重型商用汽车长下坡制动器升温模型研究

针对重型商用汽车长大下坡路段行驶制动器温度过高而导致制动失效的问题,开展配备辅助制动器的重型商用车行车制动器升温模型研究。根据汽车动力学原理、能量转化原理以及热量耗散原理,基于车辆滑行试验、发动机制动试验、排气制动试验、电涡流缓速器制动试验建立制动器升温模型并通过道路试验对行车制动器升温模型的准确性进行验证,试验结果表明:基于道路试验的重型商用车升温模型能够准确反映制动器升温特性。该模型用于不同联合制动工况制动器温度预测,对防止热衰退问题引发交通事故有重要意义。

电火工品桥丝与药剂升温模型及在可靠性设计中的应用

介绍了桥丝式电火工品的电容放电和直流输入方式的桥丝升温模型、药剂升温模型及其数值求解算法 ,提出了估算感度的能量平衡方程和用于输入可靠性设计的理论计算方法。给出了一个算例 ,并与实际产品作了比较 ,结果表明 ,将该模型用于可靠性设计的理论计算是可行的。

建筑废弃物热污染环境下升温模型分析

当前的升温模型通常面向局部建筑废弃物区域,大多基于恒温控制理论进行分析,不同局部区域的升温过程要求一致,而实际的建筑废弃物热污染环境的升温速度具有多变性,导致传统方法具有一定的局限性,提出基于变温控制的建筑废弃物热污染环境升温模型,模型中融入升温速率系数,构建废弃物热污染区域升温数学模型,考虑建筑物废弃物释热率最大值、建筑物废弃物面积、距热污染区域距离以及变温因素,分析建筑废弃物热污染区域的升温过程。实验结果说明,该方法的检测误差小于传统方法,具有较高的可信度。

考虑木材燃烧效应的大空间体育馆木结构建筑火场升温模型研究

木结构建筑因具有美观环保的特点被越来越多的建筑设计师所采用,更多建筑形式优雅、结构受力可靠的大空间木结构建筑被设计出来。然而,木材作为一种易燃材料,在经历火场高温后会发生复杂的物理化学反应,热解会导致其力学性能的退化,且大空间火灾的升温情况与普通室内火灾有所不同,这阻碍了木结构建筑的推广应用。参考大空间建筑火灾的经验公式形式,建立了适合大空间木结构建筑的多点火源燃烧火场升温分析模型。基于火灾模拟软件FDS进行有限元建模,分析在木材燃烧效应下大空间木结构建筑内火场升温状态,研究建筑面积、建筑高度、火源功率等因素对于大空间火场升温的影响。研究结果表明,当建筑面积越大、建筑高度越高、火源功率越大时,火场的最高升温就越大,且大空间建筑内的顶棚区域是火灾最为严重的区域。经对比,所提出的大空间木结构建筑火灾升温曲线可满足结构设计过程中的安全性、经济性和适用性要求,为今后大空间木结构建筑的防火研究打下坚实的基础,并为后期木构件建筑温度场的分析提供理论依据。

基于PIARC制动升温模型的避险车道选址方法研究

基于PIARC制动升温模型,结合国内外研究成果和工程实际,在道路工程长大下坡的避险车道选址中,对避险车道设置的必要性、位置、间距和数量进行研究。结果表明:避险车道应依据PIARC温升曲线,再结合地形条件、《公路避险车道设计细则》(征求意见稿)的相关建议确定位置、间距和数量。

火灾下大跨空间结构升温模型的比较分析

为验证火灾下大跨空间结构采用的传统升温模型——标准升温曲线是否合理,经理论分析该升温模型与大空间空气升温模型对结构的性能和耐火极限的结论有着很大的不同。以2008奥运羽毛球场馆实际工程为背景,采用两种模型模拟火灾,对火灾下的结构进行性能分析。标准升温曲线得出在22 min左右结构坍塌。大空间空气升温模型则得出结构在90 min时仍没有坍塌,但个别构件内力、位移变化幅度较大。研究表明:大空间升温模型可以更贴切地体现大空间结构火灾下的实际响应。

低温热水辐射地板稳定升温计算模型

针对地板稳定升温过程,根据热平衡原理建立地板升温计算模型,给出地板升温表达式,利用该式可方便快捷地预测地板升温时间及地板终值温度。为验证方程有效性,通过改变供水温度、管间距、初始温度条件,将地板升温测试数据与方程计算结果进行比较,显示两者最大误差为5.8%,因此可将该模型用于实际;同时实测与计算结果一致显示地板升温过程为指数变化规律。

