涡结构对小颗粒在圆管背风面碰撞分布的影响

针对锅炉管背风面飞灰沉积过程，采用数值模拟的方法进行了研究.对绕柱气相湍流的模拟采用了较新的分离涡模拟方法（detached eddy simulation, DES），通过对粒径为1～10 μm的颗粒在圆管背风面碰撞分布规律的计算发现背风面近壁区存在的主涡、二次涡和分离点附近小涡对颗粒在背风面的碰撞均有一定的影响.当速度较小时，随着粒径的增大，颗粒在背风面碰撞的质量逐渐增加，大颗粒在主涡和二次涡作用下均有较大的碰撞质量流量，而且二次涡的作用明显强于主涡；速度增加后，由背风面3种涡结构引起的颗粒碰撞量均有不同程度的减少，此时主涡的作用较强，而且二次涡引起的大颗粒碰撞量有明显减少.通过与实验测试结果进行对比检验，证明了数值模拟结果的准确性.     

风偏角与杆塔结构对500 kV同杆双回线路绕击耐雷性能的影响

分析500kV双回输电线路的绕击耐雷性能,对EGM进行了改进。在计算过程中为考虑风的影响,引入风偏角;同时引入了雷击避雷线与雷击地面击穿强度比值随杆塔高度h变化的系数β。用暴露弧法计算每根导线绕击跳闸率,以暴露弧为0时对应的雷电流作为雷电的最大绕击电流,并分析了风偏角、杆塔结构等因素对500kV双回输电线路各导线绕击跳闸率的影响。结果表明,风偏角增大,绕击跳闸率增大;总绕击跳闸率随避雷线横担增长而减小;各导线绕击跳闸率与杆塔结构间的关系复杂,需具体计算分析。理论分析和计算验证了该方法的实用性和有效性,具有一定的工程指导意义。     

水蒸汽诱导法成膜过程研究

在用水蒸汽诱导法制备聚偏氟乙烯(PVDF)微孔膜时,利用光学显微镜对初生态膜在水蒸汽中凝胶过程进行动态观察,结合膜在不同湿度下质量变化和表面液滴层的红外光谱图,研究了蒸汽诱导法成膜的具体过程.结果表明,蒸汽诱导法制备PVDF膜的成膜过程存在着溶剂和非溶剂的迁移,刚开始是非溶剂水的迁入占主导地位,膜质量增加;此后,溶剂与非溶剂的挥发逐渐占主导地位,膜质量在达到最大值后逐渐减少,最终稳定.湿度较高时,溶剂与非溶剂扩散速度较快,膜的凝胶速度较快;湿度较低时,膜凝胶速度则较慢.膜表面和断面电镜照片表明,随着膜在蒸汽中停留时间的延长,蒸汽诱导法最终形成的膜为粗糙多孔表面及对称的断面结构.     

Formation mechanism of gradient-distributed particles and their effects on grain structure in 01420 Al-Li alloy

Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization. The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness. The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM） and X-ray diffractometry（XRD）. The formation mechanism of the gradient particles was discussed. The results show that after aging, a gradient distribution of large particles along the thickness is observed, the particles in the surface layer（SL） are distributed homogeneously, whereas those in the center layer（CL） are mainly distributed parallel to the rolling direction, and the volume fraction of the particles in the SL is higher than that in the CL. Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL, which is the main reason for the formation of layered grain structure along the thickness in the sheets.