Enhanced performance of sandwich structure Pb0.8La0.1Ca0.1Ti0.975O3 thin film for pyroelectric applications

Using the advantages of low-temperature crystallization and high orientation in Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ (PLCT) film, a dense PLCT/porous PLCT/dense PLCT sandwich structure was obtained in the present study. It is found that dense PLCT layer can both sustain the porous density in the core layer and also lead to better preferential orientation of the sandwich structure. In the sandwich structure, low dielectric constant (ε_r = 43) and leakage current density (J < 9 × 10^− 5A/cm²) are simultaneously achieved. Because of high orientation in sandwich structure, the pyrocoefficient (p > 185 µC/m² K) is still keeping a relatively large value. The resulting high figure of merit (F_V′ = 4.5 µC/m² K, F_d′ = 228 µC/m² K) make the sandwich structure films good candidate for pyroelectric thin-film devices.     

Evaluation of MOSA condition using leakage current method

This paper covers the evaluation of metal-oxide surge arrester (MOSA) condition using the method based on the analysis of leakage current at the operating voltage of the network. A comparison is made between the following variants of this method: (1) the method based on harmonic analysis of the total leakage current; (2) the method based on the third order harmonic of the resistive leakage current; (3) the method of power loss; (4) the capacitive current compensation method; and (5) the method based on direct measurement of the amplitude of the resistive leakage current. For these methods the appropriate indicators are introduced for evaluating the MOSA condition. The application of these methods is analyzed depending on fluctuation and the presence of higher harmonics of the MOSA operating voltage. Calculations were conducted using the program MATLAB on a simplified equivalent circuit of a MOSA with a non-linear element modeled using the degree function. Based on the calculation results, a gradation was made for the applicability of individual indicators for evaluating the MOSA condition which indicates a special advantage for using the fundamental harmonic of the resistive component of leakage current and the fundamental harmonic of power loss.     

Investigating leakage and bypass flows in an HTR using a CFD methodology

An area that has been identified as significantly important in the development of a high temperature reactor (HTR) is the prediction of leakage and bypass flows. It is therefore essential to understand the influence of leakage and bypass flows on the thermal performance of an HTR.A methodology was developed to conduct an integral thermal analysis of a reactor using a CFD approach. One of the main objectives was to include leakage and bypass flow paths in order to provide a capability for simulating these very detailed flows.This paper investigates leakage and bypass flows through the PBMR reactor unit. It was found that, although these flows are dependent on the pressure drop through the pebble bed, a change in pebble bed pressure drop does not result in a similar change in the predicted leakages flows. It is also shown that the ability to account for leakage and bypass flows in an integral manner can help designers to focus their efforts on the specific regions that need to be targeted for the improvement of the life expectancy of the graphite blocks. Furthermore, leakage and bypass flows were found to reduce the pressure drop across the reactor unit while increasing the peak fuel temperatures.     

Development of Al2O3/glass-based multi-layer composite seals for planar intermediate-temperature solid oxide fuel cells

In this paper, the novel multi-layer composite seals for planar solid oxide fuel cells are studied. The composite seals with sandwiched structure include Al₂O₃-based tape as support and glass-ceramic slurry as binder connecting the interface of the neighboring components. The result finds out that glass-ceramic slurry with 20 wt% Al₂O₃ has the suitable strength and deformability. The thermal cycle characteristics are greatly improved by using the multi-layer composite seals, and the corresponding leakage rates are lower than 0.025 sccm cm⁻¹ for 20 thermal cycles at the inlet pressure ranging from 0.5 psi to 2 psi. SEM investigations show a very compact and good adhesion between the neighboring components, which can minimize the leakage paths. Single cell testing is used to examine the performance of the seals. The value of open circuit voltage is 1.17 V. At the constant discharge current density of 0.37 A cm⁻², the voltage is stabilized at about 0.85 V for 50 h. The results demonstrate that the novel multi-layer composite seals are good candidate for SOFC application.     

管壳式换热器的化学清洗及渗漏分析

叙述了管壳换热器化学清洗的基本流程，进而对清洗过程中可能引起换热器渗漏的诸多因素进行了论述及分析。     

真空中冲击电压下硅半导体的泄漏电流及沿面闪络特性

在冲击电压下 ,通过在真空中对采用和未采用化学腐蚀表面处理的硅半导体的实验表明 ,试品的表面状况对其泄漏电流和沿面闪络特性有着很大的影响 ,在沿面闪络之前 ,未经处理试品的泄漏电流表现为欧姆性电流 ,而表面处理过的试品表现为空间电荷限制电流特性 ;同时两类试品表面的放电通道也表现出不同的特征。提出了一个新的模型来描述半导体材料沿面闪络的发展过程 ,即由焦耳热效应诱导的电流细丝现象而发展成最终的闪络 ,并认为这是一个发生在半导体表层内的过程 ,在靠近真空的侧面这一表层厚度约为 2 μm。     

绝缘拼接式磁性槽楔的结构和性能分析

提出了一种绝缘拼接式磁性槽楔的结构，分析了这种槽楔对电机的齿谐波、齿间漏磁、涡流的影响。只要合理地确定结构和参数，绝缘拼接式磁性槽楔不但能提高电机效率，还能提高电机负载能力。     

Losses in diagonal MHD generator

Losses in an MHD generator not only reduce the power output but also degrade it. The losses due to heat, friction and leakage through insulating-wall/slag have been analyzed for the diagonal generator for better control and performance. The losses due to leakage are higher than the heat and friction losses. The effect of wall temperature on losses is significant. The heat and friction losses decrease with increase in wall temperature, whereas the leakage losses increase with increase in wall temperature. The slag losses reduce power output from the channel drastically.     

柱塞泵滑靴阻尼孔对滑靴/斜盘油膜的影响

根据静压支撑原理,运用计算流体力学技术,对滑靴副的流场进行仿真分析,在油膜厚度一定的情况下,选取3组不同的阻尼孔直径,对滑靴和斜盘油膜表面压力进行监控,得到底面油膜压力随着阻尼孔直径变化的压力图,讨论不同的油膜压力对滑靴副油液泄漏的影响以及对泵效率的影响。结果表明:阻尼孔直径变大,底面油膜的压力随着变大,滑靴副油液泄漏量也随着增加,而油液泄漏量又影响泵的效率。研究结果进一步揭示了滑靴阻尼孔结构对滑靴副和泵性能的影响。     

工业流体仪表控制管路泄漏的动态处理技术

本文简述了动态密封技术的基本原理和特点，并以一个成功的实例介绍了在不影响正常生产的条件下消除工业流体仪表控制管路泄漏的技巧。