Investigating fuel-cell transport limitations using hydrogen limiting current

Reducing mass-transport losses in polymer-electrolyte fuel cells (PEFCs) is essential to increase their power density and reduce overall stack cost. At the same time, cost also motivates the reduction in expensive precious-metal catalysts, which results in higher local transport losses in the catalyst layers. In this paper, we use a hydrogen-pump limiting-current setup to explore the gas-phase transport losses through PEFC catalyst layers and various gas-diffusion and microporous layers. It is shown that the effective diffusivity in the gas-diffusion layers is a strong function of liquid saturation. In addition, it is shown how the catalyst layer unexpectedly contributes significantly to the overall measured transport resistance. This is especially true for low catalyst loadings. It is also shown how the various losses can be separated into different mechanisms including diffusional processes and mass-dependent and independent ones, where the data suggests that a large part of the transport resistance in catalyst layers cannot be attributed to a gas-phase diffusional process. The technique is promising for deconvoluting transport losses in PEFCs.     

Thermophysical Properties and Normal Spectral Emittance of Iridium up to 3500 K

An ohmic pulse-heating experiment together with radiometry and μs-photopolarimetry is deployed at the Institute of Experimental Physics, Graz University of Technology, to obtain temperature-dependent thermophysical properties of conducting samples in the solid and molten states. This experimental setup has been used within the present work to gather data for solid and liquid iridium. Results for both thermophysical properties, as well as the normal spectral emittance obtained at a wavelength of 684.5 nm up to 3500 K are reported. The newly obtained values for iridium are presented in graphical and tabular form and compared to available literature data. The uncertainties for all reported properties are stated and it follows that, considering these expanded uncertainties, the recent data are in very good agreement with literature sources. Mutually motivated by these good results and by the scarce (if any) data available for the liquid state, the thermal conductivity and thermal diffusivity of liquid iridium are estimated by means of the Wiedemann–Franz law.     

Measurement of Thermal Diffusivity at Low Temperatures Using an Optical Reflectivity Technique

An experimental arrangement has been developed for measuring the transient temperature responses and the thermal diffusivities of foil materials in the range of 10 to 300K by using the optical reflectivity technique. The cryogenic system with optical windows is designed to provide temperatures from 10 to 300 K. The front surface of a foil specimen is heated by a pulsed Nd:YAG laser. In situ measurement of the reflectivity of a continuous-wave He–Ne laser at the rear surface is conducted on the microsecond time scale. Using the temperature dependence of reflectivity, the transient temperature response is deduced. The thermal diffusivity is obtained by fitting Parker's formulae to the experimental data on temperature rise. Stainless-steel foils are chosen as samples and are studied in the region from 10 to 300 K. The accuracy is examined by comparing the present results with the theoretical temperature responses and thermal diffusivity data from the literature. Good agreement is observed.     

基于激光闪光法的立式热扩散率测量装置研究

介绍了基于激光闪光法的立式热扩散率测量装置,利用脉冲激光对样品进行均匀加热,使样品内部产生一维热流,并通过红外探测器测量样品温升信号,采用立式真空加热炉控制测量温度环境,实现室温至1600℃的热扩散率测量。用该装置测量厚度为1. 1 mm,直径为10 mm的不锈钢样品,测量结果与PTB参考数据的偏差小于1%。     

Er3+: Y0.5Gd0.5VO4激光晶体的生长和热学性质

用提拉法生长出Er3 : Y0.5Gd0.5VO4单晶,用电感耦合等离子体(ICP)光谱法测定晶体中Er3 原子数分数为0.83%,有效分凝系数为1.03.在30～1300℃测量了晶体a轴和c轴的热膨胀系数分别为2.08×10-6/℃,8.87×10-6/℃;测得晶体在25℃时的比热值为0.48J/(g·K).采用激光脉冲法测量了晶体的热扩散系数,并通过计算得出晶体的热导率,在25～200℃温度范围,晶体在<100方向上的热导率为6.1～4.9W/(m·K),在<001方向上的热导率为7.7～6.2W/(m·K).     

过冷纯金属熔体中热扩散系数对其枝晶生长的影响

采用相场模型和有限差分方法,模拟了过冷纯金属熔体的枝晶生长,计算区域为二维正方形均匀网格. 建立了不同热扩散条件下尖端过冷度、速度、半径随时间变化的关系;此外研究发现枝晶稳定生长时,其尖端过冷度和速度与热扩散系数成正比,尖端半径与热扩散系数成反比.     

Computational study to understand the energy transfer pathways within amicyanin

Vibrational energy diffusivities between the residues present in Amicyanin copper protein are calculated and presented in form of communication map. From those results energy flow pathways from the copper metal ion to the inter protein residue Glu31 are identified. Our finding suggests many different pathways are possible and copper metal ion in oxidized and reduced state switches the pathways. Our finding also suggests the cooperative nature of surrounding residues and water molecules towards selecting the pathways. The major transport channels in the oxidised state are, Cu²⁺---> MET28---> LYS29---> TYR30---> GLU31 and Cu²⁺---> MET98---> TYR30--- > GLU31. And in the reduced state Cu⁺---> CYS9---> TYR30---> GLU31 and Cu⁺---> MET28---> LYS2---> TYR30---> GLU31. We studied further the interaction energies between the copper ion and neighbouring residues using B3LYP/QZVP method. Both the methods complement each other in predicting the energy flow pathways and the cooperative nature of residues.     

同轴地埋管换热器岩土热响应试验研究

岩土热物理性质是影响地源热泵系统设计和运营的关键因素,对位于武汉市洪山区的2口不同深度的同轴地埋管换热孔分别进行48 h的热响应试验,并对同轴地埋管换热器内外管之间环形空间中的平均流体温度进行测试.根据同轴地埋管换热器的几何特性,以简便实用的方式测量同轴地埋管换热器环状空间传热流体的平均温度,结合同轴地埋管换热器钻孔热...     

Effective diffusivity of lead free solder alloys

A Monte Carlo simulation based algorithm is developed to compute the effective diffusivity of lead free solder alloys. Simulations are performed to determine the vacancy diffusivity for 95.5Sn–4.0Ag–0.5Cu (SAC405) solder alloy for different paths. Temperature and micro-structural influence on diffusivity are studied. A map of diffusivity versus temperature and average grain size is developed. Significant differences between diffusivity values reported in the literature for the same solder alloy is also discussed.