微波照射下火成岩升温特性和升温预测模型研究

微波辅助破岩可有效降低刀具磨损,提高破岩效率,具有广阔的发展前景。文章选取了10种火成岩进行微波加热试验,发现岩石的升温速率主要与岩石所含矿物的种类、含量,及岩石中的Fe元素含量有关。岩石所含矿物越敏感、含量越多,岩石中的Fe元素含量越大时,其升温速率越高。整体而言,火成岩中基性岩的升温速率最高、中性岩次之、酸性岩最低,该现象与火成岩的矿物和元素组成规律有关。在试验研究的基础上,文章提出了岩石升温预测模型。该模型除考虑了矿物种类和含量的影响外,还考虑了与升温有关的比例修正系数和结构修正系数。在升温预测模型中,敏感矿物升温的比例修正系数大于1,且随含量的增加而降低,最终趋向于1;非敏感矿物升温的比例修正系数小于1,且随含量的增加而增加,最终也趋向于1。同等条件下,块体的升温速率是粉末的2~3倍,且基性岩升温的结构修正系数大于中性岩和酸性岩。

尾巷瓦斯抽采下采空区煤自燃升温的数值模拟

针对尾巷抽采瓦斯抽放对长壁工作面采空区煤自燃升温影响的问题,利用化学反应动力学理论和换热关联式建立了包含热源和空气与固体换热关系的煤自燃升温模型,借助FLUENT软件计算了不同条件下采空区氧气稳态分布情况和温度动态变化过程。结果表明:同未抽放相比,深部大流量的瓦斯抽采会显著改变采空区流态,造成氧气向采空区纵深发展,煤自燃引起的升温速率会明显加快,高温区域范围扩大并向后移动。注氮可以将一定范围内的氧气浓度控制在较低的水平,并对控制范围内高温区域的升温速率随着时间推移起到不同程度的抑制作用,但对抽放口附近区域的温度抑制帮助不大。

长大下坡路段辅助减速车道设计

文章针对重型汽车在长大下坡路段的行驶安全问题,对辅助减速车道的设计进行研究。根据排气制动和液力缓速器联合制动的行驶模型,对重型车辆在长大下坡路段的下坡能力进行研究。根据下坡时制动器的温升模型,研究长大下坡路段的辅助减速车道位置设计问题。

煤自热低温阶段“自限制”特征的理论与试验研究

为深入分析煤自燃特性,以有效减少煤矿内因火灾,根据气固反应动力学相关理论,提出外部环境允许条件下煤氧反应低温阶段温度也并非始终“加速上升”,在一定时期会内出现“自限制”特征,基于此,对颗粒煤低温绝热条件下的反应步骤进行分析,推导出考虑界面效应的煤低温绝热氧化升温理论模型,然后根据4个不同变质煤样的绝热氧化试验结果进行论证。结果表明:煤颗粒的绝热氧化反应前期,温度随时间不断增长且升温速率随试验的进行而加快,呈类指数分布特征,但后期中低变质煤升温速率随试验进行开始逐渐减慢,服从半抛物线趋势变化;随着变质程度的提高,煤低温绝热氧化反应“自限制”温度有向高温方向偏移的趋势,极大升温速率逐渐降低;低温绝热氧化升温过程可分为物理吸氧放热升温阶段、自由加速升温阶段、受限减速升温阶段和全面反应阶段,其中受限减速升温阶段主要是由于“氧化层”界面作用产生,实际自燃状态分析中应注意该效应的影响。

荷载比对短T型钢连接件抗火性能的影响

火灾中钢结构的破坏与高温下钢材的强度和刚度的退化有关,尤其对外荷载的作用十分敏感。通过加载ISO834标准升温曲线的有限元模拟方法对工程中常见的短T型钢连接件进行温度场分析及在不同荷载比条件下的热-力耦合分析,并对极限承载力进行理论计算,最终判定结构的破坏模式。结果表明:火灾发生80 min后,连接件温度趋于973.7℃不变,之后持续的火灾对结构的承载力将不会产生不利影响。高温下短T型钢板焊缝处极易发生应力集中现象。此处应力大且易失效,当荷载比增大时此处应力将增大并向四周扩散,削弱短T型钢高温下的受力性能。在相同受火时间条件下,随着荷载比增大,结构同一位置处的应变增大,T型节点的临界温度变小。该研究为短T型钢抗火连接设计提供了依据。

