NUMERICAL SIMULATION OF SWIRLING FLOW IN A CYCLONE CHAMBER

The ability to predict the influence of design parameters on the aerodynamics of cyclone chambers flows is of prime concern in furnace engineering and a number of high temperature processes. The two-dimensional Los Alamos SOLA prediction technique has been extended to include the computation of an axisymmetric swirling flow. The transient Navier-Stokes equations of an incompressible fluid are solved via their associated finite difference equations, directly in terms of the primitive pressure-velocity variables. For this, a short simple computer code has been developed, using a laminar flow simulation with ‘free slip’ wall boundary conditions. Predictions show that a useful characterization of the flowfield is now available. The simplified code represents a basic tool, to which user-oriented complexities and sophistications can be added later as required     

Characteristics of transient blood flow in MHVs with different maximum opening angles using fluid-structure interaction method

A numerical analysis has been performed to investigate the characteristics of two-dimensional transient blood flows interacting with the leaflet motion in a bileaflet mechanical heart valve with different maximum opening angles, located in the aortic position. Here, for one cycle of heartbeat the analysis has been carried out in the light of fluid-structure interaction since the blood flow and the leaflet motion are coupled with each other. Blood has been assumed to be a Newtonian and non-Newtonian fluid, where the Carreau model has been used for the simulation of non-Newtonian fluid. Physiologic ventricular and aortic pressure waveforms have been used as flow boundary conditions at the ventricle and the aorta. A finite volume computational fluid dynamics code and a finite element structure dynamics code have been used concurrently to solve the flow and the structure equations, respectively, where the two equations are strongly coupled. Flow fields, leaflet behavior, and shear stresses with time have been obtained. Also the discharge and the regurgitation flow rates have been calculated. The maximum shear stress, an important issue for valve hemodynamic analysis, has been found in the vicinity of the contact point where a leaflet contacts with housing in the final stage of the closing phase.     

Boundary-layer analysis of heat and mass transfer over a circular cylinder in crossflow

Two-dimensional laminar boundary-layer equations of momentum, heat and mass transfer have been numerically solved tinder forced convection. A finite difference approximation of the governing equations in a Göertler-type variable domain has been implemented on computer. To provide rigorous initial conditions at x 0 in the boundary-layer code, differential equations governing heat and mass transfer in the stagnation region have been set up and solved numerically. The effect of outer flow condition on skin friction as well as heat and mass transfer has been demonstrated. Results obtained made an improvement over past theoretical predictions based on analytical approximation, and agreed favorably with experimental data available.     

Magnetohydrodynamics thin film fluid flow under the effect of thermophoresis and variable fluid properties

The thin film flow of fluid over a stretching sheet with variable fluid properties under the effect of thermophoresis has been investigated. A transverse magnetic field is also applied to the fluid flow in the presence of thermal radiation. The governing equations have been transformed through suitable similarity variables into nonlinear coupled differential equations with physical conditions. The solution of the coupled problem has been obtained by using the second alternative of OHAM (OHAM‐2). The solution of the coupled problem through this new method and its fast convergence is mainly focused in this work. The effect of physical parameters appears in the problem are shown graphically and discussed. Finally, the obtained results are compared with a numerical (ND‐Solve) method to authenticate the code of the OHAM‐2. The physical and numerical agreement of these two methods has been shown. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

气液两相流管道中的瞬态流动及清管操作模型

对于气液两相流的瞬态模拟,需要对连续性方程、能量方程及动量方程进行复杂的计算.在油气管线中,可使用对气体连续性方程进行近似的稳态假设和对某一流态下的两相局部动量平衡的方法对连续性方程和动量方程进行适当的简化.使用的计算机编码程序将假设流体绝热的简化瞬态模型与流态转化准则结合应用,并通过实验数据对其模拟结果进行验证.该程...     

Air flow patterns in an industrial milk powder spray dryer

The air flow patterns in an industrial milk powder spray dryer have been investigated. Isothermal three-dimensional transient simulations in the absence of atomised liquid droplets have been carried out using the commercial CFD code (CFX10.0) in which the transient Navier–Stokes equations are solved. The shear stress transport (SST) turbulence model was implemented to model the effects of turbulence.     

