Comprehensive Computational Fluid Dynamics Model Research Articles

Heap Leaching: Modelling and Forecasting Using CFD Technology

Heap leach operations typically employ some form of modelling and forecasting tools to predict cash flow margins and project viability. However, these vary from simple spreadsheets to phenomenological models, with more complex models not commonly employed as they require the greatest amount of time and effort. Yet, accurate production modelling and forecasting are essential for managing production and potentially critical for successful operation of a complex heap, time and effort spent in setting up modelling tools initially may increase profitability in the long term. A brief overview of various modelling approaches is presented, but this paper focuses on the capabilities of a computational fluid dynamics (CFD) model. Advances in computational capability allow for complex CFD models, coupled with leach kinetic models, to be applied to complex ore bodies. In this paper a comprehensive hydrodynamic CFD model is described and applied to chalcopyrite dissolution under heap operating conditions. The model is parameterized against experimental data and validated against a range of experimental leach tests under different thermal conditions. A three-dimensional ‘virtual’ heap, under fluctuating meteorological conditions, is simulated. Continuous and intermittent irrigation is investigated, showing copper recovery per unit volume of applied leach solution to be slightly increased for pulse irrigation.

Three-dimensional computational fluid dynamics modelling and experimental validation of the Jülich Mark-F solid oxide fuel cell stack

This work is among the first where the results of an extensive experimental research programme are compared to performance calculations of a comprehensive computational fluid dynamics model for a solid oxide fuel cell stack. The model, which combines electrochemical reactions with momentum, heat, and mass transport, is used to obtain results for an established industrial-scale fuel cell stack design with complex manifolds. To validate the model, comparisons with experimentally gathered voltage and temperature data are made for the Jülich Mark-F, 18-cell stack operating in a test furnace. Good agreement is obtained between the model and experiment results for cell voltages and temperature distributions, confirming the validity of the computational methodology for stack design. The transient effects during ramp up of current in the experiment may explain a lower average voltage than model predictions for the power curve.

Wavy-tape insert designed for managing highly concentrated solar energy on absorber tube of parabolic trough receiver

Abstract In this paper, a swirl flow generator, namely wavy-tape insert, is tailored for the parabolic trough receiver (PTR) to improve its performances by mean of enhancing the heat transfer inside the absorber tube. A comprehensive computational fluid dynamics model is established to study the flow and heat transfer inside the full-size PTR equipped with wavy-tape insert. It is found that wavy-tape provokes highly-localized heat transfer enhancement effects, which exactly aim at the highly-concentrated solar heat load. Consequently, both the tube temperature and the heat loss are reduced effectively. A static mechanical analysis is performed to evaluate the thermal stress and deformation of absorber tube, both of which decrease in the presence of wavy-tape. However, the wavy-tape improves the PTR thermal-mechanical performances at the expense of increased pressure loss penalty. The overall effects of wavy-tape insert on PTR are evaluated based on different criterions. For a same flow rate, the total entropy generation rate can be reduced significantly by using wavy-tape insert. For an identical pumping power consumption, the insert not only reduces the thermal stress and the heat loss, but also gives raises to the specific enthalpy gain of the working fluid.

Performance optimization of a two-phase closed thermosyphon through CFD numerical simulations

In this paper, a comprehensive computational fluid dynamics (CFD) modeling was built to reproduce the pool boiling in the evaporator section and the liquid film condensation in a closed thermosyphon. The two phase Volume Of Fluids (VOF) model was used to simulate the heat transfer during evaporation and condensation inside a closed thermosyphon. This CFD model was validated using experimental results, and a good agreement was observed. Moreover, the results were analyzed in terms of the vapor volume fraction variation, temperature and vertical velocity at different locations along the thermosyphon. A parametric study was also conducted to enhance the performance of the thermosyphon designed for solar thermal energy applications like domestic hot water systems. It is found that the performance of the two-phase closed thermosyphon can be improved by tilted fins integration on the lateral surface of the condenser section.

