基于空气幕与排烟系统的隧道火灾烟气控制研究*

为研究隧道火灾时空气幕与排烟系统复合模式下的烟气蔓延规律,优化选择防排烟方式,以某越江隧道为研究对象,运用FDS数值模拟方法探究射流速度、排烟量和空气幕与排烟口间距对防排烟效果的影响。结果表明:空气幕与排烟口间距对射流特性与烟气蔓延有较强影响,间距为30 m的控烟效果最佳;空气幕与机械排烟复合作用的控烟效果远优于每个独立系统,可实现可靠挡烟和有效排烟;当火源功率20 MW时,随空气幕射流速度的增加挡烟效果有所增加,但射流速度不宜过大,取20~30 m/s;机械排烟对温度与可见度影响比空气幕作用效果显著,一定程度上增加排烟量可降低所需气幕射流速度;综合考虑防排烟的有效性和经济性,取射流速度为20 m/s、排烟量为100 m3/s为最优防排烟组合方式。     

Physical,Mechanical, and Morphological Characteristics of Extruded Starch Acetate Foams

Starch acetates with degrees of substitution (DS) of 0.57, 1.11, 1.68, and 2.23 were prepared and extruded with either water or ethanol. The microstructure, physical properties (radial expansion ratio [RER] and unit density), mechanical properties (spring index [SI] and compressibility), and crystalline structure of the foams were investigated. The functional properties were a function of DS and blowing agent type. When water was used as the blowing agent and DS increased, the foams were pale yellow, with rough and uneven surfaces. The cells were dense, with thick cell walls. Lower RER and SI, with higher DS, were associated with high unit density and compressibility. When ethanol was used as the blowing agent, contrary results were observed. The snow-white foams had smooth surfaces, uniform cells, and smooth cell walls. High RER and SI, and low unit density and compressibility were observed. The changes in SI and compressibility with RER also were examined and found to depend on the type of solvent. A crystalline pattern was observed because of the formation of well-ordered structures during extrusion.     

Fabrication Mechanical Properties of Unidirectional Jute/PP Composites Using Jute Yarns by Film Stacking Method

This paper mainly focuses on the fabrication process of long fibre reinforced unidirectional thermoplastic composites made using both natural (untreated) treated jute yarns. Jute yarns were wound in layers onto a metallic frame. Polypropylene films were inserted between these layers and compression moulded to fabricate unidirectional jute/PP composite specimens. Static mechanical properties were evaluated from tensile three point bending tests. Pre- post-failure examination were carried out on the test specimens using optical scanning electron microscopy to analyse the test results and investigate the correlations between their impregnation state, processing conditions, mechanical performances and fracture morphologies. For the unidirectional jute/PP film-stacked composites, the results indicated that the processing condition at the moulding temperature of 160°C and moulding pressure of 2.0 MPa for 15 min was ideally suited to obtain optimized properties. Improved wettability of resin melts due to complete matrix fusion at this processing condition facilitated thorough impregnation with minimum microstructural imperfections (microvoids) being generated. Jute/PP composites that contained treated jute yarns have shown superiority in tensile bending properties. Jute yarns polished or coated with PVA/PP (polyvinyl alcohol/polypropylene) must have contributed positively to fibre/matrix interfacial interactions leading to matrix to fibre effective stress transfer, thereby improving their reinforcing effects. Tensile strength and modulus of PP resin increased by approximately 285% and 388%, respectively, due to 50 wt% reinforcement by natural jute yarns. Further improvements in strength and modulus were achieved by approximately 14% and 10%, respectively, when treated yarns were used . The maximum bending stress modulus of jute/PP composites containing untreated yarns were approximately 190% and 460% higher than those of the virgin PP materials, and bending properties were improved by further 11% and 23%, respectively, due to coating treatments on the yarn surface.     

