Some kinetic aspects of unsteady-state partial oxidation reactions. Dynamic processes on metal oxide surfaces

It is shown that steady-state kinetic data do not allow the discrimination between the redox and associated mechanisms of the partial oxidation reactions. A discrimination between these mechanisms was performed using transient experiments. The obtained rate expressions are in agreement with experimental kinetic data for catalytic partial oxidation of o-xylene.

An influence of the conjugate oxidation of a catalyst surface on dynamics and kinetics of the heterogeneous catalytic oxidative reactions is considered. Computing simulation of methane oxidative coupling of methane reaction at lowered temperature and elevated pressure has been performed. It showed that the reaction order with respect to oxygen exceeding unity is consistent with the chain branching mechanism of the reaction in the presence of TiSi₂ and TiB₂ and showed the important role of the branching chain cycles in the low-temperature OCM reaction at elevated pressure.     

Simulation Method of Dynamic Characteristics of Turbine Flow Sensor

Computational Fluid Dynamics (CFD) simulation is one of the important methods to study the performance and in-fluencing factors of turbine flow sensors. According to the working characteristics of the turbine flow sensor, the passive simulation method based on the six degrees of freedom (6-DOF) model and dynamic mesh is proposed in this paper. The reliability of the simulation method is verified by steady-state experiments and unsteady-state experiments. The results show that the trend of meter factor with flow rate acquired from the simulation is close to the experimental results, and the deviation between the simulation result and the experiment result is low with a maximum deviation of 2.88%. In the unsteady simulation study, the impeller speed changes with the inlet velocity of the turbine flow sensor, which has a good follow-up. The passive simulation method can be used to predict the dynamic performance of the turbine flow sensor.     

Interconnection between the solidification and precipitation hardening processes of an AlSiCu alloy

Horizontal directional solidification and precipitation hardening experiments were performed with the Al5.5Si3Cu alloy. Solidification thermal and microstructural parameters such as growth and cooling rates (V_L and T_R, respectively) and the secondary dendrite arm spacing (λ₂) were determined experimentally. As-solidified samples were selected and submitted to the T6-heat treatment (T6-HT). The T6-HT was carried out considering two solution times: 8 and 5?h at 490?±?2°C, followed by quenching in warm water (60?±?2°C), aging for 5?h at 155?±?2°C and air-cooling. Higher HV values were observed for the solution time of 5 h. As highlights of this work, the influence of the processing parameters (V_L, T_R and λ₂) on the distribution, morphology and size of the eutectic Si particles has been investigated.     

Unsteady-State Model for Continuous Moving-Bed Chromatography

Abstract

Mathematical equations have been formulated to predict the longitudinal concentration distribution in the case of instantaneous behavior of a continuous chromatographic system. Partial differential equations are initially obtained from mass balance on the differential element of column height. The formulated equations are solved by Lap lace transformation and the contour integration method. Two equations are obtained, one for the column section above the feed point and the second for the column section below the feed. Both of these equations give the concentration distribution along the appropriate section of the column. The model predicts the instantaneous and steady-state behavior of the continuous moving-bed chromatographic system. The model can also be used as a tool for the design of new continuous chromatographic columns.     

柴油机壁流式过滤体非稳态捕集过程的计算模型

基于排气在柴油机壁流式过滤体内的流动特点,并在综合分析壁流式过滤体深床捕集阶段捕集特点和滤饼捕集阶段捕集特点的基础上,建立了壁流式过滤体非稳态捕集过程的计算模型.该模型通过提出容纳度的概念,有效地区分了深床捕集阶段和滤饼捕集阶段;通过提出微粒在过滤壁表面沉积效率的概念,定量地描述了沉积在过滤壁表面的微粒量.基于该模型,介绍了计算算法,并编制了相应的计算程序.使用该模型研究了过滤体的捕集效率、流动阻力以及沉积在过滤体内微粒质量的非稳态变化规律.计算结果与试验结果吻合得较好,表明该模型在工程实际应用中具有可行性.     

