Finite size gap effects on the modeling of thermal contact conductance at polymer‐mold wall interface in injection molding

Heat transfer in polymer processing by injection molding is affected by the thermal contact conductance at the interface between the polymer and the metal mold. The modeling of thermal contact conductance at such interfaces is simplified by the assumption of an isothermal condition at the two contacting surfaces. In this study we examine the validity of such an assumption for the case of an interface involving plastic (a low thermal conductivity material) and metal (a high thermal conductivity material). The study shows that at such an interface between materials of widely varying thermal conductivity, the conditions at the interface depart from the isothermal assumption, with the heat flux becoming more uniform and the temperature difference varying by a larger magnitude across the contact plane. This effect is more pronounced as the width of the gaps increases for the same area of contact. This suggests that the modeling of the contact conductance should be based on average temperatures for the contacting surfaces. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1776–1782, 2000     

基于PCA和GA-BP神经网络的锂电池容量估算方法

本文针对车用锂离子动力电池容量估算方法精度不高的问题,提出了一种利用遗传算法优化BP神经网络的锂离子电池剩余容量估算方法。首先在整理NASA锂离子电池数据集后,得到不同健康状态下电池的容量增量曲线峰值。其次将健康因子进行主成分分析对其降维处理,利用遗传算法优化BP神经网络的连接权值,对锂离子电池容量进行预测。最后在NASA不同型号的电池上应用模型进行了验证。结果表明,所提出的方法可以在不同训练量的情况下准确估算4种锂离子电池的容量,其估算的方均根误差小于2%,且与未使用遗传算法优化的预测结果相比,该方法具有较高的预测精度。     

坐标反算时的方位角计算一法

介绍了一种坐标反算时的方位角计算方法:首先根据两点间的坐标计算得出坐标增量,用坐标增量计算出边长和1个过渡角,并根据纵坐标增量ΔX的符号判断方位角与该过渡角之间的关系,从而求得坐标方位角。实践证明,该方法可以减少象限判断的步骤,便于编程计算。     

SrCO_3掺杂La_2Ti_2O_7陶瓷的电性能

通过固相反应合成法制备了La_2Ti_2O_7陶瓷,研究了SrCO_3掺杂对La_2Ti_2O_7陶瓷的电学性能的影响,并对导电机理做了初步的探讨分析.实验表明,随着Sr量的增加,电导激活能有下降的趋势,导致材料的电导率增加.在100 Hz～10 MHz频率下未掺杂Sr和掺杂量为x=0.01试样的介电常数分别为46和67,介电损耗都在1×10~(-3)数量级,说明这种材料具有较好的介电性能.     

小孔流导的理论计算与蒙特卡罗计算

用理论公式与蒙特卡罗方法分别计算了动态流量校准系统和超高/极高真空校准系统中小孔流导的修正系数,比较了2种方法的计算结果。用蒙特卡罗方法计算了小孔系统的传输几率。蒙特卡罗方法计算结果的标准偏差在4．5×10^-7到1．1×10^-5之间。     

INRIM continuous expansion system as high vacuum primary standard for gas pressure measurements below 9 × 10 Pa

The continuous expansion system can be considered the state of the art for pressure measurement in the ultra high vacuum range. In the last years, at INRIM, a new continuous expansion system was designed, assembled and characterized. The system is the high vacuum primary standard in the pressure range from 1 × 10⁻⁶ Pa to 9 × 10⁻² Pa with relative standard uncertainty ranging from 2.1% at 1 × 10⁻⁶ Pa down to 0.4% at 9 × 10⁻² Pa. The system is based on the passing of a measured gas flow through a fixed and known conductance. The gas flow is generated and measured by a primary gas flowmeter based on the constant-pressure-variable-volume method.In the first part of the paper both a correction for the effect of transitional flow through the orifice and a new analytical evaluation of orifice conductance are presented. In the second part the accuracy of the system and the pressure uncertainty evaluation are described.     

Influence of Spacer Systems on Heat Transfer in Evacuated Glazing

One attractive possibility to essentially improve the insulation properties of glazing is to evacuate the space between the glass panes. This eliminates heat transport due to convection between the glass panes and suppresses the thermal conductivity of the remaining low pressure filling gas atmosphere. The glass panes can be prevented from collapsing by using a matrix of spacers. These spacers, however, increase heat transfer between the glass panes. To quantify this effect, heat transfer through samples of evacuated glazing was experimentally determined. The samples were prepared with different kinds of spacer materials and spacer distances. The measurements were performed with a guarded hot-plate apparatus under steady-state conditions and at room temperature. The measuring chamber of the guarded hot plate was evacuated to < 10⁻² Pa. An external pressure load of 0.1 MPa was applied on the samples to ensure realistic system conditions. Radiative heat transfer was significantly reduced by preparing the samples with a low-ε coating on one of the glass panes. In a first step, measurements without any spacers allowed quantification of the amount of radiative heat transfer. With these data, the measurements with spacers could be corrected to separate the effect of the spacers on thermal heat transfer. The influence of the thermal conductivity of the spacer material, as well as the distance between the spacers and the spacer geometry, was experimentally investigated and showed good agreement with simulation results. For mechanically stable matrices with cylindrical spacers, experimental thermal conductance values ≤0.44W·m⁻² ·K⁻¹ were found. This shows that U _g -values of about 0.5W · m⁻² · K⁻¹ are achievable in evacuated glazing, if highly efficient low-emissivity coatings are used.     

荷叶碱对野生型和突变型囊性纤维化跨膜电导调节因子氯离子通道的激活作用

目的:从天然单体化合物中筛选能够激活囊性纤维化跨膜电导调节因子(CFTR) Cl^-通道转运活性的激活剂。方法:利用稳定表达人CFTR和对卤族元素碘离子高度敏感的荧光绿蛋白突变体EYFP-H148Q 的Fischer 大鼠甲状腺上皮细胞为筛选模型, 测定386 种中药单体化合物对CFTR介导的I^-内流速度的影响。结果:发现生物碱类化合物荷叶碱对野生型和△F508 突变型CFTRCl^-通道具有激活作用, 而对G551D 突变型CFTRCl^-通道无激活作用。荷叶碱对野生型和△F508突变型CFTR Cl^-通道的激活作用具有作用迅速、可逆的特点, 并且依赖于细胞内cAMP 水平。荷叶碱不提高细胞内cAMP 水平, 当CFTR 磷酸化程度达到最大时仍能进一步激活CFTR Cl^-通道激活作用, 表明它可能是通过与CFTR 直接结合而发挥作用的。结论:首次发现荷叶碱对野生型和△F508 突变型CFTR Cl^-通道的激活作用, 该天然化合物将在阐明CFR 活性机制及作为先导化合物开发与CFTR 有关的疾病治疗药物等方面具有重要用途。     

固态塑性成形过程中界面接触换热的实验研究

文章通过自制的接触换热系数测量设备对纯铜与3Cr2W8V合金钢、不锈钢与不锈钢间的接触换热系数进行了实验研究。分析了温度和载荷对接触换热系数的影响,并且分析了在铝合金和模具钢的接触面间加入玻璃润滑剂后对接触换热系数的影响。实验结果发现,接触换热系数与温度的关系并不是简单的正比关系,而与载荷的指数近似成正比关系,且在接触面涂上玻璃润滑剂后,接触换热系数可大大降低。