细小槽道换热器内相变微胶囊悬浮液对流传热DPM模拟

基于离散相模型,采用颗粒比热容随温度变化分段函数描述颗粒的相变过程,模拟了相变微胶囊悬浮液在细小槽道换热器内的对流传热特性,考察了不同入口流量时换热器进出口压差及温差的变化规律,并与纯水进行比较,分析了换热器内部及加热面温度分布,研究了换热器典型通道修正的局部努赛尔数Nux*沿流动方向的变化规律. 结果表明,相变微胶囊悬浮液在换热器内的压损随流量变化规律与纯水一致,较纯水有所增大;引入相变微胶囊颗粒减缓了加热面和流体温度升高的速率,使换热器出口及加热面的温度比纯水低;受进出口位置影响,换热器内温度呈现中间通道低、向两侧逐渐升高的分布规律. 不同通道的Nux*沿流动方向的变化规律存在一定差异,部分通道内相变材料完全融化,而部分通道内相变材料尚未完全融化就流出换热器. 需改进换热器进出口位置或对换热器内部结构进行优化设计以获得较好的流量分配特性,从而改善换热效果.     

高层建筑走廊机械排烟量与排烟口数量的数值模拟与分析

排烟量的确定是防排烟系统合理设计的一个重要因素，通过高层建筑内烟气流动的数学模型，采用κ-ε双方程三维紊流模型对高层建筑火灾时不同排烟量以及相同排烟量不同排烟口数量情况下走道的烟气状态进行模拟，通过分析满足最大安全疏散时间时，其走道人眼特征高度1．5m处的烟气的温度以及浓度，得出每平方米排烟量72m^3／h为此典型高层建筑的最合理机械排烟量．且当排烟量不变时，可通过增加排烟口数量来更好地控制走道的烟气状态，为防排烟系统的合理设计提供依据．     

基于FDS的高层建筑火灾应急疏散与安全防控策略研究

火灾中高达80%的人员死亡原因是高温烟气所造成的,这是因为高温烟气蔓延速度极快,导致建筑物内能见度降低,从而严重影响人员应急疏散。因此,本文利用火灾动态模拟软件FDS构建高层建筑模型,在自然排烟条件下对该建筑进行火灾数值模拟,研究表明:在本文构建的场景下CO浓度在火灾发生点处最高达到450 ppm;能见度在火灾发生1200 s时在安全高度所在的水平方向的能见度为7.5 m左右;除了火灾发生点外,其余空间在安全高度及以下区域的温度在230℃以下。高层建筑火灾应急疏散与安全防控策略研究可为单元式高层建筑防火设计及人员疏散逃生方案提供理论参考。     

严寒地区水泥窑协同处置垃圾坑暖通设计

通过水泥窑协同处置垃圾坑的暖通设计介绍严寒地区垃圾坑的供暖系统、通风系统及防排烟系统。通过垃圾坑供暖提高了厂区垃圾热值及垃圾坑的温度,有利于增强垃圾焚烧工艺稳定性。通过垃圾坑通风消除了垃圾坑的恶臭气体,解决了坑内空气不流通和环境污染的难题。通过垃圾坑防排烟排除火灾产生的大量烟气,阻止烟气向厂房其它区域扩散,确保主厂房内人员的顺利疏散和安全避难。     

离心渗铸充型过程中伴随有瞬态固化与再熔现象的流场变化规律

针对离心渗铸工艺中熔体浇注温度太高会带来铸件冶金质量下降问题,在充型过程中一般会发生金属熔液的瞬态固化与再熔现象,建立了旋转多孔介质内伴随有瞬态固化与再熔现象的渗流传热理论模型.通过理论分析获得了离心渗铸充型过程中瞬态压力分布计算公式,建立了不同区域界面的移动速率与温度间的耦合关系,分析了流场变化规律.结果表明：渗透前沿界面推移速度主要受离心渗透压力即渗透动力学因素的影响,而再熔界面推移速度主要受热导率和金属相变特性即材料热力学因素的影响,多孔预型体内发生的瞬态固化与再熔是决定充形过程中渗铸复合层能达到的最大厚度的重要因素.     

