中国城市热岛时空特征及其影响因子的分析

全球气候变暖背景下,城市热岛效应会加重城市地区的热胁迫,对人类健康和生存发展提出严峻挑战.近年来我国雾-霾污染情况严重,但雾-霾对城市热岛影响的认识仍较匮乏.本研究基于MODIS遥感卫星地表温度数据,明确了我国2003~2013年白天、夜间以及四季城市热岛的空间变化,并从生物物理学和生物化学角度定量分析其控制机制.结果表明,影响我国白天城市热岛强度的主要因素为人口、农田灌溉和植被活动.纬度、降水量、反照率以及气溶胶浓度是夜间城市热岛强度的主控因子.从对比城乡粗糙度、反照率等生物物理学属性的角度,揭示了乡村背景环境对城市热岛分析的重要影响.结果表明,雾-霾治理可以缓解我国夜间城市热岛现象和热胁迫,有利于缓解区域甚至全球气候变化.     

不同CDPF贵金属负载量对柴油公交车VOCs组分排放影响

基于重型底盘测功机,利用质子转移反应质谱(PTR-MS)研究了柴油公交车在中国典型城市公交车循环(CCBC)下,不同CDPF贵金属负载量对尾气中挥发性有机物(VOCs)组分排放特性的影响.结果表明,柴油公交车VOCs主要组分为含氧有机物(OVOCs)、芳香烃和烯烃等,且OVOCs占比达50%以上;在贵金属成分、配比相同时,VOCs减排率随CDPF贵金属负载量增加而增加:贵金属负载量为15 g·ft~(-3)(A型后处理装置)、25 g·ft~(-3)(B型)和35 g·ft~(-3)(C型)时,VOCs总量的减排率依次为36.2%、40.1%和41.4%.C型后处理装置对烷烃全循环减排率高达70.2%,且对OVOCs的催化有微弱优势;对于不饱和烃类,3种不同贵金属负载量的后处理装置均有一定催化效果,但无明显差异;A型对含氮有机物减排率可达50.5%,但减排率随贵金属负载量增加而降低.采用DOC+CDPF后能较好地降低公交车VOCs排放量进而降低臭氧生成潜势(OFP).同时考虑不同方案减排效果与成本因素,当加权系数分别为0.8和0.2时,B型为最优方案.     

铝合金-丁腈橡胶航空带垫卡箍典型环境损伤研究

目的研究典型环境对丁腈橡胶-铝合金带垫卡箍的损伤效应。方法通过模拟铝合金-丁腈橡胶航空带垫卡箍使用时的装配结构和应力状态,应用GJB 150A—2009中的湿热和太阳辐射两种典型老化环境,采用宏观形貌观察、卡箍保持力测试和橡胶衬垫拉伸性能测试方法,结合扫描电子显微镜和傅里叶红外光谱技术,分析带垫卡箍的性能劣化过程。结果带垫卡箍在湿热和太阳辐射环境中老化50 d后,卡箍橡胶衬垫表面出现大量微孔缺陷,拉伸性能大幅降低,导致卡箍保持力分别下降了35%和51%。结论带垫卡箍在模拟装配状态下进行湿热和太阳辐射环境暴露实验,卡箍橡胶衬垫内部结构由致密逐渐变得疏松,部分碳碳双键发生氧化交联反应,并在一定程度上提高了聚合物的交联密度,材料硬度提高,回弹性能减弱,橡胶衬垫对芯轴的包裹能力降低,导致卡箍保持力性能降低。     

金属尖化前缘模型主动式热疏导性能试验研究

目的为了更好地解决高超声速飞行器舵、翼前缘及头锥等气动热环境恶劣区域的热防护问题。方法采用主动式热疏导技术,以高温液态合金为工质,设计并制作具有主动式热疏导功能的尖化前缘金属试验模型(R=5 mm)。根据模型外尺寸设计加工一套石英灯仿形加热器和热流测试模型,开展地面热环境模拟试验。结果试件在前缘中心温度530℃左右时具有瞬态启动特性。前缘中心和大面积中心最大辐射热流密度分别为1000 kw/m^2和580 kw/m^2,试件在该环境中长时间受热状态下仍具有较好的热疏导能力。试验后试件无工质泄漏和结构破坏,具有一定的可重复使用性。结论可以此热疏导方式结合现有成熟热防护技术进一步开展工程设计与应用。     

