Heat transfer performance evaluation for turbulent flow through a tube with twisted wire brush inserts

In the present study, the heat transfer performance and friction factor characteristics in a circular tube fitted with twisted wire brush inserts were investigated experimentally. The twisted wire brush inserts were fabricated with four different twisted wire densities of 100, 150, 200, and 250 wires per centimeter by winding a 1 mm diameter of the copper wire over a 5 mm diameter of two twisted iron core-rods. Heat transfer and friction factor data in tubes were examined for Reynolds number ranging from 7,200 to 50,200. The results indicated that the presence of twisted wire brush inserts led to a large effect on the enhancement of heat transfer with corresponding increase in friction factor over the plain tube. The Nusselt number and friction factor of using the twisted wire brush inserts were found to be increased up to 2.15 and 2.0 times, respectively, than those over the plain tube values. Furthermore, the heat transfer performance was evaluated to assess the real benefits of using those type of inserts and the performance was achieved 1.85 times higher compared to the plain tube based on the constant blower power. Finally, correlations were developed based on the data generated from this work to predict the heat transfer, friction factor, and thermal performance factor for turbulent flow through a circular tube fitted with the twisted wire brush inserts in terms of wire density (y), Reynolds number (Re), and Prandtl number (Pr).     

CNTs增强Cr基复合电刷镀层的性能

以45号钢为基体,采用电刷镀制备了Cr-CNTs复合镀层。通过X射线衍射仪(XRD)、扫描电镜(SEM)、扫描电子显微镜附带能谱仪(EDS)等技术对镀层的晶粒尺寸,截面与表面形貌及CNTs在镀层表面的分布进行了表征。此外,利用显微硬度计、电化学工作站、磨损试验机等仪器对镀层的硬度、抗腐蚀性、耐磨性等进行了测试。研究结果表明:Cr-CNTs复合镀层组织致密无明显缺陷,CNTs弥散分布于镀层中,在胞状组织的交界处出现了富集;适量CNTs的加入在一定程度上细化了镀层的晶粒;在CNTs弥散强化和细晶强化等作用下,复合镀层的硬度提高了23.8%,腐蚀速率降低了49.2%,而且耐磨性能也得到了显著的改善。     

大型直流电机运行维护与保养

通过分析换向器与碳刷之间产生火花的原因,分别介绍了换向器及电刷的维护方法,并对换向器的车削方法和测试标准进行了介绍,消除了隐患,并减少故障发生率,保证设备的正常运行。     

Improved performance of a tubular microbial fuel cell with a composite anode of graphite fiber brush and graphite granules

In this study, a composite electrode combined of a graphite fiber brush and carbon granules (MFC-GFB/GG) was adopted as the anode of a tubular microbial fuel cell (MFC). Compared with an MFC with graphite granules (MFC-GG) and an MFC with a graphite fiber brush (MFC-GFB), MFC-GFB/GG showed a longer lag time during the start-up process, while it reached the highest operating voltage at 50 Ω. Furthermore, during the stable operation, the MFC-GFB/GG achieved the highest power density of 66.9 ± 1.6 W m⁻³, which was about 5.3 and 1.2 times as that of MFC-GG and MFC-GFB, respectively. The highest performance of the MFC-GFB/GG can be attributed to the highest active biomass content on the electrode and the smallest internal resistance of the MFC. The optimum COD concentration was found to be 500 mg COD L⁻¹ for MFC-GFB/GG.     

精梳机毛刷的创新

为解决普通毛刷脱毛、掉毛的问题,分析了毛刷对精梳纱品质的影响及普通毛刷存在的缺陷,介绍了一种新型毛刷。该毛刷采用热植棕毛技术,把棕毛与毛刷体合成一个整体,使毛刷的使用寿命延长2～3倍,降低了纺织厂生产成本;棕毛弹性持久,清洁作用良好,提高了设备的使用效率。     

基于PLC控制的多方位自动刷鞋机

为了实现多方位刷鞋的功能,设计一款刷鞋机,主要对其刷鞋部分的机构进行了创新型设计。利用皮带轮机构和凸轮机构传动带动毛刷运动,多方位清洗鞋子的内部和外表面,达到刷洗鞋子的目的。整个洗刷过程采用三菱PLC自动控制。该设计结构巧妙,成本低,体积小,工作稳定,性能可靠,效果良好。     

原料对低铜电刷导电性能的影响

以电解铜粉和天然石墨的混合粉为原料,采用压制、烧结工艺制备电刷试样,研究电解铜粉松装密度和石墨粒度对低铜电刷导电性能的影响,并与以铜包石墨粉为原料制备的电刷进行对比.用SEM观察粉末和试样的形貌,用电碳制品电阻率测试仪测定试样的电阻率.结果表明:以混合粉为原料制备的电刷,当铜含量w(Cu)为30％时,随着电解铜粉松装密...     

铁路转辙机系统中的无刷直流电机驱动器的设计

本文简要分析了当前我国铁路转辙机95％以上使用有刷直流电机现状,针对这种基于有刷电机的转辙机的安全隐患,提出采用无刷直流电机的方案,并对基于无刷直流电机方案的驱动部分进行了设计.本文选用控制技术成熟稳定,抗干扰性强的无刷电机控制专用芯片MC33035和MC33039为控制核心.分别对该驱动系统的电源接口部分、开关电源部分、功率部分、调速系统进行了设计.根据转辙机的特殊工作环境,整体设计考虑三防.将本文设计的产品与传统有刷相比做对比实验,表明本设计的产品环境适应能力更强,安全性更好,具有十分重要的工程前景.     

ROS-sensitive selenium-containing cationic brush polymer with potent gene transfection efficiency and biocompatibility

Smart gene delivery vectors are gaining increasing attention in gene therapy, owing to their low cytotoxicity and intrinsic responsiveness. Our previously fabricated novel cationic brush polymer, comprising C Se bonds and tertiary amine EGIn-g-PDMAEMA, shows potential for gene transfection. In this study, its high efficiency for siRNA/pDNA transfection and low cytotoxicity in reactive oxygen species (ROS)-rich microenvironments is substantiated in vitro. Its superior binding capacity with siRNA/pDNA is confirmed by agarose gel electrophoresis assay. The threshold weight ratios for siRNA/pDNA migration delay are 15 and 3 (polymer-to-nucleic acid, w/w), respectively. Fluorescence microscopy and ribonucleotide reductase regulatory subunit M2 gene silencing essay verify the biodegradability and responsive control release of nucleic acids under hydrogen peroxide stimulation in Huh-7 cells. Compared with the gold standard, polyethylenimine 25 kDa, the target polymer displays superior transfection efficiency in ROS-rich tumor cells under serum-free conditions. Furthermore, the vector–nucleic acid complexes exhibit over 90% cell viability at a high concentration of 12 μg mL⁻¹ and good colloidal stability in phosphate-buffered saline (PBS) and 10% fetal bovine serum-PBS for 24 h. The efficient control release and expression of nucleic acids in ROS environments and reduced cytotoxicity highlight the superiority of EGIn-g-PDMAEMA as a gene delivery platform for tumor gene therapy.     

3900kW同步电动机电刷跳火问题的解决

介绍了为解决3900kW同步电动机电刷跳火问题采取了多种措施,最后使问题得到了解决。