悬浮法PVC树脂粒径的影响因素

讨论了悬浮法PVC树脂生产过程中影响树脂粒径的主要因素,有针对性地从聚合釜搅拌、反应配方、体系氧含量、pH值、聚合温度和转化率等方面提出了粒径的控制方案。     

Experimental investigation of far-field human cough airflows from healthy and influenza-infected subjects

Seasonal influenza epidemics have been responsible for causing increased economic expenditures and many deaths worldwide. Evidence exists to support the claim that the virus can be spread through the air, but the relative significance of airborne transmission has not been well defined. Particle image velocimetry (PIV) and hot-wire anemometry (HWA) measurements were conducted at 1 m away from the mouth of human subjects to develop a model for cough flow behavior at greater distances from the mouth than were studied previously. Biological aerosol sampling was conducted to assess the risk of exposure to airborne viruses. Throughout the investigation, 77 experiments were conducted from 58 different subjects. From these subjects, 21 presented with influenza-like illness. Of these, 12 subjects had laboratory-confirmed respiratory infections. A model was developed for the cough centerline velocity magnitude time history. The experimental results were also used to validate computational fluid dynamics (CFD) models. The peak velocity observed at the cough jet center, averaged across all trials, was 1.2 m/s, and an average jet spread angle of θ = 24° was measured, similar to that of a steady free jet. No differences were observed in the velocity or turbulence characteristics between coughs from sick, convalescent, or healthy participants.     

不同粒度纳米碳酸钙的可控制备

不同粒度的纳米碳酸钙具有不同的特性和应用范围,目前不同粒度纳米碳酸钙的可控制备方法还未见报道。以氯化钙、碳酸铵为原料,以乙醇、柠檬酸和焦磷酸钠为分散剂,采用复分解法研究了不同制备条件对纳米碳酸钙粒径的影响规律,在此基础上制备出平均粒径为17~71 nm的碳酸钙,并对其进行了表征。实验结果表明,所制备的纳米碳酸钙均为球霰石型,纯度很高,而且形貌近似球形。制备条件对纳米碳酸钙的粒径有显著的影响：随着反应温度升高,纳米碳酸钙的粒径减小;随着氯化钙滴加时间的增加,纳米碳酸钙的粒径增大;随着反应物浓度的提高,纳米碳酸钙的粒径先减小后增大;当分散剂为柠檬酸和焦磷酸钠的混合溶液时所得纳米碳酸钙的粒径最小,当分散剂为乙醇和焦磷酸钠的混合溶液时所得纳米碳酸钙的粒径最大。利用这些影响规律通过控制制备条件可以实现所需粒径纳米碳酸钙的可控制备。     

电磁场作用下球形磁极辅助研磨弯管内表面研究

弯管弯曲成形后,在弯折处易产生微裂纹、褶皱等表面质量缺陷问题。本文通过采用六自由度机械手拖动电磁场发生装置沿加工轨迹往复运动,电磁场发生装置驱动球形辅助磁极绕管件内壁转动,实现了对弯管内表面的光整加工。在此基础上,通过对弯管轮廓采集及曲线拟合,重新构建了弯管中心线并转换为新的研磨加工轨迹。采用超景深3D电子显微镜和触针式表面粗糙度测量仪对研磨试验前后弯管内表面的形貌和粗糙度进行了对比分析。结果表明,通过重新构建研磨加工轨迹,试验装置有效解决了研磨弯折处的干涉与研磨不均匀等问题。研磨55 min后,表面粗糙度由原始的0.713μm降低到0.194μm,铜合金弯管内表面原始质量缺陷基本去除,表面纹理较为致密均匀。该方法有效避免了未规划研磨轨迹时出现的犁耕等纹理缺陷,提高了弯管的服役可靠性。     

频率可调太赫兹回旋振荡管互作用电路的设计与研究

根据动态核极化核磁共振成像技术对回旋振荡管的要求,设计了130 GHz 回旋振荡管的注波互作用电路,基于线性理论对互作用电路进行了研究并选择了合适的工作点,分析了电路的频率调节特性。利用相对论电子回旋脉塞非线性理论对互作用系统进行了模拟和计算,优化了工作参数,计算了磁场及电子注参数对输出功率及效率的影响。最后,用粒子模拟方法进行了模拟并与非线性理论结果进行了比较,两者符合得很好。模拟结果显示,当电压为10 kV、电流为0.3 A、磁场强度由2.34 T 增加到2.41 T 时,输出功率由1310 W 减小到230 W,对应的效率分别为43.6%和7.7%,振荡管的频率可调范围约为2.7 GHz。     

某高硫铜硫矿工艺矿物学研究

研究了某高硫铜硫矿的工艺矿物学。结果表明,原矿中铜品位为2.85%,硫品位为24.32%,金含量为0.48g/t,铜、硫、金是主要回收的元素。原矿中的金属矿物有黄铜矿、黄铁矿、蓝辉铜矿。目的矿物黄铜矿和黄铁矿的嵌布粒度差异较大,且铜矿单体解离度相对较差。在选择工艺流程时应该注重氧化铜矿物的回收,同时要选择合适的磨矿细度,保证目的矿物单体解离。     

