立式循环撞击流反应器不同倾角桨叶的混合性能比较

采用FLUENT软件对不同倾角桨叶和转速下的立式循环撞击流反应器流场分布进行了数值模拟。分析结果表明,同一转速下时,特征撞击面上速度分布的平均值比较接近,说明倾角对撞击混合的传质效果影响不大;同一转速时,桨叶倾角为45°的撞击面上速度沿径向分布的均方根差σ值最大,这表示速度沿径向分布的离散程度最大,撞击混合效果最佳。     

径向流动反应器流体力学特性研究

本文提出了表征径向流动反应器内流体流动规律的数学模型.该模型为一特殊的二阶微分方程的边值问题.对于Ⅱ型流动:Au′u″+Bu′u+Cu~2=0对于Z型流动:Au′u″+Bu′u+Cu′+Eu~2+F(1-u)~2=0边界条件为y=0,u=1;y=1,u=0式中模型参数A、B、C、E、F决定于径向反应器分布流道结构尺寸、穿孔阻力系数和径向床层特性等因素.为简化Ⅱ型径向反应器边值问题的求解过程,本文推荐一种解析求解方法.该模型应用于径向氨氧化炉操作工况和径向氨合成塔设计工况的模拟,揭示了径向流动反应器内的流体力学特性.     

Dispersed plug flow model for steady-state laminar flow in a tube with a first order sink at the wall

Steady state, laminar flow transport in a tube with a first order sink at the wall involves two dimensions—radial and axial. In this paper, a novel iterative technique has been proposed for reducing such a two-dimensional model to an equivalent one-dimensional dispersed plug flow model. The latter yields an analytical expression for the equivalent axial dispersion and a simple, closed form, but approximate, analytical solution of the original two-dimensional problem. The operating range in which this analytical solution is useful has been investigated for a system with mass transfer at the wall.     

不均匀流动对径向氨合成塔性能的影响

通过导出考虑床层流速分布的径向床二维非均相模型,考察了不均匀流动对三段径向冷激式氨合成塔性能的影响,模拟计算表明了不均匀流动会对径向合成塔性能造成一定的影响,在各种不同的床层进口温度,人口氨浓和活性系数下,流动的不均匀度所造成的影响是不同的,提高进口温度、降低入口氨浓和提高活性系数有利于降低流动不均匀度的影响。流动不均匀对三段径向合成塔净值和生产能力的影响是有限的,在计算条件下,均匀流动和不均匀度     

A Re‐Examination of heat transfer in laminar divergent flow between two parallel fixed discs

Upon a critical review of pertinent literature, new theoretical expressions for dimensionless heat transfer rates between two parallel fixed circular discs and a fluid in radial divergent laminar flow are established and compared to previously published theory and experimental data. Based on the logarithmic mean temperature difference, the new analytical relationships are shown to adequately predict dimensionless heat transfer rates, and it is recommended that they be used in preference to certain earlier expressions which are either erroneous or of strongly limited applicability.     

Analysis of hollow fiber reverse osmosis membrane module of axial flow type

Several analyses of hollow fiber reverse osmosis (RO) modules in which permeate water flows from the outer to the inner side of the membrane have been attempted over the past 20 years. In our previous work, an FCP (Friction Concentration Polarization) model showed good agreement with a wide range of actual performance data of a hollow fiber RO membrane module of radial flow type. In this work, this analytical model was applied to axial flow type hollow fiber modules. The performance of the axial flow type module with high packing density of hollow fibers was analyzed, taking into consideration the axial concentration profile in the module. It was confirmed that this model showed good agreement with experimental data for an axial flow type RO membrane module. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Semianalytical solution for power‐law polymer solution flow in a converging annular spinneret

A semianalytical solution for a power‐law fluid flowing through a conical annulus was derived to estimate the velocity profile in the axial direction, the shear rate and the elongation rate within a spinneret during the spinning of hollow fiber membranes. The angle coefficient was introduced as a new parameter to account for the effect of radial flow and to modify the governing equation, which initially neglected the effect of radial flow. The results estimated from this semianalytical solution agreed more closely with computational fluid dynamics simulation results than those obtained from the approximate analytical solution in our previous study. By accurately predicting the velocity profile in the axial direction and the shear and elongation rates in a conical annulus, the solution derived in this study is expected to provide a reliable criterion for spinneret design to achieve a specified membrane morphology with a desired performance. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3489–3499, 2015     

