Numerical investigation of water and temperature distributions in a proton exchange membrane electrolysis cell

Science China Technological Sciences - A three-dimensional, non-isothermal, two-phase model for a PEM water electrolysis cell (PEMEC) is established in this study. An effective connection between...     

Visualization study on atomization characteristics and heat transfer performance of R1336mzz flash spray cooling

Visualization experiments are carried out to investigate the atomization characteristics of R1336mzz flash spray cooling. The influences of superheat, spray distance, and nozzle orifice diameter on spray cooling performance are analyzed experimentally. As the superheat increases, finer droplets and thinner liquid film are observed; this is helpful to improve the two-phase heat transfer efficiency. Enlarging atomization angle under high superheat is also observed for flash spray cooling, and it benefits for reducing the spray distance. It can be found that when the inlet superheat is 19.8°C and the spray distance is 6 mm, the critical heat flux (CHF) reaches 251 W/cm² and the maximum heat transfer coefficient (HTC) reaches 37.4 kW/(m² °C), which are 55% and 11.6% higher than those when the inlet subcooling is 6.9°C and the spray distance is 12 mm, respectively. Using flash spray reduces the spray distance, which benefits for designing compact spray cooling device. In addition, the nozzle orifice diameter has great influence on the cooling performance of flash spray, and the choice of the nozzle depends on the superheat. This study provides a physical insight into the heat transfer enhancement in flash spray cooling.

     

农业转移人口阶段性市民化策略研究——基于社会组织赋能视角

市民化既是一种结果,也是一个过程.本文根据从时间上按照市民化意愿需求与制度供给的关系进行阶段划分的研究视角,基于安徽省H市的实地调查经验,通过分析农业转移人口在市民化推进过程的不同阶段所面临的障碍,从社会组织赋能的角度提出了匹配不同市民化阶段的对策.研究发现,在农业转移人口进入城市之前,其农村利益是否得到保障、城乡文化的差异以及留守人员的民生问题成为阻碍他们进城的主要障碍.在进入城市之后,首当其冲的是民生问题,另外其社会、人力和心理资本过低也成为阻碍其市民化的几个障碍.在此期间社会组织开展有针对性的支持项目匹配不同市民化阶段的农业转移人口,可以更加有针对性地满足诉求、化解矛盾、扩展社会交往并实现基层治理秩序,最终达到"城镇融合"的理想状态,完成市民化发展的最终目标.     

基于文献计量学的水资源承载力研究进展综述

为分析水资源承载力研究发展状况与趋势,本研究以WOS核心合集和中国科学引文数据库文献作为原始数据,利用CiteSpace程序绘制知识图谱,梳理总结了学科知识基础、研究热点.研究结果揭示了水资源承载力领域的演变特征与发展趋势,有助于加深对该领域的整体认识,为我国水资源承载力领域开拓新的研究前沿提供理论参考和借鉴的意义.     

电缆中间接头受潮时电场分布研究

通过ANSYS软件建立10 kV电缆冷缩式中间接头的三维模型,并仿真计算静电场,主要分析不同受潮情况下电场分量的分布情况.结果表明:接头绝缘材料受潮时,复合界面上的电场增大;接头浸水时间越长,电场畸变越严重;主绝缘内侧受潮时水膜对周围的电场分布几乎没有影响,水膜处电场增大,但场强依然保持在极低的水平.     

电力线交跨测量无纸化作业系统开发及应用

在Visual C#平台下,开发一套电力线交跨测量无纸化作业系统.该系统实现全站仪GSI/XML数据记录文件的读取、交跨测量点的绝对坐标计算、野外观测记录手簿的生成,还可转换成软件内部的交跨命令,具有操作简单、实用性强等特点,在多项电力线路工程测量中得到成功应用.     

基于航空双涵道技术的耦合风机设计及舒适性提升研究

传统空调器制冷运行时,存在远近冷热不均、局部位置循环不充分导致空调在制冷时用户感受较差的问题.基于单一风机类型存在的送风范围及风感问题,采用航空双涵道的原理设计轴流离心耦合风机.结合两种风机的固有特性,通过两股气流的风控制风,进行多种气流形式的转换,从而实现全域无风感和全域均匀风的舒适风感.     

Interactions of dynamic supercritical CO2 fluid with different rank moisture-equilibrated coals:Implications for CO2 sequestration in coal seams

The interactions between CO2 and coals during CO2-ECBM (CO2 sequestration in deep coal seams with enhanced coal-bed methane recovery) could change pore morphology and chemistry property of coals,thereby affecting adsorption,diffusion and flow capability of CO2 and CH4 within coal reservoirs.To sim-ulate CO2-ECBM process more practically,the dynamic interactions of supercritical CO2 (scCO2) and moisture-equilibrated coals were performed at temperature of 318.15 K,pressure of 12.00 MPa,and duration of 12.00 h.The impacts of the interactions on physicochemical properties of coals were inves-tigated.Results indicate that scCO2/H2O exposure shows minor effect on micropores of coals.However,the exposure significantly decreases the mesopore surface area of bituminous coals,while increases that of anthracites.The mesopore volume and the average mesopore diameter of all the coals after scCO2/H2O exposure decrease.The multi-fractal analysis verifies that the scCO2 exposure can enhance the pore con-nectivity of various rank coals.Apart from the pore morphology,the exposure of scCO2/H2O also affects the oxygenic functional groups on coal surface.Particularly,the exposure of scCO2/H2O reduces the con-tent of C-O and C=O of coals.The content of COOH of low rank coals including Hehua-M2# coal,Zhongqiang-4# coal,Buliangou-9# coal and Tashan-5# coal decreases,while the high rank Laochang-11# coal and Kaiyuan-9# coal witness a growth in COOH.The content of total oxygenic functional groups of all coals after interaction with scCO2/H2O decreases;on the contrary,that of C-C/C-H of all coals after SCCO2/H2O exposure increases.In summary,the interaction with SCCO2/H2O significantly changes the pore system and oxygenic functional groups of various rank coals,which needs further attention regard-ing CO2-ECBM.     

Coalescence dynamics of two droplets of different viscosities in T-junction microchannel with a funnel-typed expansion chamber

The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion cham-ber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratio η of two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when 1 ＜ η＜ 6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time (Tdr) and critical capillary number (Cac) were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size dif-ference and viscosity ratio of the two droplets:Tdr ～ (ld)0.25±0.04 and Tdr ～ (η)-0.1±002.For droplet coales-cence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac =0.48λ0.26l-2.64,while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac =0.11 η-0.07ls-2.23ld0.16.     

共沉淀法制备透明质酸修饰超小纳米氧化铁影响因素的研究

采用共沉淀法,通过改变透明质酸及氨水与铁离子的比例、反应物浓度、温度和反应体系大小等反应参数制备出透明质酸修饰的超小超顺磁氧化铁纳米颗粒(Fe3 O4@HA),并对所合成的样品进行了尺寸、形貌和磁性的表征.实验结果表明:使用共沉淀方法时,所制备的Fe3 O4@HA的饱和磁化率受反应参数的影响较小,且都介于55～80 emu/g之间;但纳米颗粒的形貌、水合粒径受反应参数的影响较大.对于初始反应体积为50 mL的体系,透明质酸1.5 g、铁离子0.9 mmol、氨水用量15 mL、温度为80℃是本实验筛出的最佳条件.此外,根据最佳反应条件进行30倍放大,可一次制备出2 L的Fe3 O4@HA溶液,证明本体系具备工业化生产的潜力.