吸热式氮基气氛与钢复杂平衡体系的热力学计算(Ⅰ)

本文用独立组元法对吸热式氮基气氛与碳钢间的多元反应复杂平衡体系在前人简单反应的工作基础上进行了热力学计算,得到了有关的方程式。对体系中各组分在不同温度下的平衡组成和碳势,以及不同氮含量时气氛的碳势进行了计算。计算结果表明,在一定温度下,气氛的碳势随CO_2浓度的增加而减少;在一定CO_2含量时,炉温越高,则气氛的碳势越低。     

催化裂解简单合成离散的短纳米碳管

研究了一种简单催化裂解生长离散纳米碳管技术.不需要使用基底,于700℃,直接催化裂解Fe(NO3)3·9H2O和无水乙醇的混合溶液,反应30分钟,合成了长度较短的纳米碳管.需要指出的是,该研究与已有的催化裂解无水乙醇生长纳米碳管的区别在于:实验设备简单,工艺参数易于实现,反应温度较低,时间较短,碳源和催化剂间的反应在均相中发生.所得产物的扫描电镜、透射电镜表征显示,合成的纳米碳管呈开口状,相互缠绕程度较小,离散度较大.拉曼光谱检测表明产物为单壁纳米碳管和多壁纳米碳管混合物.文章还对纳米碳管的生长过程进行了探讨.     

吸热式氮基气氛与钢复杂平衡体系的热力学计算(Ⅱ)

本文用自由能最小化法对吸热式氮基气氛与碳钢间的多元反应复杂平衡体系进行了热力学计算,得到了有关方程式.计算了体系中各组份在不同温度下的平衡组成和碳势,以及不同氮含量时气氛的碳势.结果表明,在一定温度下气氛的碳势随CO_2浓度的增加而减小;在一定CO_2含量时,炉温越高则气氛的碳势越低.此结论与用独立组元法处理得到的结果相符.     

多壁纳米碳管振子及其能量耗散的分子动力学模拟

运用分子动力学模拟的方法,模拟了不同温度下,不同管型的多壁纳米碳管振子;讨论了温度变化、壁面原子间的匹配程度对振动特性及振动过程中能量耗散的影响,根据能量的消耗来计算管壁间的摩擦力的大小.模拟结果表明,多壁纳米碳管振子在作减幅振动过程中不断有能量的消耗,振动频率可以超过80吉赫(GHz),振动时的恢复力与内外碳管重叠面积无关,通过统计消耗能量所计算的摩擦力大小在10-5 nN/atom量级;摩擦力的大小随温度升高有增大的趋势,但与管壁间原子匹配程度的相关性不大.     

不同温度下复杂反应体系平衡计算方法的探讨

对多个反应的复杂体系,难于导出体系中各物种的平衡组成随温度变化的函数关系式,我们采取的方法是在计算一定条件下复杂反应体系平衡组成程序外嵌套温度循环,对不同温度逐点进行计算,进而绘制出平衡温度随温度变化的关系曲线。此方法可用于大部分复杂反应体系不同温度下平衡组成的计算,具有通用性的特点。该方法成败的关键是运用较好的计算平衡组成的方法以及温度循环步长的选定。     

采空区内煤自燃气体特征及产生规律分析

针对目前对在模拟逐渐升温的采空区环境条件下不同变质程度煤自燃现象的研究较少的问题,以采集的4种变质程度的焦瘦煤、气肥煤、无烟煤、肥焦煤为例,利用煤自燃模拟系统进行了煤自燃实验,研究在采空区环境条件下煤的燃烧特征及自燃气体的产生规律。实验结果表明,焦瘦煤、气肥煤、无烟煤、肥焦煤自燃时,温度会呈现"S"型上升趋势,前期温度先缓慢积累,而后开始快速升温,最后在300℃时趋于平衡,而后缓慢上升;不同煤样在自燃过程中均会产生碳氢化合物和碳氧化合物等挥发性气体,且生成速率受温度影响,并出现极大值和极小值2个拐点;无烟煤温度上升曲线近似于直线,气体曲线随温度波动不明显;气肥煤和肥焦煤自燃时会产生大量CO和CH4,气肥煤产生CO的速率最快,CO最大体积分数可达8%,肥焦煤产生CH4的速率最快,CH4最大体积分数可达14%,焦瘦煤和无烟煤产生的CO和CO2的体积分数分别在2%和4%左右。     