Anisotropic in-plane permeability of fabric media

An elegant procedure is proposed for obtaining components of the orthotropic or anisotropic in-plane permeability tensor from experimental data on flow front position and time. A radial flow geometry allows the shape of the advancing flow front to be dictated by the in-plane permeability of the fabric media. The directional permeabilities in the fabric plane are directly calculated from fluid and fabric properties together with data from the mold filling experiment (resin injection pressure and flow front position with time). The simplicity of the apparatus and proposed analytical procedure permit easy testing and comparison of different types of fibrous media.     

Mass transport corrected Tafel analysis of voltammetric waves: When can it be applied?

The derivations of mass transport corrected Tafel equations are presented for a heterogeneous electron transfer. It is shown that the equations are valid for an electrode which is uniformly accessible to the electroactive species in solution. It is also shown that the equations are valid for any electrode geometry when the electron transfer is fast and reversible and the chemical species involved have equal diffusion coefficients. The microdisc and tubular flow electrodes are used as examples of non-uniformly accessible electrodes. The case is considered when the electron transfer is fast and reversible, the electrode is non-uniformly accessible and the species involved have unequal diffusion coefficients. Under these conditions it is shown by analytical solution that the Tafel equation is valid at the tubular flow electrode when axial and radial diffusion are insignificant. It is shown by numerical solution that at the same electrode the Tafel equation is not valid when axial and radial diffusion are significant.     

A model for gas flow in jet spouted beds

A model of general application that is based on the definition of streamlines and that is in agreement with the bed geometry has been proposed in order to describe the gas flow in a jet spouted bed in conical contactors. The model quantifies the dispersion in the direction of the streamlines by using a characteristic modulus. The validity of the model has been experimentally proven on the basis of the measurement and analytical correlation of gas velocity profiles at different radial and longitudinal positions in the contactor, and of the application of the stimulus response technique for the calculation of the residence time distribution function.     

高速永磁电机转子碳纤维护套的缠绕张力计算研究

表贴式高速永磁电机转子的永磁体不能承受高速旋转时产生的离心力,为此研究了一种特殊的大张力环向缠绕碳纤维护套,由于缠绕时张力的施加,这种碳纤维护套会在永磁体外表面形成一定的预压力,从而保护永磁体在高速旋转时不被离心力破坏。基于弹性力学相关理论,提出了计算缠绕张力作用下纤维层应力分布及其对永磁体预压力的方法。通过不同张力缠绕实验确定碳纤维缠绕工艺极限张力,以此为基础,分别采用解析法和有限元法计算了不同张力制度下的纤维层剩余应力,并在大张力缠绕电机转子实验中测试了纤维层提供的预压力。结果表明,解析法能较为准确地预测出碳纤维缠绕层的应力分布情况及其对永磁体的压紧力,且解析结果和有限元的误差很小,和实验测试结果的误差在可接受范围之内,所提出的大张力环向缠绕碳纤维护套可以满足永磁电机转子高速旋转的要求。     

Evaluation of the Berman-Olander Long-Bowl Gas Centrifuge Solution

The hydrodynamic equations for a long-bowl gas centrifuge can be simplified to obtain a one-dimensional differential equation for the variation of the non-dimensional axial velocity in the radial direction. In this study the solution of the one-dimensional differential equation was revisited and an approximate finite element solution of the differential equation was developed. The primary analytical solution was found to be consistent with the finite element solution, but the associated simplified solutions were found not always to be consistent with the finite element solution. Improved values for the originally published centrifuge flow function parameters are also presented.     

