Small and large scale segmental motion in polymers: estimating cooperativity length by ordinary relaxation experiments

We derive a suitable expression for estimating the size of the cooperatively rearranging regions (CRRs) in supercooled polymer melts by fitting data worked out by ordinary relaxation experiments carried out in isothermal conditions. As an example, the average CRR size in poly(n‐butyl methacrylate) in proximity to the glass transition temperature is derived from a stress relaxation experiment performed by means of an atomic force microscopy setup. Good agreement is found with results in the literature derived from measurements of temperature fluctuations (the so‐called Donth method). The temperature dependence of the CRR size is explored for poly(butadiene); in this case the segmental relaxation function is derived through a novel method for the analysis of the efficiency with which free induction decay echoes are refocused in ¹H NMR experiments. It is found that the CRR size increases upon cooling. The results derived from the analysis of the NMR data are found to be in satisfactory agreement with those worked out from broadband dielectric spectroscopy data in the literature. © 2015 Society of Chemical Industry     

新型六分扇形螺旋折流板换热器壳程传热及流动特性

针对现有四分螺旋折流板换热器中心区域漏流明显的特征,提出了一种新型的六分扇形螺旋折流板换热器。建立了六分扇形螺旋折流板换热器的三维物理模型,应用Ansys CFX软件对其壳程流动与传热特性进行数值模拟,分析了不同螺旋角(10°、20°、30°、40°)和不同工况下六分扇形螺旋折流板换热器的壳侧性能,并与传统的弓形折流板换热器作对比。结果表明,六分扇形螺旋折流板可以显著减少三角区漏流现象的发生,壳程流体旋流特性较好。随着螺旋角的增大,壳侧速度场与温度场分布更加均匀,综合换热性能逐步提高。     

Development of a new thermoplastic laminate system

In this investigation an all-olefin thermoplastic laminate was developed and characterized. Commingled glass-fiber polypropylene (PP) composite was used as skin and HDPE (PE) foam with closed cells as core. Infra-red heating was used for melting the surfaces of the substrates for surface fusion bonding with a cold press. Two tie-layer films, viz., ethylene-propylene copolymer (EPC) and HDPE/elastomer blend were used as hot-melt adhesives for bonding the substrates. Singlelap shear joints were prepared from PP composite and PE foam adherends with a bonding area of 25.4 mm × 25.4 mm to determine the bond strength. EPC tie-layer adhesive provided higher bond strength (2.68 × 10⁶ N/m²) to the all-olefin laminate than that based on HDPE/elastomer blend (1.93 × 106 N/m²). For EPC tie-layer-based laminates, a mixed mode of failure was observed in the failed lap shear samples: about 40% was cohesive failure through the tie-layer, and the rest of failure was interfacial, either at PP composite or PE foam surfaces. Environmental scanning electron micrographs (ESEM) revealed that in the process of surface fusion bonding, PE foam cells in the vicinity of interphase (800-μm-thick) were coalesced with high temperature and pressure. No macro-level penetration of the tie-layer melt front into the foam cells was observed. As the surface morphology of foam was altered due to IR surface heating and the PP composite bonding side had a resin-rich layer, the bonding situation was closer to that between two polymer film surfaces.     

山地高落差地形焦化升级改造项目的设计和建设

由于鑫泰能源处山地地形且无法进行空间扩展,焦化升级改造项目需建设在水平标高高于原生产系统12 m的地形位置,且在凉焦台和运焦通廊的下方是无法占用的国家铁路线,需综合利用山地地形高落差的特点进行项目设计和建设。通过大跨度输送物料,悬空在火车轨道上方建设凉焦台、拦焦轨道、人员行走平台等设备设施,设置天车转运检修熄焦车等方式,合理布置XJL6253D型捣固焦炉的装置和环保除尘设施,解决了物料输送和装置安装等方面的问题,在不影响原有焦化系统正常运行的情况下,完成升级改造项目的设计和建设工作,并综合利用原有煤气净化系统。     

超大跨径三塔悬索桥加劲梁吊装方案

为了寻找超大跨径三塔悬索桥建设中更为有利的加劲梁吊装方案,以主跨2 000 m三塔悬索桥为对象,运用参数分析结合有限元数值模拟的方法研究了主、边跨加劲梁不同吊装顺序对边塔鞍座偏移量、主缆线型、合龙位置、合龙段施工方法以及吊装过程中结构动力响应的影响.结果表明,超大跨径三塔悬索桥主跨加劲梁宜从跨中向索塔方向吊装,边跨加劲梁宜从锚碇向边塔方向吊装,该方案下主缆水平倾角小,扭转基频较大,颤振稳定性更好,且采用预偏合龙方法时所需要的牵引力小,因而按该方案吊装对桥梁建设更为有利.     

武昌火车站无站台柱雨棚钢管桁架结构安装技术

根据铁路车站无站台柱雨棚多专业同期施工和吊装只能在夜间停轮点或股道封锁要点的实际情况,在不影响铁路客运既有线正常运营的环境下,经过对无站台柱雨棚工程施工的细致分析,摸索总结出一套安全高效的安装方法,对同类型工程施工具有一定的指导价值。     

Practical crack control during the construction of precast segmental box girder bridges

Cracks that occurred in the bottom slab of a precast segmental bridge were investigated through a construction sequence analysis, which revealed that the cracks were caused by excessive deformation during temporary post-tensioning while joining the segments. In addition, a parametric study was performed to evaluate the effects of the prestressing sequence, bottom slab thickness, and position of the prestressing anchors. The structural behavior of the girder sections was greatly affected by the thickness of the bottom slab and the position of prestressing anchors, but not by the prestressing sequence. Based on the results, a construction method that prevents the cracks is proposed.     

锅炉构架叠梁的安装工艺

韶关发电厂300MW机组W形火焰锅炉承重构架有3根大板梁为叠梁，由梁和下梁叠合为整体梁。在安装施工时，由于叠梁的长度和高度较大，必须把下梁和上梁分别吊装，就位后才组合，使得安装存在一定的难度。对此，分析了叠梁的设计特点并提出了合理的安装工艺。该施工方案解决了受场地所限造成的吊机布置问题和解决了下梁就位后处于简支梁状态的下梁因自重所产生的向下挠度问题，使上、下梁就位后能顺利装配。实践证明，施工方案是可行的，达到了预期目的。     

谈预制预应力空心桥板的施工监理质量控制

论述了预应力钢筋混凝土预制空心桥板支模、拆模和钢筋、预应力钢绞线等监理工作要点，以利于提高监理工作质量。     

偏心振捣搭设钢架平台的应用

随着我国水利基础设施建设的快速发展,钻孔灌注桩作为一种基础处理形式被广泛地应用于水利堤防、沿海围垦、内河闸站及其他工程领域。但由于影响灌注桩施工的因素很多,所以对其施工过程每一环节都必须严格要求,特别是针对某些无法直接陆地施工的特殊地段,需要搭设钢架平台代替陆地施工。结合水上钻孔灌注桩的施工特点,利用偏心振捣器的偏心振捣原理,用手动葫芦辅助下沉配合施工搭设钢架平台,代替了以往船上挖机压打钢管搭设钢架平台的施工,加快了钢架平台的搭设进度,节省了成本,减少了安全隐患。