An Experimental Study on the Void Fraction for Gas-Liquid Two-Phase Flows in a Horizontal Pipe

The flow patterns and the void fraction related to a gas-liquid two-phase flow in a small channel are experimentally studied.The test channel is a transparent quartz glass circular channel with an inner diameter of 6.68 mm.The working fluids are air and water and their superficial velocities range from 0.014 to 8.127 m/s and from 0.0238 to 0.556 m/s,respectively.The void fraction is determined using the flow pattern images captured by a high-speed camera,while quick closing valves are used for verification.Four flow patterns are analyzed in experiments:slug flow,bubbly flow,annular flow and stratified flow.For intermittent flows(bubbly flow and slug flow),the cross-sectional void fraction is in a borderline condition while its probability distribution function(PDF)image displays a bimodal structure.For continuous flows(annular flow and stratified flow)the cross-sectional void fraction behaves as a fluctuating continuous curve while the(PDF)image displays a single peak structure.The volumetric void fraction data are also compared with available predictive formulas,and the results show that the agreement is very good.An effort is also provided to improve the so-called Gregory and Scott model using the available data.

A 2D numerical study on the condensation characteristics of three non-azeotropic binary hydrocarbon vapor mixtures on a vertical plate

To improve the transportation efficiency and reduce the supply cost,the liquefaction becomes an important technology to store and transport the natural gas.During the liquefaction,the various components(e.g.propane,ethane,methane etc.)undergo fractional condensation phenomenon due to their different boiling points.This means that when one component condenses,others play a role of non-condensable gas(NCG).In order to reveal the influence mechanism of NCG on this condensation process,a numerical method was employed in this paper to study the condensation characteristics of three non-azeotropic binary hydrocarbon vapor mixtures,namely the propane/methane(80%–95%),ethane/methane(65%–85%)and methane/nitrogen(2%–13%)mixtures,on a vertical plate.The model was proposed based on the diffusion layer model,and the finite volume method was used to solve the governing equations.A user defined function was developed by cell iterative method to obtain the source terms in the condensation process.The numerical results show that the gas phase boundary layer formed by the NCG becomes the main resistance to the reduction of heat transfer coefficient.And for the above three mixtures,there is a negative correlation between the NCG concentration and the heat transfer coefficient.Meanwhile,the results show a good agreement with the experimental data,meaning that the proposed model is reliable.Three mixtures within same non-condensable mole fraction of 20%were also investigated,indicating that the mixtures with a higher binary hydrocarbon molecular ratio have a lower heat transfer coefficient.As a result,the presence of the lighter NCG contributes to a thicker boundary layer.

硅基毫米波集成电路设计发展现状与挑战

毫米波相控阵系统因其大带宽、高速率和多波束的优点,在移动通信和雷达感知系统中得到了广泛的应用.硅基毫米波集成电路设计是其中的关键核心技术.本文基于国家自然科学基金委员会第347期“双清论坛(青年)”的研讨成果,根据毫米波集成电路与集成系统研究方面的重大需求,针对硅基毫米波集成电路设计的关键挑战和科学问题,按照相控阵架构、关键电路和器件模型3个层级,总结梳理了国内外硅基毫米波集成电路设计领域近年来所取得的主要进展和成就,凝炼了该领域未来5~10年的重大关键科学问题,探讨了前沿研究方向和科学基金资助战略.

配戴散光设计型角膜塑形镜对人眼像差的影响

目的：通过观察散光设计型角膜塑形镜配戴后人眼高阶像差的变化，评价该角膜塑形镜对人眼视觉质量的影响。方法：回顾性研究。选取石迎辉眼科诊所门诊2015年2月至2016年8月期间配戴散光设计型角膜塑形镜患者25例（50眼），测量配戴塑形镜前，戴镜后1个月、3个月、6个月、1年，在5、7mm瞳孔直径下的高阶像差均方根（RMS）值。戴镜前后各像差值比较采用重复测量方差分析，各组间比较采用LSD检验，当校正系数Epsilon〈0．7时，采用Bonferroni法进行两两比较。结果：戴镜后在5mm和7mm瞳孔直径时像散、彗差、球差、剩余像差及总高阶像差较戴镜前均增加，差异有统计学意义（5mm：F=5．15、11．11、10．73、6．95、11．18，均P〈0．05；7mm：F=2．93、4．71、9．34、5．01、5．70，均P〈0．05）。随着戴镜时间的延长，各像差值逐渐增大，戴镜3个月时达到最大值，随后逐渐降低。结论：角膜散光较大患者配戴散光设计型角膜塑形镜后高阶像差增加，人眼视觉质量下降。