固定床反应器中邻二甲苯氧化的一维非均相模拟

采用一维非均相模型,同时考虑催化剂颗粒的内外扩散,模拟了邻二甲苯氧化固定床反应器,使用变步长Runge-Kutta积分法求解气相方程,使用中心差分并结合迭代方法求解颗粒相方程,使用C 编程并进行求解,首先进行了网格无关性计算．将一维拟均相模型和一维非均相模型的结果进行了比较,并将结果与文献中的二维模型进行比较．另外比较了利用Leva方程,Ergun方程和Kozeny方程求解压降的差别,讨论了管径的变化对反应产率和转化率的影响,从而寻找最适合的参数和方程进行最终计算．     

制取苯酐模型的S系统解析

高精度的数值法被用于求解邻二甲苯制取苯酐模型中。此方法是将基本的微分方程改写为S系统(synergisticandsaturablesystem)的标准形式,结合变阶变步长的泰勒级数法进行求解,得到了不同进料温度和不同压强下的苯酐和二氧化碳收率分布以及反应器床层的轴向温度分布曲线,并与龙格库塔法的计算结果做了对比。分析得出热点温度和苯酐及二氧化碳收率随着进料温度增大而增大,同时苯酐及二氧化碳收率也随着操作压强的增大而增大。当进料温度为638K时热点温度变的非常高,而且进料温度相差1度时热点温度会相差几十度。精确求解不同进料温度和操作压强下的热点温度对工程实际操作中催化剂的保护和设备维护有着十分重要的指导意义。     

解扩散方程的指数时间差分方法

指数时间差分方法是近年来提出求解刚性常微分方程的一种新的数值计算方法.指数时间差分方法是一种积分方法,而不是经典的差分方法.利用指数时间差分方法求解扩散方程,如一维拟线性对流扩散方程和Allen-Cahn扩散方程.扩散方程在空间方向离散后转化成刚性常微分方程.用显式指数时间差分方法和相应阶的显式Runge-Kutta方法求解刚性常微分方程.数值结果表明显式指数时间差分方法具有相同阶的显式Runge-Kutta方法相应的精度,稳定性显著提高,而且能很好地模拟扩散方程的演化行为.指数时间差分方法可用于刚性常微分方程的数值计算.     

固定床中邻二甲苯氧化的二维非均相模拟

采用二维非均相模型，模拟了邻二甲苯固定床氧化反应器，对于气相方程，使用Ｃｒａｎｋ－Ｎｉｃｏｌｓｏｎ预测－校正格式求解，对于颗粒相方程，使用中心差分并结合迭代方法求解，比较了二维非均相模型和二维拟均相模型的差别，使用二维非均匀相模型，分析了原料进口温度、进料气速、进口浓度、熔盐温度和催化剂尺寸的大小对反应的影响。     

一维Tyson反应扩散系统的格子Boltzmann方法模拟

建立基于格子Boltzmann模型的一维Tyson反应扩散系统的数值求解法.利用浓度分布的Chapmann-Enskogz展开及多尺度技术,获得激励介质在反应与扩散机制同时作用的一维反应扩散方程,用于求解Tyson反应扩散的反应物和催化剂随时间的浓度空间分布值.数值结果表明本文中所提供的方法是有效的.     

甲醇合成平行反应体系催化剂效率因子的求解──（Ⅱ）二维有限元法

由ＣＯ，ＣＯ_２加氢合成甲醇的反应是一个复合反应体系。在圆柱状催化剂内的浓度分布的表征方程为二阶偏微分方程组。本文运用有限元方法求解此方程组，得到催化剂内的浓度分布及效率因子的数值解，与实验结果比较，吻合较好。     

甲醇合成平行反应体系催化剂效率因子的求解（II）二维有限…

由ＯＣ，ＣＯ２加氢合成甲醇的反应是一个复合反应体系。在圆柱状催化剂内的浓度分布的表征方程为二阶偏微分方程组。本文运用有限元方法求解此方程组，得到催化剂内的浓度分布及效率因子的数值解，与实验结果比较，吻合较好。     

四阶高分辨率熵相容算法

针对一维Burgers方程和一维Euler方程组的数值求解问题,提出了一种四阶高分辨率熵相容算法。新算法时间方向采用半离散方式,空间方向应用四阶中心加权基本无振荡(CWENO)重构方法,数值通量引入Ismail通量函数,将新的四阶算法应用于静态激波问题、激波管问题以及强稀疏波问题的数值求解中,并将所得结果同准确解以及已有算法所得结果进行了分析与比较。数值结果表明:新算法计算结果正确、分辨率高,能够准确捕捉激波及稀疏波,并能有效避免膨胀激波的产生。新算法适用于准确解决一维Burgers方程和一维Euler方程组的数值求解问题。     