Modeling of the slab heating process in a walking beam reheating furnace for process optimization

A new methodology involving the integration of a three-dimensional (3D) Computational Fluid Dynamics (CFD) model and a two-dimensional (2D) heat transfer model for the study of the slab reheating process in a walking beam reheating furnace has been proposed. A comprehensive 3D CFD model has been developed to simulate the flow characteristics, combustion process and multi-mode heat transfer phenomena inside an industrial slab reheating furnace. A customized 2D heat transfer model for the slab reheating process has also been developed based on the finite difference method. The simulation results from the 3D CFD model provide detailed heat transfer boundary conditions for the 2D heat transfer model. Instrumented slab trials were conducted under typical operating conditions of the furnace and the results were used to calibrate the 2D model. By comparing the slab temperatures measured from the instrumented slab trials and those predicted using the models, it was demonstrated that the 3D CFD and 2D heat transfer models predict the reheating process reasonably well. The proposed methodology is fairly easy to be used by mill engineers for trouble shooting and optimizing of the slab reheating process.

VOF modelling of gas–liquid flow in PEM water electrolysis cell micro-channels

In this study, the gas–liquid flow through an interdigitated anode flow field of a PEM water electrolysis cell (PEMEC) is analysed using a three-dimensional, transient, computational fluid dynamics (CFD) model. To account for two-phase flow, the volume of fluid (VOF) method in ANSYS Fluent 17.2 is used. The modelled geometry consists of the anode channels and the anode transport layer (ATL). To reduce the complexity of the phenomena governing PEMEC operation, the dependence upon electro-chemistry is disregarded. Instead, a fixed source of the gas is applied at the interface between the ATL and the catalyst layer. An important phenomenon that the model is able to capture is the gas–liquid contact angle on both the channel wall and ATL-channel interface. Particularly, the latter interface is crucial in capturing bubble entrainment into the channel. To validate the numerical simulation, photos taken of the gas–liquid flow in a transparent micro-channel, are qualitative compared against the simulation results. The experimental observations confirm the models prediction of long Taylor bubbles with small bubbles in between. From the simulation results, further intriguing details of the flow are revealed. From the bottom to the top of the outgoing channel, the film thickness gradually increases from zero to 200 μm. This increase in the film thickness is due to the particular superficial velocity field that develops in an interdigitated flow. Here both the superficial velocities change along the length of the channel. The model is capable of revealing effect of different bubble shapes/lengths in the outgoing channel. Shape and the sequence of the bubbles affect the water flow distribution in the ATL. The model presented in this work is the first step in the development of a comprehensive CFD model that comprises multiphase flow in porous media and micro-channel, electro-chemistry in catalyst layers, ion transport in membrane, hydrogen evolution, etc. The model can aid in the study of gas–liquid flow and its impact on the performance of a PEMEC.

Comprehensive computational fluid dynamics model of solid oxide fuel cell stacks

This paper describes the development and application of a novel computational fluid dynamics model which allows the investigation of large solid oxide fuel cell stacks in practical computation times. Comparisons with a previously verified model match quantitatively to within 3% difference for all parameters of a benchmark case and solve within 1.5% the computation time for parallel flows of air and fuel in a cell, verifying the present model as a practical option in stack design. The model is used to demonstrate that the distribution of flow rates to each cell in a 100 cell stack significantly affects the temperature distribution and overall electrochemical performance. In a further analysis, it is quantitatively demonstrated that it would be misleading to attempt to predict performance or optimise manifold designs based on a model with uncoupled transport and electrochemistry.

A review on numerical consideration for computational fluid dynamics modeling of jet mixing tanks

Over two decades or so, the computational fluid dynamics (CFD) modeling of various jet mixing tank configurations was developed and published. Further, the studies of various parameters used in experimental and CFD works were also reviewed to obtain the optimal design procedure. However, the numerical setup for jet mixing tank modeling was not studied and reported. Hence, in this review paper, the important numerical setup for CFD simulation of jet mixing tanks, including numerical solution techniques, turbulence model selection, boundary conditions, numerical methods, solution strategy, and CFD grid, are clearly demonstrated to achieve the comprehensive CFD modeling guideline for jet mixing tank. Further, the validations for jet mixing tank models are also represented.