单颗粒褐煤高温烟气干燥过程实验研究

针对10mm~25mm粒径的大唐五间房褐煤,通过单颗粒高温烟气干燥实验,得到了600℃~900℃烟气温度下的干燥特性曲线,研究了干燥介质温度和粒径对褐煤高温脱水效果的影响,发现干燥过程主要处于降速干燥阶段;高温条件下,温度对干燥速率的影响并不显著;针对褐煤水分在干燥过程中的迁移特点以及大唐五间房褐煤的孔隙特征,基于努森扩散定律,建立了水分蒸发为蒸汽再扩散出煤粒的缩核干燥动力学模型;得到了不同温度下的有效水分扩散系数,并利用Arrhenius公式求出了10mm~25mm粒径下的干燥活化能.     

基于AERMOD模型的大气环境影响评价对项目的优化建议——以福建省某拟建生活垃圾焚烧发电项目为例

运用AERMOD模型预测不同地表类型、烟囱高度、烟气流速、排烟温度对大气环境影响变化规律,以期能为项目选址、设计提供优化建议。结果表明：（1）不同土地利用类型的各污染物网格点最大贡献浓度占标率依次为针叶林<落叶林<城市外围<农作物<草地;（2）烟气出口流速对大气污染物扩散影响很小（变幅<1%）,烟囱高度、排烟温度对大气污染物扩散影响较大;（3）拟建项目推荐方案为选址在周边内3km为针叶林,烟囱高度为90m,烟气流速取10～20m/s,排烟温度在130～150℃之间。     

单颗粒褐煤高温烟气干燥过程数值模拟

褐煤干燥对于提高其品质具有重要意义。为了模拟高温烟气干燥这一高温差、变温差非稳态传热传质过程中褐煤内水分蒸发过程,采用有限体积法建立了一维球坐标系下蒸发界面向内迁移的单颗粒褐煤干燥数学模型,并利用该模型分析了初始烟气温度和颗粒粒径对单个褐煤颗粒干燥特性的影响。模型模拟结果与实验结果对比表明二者变化趋势一致,所建模型能较好地反映出高温烟气干燥过程中褐煤内水分蒸发过程。结果表明,初始烟气温度越高,颗粒粒径越小,蒸发界面向内迁移速度越快,水分脱除越快,干燥时间越短;蒸发界面平均迁移速度均与初始烟气温度和颗粒粒径呈线性关系;在初始烟气温度700℃下,较短的停留时间使得颗粒表面温度未达到挥发分析出温度,本研究中不同粒径褐煤颗粒在干燥过程中基本没有挥发分的析出。     

高层建筑利用电梯疏散的可行性及防烟措施研究

当前,我国的经济发展越来越迅速,一栋栋高层建筑伴随着GDP的腾飞拔地而起。因此,研究和分析高层建筑在火灾情况下,电梯防烟、供电、防护等系统以及如何更好的利用电梯进行安全疏散的利与弊,具有非常实际的研究价值。本片文章,通过分析以往高层建筑成功疏散的实例,提出来火灾情况下人员利用电梯安全逃生的可行性,并对利用电梯进行安全疏散提出了相应的软、硬件改进措施。研讨结论将有助于人们在高层建筑内运用电梯开展疏散。     

火灾烟气扩散数值模拟与控制研究

描述了高层建筑火灾危险性的特点和现实情况,分别介绍了目前国内外在建筑火灾烟气扩散领域的研究和成果,指出了需进一步改进的问题,并提出了采用分区模拟的手段来实现高层建筑火灾烟气扩散的计算机模拟。     

Diffusion of lignin macromolecules within the fibre walls of kraft pulp. Part I: Determination of the diffusion coefficient under alkaline conditions

The intrinsic rate of diffusion of soluble lignin from fibre walls to bulk liquor has never been determined previously because of experimental difficulties; for example, the diffusion rate determined in a stirred cell is affected by the mechanical action of stirring. In our work, the intrinsic rate of diffusion of lignin macromolecules from the fibre walls of a softwood kraft pulp was determined under alkaline conditions using a displacement cell which eliminated external heat and mass transfer resistances and pulp fibre disturbances. The effects of such experimental conditions as pulp bed height and liquid flow rate were studied. The diffusion rate can be described by a diffusion model for a hollow cylinder with a very wide range of diffusion coefficients. The diffusion rate increased with increasing pH. Our results provide a new understanding of the lignin diffusion process in fibre walls, which is affected by the size of lignin molecules and the pores, and by the electrostatic interactions between intrafibre pore walls and lignin.     