频域子结构方法在力学环境预示中的应用研究

目的利用频域子结构方法(FBSM,FRF Based Sub-structuring Method)对结构的力学环境进行准确高效地预示。方法分别对处理子结构间为刚性连接和弹性连接两种问题的FBSM进行理论推导。为了验证FBSM的正确性,设计连接为刚性连接和弹性连接两种算例结构,并将FBSM对算例结构频响函数的计算结果与有限元方法(FEM,Finite Element Method)的对应计算结果进行对比。其中,弹性连接利用空间梁单元进行等效,并将该等效方法与利用六自由度标量弹簧的等效方法进行对比。结果对于刚性连接和弹性连接两种情况,FBSM对频响函数的计算结果均与FEM的对应计算结果吻合程度良好。此外,空间梁单元的结点刚度矩阵为非对角阵,与六自由度标量弹簧相比,可更为准确地等效工程实际中的弹性连接。结论FBSM可对结构的力学环境进行准确高效的预示,且在处理具有弹性连接结构的力学环境预示问题时,可采用空间梁单元等效弹性连接。     

等离子球磨机的研制及其振动平台试验

目的实现球磨室在常压下的大面积介质阻挡放电等离子体,开发出商用等离子球磨机。方法通过在不同弹簧和平台质量条件下,利用振动传感器测试平台的振幅(峰峰值)和加速度(有效值)数值,对比确定最优配置和机械振动参数。结果当振动平台振幅接近球磨室内径时,获得高振幅和高加速度的磨球,显著缩短了气体放电间距,实现了球磨室在常压下的大面积介质阻挡放电等离子体。所设计的单筒等离子振动球磨机,其振动平台可选用φ7 mm、φ8 mm两组弹簧,根据平台质量的不同,选择不同类型的激振块组合,可以在30 Hz转速以上实现平台振幅峰峰值达到或者接近球磨罐内径值,同时拥有10g以上的加速度有效值。结论本试验综合机械振动学、高压绝缘放电和材料加工技术,所研制的等离子体球磨机实现了机械能和等离子体能在球磨过程中的协同作用,显著提高了粉末活性,降低了化合物合成反应激活能,从而显著提高了所制备材料的性能。     

电选法回收利用废印刷线路板

废印刷线路板含有多种有价值的物质,随意丢弃或处理处置方法不当既污染环境,又造成资源流失。采用剪切式破碎和电力分选技术对废印刷线路板的机械分离进行了研究。结果表明,电选法可以实现废印刷线路板中金属和玻璃纤维、树脂的分离;在实验的粒径范围内(-14+20目到-120+200目分为5个粒径级别),金属主要集中在-20+120目粒级范围内,且该粒级范围分选效果最好。     

含铌微合金钢焊接性能研究

采用金相及透射电镜等方法研究了含铌微合金钢 14MnNbq焊接时焊缝区的组织特征 ,测试了其力学性能 ,结果表明钢中由于Nb的存在 ,使焊接区及热影响区组织发生变化 ,粗晶区得到细化 ,同时降低了焊缝脆化的倾向 ,使钢具有良好的焊接性能与力学性能。     

轴装式转碟曝气机的研制

针对转碟曝气机在使用过程中出现的问题,进行重新设计,改善受力状况和工作条件,提高设备运行的可靠性,减少维护工作量,降低维护的难度和费用。     

Use of recycled plastics in wood plastic composites – A review

The use of recycled and waste thermoplastics has been recently considered for producing wood plastic composites (WPCs). They have great potential for WPCs manufacturing according to results of some limited researches. This paper presents a detailed review about some essential properties of waste and recycled plastics, important for WPCs production, and of research published on the effect of recycled plastics on the physical and mechanical properties of WPCs.     

MPP协同MF@ADP阻燃低密度聚乙烯性能研究*

为提高低密度聚乙烯（LDPE）阻燃性能和阻燃LDPE复合材料的力学性能与抑烟性能,采用原位聚合法制备三聚氰胺-甲醛（MF）树脂包覆二乙基次磷酸铝（ADP）的MF@ADP微胶囊,再引入三聚氰胺聚磷酸（MPP）与MF@ADP进行协效复配,熔融共混制备阻燃LDPE复合材料。通过氧指数、热重分析、力学测试和烟密度测试等研究复合材料的阻燃、力学和抑烟性能。研究结果表明:MF@ADP微胶囊能改善阻燃剂与复合材料之间的相容性,与MPP复配构成的磷-氮膨胀阻燃体系能有效提高LDPE的抑烟性能;当MF@ADP∶MPP的质量比为2∶1时,材料的LOI达到了30.6%,垂直燃烧测试达到UL-94 V0级,拉伸强度为11.8 MPa,且形成的P/N/O高聚物炭层稳定性更高,可减少LDPE燃烧释放的烟雾量。