数值法解催化剂粒内模型及内扩散有效因子

采用直接法即通过求解常微分方程边值问题形式的催化剂粒内反应扩散模型 ,得到粒内浓度分布 ,进而由定义式经积分求得复杂动力学模型的催化剂内扩散有效因子。微分方程的求解采用打靶法和正交配置法等数值解法 ,内扩散有效因子的计算通过Gauss Legendre数值积分求得。     

原位脱碳流化床煤气化反应器的数值模拟

为了减少温室效应,对于煤气化过程中CO_2的减排与零排放技术的研究成为必要。本文建立了全面的煤气化反应器的数值模型,对以CaO作为吸收剂的原位脱碳的流化床煤气化反应器进行了数值模拟。模拟以简化结构的二维反应器为求解域,应用标准k-ε模型描述气相湍动,EDC模型描述反应器中湍流与反应的偶合,EDC模型将详细的化学动力学融入到湍流混合中。讨论了反应器中温度、气速、压力及气体产物的分布。     

Darcy–Forchheimer flow and heat transfer augmentation of a viscoelastic fluid over an incessant moving needle in the presence of viscous dissipation

The main focus of the present study is to analyse the effect of viscous dissipation Darcy–Forchheimer flow and heat transfer augmentation of a viscoelastic fluid over an incessant moving needle. The governing partial differential equations of the defined problem are reduced into a set of nonlinear ordinary differential equations using adequate similarity transformations. Obtained set of similarity equations are then solved with the help of efficient numerical method fourth fifth order RKF-45 method. The effects of different flow pertinent parameters on the flow fields like velocity and temperature are shown in the form of graphs and tables. The detailed analysis of the problem is carried out based on the plotted graphs and tables.

     

Pattern formation in enzyme inhibition and cooperativity with parallel cellular automata

Enzyme reactions with inhibition and cooperativity are modelled in terms of a pair of coupled nonlinear reaction–diffusion equations. The governing equations are solved using stochastic cellular automata with local rules derived from the corresponding nonlinear partial differential equations. The parallel cellular automaton is implemented using domain decomposition according to the nature of the locality of its update rules. Numerical simulations show stable 2-D and 3-D pattern formation, and complex patterns have the interesting feature of self-organized criticality. The numerical results of cellular automata are also compared with results obtained from finite difference and finite element methods.     

燃煤发电厂高温高尘烟气流速静电测量技术研究

高温烟气流速(流量)是实现燃煤电厂选择性催化还原脱硝(SCR)过程优化控制的关键参数之一,提高烟气流量测量的准确性对于提高SCR系统脱硝系统效率和控制NOX排放浓度具有重要意义。针对燃煤电厂烟气管道管径大、截面速度分布不均匀、含尘量高等特点,利用烟道内飞灰颗粒起电,开展了基于静电原理的SCR区高温高尘烟气流速测量方法研究。开发了接触式棒状静电互相关高温烟气流速测量系统,在实验室输送带装置上进行了性能实验评价研究,并对某330 MW燃煤机组锅炉脱硝系统入口烟气流量进行了现场测试。试验结果表明在3.1 m/s^43.6 m/s速度范围内,速度相对误差优于4.8%,重复性误差小于4.1%,验证了静电法烟气流量测量方法的可行性和准确性,并适用于高温高尘烟气恶劣现场环境,为开发新型可靠的高温烟气流速在线测量系统提供了技术基础。     

Analytical solution for suction and injection flow of a viscoplastic Casson fluid past a stretching surface in the presence of viscous dissipation

In this study, steady two-dimensional flow of a viscoplastic Casson fluid past a stretching surface is considered under the effects of thermal radiation and viscous dissipation. Both suction and injection flows situations are considered. The partial differential governing equations are transformed into ordinary differential equations and solved analytical. Analytical solutions for velocity and temperature are obtained in terms of hypergeometric function and discussed graphically. Moreover, numerical results are also obtained by Runge–Kutta–Fehlberg fourth–fifth-order (RKF45) method and compared with the analytical results. The results showed that the injection and suction parameter can be used to control the direction and strength of flow. The effects of Casson parameter on the temperature and velocity are quite opposite. The effects of thermal radiation on the temperature are much more stronger in case of injection. The heat transfer coefficient shows higher value for Casson fluid while for Newtonian fluid is the lowest.