Scheduling distributed flowshops with flexible assembly and set-up time to minimise makespan

The scheduling problems under distributed production or flexible assembly settings have achieved increasing attention in recent years. This paper considers scheduling the integration of these two environments and proposes an original distributed flowshop scheduling problem with flexible assembly and set-up time. Distributed production stage is deployed several homogeneous flowshop factories that process the jobs to be assembled into final products in the flexible assembly stage. The objective is to find a schedule, including a production subschedule for jobs and an assembly subschedule for products, to minimise the makespan. Such a scheduling problem involves four successive decisions: assigning jobs to production factories, sequencing jobs at every factory, designating an assembly machine for each product and sequencing products on each assembly machine. The computational model is first established, and then a constructive heuristic (TPHS) and two hybrid metaheuristics (HVNS and HPSO) are proposed. Numerical experiments have been carried out and results validate the algorithmic feasibility and effectiveness. TPHS can obtain reasonable solutions in a shorter time, while metaheuristics can report better solutions using more yet acceptable time. HPSO is statistically comparable yet less robust compared with HVNS for small-scale instances. For the large-scale case, HPSO outperforms HVNS on both effectiveness and robustness.     

Precipitation location of secondary phase and microstructural evolution during static recrystallization of as-cast Ti-25V-15Cr-0.3Si titanium alloy

The microstructural evolution and precipitation location of the secondary phase of an as-cast Ti-25V-15Cr-0.3Si titanium alloy were investigated via isothermal compression experiments and heat treatment. The average aspect (length-to-width) ratio, average area and size of the grains at different heat treatment temperatures and holding time were analyzed and the effects of deformation and annealing time on the grain area and size were considered. It was found that the grain size was strongly influenced by the height reduction and holding time. Grain growth was significant when annealing time increased from 10 min to 2 h at 950 °C and height reduction of 30%; however, grain growth was minimal at annealing time between 2 and 4 h. Many dispersion particles were observed to form in continuous chains; the precipitation location was confirmed to be along initial grain boundaries, and the dispersion particles were identified to be Ti₅Si₃ phase by TEM.     

微裂隙中水泥浆液渗滤效应的可视化试验研究

在微裂隙岩体注浆过程中,水泥浆液的渗滤效应对注浆效果的影响显著。自主研制了一套微裂隙注浆可视化试验系统,该系统由注浆系统、微裂隙模型以及监测系统3个部分组成,监测系统又分为显微监测系统和压力流量监测系统。当水泥浆液进入微裂隙模型后,利用显微监测系统对裂隙入口处的渗滤效应进行实时观测。利用压力流量监测系统对注浆试验过程中的注浆压力以及累计流量进行自动记录。运用自主设计的微裂隙注浆可视化试验系统,对微裂隙中的水泥浆液渗滤过程进行试验研究。采用3种水泥浆材(超细水泥Ⅰ、超细水泥Ⅱ和普通水泥),研究在注浆压力2.0 MPa、水灰比1.0的条件下,不同水泥颗粒粒径大小在不同裂隙开度下的浆液渗滤效应。通过试验发现,当裂隙开度较小时,在裂隙入口处形成了完整的半圆拱形滤饼;随着裂隙开度的增加,在裂隙入口处形成断续分布状滤饼;当裂隙开度增加到无渗滤发生时,裂隙入口处仅残留少量水泥颗粒附着物。通过试验获得了3种水泥的最小可注入裂隙开度大小b min和最小无渗滤裂隙开度大小b crit:超细水泥Ⅰ的b min和b crit分别为80和280μm;超细水泥Ⅱ的b min和b crit分别为100和300μm;普通水泥的b min和b crit分别为140和310μm。研究结果发现水泥粒径的减小对最小可注入裂隙开度大小的影响较大,但对最小无渗滤裂隙开度大小的影响较小。结合渗滤趋势k值,发现随着水泥粒径的减小,相应的k min和k crit值会随之增加,水泥浆液更容易在裂隙入口处发生渗滤,这是因为超细水泥比表面积更大,水泥颗粒间易发生团聚。     

Effects of particle fouling and magnetic field on porous fin for improved cooling of consumer electronics

The combined effect of particulate fouling and magnetic field on the efficiency of a convective–radiative porous fin heatsink with temperature‐dependent thermal conductivity is presented. The developed thermal models are solved using differential transformation method. The effects of thermal conductivity, porosity, convection, radiation parameter, and thermal fouling number on the fin thermal efficiency are investigated. The presence of thermal fouling on the surface of the fin is shown to increase the temperature distribution. The presence of particle deposition on the fin surface significantly decreases the rate of heat transfer as additional thermal resistance of the fouling layer decreases the thermal performance of porous fin heatsink. Moreover, the fin efficiency decreases as the value of fouled Biot, Darcy, radiation number, and thermogeometric parameter increases. It is established that M_f < M_c, which indicates that the efficiency of the fouled fin is greater than the efficiency of the clean fin. Furthermore, the result of the present study is validated with the established results of Chebyshev spectral collocation method and fourth‐order Runge–Kutta with shooting method and an error margin of 0.000000023 is established.