to correlate coating quality with fuel cell performance via polarization curves and electrochemical active surface area measurements. We found that the coating configurations can affect the performance of lab-made CCMs in PEMFCs. After the repeatability of the performance obtained by our coating method has been proved, we show that: (i) edge effects, due to mask shadowing - cannot be neglected when the active surface area is low, (ii) a heterogeneous thickness electrode produces performance lower than a homogeneous thickness electrode, and (iii) the origin and storage of platinum on carbon powders are a very important source of variability in the obtained results.     

Ultrasonic tomographic velocimeter for visualization of axial flow fields in pipes

An ultrasonic tomographic velocimeter to provide quantitative images of axial flow fields in pipes is developed and presented in this work. To detect the flow in various directions and positions, a novel transducer configuration strategy is proposed. All-in-one transducers are mounted in two sectional planes of the pipe. In each plane, N transducers are equally spaced along the circumference. Overlapped propagation paths are introduced by the configuration strategy, and the influence of the vortex flow can be eliminated theoretically by averaging the line velocities of the overlapped paths. To achieve a fast detection speed, the projection data is collected via an electrical scan in a fan-beam mode. After rearrangement and interpolation of the projection data, the parallel beam filtered back projection (FBP) algorithm is implemented to reconstruct the axial flow field. Numerical simulations with the theoretical velocity profiles were performed. The compensation method for the vortex flow is proved to be effective and necessary, and the number of transducers required for reconstruction of common flow profiles was estimated. Accordingly, an ultrasonic tomographic velocimeter consisting of 2×12 transducers was fabricated. Experiments were conducted in the straight pipe and downstream of a single bend pipe and compared with the computational fluid dynamics (CFD) simulation results. As demonstrated, the ultrasonic tomographic velocimeter was capable of visualizing both symmetric and asymmetric axial flow fields with high reliability.     

A review on ultrasonic spot welding of copper alloys

As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided.     

The influence of the waveguide on the quality of measurements with ultrasonic Doppler velocimetry

The article is devoted to the study of the influence of geometric parameters of sound-conducting walls on the quality of measurement of liquid metal flow velocities by ultrasonic Doppler velocimetry. It was shown that the thickness and radius of a sound-conducting wall (waveguide) have a notable effect on the resulting velocity profiles. The flow in a round pipe, the length of which is much larger than its diameter, is considered as a reference flow. The positive effect of a stepwise waveguides with a diameter smaller than the diameter of the piezoelectric element of an ultrasonic transducer on the quality of velocity measurements was verified experimentally. It was found that the accuracy of the resulting velocity profiles largely depends on the length and the material of the waveguides, as well as the velocity of the incoming flow of liquid metal.     

Process and joint quality of ultrasonic vibration enhanced friction stir lap welding

In order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects.     

高导电性原油电脱盐工艺研究

南阳原油中金属含量较高,掺有部分3次采油采出原油,加工时易造成电脱盐装置原油乳化,电导率高,脱盐难度较大。装置投产十几年来脱后含盐一直不合格,经过改造仍然超标,常压塔顶腐蚀严重。为此,对原油进行了电脱盐工艺条件及破乳剂研究,研制出了高效电脱盐设备和生物复合脱盐剂及降电流剂,采用平流弓形电极进行改造,解决了该原油的电脱盐问题,使脱后含盐达到3 mg/L。     

油井参数对超声透射系数的影响

为了研究油井各参数对超声波透射系数的影响，根据超声波在媒质中的波函数和边界条件，求出了油井中超声波的透射系数。当井液和水泥层的声速和密度增大时，超声波的透射系数也随之增大，但变化幅度不大，特别是水泥层密度对超声波的透射系数影响很小；当岩层的声速增大时，超声波的透射系数会出现一个极大值；岩层密度对超声波的透射系数影响较大，且随岩层密度的增大超声波的透射系数随之降低。     

超声波清洗在贵/廉金属复合材料生产过程的应用研究

本文结合“ODS清洗剂消费淘汰项目”的实施，并对新型超声波清洗机及新型ODS清洗液进行了工艺试验，阐述了超声波清洗技术是贵／廉金属复合材料生产过程中无可替代的清洗技术。     

超声波车辆车轴探头的研制与应用

提出了一种用于检测在役车辆车轴产生疲劳裂纹的超声波方法,设计了中心孔探头与斜角探头一起,完成了对车辆车轴的关键区域探伤。     

碳素材料超声检测的信号处理方法

针对碳素材料超声无损检测存在信噪比较低的问题,从自相关性出发分析了典型超声检测信号的组成成分,提出了在自相关分析的基础上的小波去噪思想,探讨了自相关分析和小波分析相结合的信号处理方法。利用此方法进行实际超声信号分析效果良好。