     

Magnetohydrodynamic (MHD) flow of a micropolar fluid towards a stagnation point on a vertical surface

The steady MHD mixed convection stagnation point flow towards a vertical surface immersed in an incompressible micropolar fluid is investigated. The external velocity impinges normal to the wall and the wall temperature is assumed to vary linearly with the distance from the stagnation point. The governing partial differential equations are transformed into a system of ordinary differential equations, which is then solved numerically by a finite-difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. It is found that dual solutions exist for the assisting flow, besides that usually reported in the literature for the opposing flow.     

火电SCR脱硝系统混合与均流CFD仿真

火电烟气脱硝系统能否达到高脱硝率与低氨气逃逸率,很大程度上取决于进入脱硝反应器之前烟气中的氮氧化物与还原剂氨气混合均匀程度和烟气速度分布。为此,需在脱硝反应器之前的烟道内安装烟气-氨混合器、导流板均流装置。采用计算流体力学仿真软件对烟道中的流态进行了仿真,结果表明,格栅型混合器的使用能够增强气体径向混合,改善烟气与氨气混合的均匀程度;在烟道转弯处加入导流板可以明显减少出口速度分布偏差。所用计算流体力学仿真软件可以给出烟道内任意位置的速度和浓度可视化输出,在经过流态模型实验的验证后,这些信息可以成为烟道内混合与均流装置优化设计的依据。     

A mathematical model of MHD nanofluid flow having gyrotactic microorganisms with thermal radiation and chemical reaction effects

In this article, we have examined three-dimensional unsteady MHD boundary layer flow of viscous nanofluid having gyrotactic microorganisms through a stretching porous cylinder. Simultaneous effects of nonlinear thermal radiation and chemical reaction are taken into account. Moreover, the effects of velocity slip and thermal slip are also considered. The governing flow problem is modelled by means of similarity transformation variables with their relevant boundary conditions. The obtained reduced highly nonlinear coupled ordinary differential equations are solved numerically by means of nonlinear shooting technique. The effects of all the governing parameters are discussed for velocity profile, temperature profile, nanoparticle concentration profile and motile microorganisms’ density function presented with the help of tables and graphs. The numerical comparison is also presented with the existing published results as a special case of our study. It is found that velocity of the fluid diminishes for large values of magnetic parameter and porosity parameter. Radiation effects show an increment in the temperature profile, whereas thermal slip parameter shows converse effect. Furthermore, it is also observed that chemical reaction parameter significantly enhances the nanoparticle concentration profile. The present study is also applicable in bio-nano-polymer process and in different industrial process.

     

Analysis of magnetohydrodynamic flow and heat transfer of Cu–water nanofluid between parallel plates for different shapes of nanoparticles

The present study analyzes the heat transfer in the flow of copper–water nanofluids between parallel plates. For effective thermal conductivity of nanofluids, Hamilton and Crosser's model has been utilized to examine the flow by considering different shape factors. By employing the suitable similarity transformations, the equations governing the flow are transformed into a set of nonlinear ordinary differential equations. The resulting set of equations is solved numerically with the help of Runge–Kutta–Fehlberg numerical scheme. The graphical simulation presents the analysis of variations, in velocity and temperature profiles, for emerging parameters. A comprehensive discussion also accompanies the graphical results. Moreover, the effects of relevant parameters, on skin friction coefficient and Nusselt number, are highlighted graphically. It is noticed that the velocity field is an increasing function of all the parameters involved. Furthermore, the temperature of the fluid is maximum for the platelet-shaped particles followed by the cylinder- and brick-shaped particles.

     

Analysis of inhomogeneous anisotropic viscoelastic bodies described by multi-parameter fractional differential constitutive models

The response to static loads of plane inhomogeneous anisotropic bodies made of linear viscoelastic materials is investigated. Multi-parameter differential viscoelastic constitutive equations are employed, which are generalized using fractional order time derivatives. The governing equations, which are derived by considering the equilibrium of the plane body element, are two coupled linear fractional evolution partial differential equations in terms of the displacement components. Using the Analog Equation Method (AEM) in conjunction with the Boundary Element Method (BEM) these equations are transformed into a system of multi-term ordinary fractional differential equations (FDEs), which are solved using a numerical method for FDEs developed recently by Katsikadelis. Numerical examples are presented, which not only demonstrate the efficiency of the solution procedure and validate its accuracy, but also permit a better understanding of the response of plane bodies described by different viscoelastic models.