Hydrodynamics of binary fluidization in a riser: CFD simulation using two granular temperatures

A new computational fluid-dynamic (CFD) model with a separate granular temperature (2/3 random particle kinetic energy per unit of mass) equation for each phase or particle size was developed using constitutive equations derived earlier by Huilin, Gidaspow and Manger. In agreement with the experiment and model of Mathiesen, Solberg and Hjertager the new model computes the observed core-annular flow regime. It predicts the trends of the observed radial and axial particle diameter distributions. For elastic particles the computed particle velocity distributions are parabolic. They are close to the laminar type approximate analytical solution for flow in a pipe, where the mean velocity equals the inlet flux divided by the particle density and volume fraction. The computed turbulent intensity is lower for large particles than for small particles, as measured. This is in agreement with an approximate analytical solution for the granular temperature in the developed flow region of a riser for elastic particles. Computations show that for sufficiently inelastic particles the granular temperature in the center can be lower than near the wall resembling the measured particle fluctuating velocity distribution.     

真空变压吸附制氧径向流吸附器的流动特性模拟

真空变压吸附制氧是一个复杂的动态过程,深入了解真空变压吸附制氧过程中吸附器内的流动特性是吸附器设计与完善的基础.基于Fluent中的多孔介质模型,通过用户自定义函数功能,建立了真空变压吸附制氧用径向流吸附器的二维轴对称模型,研究了真空变压吸附首次和第二次循环中径向流吸附器的流动特性,对比分析了吸附剂颗粒直径、流道截面积...     

带纵向涡发生器喷动床内颗粒流动特性PIV实验

针对喷动床内环隙区颗粒缺少横/径向运动的特点,通过实验将纵向涡流发生器及纵向涡流效应引入喷动床。采用粒子图像测速技术研究了在内径为152 mm的喷动床内纵向涡流及颗粒设计参数对喷动床内喷射区及环隙区颗粒相径向速度的影响,研究结果表明,纵向涡发生器在扰流元件上方横截面内颗粒相运动出现大量二次涡流,相比较于无纵向涡流扰流件情况,喷动床内的颗粒径向速度得到了显著增加,表明纵向涡发生器能够增强颗粒相在喷射区及环隙区的径向运动能力。在喷动床稳定喷动范围内,颗粒直径及颗粒密度越小,纵向涡流对颗粒相径向运动的强化效果越佳。     

Flow through a circular tube with a permeable Navier slip boundary

For Newtonian fluid flow in a right circular tube, with a linear Navier slip boundary, we show that a second flow field arises which is different to conventional Poiseuille flow in the sense that the corresponding pressure is quadratic in its dependence on the length along the tube, rather than a linear dependence which applies for conventional Poiseuille flow. However, assuming that the quadratic pressure is determined, say from known experimental data, then the new solution only exists for a precisely prescribed permeability along the boundary. While this cannot occur for conventional pipe flow, for fluid flow through carbon nanotubes embedded in a porous matrix, it may well be an entirely realistic possibility, and could well explain some of the high flow rates which have been reported in the literature. Alternatively, if the radial boundary flow is prescribed, then the new flow field exists only for a given quadratic pressure. Our primary purpose here is to demonstrate the existence of a new pipe flow field for a permeable Navier slip boundary and to present a numerical solution and two approximate analytical solutions. The maximum flow rate possible for the new solution is precisely twice that for the conventional Poiseuille flow, which occurs for constant inward directed flow across the boundary.     

蜗壳结构对立式高温熔盐泵性能的影响

引言熔盐泵是诸多化工流程中的关键设备,主要用于输送熔融硝酸盐、亚硝酸盐、离子膜烧碱。近年来在三聚氰胺、制盐、制碱及苯酐等化工流程中得到广泛应用,同时,随着工业用铝的大幅增加,熔     

Influence of Anvil Properties on RDX Thin Layer Ignition Behavior

We report on a drop‐impact protocol that arrests sample radial flow to isolate how anvil properties influence ignition in a thin layer of RDX powder. To eliminate sliding friction as a probable heating mechanism, flow arrestment was provided by a waxed weighing paper that shielded the RDX layer from direct contact with the impact surfaces. RDX reaction sensitivity under bare and shielded conditions for the standard O1 hardened steel anvil was compared with that for two deformable anvil types: 1018 steel and C110 copper. Profilometer measurements of anvil deformation and paper impressions quantified anvil plastic work and final radial flow displacement. Post‐test particle analyses correlated particle size distribution to ignition results. Experiments indicated that the impact energy absorbed by the anvils was varied and inhibited ignition accordingly. For the standard anvil, ignition was not inhibited under flow arrestment, suggesting that significant radial sliding or flow is not essential for thin layer ignition.