局部火作用下大空间网架结构温升的数值计算

根据传热学的基本理论,建立了钢构件升温计算模型。通过编制Fortran程序,对局部火作用下大空间网架结构温升情况进行数值计算,并对温升的主要影响因素进行分析。结果表明:杆件与火源距离越近,温升越大;杆件截面系数越大,温升速率越大;火源功率不变时,改变火源面积,对杆件温升基本无影响;杆件与火源距离越远,其温升受火焰辐射的影响越小,随着火势的发展,杆件温升受火焰辐射的影响变小。经实例验证,编制的网架结构温度场数值计算程序正确简便,可用于大空间网架结构的耐火设计。

Study on ReactiveAdsorption Desulfurization of Model Gasoline on Ni/ZnO-HY Adsorbent

The reactive adsorption desulfurization of model gasoline was carried out on Ni/ZnO-HY adsorbent.The Ni/ZnO-HY adsorbent was characterized by N2adsorption-desorption test(BET),X-ray diffractometry(XRD),and temperature-programmed reduction(TPR)analysis.The test results have demonstrated that HY-zeolite is a feasible support for Ni/ZnO components used in reactive adsorption desulfurization.The results of XRD and TPR analyses showed that most of nickel element was present as Ni2+species with only a small part existing as Ni3+species,and the Ni2+species had interactions with HY-zeolite.Under the conditions of this study,which specified a 50% ratio of HY-zeolite in the adsorbent,a Zn/Ni molar ratio of 10,and a reduction temperature of 400℃,the Ni/ZnO-HY adsorbent showed the best desulfurization performance.The sulfur capacity of Ni/ZnO-HY adsorbent could be recovered to 92.19% of the fresh one after being subjected to regeneration at 500℃,and could be maintained at 82.17% of the fresh one after 5 regeneration cycles.

Optimal dynamic dispatch of surplus gas among buffer boilers in steel plant

As valuable energy in iron-and steel-making process,by-product gas is widely used in heating and technical processes in steel plant.After being used according to the technical requirements,the surplus by-product gas is usually used for buffer boilers to produce steam.With the rapid development of energy conservation technology and energy consumption level,surplus gas in steel plant continues to get larger.Therefore,it is significant to organize surplus gas among buffer boilers.A dynamic programming model of that issue was established in this work,considering the ramp rate constraint of boilers and the influences of setting gasholders.Then a case study was done.It is shown that dynamic programming dispatch gets more steam generation and less specific gas consumption compared with current proportionate dispatch depending on nominal capacities of boilers.The ignored boiler ramp rate constraint was considered and its contribution to the result validity was pointed out.Finally,the significance of setting gasholders was studied.

Thermodynamic properties of metamizol monohydrate in pure and binary solvents at temperatures from(283.15 to 313.15) K

The thermodynamic properties of metamizol monohydrate in pure solvents(methanol,ethanol,n-propanol and isopropanol) and two binary mixed solvent systems including(methanol+ethanol) and(methanol+isopropanol) were measured from 283.15 K to 313.15 K by gravimetric method under atmospheric pressure thought as 0.1 MPa.The modi fied Apelblat equation,the CNIBS/R-K equation,the Hybrid model and the NRTL model were used to correlate the solubility of metamizol monohydrate,respectively.The results show that the solubility of metamizol monohydrate in all the tested solvents increases with the rising temperature which means that it has temperature dependence.What's more,the effects of solvent components of the binary solvent mixtures on solubility were discussed,it illustrates that the increasing of the molar fraction of methanol gives the system a greater dissolving power.Furthermore,according to the NRTL model,the enthalpy,the Gibbs energy and the entropy of the mixing process were also obtained and discussed.

Two-and Three-Dimensional Urban Core Determinants of the Urban Heat Island： A Statistical Approach

There is no doubt that the UHI （urban heat island） is a mounting problem in built-up environments, due to the energy retention by surface dense building materials, leading to increased temperatures, air pollution, and energy consumption. Much of the earlier research on the UHI has used two-dimensional （2-D） information, such as land uses and the distribution of vegetation. In the case of homogeneous land uses, it is possible to predict surface temperatures with reasonable accuracy with 2-D information. However, three-dimensional （3-D） information is necessary to analyze more complex sites, including dense building clusters. In this research, 3-D building geometry information is combined with 2-D urban surface information to examine the relationship between urban characteristics and temperature. The research includes the following stages： （1） estimating urban temperature; （2） developing a 3-D city model; （3） generating geometric parameters; and （4） conducting statistical analyses using both linear and non-linear regression models. The implications of the results are discussed, providing guidelines for policies aiming to reduce the UHI.