Step response analysis of phosphoric acid fuel cell (PAFC) cathode through a transient model

Transient state response analysis of phosphoric acid fuel cell (PAFC) cathode is important to understand various competitive processes like diffusion, reaction and product back diffusion occurring at various layers of the composite cathode. A two-dimensional unsteady state model for simulating PAFC cathode is developed as an extension of the previously developed steady-state model [S. Roy Choudhury, M.B. Deshmukh, R. Rengaswamy, A two-dimensional steady-state model for phosphoric acid fuel cells (PAFC), J. Power sources 112 (2002) 137–152]. The transient model is solved to study the impact of various parameters such as Tafel slope, diffusivity etc on the step response of the fuel cell. The effect of partial pressure variation in bulk gas for large sized PAFC cathode is also analysed. Trend analysis based on the model output is also experimentally verified using a small unit cell setup. The effect of various parameters on the settling time of the cathode, as revealed in this study, suggests possible development of a diagnostic tool employing such transient model.     

固定床F-T合成反应器稳态和动态行为

根据有关文献和固定床Ｆ－Ｔ合成反应器的特点,建立了固定床Ｆ－Ｔ合成反应器的两维两相模型,选择了适宜的数值计算方法。考察了操作条件（反应动力学的指前因子、Ｐｅｃｌｅｔ准数、管壁温度与反应物进口温度和流量）对固定床Ｆ－Ｔ合成反应器动态行为的影响;研究了反应器进口操作条件（进口温度、流速及冷却介质温度）突变后反应器的动态响应行为。模拟结果说明,在一定条件下,可能出现逆响应现象（Ｗｒｏｎｇ－ＷａｙＢｅｈａｖｉｏｒ）。     

非稳态气驱水法火山岩相对渗透率曲线实验

火山岩储层属于特低渗透率气藏,但是由于具有较多的天然气孔,裂缝发育,因此可进行工业化开发。气水相对渗透率曲线在气藏开发的动态分析和数值模拟中是一项重要的参考资料。以吉林某火山岩气藏岩心为例,使用非稳态气驱水法,测定并绘制了火山岩岩心的气水相对渗透率曲线。结果表明,束缚水饱和度、残余气饱和度及等渗点处含水饱和度均较高,等渗点处相对渗透率较低,端点处水相相对渗透率较低;围压及驱替压差对结果有重要影响;火山岩储层非均质性严重。     

A PROBABILISTIC MODEL OF THE FISCHER-TROPSCH SYNTHESIS IN A FLOW REACTOR

The Fischer-Tropsch synthesis is usually carried out in flow reactors, such as fluidized-bed and bubble column slurry reactors. The nature of multiphase flow together with the well-known random nature of chemical reactions renders the performances of such flow reactors stochastic. In this work, stochastic processes, more specifically continuous time Markov chains, are employed for analyzing and modeling both the dispersive mixing and chemical kinetics in a flow reactor for the Fischer-Tropsch synthesis. The model predicts the distributions of products inside as well as outside the reactor at any time Under a steady state operation, the model gives rise to the Flory equation. Other results include expressions for predicting the mole fraction of chains with j carbon atoms inside and outside the reactor. This approach can be applied to both time homogeneous and heterogeneous processes.     

埋地热油管道停输三维非稳态传热过程的数值模拟

针对埋地热油管道停输过程进行研究,结合有限差分法和有限容积法建立埋地热油管道正常运行及停输过程的非稳态传热模型,考虑了管道正常运行及停输过程中管内原油粘度,密度,比热,导热系数随温度的变化关系,同时考虑了停输过程原油凝固潜热对温降的影响,地表温度采用周期性边界条件,数值模拟了埋地热油管道运行至第二年3月末停输温降过程。研究表明,随着停输时间的延长,管道沿线各截面处管内原油固化过程各异且土壤温度场变化明显,确定合理停输时间,为管道安全启动提供理论指导。