CFD studies on biomass gasification in a pilot-scale dual fluidized-bed system

A comprehensive CFD (Computational Fluid Dynamics) model using the MP-PIC (Multiphase Particle-In-Cell) method was developed to simulate a pilot-scale (6 tons/day, 1 MW th) dual fluidized-bed biomass gasification system. In this model the particulate phase was described with the blended acceleration model. The momentum, mass, and energy transport equations were integrated with the kinetics of heterogeneous biomass and char reactions and homogeneous gas-phase reactions to predict the particle circulation, producer gas composition, and reactor temperature. The simulation results were compared with experimental data from the pilot-scale gasification system to validate the model at different operating conditions. Parametric studies were conducted to investigate the impact of gasifier temperature, steam to biomass ratio (S/B), and air supply to the combustor on the producer gas composition. The studies showed that increasing gasifier temperature and steam to biomass ratio (S/B) promoted syngas (CO + H2) production and increased hydrogen content in producer gas. The effect of air supply was minor, because for the dual fluidized-bed system air was not directly involved in biomass gasification.

Eulerian–Lagrangian modeling and computational fluid dynamics simulation of wire mesh demisters in MSF plants

This study focuses on computational fluid dynamics model (CFD) for simulation of demisters in multistage flash desalination (MSF). The Eulerian–Lagrangian model (steady-state and two-dimensional) was developed to simulate the demister. The model was used to simulate the flow of water vapor and brine droplets in the demister. The computational domain includes the following three zones: the vapor space above the demister, the vapor space below the demister, and the demister. The demister zone was modeled as tube banks. A sensitivity analysis of the model revealed that vapor velocity is the main parameter that affects demister performance. Additionally, the analysis indicated that vapor temperature had no effect on the pressure drop across the demister. The developed model was validated using data from both the literature and real MSF plants. Analysis indicated that model predictions and experimental data were consistent. This work gives extensive details for CFD modeling of the MSF demister. The work is based on a previous study by Al-Fulaij et al. (2014). This work is part of a group effort to develop a comprehensive CFD simulation for the entire flashing stage of the MSF process, which would provide an extremely efficient and inexpensive design and simulation tool to the desalination community.

Computational Fluid Dynamics Study of Heat Transfer in an Industrial Heat-carrier-free Regenerative Rotating Bed

Abstract In this paper, a comprehensive computational fluid dynamics model was built to study the heat transfer of coal in the Heat-Carrier-Free Regenerative Rotating Bed (HRRB). In comparison to the experimental data in the pilot scale HRRB, the model gave a satisfied prediction and was further extended to study the flow field and temperature distribution in the industrial HRRB. The effect of heating conditions on the temperature distribution of coal was also obtained. The results indicated a promising way to improve the output of upgraded coal in the industrial HRRB.

CFD modeling of two immiscible fluids mixing in a commercial scale static mixer

A Computational Fluid Dynamics model based on the Eulerian formulation for multiphase flow was developed to model the mixing hydrodynamics of two immiscible fluids in a commercial scale static mixer. The two immiscible liquids were condensate and caustic solutions and were considered as two phases that are interpenetrating each other. The aim of this study was to develop a comprehensive Computational Fluid Dynamics model for predicting the impact of hydrodynamic parameters such as length, diameter and the arrangement of the corrugated plates of a static mixer on the degree of mixing and the pressure drop of the mixture. The model has been evaluated by comparing predictions of the degree of mixing and the mixture pressure drop with the same data available for the static mixer of the desulfurization plant of the Kharg petrochemical company. It has been shown that the predictions of the developed model are well adapted to the experimental data.