UH model considering temperature effects

The influences of temperature on the mechanical behavior of saturated clays are discussed first. Based on the concept of true strength and the revised calculation method of the potential failure stress ratio, the equation of the critical state stress ratio for saturated clays under different temperatures is deduced. Temperature is introduced as a variable into the UH model （3-dimensional elastoplastic model for overconsolidated clays adopting unified hardening parameter） proposed by Yao et al. and then the UH model considering temperature effects is proposed. By means of the transformed stress method proposed by Yao et al., the proposed model can be applied conveniently to 3-dimensional stress states. The strain-hardening, softening and dilatancy behavior of overconsolidated clays at a given temperature can be described using the proposed model, and the volume change behavior caused by heating can also be predicted. Compared with the modified Cam-clay model, the proposed model requires only one additional parameter to consider the behavior of the decrease of preconsolidation pressure with an increase of temperature. At room temperature, the proposed model can be changed into the original UH model and the modified Cam-clay model for overconsolidated clays and normally consolidated clays, respectively. The considered temperature range here is from the melting point to the boiling point of the pore water （e.g. the experimental temperatures （20℃-95℃） mentioned in this paper are within this range）. Comparison with existing test results shows that the model can reasonably describe the basic mechanical behavior of overconsolidated clays under various temperature paths.

Model study of relationship between local temperature and artificial heat release

In recent decades,it presents a more obvious temperature rise in urban area along with the global warming.City is generally the center of human society,so the study on urban temperature variation will be helpful to our city development planning that is to reduce urban warming.The study is also helpful to a more comprehensive understanding of the causes of climate warming,which could provide a theoretical support to the government to make more reasonable international energy policies.Local temperature rise has different mechanisms with the global warming:large quantities of artificial heat release from the energy consumption will stay in urban areas for a period of time,which will inevitably influence the short-term trend of the local temperature change.Based on that view,a structural thermodynamic model was established in this paper to investigate the effect of the artificial heat release on the urban local temperatures.In the model,the city environment was divided into Human,Local,Outer three blocks,and then the heat and temperatures of the blocks were analyzed based on the laws of thermodynamics.After that,the effect of artificial heat release in Human block on the local temperatures was clarified.The model shows that the artificial heat release has an approximately linearly promoting effect on the local temperature rise,and the more the heat release is,the stronger the effect is.In addition,a validation of that model was carried out based on some national statistical data.The data of temperatures and artificial heat release of some provincial capitals of China were analyzed with linear regression extrapolation method and Pearson correlation statistical method.The results show that in most capital cities,the temperature variations basically depend on the artificial heat release in a linear relationship,which usually becomes more apparent with the increase of the artificial heat release in both spatial and temporal dimensions.The conclusions of the statistics have good conformity with the model and the rationality of the model is verified.

Recent leveling off of vegetation greenness and primary production reveals the increasing soil water limitations on the greening Earth

Global vegetation photosynthesis and productivity have increased substantially since the 1980s,but this trend is heterogeneous in both time and space.Here,we categorize the secular trend in global vegetation greenness into sustained greening,sustained browning and greening-to-browning.We found that by 2016,increased global vegetation greenness had begun to level off,with the area of browning increasing in the last decade,reaching 39.0 million km^(2)(35.9%of the world’s vegetated area).This area is larger than the area with sustained increasing growth(27.8 million km^(2),26.4%);thus,12.0%±3.1%(0.019±0.004 NDVI a^(-1))of the previous earlier increase has been offset since 2010(2010–2016,P<0.05).Global gross primary production also leveled off,following the trend in vegetation greenness in time and space.This leveling off was caused by increasing soil water limitations due to the spatial expansion of drought,whose impact dominated over the impacts of temperature and solar radiation.This response of global gross primary production to soil water limitation was not identified by land submodels within Earth system models.Our results provide empirical evidence that global vegetation greenness and primary production are offset by water stress and suggest that as global warming continues,land submodels may overestimate the world’s capacity to take up carbon with global vegetation greening.