抑烟环保型沥青性能试验分析

为了解决沥青路面摊铺会产生的大量有毒气体这一问题,本文在70^#基质沥青中添加抑烟剂制备抑烟沥青,并对其性能进行分析。首先通过自制沥青烟气收集装置分析了掺加不同比例的Sasobit和纳米CaCO₃在单掺和复配时对沥青抑烟效果的影响,然后采用动态剪切试验、弯曲流变试验以及储存稳定性试验分析了Sasobit和纳米CaCO₃对沥青性能的影响。试验结果表明,在最佳复配比例下的Sasobit和纳米CaCO₃,能使沥青烟气抑制效果达到12%,能明显改善70^#基质沥青的高温性能,对储存稳定性无影响。     

THERMAL EFFECT ON DIFFUSION OF GASES IN ZEOLITES

A new technique for measuring simultaneously adsorption rate and temperature variation in zeolite hasbeen developed.The transient temperature process during adsorption of gas on zeolite was analyzed by meansof a simple model.It was found that the diffusion of gas in zeolite crystallines could be made almost iso-thermal if the experimental conditions were appropriately designed.Thus the thermal effect on determinationof diffusion coefficient of gas in zeolite could be neglected.     

热效应对气体在沸石中扩散的影响

本文提出一种同时测量沸石吸入气体的速率曲线和沸石温度变化曲线的新方法.用简单的数学模型分析了沸石吸入气体的温度瞬变过程.数学分析和实验结果表明,只要实验条件选择得当,气体在沸石晶体中的扩散接近等温过程,热效应对扩散系数测定的影响可以忽略.     

Characterization of Epoxy Prepreg Curing Process

The isothermal and dynamic curing process of epoxy composite was studied using differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and other techniques. The variation of degree of curing with time and temperature was analyzed. The degree of curing was limited at any particular temperature because of the diffusion control in isothermal curing process. Half-life and maximum cure time were discussed in the analysis of the isothermal curing process. The modeling result from isothermal curing process indicated that degree of curing calculated with diffusion control agreed well with experimental data. The degree of curing calculated by two methods for dynamic curing process had a deviation with experimental data in either earlier or later cure stages. The relationship between T_g and the degree of curing was described by two models. Both models agreed well with the experimental T_g. The isothermal curing diagrams of time-temperature-transformation (TTT) and conversion-temperature-transformation (CTT) were constructed. Each region in TTT and CTT diagrams corresponded to the phase state of the curing process, so that the curing mechanism was clearly reflected in diagrams. The thermal stability analysis indicated the epoxy resin system was very thermally stable under temperature of 300°C.     

An aging theory-based mathematic model for estimating the wax content of wax deposits using the Fick's second law

In this study, a mathematic model is proposed for estimating the wax content of wax deposits. The proposed model was built based on the diffusion of wax molecules and counter-diffusion of oil molecules and described using the Fick's second law, allowing for the stacking fraction and orientational order of precipitated wax crystals and the tortuosity of diffusion path of de-waxed oil molecules during the counter-diffusion. The calculated results were verified by comparing with the flow-loop wax deposition experimental results. Dependence of radial position, deposition duration, bulk temperature, and wall temperature were investigated. These factors significantly affected the wax content during wax deposition. Good agreements were observed between the predictions and experimental results. The variation trends of wax content affected by various aspects are consistent with the existing studies.     