Modelling of particulate matter transformations and capture efficiency

In the current work, a comprehensive computational fluid dynamics (CFD) model is developed for an accurate description of the transport and transformation of automotive particulate matter (PM) in monolithic reactors. The model accounts for the developing gas flow, the evaporation of hydrocarbons (HCs) from the particles, and the adsorption of HCs in the washcoat, as well as motion, shrinkage, and deposition of particles in the channel. The comprehensive CFD model is used to validate a simplified tanks‐in‐series approach with a conceptual model for PM transformations. In the development of more detailed and accurate chemical kinetics for the reactions of PM in filters, it will be necessary to also predict the time‐resolved properties of the particles collected in the filter (e.g., reactivity, amount of adsorbed HCs). It is shown in this work how the data necessary to construct such models can be obtained in situ with the aid of the conceptual model and PM measurements over an inert open substrate.

A Detailed Heat and Fluid Flow Analysis of an Internal Permanent Magnet Synchronous Machine by Means of Computational Fluid Dynamics

This paper presents a comprehensive computational fluid dynamics (CFD) model of a radial flux permanent magnet synchronous machine with interior magnets. In the CFD model, the water jacket cooling and a simplified model of the topology of the distributed stator winding are considered. The heat sources of the CFD model are determined from a finite-element analysis of the machine. The numerically determined temperature distributions of the machine are compared with measurement results from sensors located both in the stator and rotor. The particular focus of this paper is the analysis of the temperatures and the heat flow in the air gap and from the stator winding heads and the rotor to the inner air. Different operating conditions and two particular rotor designs with different inner air flow configurations are investigated. The potential of improving the thermal utilization of a rotor design with fan blades attached to the mounting plates of the rotor is shown.

An experimentally validated mathematical and CFD model of a supply air window: Forced and natural flow

Computational Fluid Dynamics (CFD) has been used, with considerable success, in modelling the physics in supply air windows. In this research, a comprehensive three-dimensional CFD model is proposed. Under the conditions investigated, the temperature rise and heat gain ranged from 6K to 24K and 23.45W/m2 to 96.34W/m2, respectively. The temperature rise and heat gain were higher in the natural flow case than in the forced flow cases. The models were experimentally validated in terms of velocity field, flow field and temperature rise. The velocity field was measured using Laser Doppler Velocimetry (LDV) and the overall flow field was captured using smoke for flow visualisation. Qualitatively, the CFD predictions are in good agreement with experiment. Quantitatively, there is noticeable error between experiment and CFD. The average error between CFD and experiment is: 3.46K for temperature values at the outlet, 35% for axial velocities in the cavity and 44% for turbulence intensity in the cavity. The results indicate that good agreement could be obtained, between experiment and CFD, if the LDV seeding issues are resolved and a turbulence model that is capable of resolving anisotropic turbulence and transition is used.

Computational Fluid Dynamics Analysis of 3D Hot Metal Flow Characteristics in a Blast Furnace Hearth

The campaign life of an iron blast furnace depends on hearth wear. Distributions of liquid iron flow and refractory temperatures have a significant influence on hearth wear. A 3D comprehensive computational fluid dynamics model has been developed specifically for simulating the blast furnace hearth. It includes both the hot metal flow and the conjugate heat transfer through the refractories. The model has been extensively validated using measurement data from Mittal Steel old, new IH7 blast furnace and U.S. Steel 13 blast furnace. Good agreements between measured and calculated refractory temperature profiles have been achieved. It has been used to analyze the velocity and temperature distributions and wear patterns of different furnaces and operating conditions. The results can be used to predict the inner profile of hearth and to provide guidance for protecting the hearth.

Reduced-dimensional models for straight-channel proton exchange membrane fuel cells

A comprehensive description of proton exchange membrane fuel cell (PEMFC) performance includes the transport phenomena, phase change and electrochemical reaction inside the several components, which possess disparate characteristics and together form a complex three-dimensional geometry. Much of the modelling work in this area has, therefore, relied on the techniques of computational fluid dynamics (CFD). The comprehensive three-dimensional (3D) approach can, however, be prohibitively time consuming. Consequently, it is not the ideal basis for a rapid screening tool that operates under a wide range of design options and operating conditions. Mathematical models and solution procedures using simplified models with reduced dimensions have been proposed to address this issue. Such approaches are computationally efficient, but no systematic study has been conducted to qualitatively or quantitatively assess the impact of the neglected dimensionality on the accuracy of the resulting model. In this paper, we compare results from a hierarchy of reduced-dimensional models to the results from a comprehensive 3D CFD model for a single, straight-channel unit cell. The quality of the simulation results from reduced-dimensional models, including the cell voltage and the distributions of current density and relative humidity, are assessed. We demonstrate that the 2 + 1D approach, which includes mass transport in the 2D cross-section of the channel and membrane electrode assembly and integrates along the flow channel, is optimal in terms of both efficiency and accuracy. It provides a sound basis for a simulation tool that can be used in the early stages of a unit-cell design cycle.

