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.     

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.     

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）。     

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.     

基于双层非稳态导热过程的井筒温度场半解析模型

在油气井酸化、压裂增产施工中,温度控制着入井工作液的流变性和酸岩反应速度,是影响裂缝几何形态、酸蚀导流能力和措施后产能的重要因素。但目前的井筒温度场模型还缺乏对非稳态过程的严密推导和精确描述。为此,首先在物性分析的基础上,建立了轴向上离散、径向上解析的双层非稳态导热井筒温度场半解析模型,并通过拉普拉斯变换和Stehfest数值反演方法进行了求解;其次,分析了不同水泥环导热过程处理方法对井筒温度分布的影响,认为假设水泥环具有稳态热阻,模拟输出的误差过大且难以修正;最后,对地层和施工参数进行了敏感性分析,认为岩性、施工排量和注入温度变化对井筒温度分布具有显著的影响,而油管腐蚀的影响则可以忽略。现场实际应用效果表明,该数学模型精度较高,模拟结果与监测结果吻合良好。该成果对于提高单井酸化压裂成功率、增加措施后的产能和油气田采收率具有重要意义。     

Comments on “Role of power-to-gas in an integrated gas and electricity system in Great Britain”, Int J Hydrogen Energ 40 (2015) 5763–5775

In the article published by Qadrdan et al. in INT J HYDROGEN ENERG 40 (2015) 5763–5775, the role of power-to-hydrogen in the GB's combined gas and electricity network (CGEN) was presented. The purpose of this comment is to point out the errors associated with the CGEN's unsteady-state gas model. No agreement can be found when one compares the proposed modelling approach with the governing (continuity and momentum) equations. The selected base-length, and initial/boundary conditions were not described by the authors. No mathematical proof and model validation (with available software packages) were presented for their proposed approach. In addition, the authors did not consider the change of hydrogen concentration along the pipes and its impact on the gas density and heating value.     

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.