COMBINED CONDUCTION-MIXED CONVECTION-SURFACE RADIATION FROM A UNIFORMLY HEATED VERTICAL PLATE

The present article reports the results of a numerical study on combined conduction-mixed convection-surface radiation from a vertical plate with uniform internal heat generation. The study considers the governing fluid flow and heat transfer equations without boundary layer approximations. Air is taken to be the cooling medium. Stream function-vorticity formulation, coupled with finite volume method, is used to solve the problem. A computer code has been written for the purpose, and results are validated with available experimental and analytical results for asymptotic limiting cases. In addition to making comprehensive parametric studies, useful correlations for evaluating the nondimensional maximum and average temperatures of the plate and mean friction coefficient are deduced based on a large set of data generated from the code.     

A fully coupled quadrature-based moment method for dilute to moderately dilute fluid–particle flows

A third-order quadrature-based moment method for simulating dilute and moderately dilute fluid–particle flows has been implemented with full coupling in a computational fluid dynamics code. The solution algorithm for the particle phase uses a kinetic-based finite-volume technique to solve the velocity moment equations derived from kinetic theory. The procedure to couple the particle-phase volume-fraction and momentum equations with the Eulerian solver for the fluid phase is explained in detail. As an example application, simulations of a particle-laden vertical channel flow at fluid-phase Reynolds number 1379 and particle Stokes numbers 0.061 and 0.61 were carried out. The fluid and particle velocities, particle-phase volume fraction and granular temperature were observed to reach a steady state in the case of Stokes number 0.061, while instabilities that led to the formation of structures and initiated the particle segregation process were observed in the case with the higher Stokes number. These results are validated against results from a classical two-fluid model derived from the kinetic theory of granular flows in the small Knudsen number limit, and Euler–Lagrange simulations of the same flow.     

A collocation solver for systems of boundary-value differential/algebraic equations

A spline collocation procedure has been implemented to solve systems of multi-point boundary-value problems for mixed order differential/algebraic equations (BVP-DAEs). This implementation is based on the modification of an existing code “COLSYS”, which solves boundary-value ordinary differential equations (BVP-ODEs) alone. With minor changes to the original COLSYS code, the resulting procedure offers robust solutions to systems of DAEs, in addition to ODEs. A numerical example with application in chemical engineering is shown to demonstrate the superior ability of this procedure over other software.     

Particle Transport and Deposition in a Hot-Gas Cleanup Pilot Plant

ABSTRACT

Development of hot-gas filtration systems for advanced clean coal technologies has attracted considerable attention in recent years. The Integrated Gasification and Cleanup Facility (IGCF), which is an experimental pilot plant for testing performance of ceramic candle filters for hot-gas cleaning, has been operational at the Federal Energy Technology Center (FETC) in Morgantown, West Virginia, for several years. The present work describes a computer simulation study of gas flow and particle transport and deposition in the IGCF filter vessel with four filters. The stress transport model of FLUENT? code is used for evaluating the gas mean velocity and the root mean-square fluctuation velocity fields in the IGCF filter vessel. The instantaneous fluctuation velocity vector field is simulated by a filtered Gaussian white-noise model. Ensembles of particle trajectories are evaluated using the recently developed PARTICLE code. The model equations of the code include the effects of lift and Brownian motion in addition to gravity. The particle deposition patterns on the ceramic filters are evaluated, and the effect of particle size is studied. The results show that, for a clean filter (just after the backpulse), the initial deposition rate of particles on the candle filters is highly nonuniform. Furthermore, particles of different sizes have somewhat different deposition patterns, which could lead to nonuniform cake compositions and thicknesses along the candle filters. The effects of variations in the filter permeability on the vessel gas flow patterns and the pressure drop, as well as on particle transport patterns, are also studied.     