Multiple Linear Regression Model Approach for Aerosol Dispersion in Ventilated Spaces Using Computational Fluid Dynamics and Dimensional Analysis

Aerosol dispersion in living spaces especially bioaerosols, due to accidents or deliberate acts, is of significant current interest. Computational fluid dynamics (CFD) provides an accurate and detailed platform to study the influence of different parameters on aerosol distribution in indoor spaces. The simulations however are time consuming and site-specific. The work here introduces an approach toward addressing this challenge. During emergencies, an accurate, quicker, and more general model is required to give rapid answers to first responders. Significant parameters influencing aerosol behavior in an office room were identified and through dimensional analysis, nine dimensionless groups were developed. Fractional factorial design was used to build sixteen scenarios to explore the design space. These scenarios were then simulated using a comprehensive CFD model. Large eddy simulation with the Smagorinsky subgrid scale model was applied to compute the airflow. Aerosols were modeled as a dispersed solid p...

A validated 2-D diffusion–advection model for prediction of drift from ground boom sprayers

Correct field drift prediction is a key element in environmental risk assessment of spraying applications. A reduced order drift prediction model based on the diffusion–advection equation is presented. It allows fast assessment of the drift potential of specific ground boom applications under specific environmental wind conditions that obey the logarithmic wind profile. The model was calibrated based on simulations with a validated Computational Fluid Dynamics (CFD) model. Validation of both models against 38 carefully conducted field experiments is successfully performed for distances up to 20 m from the field edge, for spraying on flat pasture land. The reduced order model succeeded in correct drift predictions for different nozzle types, wind velocities, boom heights and spray pressures. It used 4 parameters representing the physical aspects of the drift cloud; the height of the cloud at the field edge, the mass flux crossing the field edge, the settling velocity of the droplets and the turbulence. For the parameter set and range considered, it is demonstrated for the first time that the effect of the droplet diameter distribution of the different nozzle types on the amount of deposition spray drift can be evaluated by a single parameter, i.e., the volume fraction of droplets with a diameter smaller than 191 μm. The reduced order model can be solved more than 4 orders of magnitude faster than the comprehensive CFD model.

A novel meso-scale combustion system for operation with liquid fuels

A novel meso-scale combustion concept utilizing a flow-blurring injector to produce fine fuel droplets, a counter-flow heat exchanger to preheat reactants using product gas enthalpy, and porous inert medium to homogenize reactants and stabilize the flame is presented. The overall system is 30 mm long and 17 mm in diameter, with combustor diameter of 10 mm. For atmospheric pressure operation on kerosene fuel, the combustion system achieved heat release rate of up to 460 W, pertaining to energy density of 90 MW/m 3 based on the total volume and 230 MW/m 3 based on the combustor volume. The combustor performance was determined from surface temperatures measured by an infra-red camera, product gas temperature measured by an R-type thermocouple probe, and carbon monoxide (CO) and nitric oxide (NO x ) concentrations measured by a miniature sampling probe attached to gas analyzers. A comprehensive Computational Fluid Dynamics (CFD) model incorporating conjugate heat transfer, radiation heat exchange, flow and heat transfer in PIM, and heat release by combustion was developed and validated in this study. The CFD model accurately predicted the thermal performance of the combustion system. A 1D, burner-stabilized flame model incorporating detailed chemical kinetics was used to predict the flame structure. Model predictions are compared with measured CO and NO x concentrations, and subsequently, analyzed to identify the key reactions affecting the NO x production.