烯烃催化裂解反应动力学的研究

根据脉冲微反条件下C5～C8烯烃裂解产物分布,建立烯烃裂解反应网络,通过参数估计方法确定反应网络动力学常数、反应活化能和指前因子.结果表明,随着碳数的增加,C5～C8烯烃单分子裂解反应速率加快.反应温度600℃时C5～C8正构烯烃裂解生成丙烯,其反应速率常数的比值为1:8.18:38.48:27.98,最快生成丙烯的是1-庚烯.反应温度相同,1-烯烃的主要裂解反应速率是碳数相同的2-甲基-2-烯烃的1.1～1.6倍.C5烯烃裂解为单、双分子裂化并存的反应体系,但双分子裂解反应速率远大于单分子裂解,双分子反应占优势.     

甲烷部分氧化合成燃气过程能量耦合工艺的研究

从反应温度、压力和进料量(CH_4、CO_2、H_2O和O_2)等6个变量中固定任意5个,优化剩下的一个变量的方案,研究甲烷部分氧化合成燃气含水蒸气、二氧化碳重整的能量耦合工艺(即平衡时体系的热效应为零)。建立为能量耦合的双层优化模型,即内层通过求解吉布斯自由能的最低限度得到平衡组成;外层通过改变进料组成实现体系的能量耦合。结果表明:0．1 MPa下反应体系的最佳操作温度范围为1 050～1 150 K;固定其他条件,总可通过优化O_2的量使反应体系实现能量耦合,且平衡时加入的O_2可以反应完全;平衡组分中H_2/CO比值主要取决于进料中H_2O/CO_2比值,与O_2量关系不大;另外还得出了能量耦合时变量间的关系和消炭条件。石英管反应器的热中性温度下的实验结果与本文计算结果基本一致。     

非理想二组元液态混合物气-液相平衡计算及过程的计算机模拟

利用二组元液态混合物中各组分活度系数计算的Var—Larr和Margules模型,以异戊二烯一己腈和氯仿．乙醇系统为例,计算了三种不同温度和三种不同压力下二组元非理想液态混合物的气-液相平衡;同时对恒沸状态的温度、压力及组成等参数亦进行了相关计算。本文利用VC＋＋语言强大的计算能力,编写了上述相关计算程序,实现了上述系统压力-组成图和沸点．组成图的计算及相图绘制的计算机模拟。通过对非理想液态混合物气-液相图的半经验计算,为化学工程中物质的分离、提纯提供了计算相图依据,也为高校工科相关课程的教学提供了生动的图像和动画演示。     

浆态床法合成二甲醚的模拟研究

对于直接以合成气作为原料，使用Cu-Zn-Al和γ-Al2O3构成的双重催化剂、采用浆态床法合成二甲醚的反应体系，使用全混流反应器模型结合化学反应动力学进行模拟。组分方程使用超松弛迭代方法并结合C 编程进行求解，编制了计算机程序。通过模拟计算，讨论了压力、温度、空速、催化剂配比、反应气中不同氢碳比以及CO2含量对反应收率、DME选择性的影响，并讨论了在不同氢碳比下对CO转化率和CO与H2总转化率的影响，从而寻找合适的反应条件，为工业化生产提供参考。     

液体空气汽液平衡计算模型

汽液平衡计算是精馏塔模拟计算中重要的组成部分。以液体空气汽液平衡计算为研究对象,利用神经网络技术,建立了总压（P）和各组分液相组成（X1、X2、X3）为输入节点,3种不同参数作为输出节点。（1）平衡温度（T）、各组分汽相组成（Y1、Y2、Y3）;(2)平衡温度（T）、各组分平衡常数（K1、K2、K3);（3）平衡温度（T）、汽相氮组成（Y1）及氩、氧平衡常数（K2、3））的BP神经网络模型。通过计算比较,第三种参数作为输出节点的液体空气汽液平衡计算模型,不仅具有良好的学习能力,而且预测结果也比较满意。对进一步研究并应用于空分塔模拟计算具有一定的指导意义。     