Population balance and computational fluid dynamics modelling of ice crystallisation in a scraped surface freezer

Ice crystallisation in a scraped surface freezer is exceedingly complex and there is very limited fundamental understanding of the influences of fluid flow and heat transfer on ice crystal size, number and shape. This paper presents a computer modelling study that combines population balance method and computational fluid dynamics method. Ice crystal nucleation and growth kinetics has been described by discrete population balance equation. Algorithms for solving the coupled equations of fluid flow, heat transfer and discrete population balance of ice crystallisation have been developed and implemented into a commercial code. Demonstrated is a 2-D computer simulation of ice crystallisation in a scraped surface freezer. Although the simulation makes several assumptions including simplified fluid flow conditions, the predicted ice crystal size distribution is comparable to the experimental data. It is shown that with combined computational fluid dynamics and population balance modelling much insight into the interaction of fluid flow, heat transfer and ice crystallisation in the scraped surface freezer can be obtained.     

垂直圆管内液氮流动沸腾的理论模型及数值模拟

分析了液氮流动沸腾过程中气液两相间动量、能量以及质量的传输规律,建立了相应的理论模型,新模型重点修正了界面面积浓度和气泡挣脱直径的计算式;采用新建立的理论模型作为封闭方程对CFX-4.3中内建的双流体模型进行了修正,并采用修正后的双流体模型模拟了液氮在垂直圆管内的流动沸腾过程.数值模拟的结果与文献中的实验数据吻合较好,证明了本文所建模型的合理性.通过数值模拟发现,两相流参数分布的不均匀性对液氮流动沸腾过程中的热质传输特性有重要影响.     

Computer modelling and numerical analysis of hydrodynamics and heat transfer in non-porous catalytic reactor for the decomposition of ammonia

Chemical reactors exhibit very complex behaviours such as multiple steady states, oscillations, etc. resulting from complex linkage between the transport processes and the non-linear chemical reaction kinetics. Ammonia is a potential hydrogen source for a number of fuel cell applications for small scale power generation useful for portable equipments. In the present work, we analyse the fluid dynamics and heat transfer in catalytic microreactor systems for the decomposition of ammonia over a monolayer Ni non-porous catalyst. The overall model for this convective-diffusive-reactive system consists of a flow model, a mass transport model, an energy conservation model and a reaction kinetics model for ammonia decomposition. The flow model is described by the Stokes equation for a creeping flow regime. The mass transport and energy conservation models are based on convective-diffusion equations. The rate of ammonia decomposition can be measured as a function of the catalyst activity and ammonia concentration. A standard Galerkin finite element technique has been applied for the solution of the flow equations. A slightly perturbed form of the mass continuity equation is used to satisfy the Ladyzhenskaya-Babuška-Brezzi stability criterion. For the solution of convection-diffusion equations, a streamline inconsistent upwind finite element scheme has been chosen to avoid any spurious oscillations. C⁰-continuous 9-noded Lagrangian biquadratic isoparametric finite elements are used for the approximation of the field variables. A second-order Taylor-Galerkin time-stepping scheme has been chosen for the temporal discretisation of the flow equations whilst an implicit theta method has been used for convection-diffusion equations. The results are presented in the form of velocity vectors and concentration, temperature contours and are examined for stability, convergence and theoretical consistency.     

Simulation and interpretation of catalytic combustion experimental data

The catalytic combustion of CH₄/air in monoliths has been simulated through a commercial numerical fluid dynamic code. The program has been suitably modified in order to describe the heterogeneous reaction at the channel walls. Different flow arrangements have been studied in an attempt to closely match an experimental investigation reported in the literature. Single step overall rate equation has been used and identification of suitable kinetic constants performed through the use of optimization techniques. A framework for kinetic investigation accounting for complex flow structure and interaction with the chemistry is suggested. The relevant and sometimes overwhelming role of transport phenomena is discussed.     

Two Dimensional Heat and Mass Transfer During Convective Drying of Porous Media

In this paper, we study numerically two-dimensional heat and mass transfer during convective drying in porous media. The set of macroscopic equations is very comprehensive and takes into account the effect of gaseous pressure. A numerical code has been established. This code has allowed us to determine t.he space-time evolution of the temperature, the total pressure and the moisture content.     

