纤维和小颗粒填充滴流床的流体力学性能比较

在内径为０．０４７ｍ的有机玻璃管内，采用空气水为介质，对纤维，小玻璃珠填充滴流床的流体力学性能进行了考察。结果表明，因为均为滴流床，流体力学性能有某些相似这处，但又由于纤维和小玻璃珠存在不同的性质和尺寸，滴流床内流道结构的巨大差异，使得两种床层内流体操作范围，床层空隙率，流型过渡，床层和，持液量，流体力学滞后现象等都存在显著差异。     

小颗粒滴流床反应器的流体力学研究

在内径为０．０４７ｍ，床层高０．７ｍ的滴流床反应器内，采用空气－水－玻璃珠（１．８，３．１８ｍｍ）体系，在常温、常压下进行实验。气、液流速分别在０．０５４－０．２３ｋｇ／（ｍ＾２ｓ）和３．２０－１４．７３ｋｇ／（ｍ＾２ｓ）内，用电导信号脉动法、压降波动法结合目测法测定了滴流床的流动状态及其变化，实验结果可用于确定不同操作条件下的流动状态。本研究还分别是用差计、示踪剂法和体积法对滴流床的压降，总持流     

滴流床式固定化植物细胞反应器中的压降和持液量

滴流床式固定化植物细胞反应器中的压降和持液量袁丽红，周名立，欧阳平凯（南京化工学院应用化学系，南京２１０００９）关键词：滴流床反应器，固定化植物细胞，压降，持液量１前言植物细胞的固定化通常采用海藻胶进行包埋，然后源源不断地提供其营养成分并通入空气，以...     

DISCREPANCY IN THE DETERMINATION OF THE ACTIVATION ENERGY BY CATALYTIC WIRE TECHNIQUES, NH3 OXIDATION

In this work we have studied the effects of isothermal multiplicity on the determination of the activation energy in ammonia oxidation over platinum wires. By including the activity in the rate expression and following the treatment proposed by Luss et al. (1980), it was possible to unify reported data on this reaction. Experimental results show that, in the multiplicity region, the reaction rate order is zero and the characteristic activation energy is 3.4 kcal/mol.     

Trickle-bed CFD studies in the catalytic wet oxidation of phenolic acids

An Euler-Euler computational fluid model was developed successfully for the hydrodynamic prediction of a trickle-bed reactor (TBR) designed for advanced wastewater treatment facilities. Catalytic wet air oxidation of phenolic acids was simulated in a TBR by means of computational fluid dynamic (CFD) in the temperature range and pressures . The hydrodynamic model validation was accomplished through the comparison of simulated pressure drop and liquid holdup with experimental data from the literature. In a broad range of gas and liquid flows studied (G=0.10-0.70 and ) at different operation conditions, CFD demonstrated the considerable effect of operating pressure in pressure drop, whereas a minor influence was detected for the liquid holdup. CFD runs were then performed for the catalytic wet air oxidation of aqueous phenolic acids solution. The reactor behaviour was analysed by means of total organic carbon profiles which reflected the influence of temperature, pressure, gas-liquid flows and initial pollutant concentration.     

Turbulence modelling of multiphase flow in high-pressure trickle-bed reactors

Computational fluid dynamics (CFD) has been used as a successful tool for single-phase reactors. However, fixed-bed reactors design depends overly in empirical correlations for the prediction of heat and mass transfer phenomena. Therefore, the aim of this work is to present the application of CFD to the simulation of three-dimensional interstitial flow in a multiphase reactor. A case study comprising a high-pressure trickle-bed reactor (30 bar) was modelled by means of an Euler-Euler CFD model. The numerical simulations were evaluated quantitatively by experimental data from the literature. During grid optimization and validation, the effects of mesh size, time step and convergence criteria were evaluated plotting the hydrodynamic predictions as a function of liquid flow rate. Among the discretization methods for the momentum equation, a monotonic upwind scheme for conservation laws was found to give better computed results for either liquid holdup or two-phase pressure drop since it reduces effectively the numerical dispersion in convective terms of transport equation.After the parametric optimization of numerical solution parameters, four RANS multiphase turbulence models were investigated in the whole range of simulated gas and liquid flow rates. During RANS turbulence modelling, standard k-ε dispersed turbulence model gave the better compromise between computer expense and numerical accuracy in comparison with both realizable, renormalization group and Reynolds stress based models. Finally, several computational runs were performed at different temperatures for the evaluation of either axial averaged velocity and turbulent kinetic energy profiles for gas and liquid phases. Flow disequilibrium and strong heterogeneities detected along the packed bed demonstrated liquid distribution issues with slighter impact at high temperatures.     