On-line inference of tube-wall temperature in an industrial olefin pyrolysis plant

A major difficulty in the efficient functioning of industrial pyrolysis is the lack of suitable on-line tube-wall temperature measurements. In this paper, an inferential scheme is developed to predict the tube-wall temperature, which is called skin temperature, in an industrial olefin pyrolysis plant. Based on a theoretically-derived model, the skin temperature is predicted from the available on-line measured process variables, such as gas temperature around the tube, fuel gas flowrate, and naphtha feed flowrate. Using the infrequently off-line measured skin temperature with the on-line measurements, adjustable parameters of the model are updated on-line according to the Kalman filter technique. The application of this scheme then is illustrated using operating data obtained from an industrial olefin pyrolysis plant. The results of the proposed scheme show that, by taking infrequent measurements of the skin temperature for model adaptation, the skin temperature can be predicted successfully for every tube in the pyrolysis over an extended time interval. Simulations suggest that as few as one or two manual measurements of the skin temperature, taken during the entire cracking operation, provide sufficient information to maintain the developed inferential system at a practical level.     

Precipitate/austenite equilibrium in a titanium-niobium ultra low carbon steel

The variation in the equilibrium compositions of austenite and titanium-niobium-carbonitride precipitates in Fe-Ti-Nb-C-N-Mn-Si-Mo is considered over a range of temperatures between 1050 and 1500K and for an alloy composition which is typical of ultra-low carbon titanium-niobium microalloyed steels. The Kohler temperature dependent-subregular solution model is used to describe the austenite phase. The (Ti,Nb)(C,N)_x precipitate phase is described by the Hillert-Staffansson sublattice model for a four-component solution, with components mixed in pairs. The equilibrium between the two phases is explored while allowing for the nonstoichiometry of the precipitate phase. The results are shown to be in good agreement with experimental data on ultra-low carbon microalloyed steels.     

渣油制氨气化—变换系统流程模拟

本文对UBE型渣油制氨的气化—变换系统进行稳态模拟。用马丁-候状态方程作为热力学模型来计算真实气体的热力学性质,并在此基础上引入平衡温距的概念来描述高温高压下的气化反应。根据Prausnitz提出的方法建立了8.7MPa压力下的汽液平衡模型,用校正的动力学方程来计算变换反应速度,采用序贯模块法进行了流程模拟。以设计工况为基准的实例分析表明模拟结果与实际数据符合良好。对各关键单元进行的模拟操作分析,为该系统的优化计算和改进现行操作工况提供了较好的依据。     

Kinetic approach to the determination of the phase diagram of a solid solution

A binary mixture of 1,4-dichlorobenzene and 1,4-dibromobenzene, as a representative of a system that forms a solid solution, was measured in an adiabatic calorimeter. Several mixtures of different compositions were heated to 380 K, kept in the liquid phase at this temperature overnight, and then cooled slowly down to 250 K. The enthalpy path of the mixture measured during cooling carries the information that enables us to describe the crystallization process. In the first stage, crystallization develops rapidly and clearly deviates from equilibrium, while in the second stage it proceeds significantly slower, whereby we assume that the surface of the solid is in equilibrium with the existing liquid phase at the given temperature during cooling. Such an approach opposes the one that assumes equilibrium between the liquid and solid bulks, known as the equilibrium model. We show that by employing the kinetic model, the experimental enthalpy path of the mixture during cooling in the adiabatic calorimeter can be very successfully reproduced, while the equilibrium model fails in this aspect. Furthermore, we propose a procedure where the kinetic model is used to obtain the excess thermodynamic properties of the solid phase. These quantities enable the calculation of the liquid–solid phase diagram using the excess parameters obtained from the approach that does not assume the overall equilibrium between the phases during the crystallization process.     