A NEW FEATURE SCALE MODEL AND EXPERIMENTS OF THE HYDROGEN PLASMA ASSISTED CHEMICAL VAPOR DEPOSITION OF COPPER

A new feature scale model has been developed for the hydrogen plasma assisted chemical vapor deposition (PACVD) of copper from Copper(II) bis-hexafluoroacetylacetonate, CufHfa)₂. PACVD of CufHfa)₂ enables low temperature deposition and conformal coverage to be achieved. Copper is formed via a surface reaction between dissociatively adsorbed precursor and the atomic hydrogen that is produced in the plasma by the dissociation of molecular hydrogen. Our feature model shows that the transport of CufHfa)₂ and atomic hydrogen into irenches/vias is restricted by the feature walls, which reduces gap fill. Also, ii predicts conservatively that the concentration of Cu(Hfa)₂ is essentially constant and that the formation of voids is due largely to the variation in the concentration of atomic hydrogen. Using a variable diffusion, free boundary model that we have applied to copper PACVD, we show that gap fill can be very good and that voidless via fill can be achieved under proper conditions. These conditions are sensitive to the pressure and the angle of the walls, and they insure high diffusion rates of atomic hydrogen from the reactor space through the mouth of the feature and low recombination rates to molecular hydrogen along the feature walls. Furthermore, increasing the slope of the feature walls increases the effective diffusion rate of atomic hydrogen, which improves the gap fill markedly. A favorable agreement between the variable diffusion model calculations and experiments also is demonstrated.     

A NEW FEATURE SCALE MODEL AND EXPERIMENTS OF THE HYDROGEN PLASMA ASSISTED CHEMICAL VAPOR DEPOSITION OF COPPER

A new feature scale model has been developed for the hydrogen plasma assisted chemical vapor deposition (PACVD) of copper from Copper(II) bis-hexafluoroacetylacetonate, CufHfa)₂. PACVD of CufHfa)₂ enables low temperature deposition and conformal coverage to be achieved. Copper is formed via a surface reaction between dissociatively adsorbed precursor and the atomic hydrogen that is produced in the plasma by the dissociation of molecular hydrogen. Our feature model shows that the transport of CufHfa)₂ and atomic hydrogen into irenches/vias is restricted by the feature walls, which reduces gap fill. Also, ii predicts conservatively that the concentration of Cu(Hfa)₂ is essentially constant and that the formation of voids is due largely to the variation in the concentration of atomic hydrogen. Using a variable diffusion, free boundary model that we have applied to copper PACVD, we show that gap fill can be very good and that voidless via fill can be achieved under proper conditions. These conditions are sensitive to the pressure and the angle of the walls, and they insure high diffusion rates of atomic hydrogen from the reactor space through the mouth of the feature and low recombination rates to molecular hydrogen along the feature walls. Furthermore, increasing the slope of the feature walls increases the effective diffusion rate of atomic hydrogen, which improves the gap fill markedly. A favorable agreement between the variable diffusion model calculations and experiments also is demonstrated.     

塑料薄膜在流延辊上冷却过程的数值模拟

用Fluent软件对塑料薄膜在流延辊上的冷却过程进行了数值模拟,分析了塑料薄膜在流延辊上的冷却机理及塑料薄膜、冷却水、流延辊之间导热、对流、辐射综合的非稳态传热过程,得到了塑料薄膜及流延辊辊面温度的变化规律以及塑料薄膜冷却速率的主要影响因素。实际应用结果表明:该研究能为流道参数的优化及流延辊结构的合理设计提供指导。     

冻结液滴融化过程中的表面及界面演化特性分析

液滴在血浆储存、航空航天等技术领域广泛存在,而其机理研究主要集中在冻结阶段,对融化阶段的研究则相对较少。故此,本文通过液滴可视化实验,发现并归纳了冻结液滴在不同材料表面、不同基底温度下融化过程的动态表面及界面演化模式,总结了液滴表面扩散系数、高度系数、相界面偏离度等形态演化参数与相变时间之间的变化规律并对其展开分析。结果表明：冻结液滴存在3种不同的表界面演化模式;在熔融中后阶段,金属材料（纯铝板、镀锌板）表面冻结液滴的冰相区以颗粒群状分布态融化,冰晶结合度低,而高分子聚合物材料[有机玻璃（PMMA）及聚氯乙烯（PVC）试板]表面冻结液滴的冰相区呈块状分布态融化,冰晶结合度高;金属类材料表面冻结液滴的相变速率高于聚合物类材料表面冻结液滴的相变速率,金属表面相变时间在100s以内,而聚合物表面冻结液滴的相变时间在300s以内;金属表面最大扩散系数分布区间为0.950~1.021,聚合物表面最大扩散系数分布区间为1.000~1.076,温度高,则各类材料表面液滴的微观前驱膜移动受阻,液滴的表面润湿过程受阻;金属表面冻结液滴的高度系数及冰相高度变化率受冰相区变化影响,聚合物表面则主要受温度影响;温度升高会使热量传递过程不稳定,加剧聚合物表面冻结液滴偏离度位移的波动性。