湘中矿区不同用地类型面源Cd输出负荷的原位实验研究

受污染土壤重金属随降雨径流输出已成为河流、湖泊等水体重金属超标的主要来源之一,近年来日益受到关注.研究表明湘江中下游农田土壤重金属超标问题日益严峻,以镉超标最为严重.研究以湘中矿区Cd超标农业小流域为实验场,选取流域内水稻、旱田、荒草地这3类土地利用模式设置径流小区进行自然降雨水文过程的原位观测.结果表明,雨水pH值由春季到夏季呈升高趋势,径流水相溶解态Cd浓度呈明显的季节性差异,春季显著高于夏季,雨水pH值可显著影响土壤溶解态Cd向径流水相迁移,与径流水相溶解态Cd浓度呈负相关关系.相同降雨条件下,稻田径流水相溶解态Cd浓度显著低于旱田和荒草地,旱田与荒草地Cd面源输出负荷显著高于水稻田,由于降雨量差异,3类土地利用类型溶解态Cd面源输出负荷的季节性规律不明显.本研究可为流域尺度重金属面源输出负荷定量估算以及湘江流域水环境安全与水质预警提供数据支持和科学依据.     

Minimizing leakage from a smelter off-gas system by enhanced control

The off-gas handling system is a vital component of a smelter and it is essential that it operates in accordance with environmental regulations. A key feature of the off-gas management system is maintaining a slightly negative system pressure to prevent gas leakage, such as SO₂, out into the work and external environments. To enhance sustainable development, there is also growing interest in capturing and reusing the significant amount of heat and CO₂ contained within off-gas. The potential incorporation of heat and CO₂ recovery systems places importance on enhancing control to minimize the risk of both gas leakage and disturbance of the smelting process. With these requirements in mind, an easily implementable feedforward control enhancement to existing control schemes is proposed to help provide improved performance.     

Environmental and economic assessment of a greenhouse waste heat exchange

As the economic costs of energy and the negative externalities associated with the combustion of fossil fuels threaten the economic viability of greenhouses in northern climates there is a renewed interest in the use of waste heat. This paper presents a technical and economic methodology to determine the viability of establishing waste heat greenhouses using the waste heat from industrial processes in northern climates. A case study is presented of an exchange between a tomato greenhouse and a flat glass manufacturing plant, which found the waste heat system is significantly more economic to operate than a purely natural gas system.     

动力与热力抬升对烟气抬升高度的影响分析

通过模式选择和计算,得出烟气抬升高度的增加与动能和热能的关系,表明当烟囱出口处风速分别为3 m/s、2 m/s和1 m/s时欲增加同样大小的烟气抬升高度,需要的动能比热能要高,结论认为烟气的热力提升比动力提升的贡献大。     

Microstructure of 2205 duplex stainless steel joint in submerged arc welding by post weld heat treatment

The 2205 duplex stainless steel (DSS) is of both good properties austenitic steel and ferritic steel, which applies to the shipbuilding industry usually. In this paper, the OM, XRD and microhardness test methods are used to analyze the variation of submerged arc welded (SAW) joints with and without post weld heat treatment (PWHT). The research results show that the σ phase disappear in the fusion edge zone near heat affect zone (HAZ) and an increase in the welded center zone during the follow-up PWHT, while the amount of γ phase is decreased in the welded center zone with PWHT. A segregation distribution of some second phases is also found in the welded center zone after PWHT. There have two pick values of microhardness arise in the fusion edge zone and the welded center zone separately without PWHT. However, a maximum value of microhardness at the fusion edge zone near HAZ is disappeared and the other is still held at the welded center zone during PWHT. It can be attributed to the changes of second phases, element diffusions and particle segregation during PWHT. A developing mechanism is issued to demonstrate the second phases transferring of the 2205 DSS SAW joints by PWHT.     

Improvement of welding heat source models for TIG-MIG hybrid welding process

Tungsten inert gas-metal inert gas (TIG-MIG) hybrid welding process is an effective way to improve welding productivity and quality due to advantages of the two processes. Mathematical analysis is crucial to fundamentally understand this synergetic welding process. In this study, based on experimental visualization of arc behaviors, some assumptions are proposed to deduce adaptive plane and volumetric heat source models separately for each involved welding method first. The influence of torch angles on distribution of temperature and geometry of weld bead are calculated and compared with experimental results. It shows that this developed algorithm of heat source can be employed to accurately predict welding process whether the electrode gun is slanted backward or forward to the direction of welding. Then TIG-MIG hybrid welding process is simulated and analyzed without considering the attractive or repulsive force of two arcs. The characteristic of TIG-MIG welding process is discussed compared to single MIG. It lays the foundation for the further research on the interaction of the two arcs during TIG-MIG hybrid welding.