The NETmix reactor: Pressure drop measurements and 3D CFD modeling

NETmix is a new static mixing technology based on a network of mixing chambers interconnected by channels. Three NETmix reactors with different geometries were used to obtain experimental data for pressure drop and a generalized model for pressure drop in NETmix reactors has been developed. This model features a single adjustable parameter and it is only dependent on the geometric configuration of the NETmix design. The Z factor and the power number were also determined to compare the performance of different NETmix configurations with other existing mixers. The dynamic measurement of pressure drop was used to evaluate the mixing dynamics in the NETmix chambers and, above the critical Reynolds number, the natural oscillation frequency was quantified. Furthermore, a three-dimensional computational fluid dynamic transport model was also developed and validated. The energy performance of the three NETmix prototypes was quantified and shown to be very competitive with the compared existing static mixers. The developed 3D CFD transport model, validated by the reported experimental data, enables the computation of transport properties for any geometrical design and fluid properties, and avoids the need for experimental data each time a new NETmix configuration is designed.     

Dynamics of catalytic reactions and reactors

Heterogeneous catalytic reactions and catalytic reactors are known to exhibit complex dynamic behavior and significant progress has been made, in the past two decades, in understanding this complexity using the tools of nonlinear dynamics and advanced experimental methods. This article presents an overview of complex dynamic behavior in heterogeneous catalysis and points out their intriguing nature along with practical implications. The issues discussed are the source of oscillatory behavior, classification of complex motions, transitions to chaotic solutions and spatiotemporal patterns in reactors of various geometries.     

ENERGY DISSIPATION DISTRIBUTION AND MIXING IN A TORUS REACTOR

Previous works devoted to the development of the swirl flow generated by rotation of the marine screw impeller in the loop toroidal reactor show that the flow structure is characterized by the existence of a secondary flow. The deformation of the axial velocity profile, due to the bends curvature and the rotation of the agitator, modify considerably the friction and the transfer near the wall. The objective of this work is to study the toroidal flow and to characterize the wall turbulence. The wall shear stress distribution in the torus were performed by using an electrochemical method. The measurements of the wall shear stress were carried out in the inner and outer walls. The evolution of the wall velocity gradient with the longitudinal distance depends on the location in the torus. These results allow to obtain information about the friction factor, which is compared with the one measured directly by using piezometric connections. The experimental determination of the axial dispersion coefficient is obtained by using the dispersion plug flow model with a total recirculation. Finally, a relationship between the turbulent characteristics and the mixing parameters has been established.     

A radiant heating wire mesh single-particle biomass combustion apparatus

A computer controlled wire mesh apparatus has been developed that uses radiant heating elements at 900 °C to combust individual biomass particles. Optical access allows particle combustion characterisation by video image analysis.Combustion test results are presented for roughly cubic particles of European ash at a range of sizes with different moisture contents. As the moisture content of the particles increased the overall times required for drying, devolatilisation and burnout increased. The effect of moisture content, however, had a lesser effect upon total burning time than the effect of particle mass, which was shown to dominate the total combustion time for this single biomass type.     

低管径比固定床反应器床层特性及流动传热模拟

管式固定床常用于高温催化裂解工艺,探究低管径比固定床结构特性和高温下流动传热规律,可以为优化固定床高温催化裂解工艺提供参考.针对粒子解析法中离散元DEM方法对颗粒描述不准确和网格划分困难的问题,采用基于刚体动力学的blender生成床层堆积模型,并提出了新的接触点处理方法.该方法不改变颗粒和床层形状参数,适用于各种形状颗粒,减小了模型接触处理难度.生成了三种反应管内径与柱状颗粒的等比表面积球当量直径之比(管径比D/dp)的圆柱状颗粒床层和一种球状颗粒床层,探究了管径比和颗粒形状对床层结构和流动传热特性的影响.结果表明,床层总体空隙率随着管径比增大而减小,颗粒堆积呈圈层分布,径向空隙率和轴向平均速度的径向分布曲线高度一致,压降与Eisfeld修正式基本吻合.此外,床层流场分布与床层结构高度相关,流道空隙的大小会直接影响沟流现象的产生,进一步影响其温度场分布和传热.球状颗粒床层有更均匀的温度场分布,但传热弱于圆柱状颗粒床层.     

填料因子的确定方法和物理意义

本文提出了确定填料因子的简便方法，探讨了填料因子的物理意义。认为引入湿填料因子和液泛填料因子是不恰当的，推荐按Ｋｉｓｔｅｒ－Ｇｉｌｌ经验关联式计算国产填料的泛点压降。     

旋风预热器阻力损失的构成及其影响因素

从理论上对旋风预热器阻力损失的构成做了简单介绍,并在研究了国内外20多种不同形式预热器之 后,对影响旋风筒实际压降的结构参数和非结构参数进行了详细的分析研究,归纳出最佳的匹配参数。     

Catalytic reactors based on porous ceramic membranes

This overview discusses some of the developments and outstanding opportunities in the field of catalytic reactors based on porous ceramic membranes, both inert and catalytic. This is an emerging area, where inputs from heterogeneous catalysis, material science and reactor engineering are playing the key roles. Rather than attempting a thorough review of the relevant literature, this work deals with some general concepts and then concentrates on a few selected examples that illustrate the application of membrane reactors.