On the modeling of electro-hydrodynamic flow in a wire-plate electrostatic precipitator

Modeling of the flow velocity fields for the electrohydrodynamic (EHD) flow in a wire-to-plate type electrostatic precipitator (ESP) was achieved. Solutions of the steady, two-dimensional Navier-Stokes equations have been computed. The equations were solved in the conservative finite-difference form on a fine uniform rectilinear grid of sufficient resolution to accurately capture the momentum boundary layers. The numerical procedure for differential equations was used by SIMPLEST [Michel, 2002], a derivative of Patankar’s SIMPLE algorithm, to bring rapid convergence. The Phoenics (Version 3.5.1) CFD code, coupled with Poisson’s and ion transport equations and electric body force in the momentum equation, developed in this study, was used for the numerical simulation. From calculations for the flow employing different flow models, the Chen-Kimk-ε turbulent model appeared to be the most appropriate choice to obtain a quantitative image of the resulting mean flow field and downstream wake flow of the rear wire, although this was obtained from a qualitative analysis due to the lack of experimental verification. The flow velocity field pattern showed a strong EHD secondary flow, which was clearly visible in the downstream regions of the corona wire despite the low Reynolds number for the electrode (Re_CW=12.4). Secondary flow vortices were also caused by the EHD with increases in the discharge current     

Numerical simulation of complex particle-fluid flows

This paper presents a numerical study of particle-fluid flow in complex three-dimensional (3D) systems by means of Combined Continuum and Discrete Method (CCDM). In the CCDM, the motion of discrete particles phase is obtained by Discrete Element Method (DEM) which applies Newton's laws of motion to every particle and the flow of continuum fluid is described by the local averaged Navier-Stokes equations that can be solved by the traditional Computational Fluid Dynamics (CFD). This method has been increasingly used worldwide, but so far its application is limited to relatively simple flow systems. In this work, the simulation is achieved by incorporating a DEM code into the commercial CFD software package Fluent that can be readily used for complex CFD problems. The applicability of this development is demonstrated in the study of the particle-fluid flow in various 3D systems including pneumatic conveying bend, cyclone separator and circulating fluidized bed. It is shown that the numerical results are, either qualitatively or quantitatively depending on the availability of experimental data for comparison, in good agreement with those measured, and can generate information leading to better understanding of the internal flow structure of these systems.     

Engineering Model of a Nonisobaric Heavily Laden Gas‐Particle Jet

An axisymmetrical model of a rapid nonisobaric heavily laden gas‐particle jet is developed. The model is based on the general functions for both axial and radial pressure distributions, which were discovered by a numerical study of rapid gas‐particle jets by the CFD code. The model equations were solved analytically. The results obtained by the model developed are in good agreement with those computed by the CFD code for a wide range of flow parameters.     

Modeling of Drying in Moving Bed

The aim of this work is to study the simultaneous heat and mass transfer between air and soybean seeds in moving bed dryers with parallel flow (concurrent and countercurrent), by means of an experimental and simulation work, verifying the validity of classical assumptions. The numerical solution of a one-dimensional boundary value problem was obtained by means of a computational code based on axial integration through DASSL code. Deviations from flat air velocity profile were taken into account considering empirical and mechanistic equations found in the literature that describes air profile as function of radius. The experimental data of air humidity, temperature, and seed moisture content and temperature at the dryer outlet were compared to the simulated values.     

Modeling of Drying in Moving Bed

The aim of this work is to study the simultaneous heat and mass transfer between air and soybean seeds in moving bed dryers with parallel flow (concurrent and countercurrent), by means of an experimental and simulation work, verifying the validity of classical assumptions. The numerical solution of a one-dimensional boundary value problem was obtained by means of a computational code based on axial integration through DASSL code. Deviations from flat air velocity profile were taken into account considering empirical and mechanistic equations found in the literature that describes air profile as function of radius. The experimental data of air humidity, temperature, and seed moisture content and temperature at the dryer outlet were compared to the simulated values.