Multi-scale simulations of in-depth pyrolysis of charring ablative thermal protection material

Charring ablative thermal protection systems have been commonly used to protect the payload of a hypersonic or space exploration vehicle from exposure to high heat loads. The physical phenomena associated with the pyrolysis of the charring ablative material are very complex. The existing surface ablation models were built upon various assumptions, which introduce large uncertainties in the engineering design process and disable the direct assessment of uncertainties at engineering level. The current study proposes a multi-scale numerical model to simulate the in-depth pyrolysis process of a charring ablator. First, a numerical model for simulating the transport and chemical reactions of the pyrolysis gas as a continuum through the porous char layer of an ablative material is developed, validated, and verified. The continuum numerical model is designed to account for the effects of in-depth heat and mass transfer, and chemical kinetics of the pyrolysis gas, which are missing from the existing surface ablation models. Next, atomistic simulations are used as a tool to determine the pyrolysis gas composition entering the char layer from the virgin material, and to identify the main reaction pathways for the interaction between the pyrolysis gases. The pyrolysis gas composition and kinetic chemistry model are intended to be used to reduce the uncertainty associated with the continuum numerical model used to simulate transport and reaction of the pyrolysis gas through the char in the surface ablation process. The current status of the multi-scale pyrolysis model development and results from the validation and verification studies are presented in the paper.     

The effect of gas‐dynamic factors on selective carbon‐nanotube synthesis by injection CVD method for field‐emission cathodes

Abstract— Reversible selective growth of carbon‐nanotube (CNT) arrays on Si/SiO₂ topologies was investigated for field‐emission‐display applications. The method used was that of high‐temperature pyrolysis of fluid hydrocarbon (p‐xylene [C₈H₁₀]) in a mixture with volatile catalyst (ferrocene [Fe(C₅H₅)₂]) using Ar as the gas carrier. The synthesized CNT arrays were analyzed by SEM, TEM, Raman, and TGA analyses. Reversible CNT growth both on Si and SiO₂ surfaces was found to be sensitive to the gas‐carrier flow rate and the catalyst/hydrocarbon solution injection rate into the synthesis zone. This phenomenon can be explained by inverse domination of active sites on Si and SiO₂ surfaces at different flow rates of gas mixture, causing different types of catalyst precipitation followed by subsequent CNT growth. In principle, the possibility of growing CNTs using the proposed technology will allow the creation of precise geometries of field‐emission cathodes excluding the step of catalyst localization.     

Development of an ozone gas sensor using single-walled carbon nanotubes

This study deals with the fabrication of an ozone gas sensor using single-walled carbon nanotubes (SWCNTs) as sensing material. The SWCNTs are dispersed by N,N-dimethylformamide (DMF). The CNT-DMF solution was dropped between interdigitated electrodes’ fingers to fabricate ozone gas sensor. For ozone environment, a commercial ozone generator was introduced. To improve sensor response, the deposited carbon nanotubes network was thermally treated at high temperature in a furnace. The sensor exhibits high sensitivity to ozone gas at concentration as low as 50 ppb, and fast response time, which is promising for future commercialization of carbon nanotubes based ozone gas sensor.     

Gas sensing properties at room temperature of a quartz crystal microbalance coated with ZnO nanorods

Gas sensors based on a quartz crystal microbalance (QCM) coated with ZnO nanorods were developed for detection of NH₃ at room temperature. Vertically well-aligned ZnO nanorods were synthesized by a novel wet chemical route at a low temperature of 90 °C, which was used to grow the ZnO nanorods directly on the QCM for the gas sensor application. The morphology of the ZnO nanorods was examined by field-emission scanning electron microscopy (FE-SEM). The diameter and length of the nanorods were 100 nm and 3 μm, respectively. The QCM coated with the ZnO nanorods gas sensor showed excellent performance to NH₃ gas. The frequency shift (Δf) to 50 ppm NH₃ at room temperature was about 9.1 Hz. It was found that the response and recovery times were varied with the ammonia concentration. The fabricated gas sensors showed good reproducibility and high stability. Moreover, the sensor showed a high selectivity to ammoniac gas over liquefied petroleum gas (LPG), nitrous oxide (N₂O), carbon monoxide (CO), nitrogen dioxide (NO₂), and carbon dioxide (CO₂).