Search results
1 – 10 of 42Hala Al-Fulaij, Andrea Cipollina, Giorgio Micale, Hisham Ettouney and David Bogle
The purpose of this study is to focus on simulation of wire mesh demisters in multistage flash desalination (MSF) plants. The simulation is made by the use of computational fluid…
Abstract
Purpose
The purpose of this study is to focus on simulation of wire mesh demisters in multistage flash desalination (MSF) plants. The simulation is made by the use of computational fluid dynamics (CFD) software.
Design/methodology/approach
A steady state and two-dimensional (2D) model was developed to simulate the demister. The model employs an Eulerian-Eulerian approach to simulate the flow of water vapor and brine droplets in the demister. The computational domain included three zones, which are the vapor space above and below the demister and the demister. The demister zone was modeled as a tube bank arrange or as a porous media.
Findings
Sensitivity analysis of the model showed the main parameters that affect demister performance are the vapor velocity and the demister permeability. On the other hand, the analysis showed that the vapor temperature has no effect on the pressure drop across the demister.
Research limitations/implications
The developed model was validated against previous literature data as well as real plant data. The analysis shows good agreement between model prediction and data.
Originality/value
This work is the first in the literature to simulate the MSF demister using CFD modeling. 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.
Details
Keywords
Yan Chen, Wenzhuo Chen, Bo Li, Gang Zhang and Weiming Zhang
The purposes of this paper are to review the progress of and conclude the trend for paint thickness simulation for painting robot trajectory planning.
Abstract
Purpose
The purposes of this paper are to review the progress of and conclude the trend for paint thickness simulation for painting robot trajectory planning.
Design/methodology/approach
This paper compares the explicit function-based method and computational fluid dynamics (CFD)-based method used for paint thickness simulation. Previous research is considered, and conclusions with the outlook are drawn.
Findings
The CFD-based paint deposition simulation is the trend for paint thickness simulation for painting robot trajectory planning. However, the calculation of paint thickness resulting from dynamically painting complex surface remains to be researched, which needs to build an appropriate CFD model, study approaches to dynamic painting simulation and investigate the simulation with continuously changing painting parameters.
Originality/value
This paper illustrates that the CFD-based method is the trend for the paint thickness simulation for painting robot trajectory planning. Current studies have been analyzed, and techniques of CFD modeling have also been summarized, which is vital for future study.
Details
Keywords
E. Daniel, R. Saurel, M. Larini and J.C. Loraud
This paper investigates the multi‐phase behaviour of dropletsinjected into a nozzle at two separate wall locations. The physical featuresof the droplets (rate of mass, density and…
Abstract
This paper investigates the multi‐phase behaviour of droplets injected into a nozzle at two separate wall locations. The physical features of the droplets (rate of mass, density and radius) at each injector location are identical. This system can be described by a two‐phase Eulerian—Eulerian approach that yields classical systems of equations: three for the gaseous phase and three for the dispersed droplet phase. An underlying assumption in the two phase model is that no interaction occurs between droplets. The numerical solution of the model (using the MacCormack scheme) indicates however that the opposite jets do interact to form one jet. This inconsistency is overcome in the current paper by associating the droplets from a given injection location with a separate phase and subsequently solving equations describing a multiphase system (here, three‐phase system). Comparison of numerical predications between the two‐phase and the multiphase model shows significantly different results. In particular the multiphase model shows no jet interaction.
Details
Keywords
Zhizhong Kang, Shixing Ding, Zhi-ang Shuai and Baomin Sun
This paper aims to shows the ability of the EDC model with a global reaction mechanism to describe reactions in the Eulerian simulation of a circulating fluidized bed (CFB).
Abstract
Purpose
This paper aims to shows the ability of the EDC model with a global reaction mechanism to describe reactions in the Eulerian simulation of a circulating fluidized bed (CFB).
Design/methodology/approach
The eddy dissipation concept (EDC) model is embedded in an Eulerian-Eulerian approach to simulate homogeneous reactions.
Findings
EDC_G is better than ED_FR in describing chemical reactions. The reaction of CH4 with O2 is faster than that of CO with O2, and NH3 is more liable to be converted than HCN. The combustion rate is higher than the Boudouard reaction rate of coal particles.N2O is mainly reduced by carbon, and NO is mainly converted by carbon into N2 and CO2.
Originality/value
The EDC model with a global reaction mechanism is embedded in a multi-fluid Eulerian approach to simulate the homogeneous reactions in the coal combustion in a CFB, including combustion of volatile gases, desulfurizing reactions and NOx reactions.
Details
Keywords
Ali Ayyed Abdul-Kadhim, Fue-Sang Lien and Eugene Yee
This study aims to modify the standard probabilistic lattice Boltzmann methodology (LBM) cellular automata (CA) algorithm to enable a more realistic and accurate computation of…
Abstract
Purpose
This study aims to modify the standard probabilistic lattice Boltzmann methodology (LBM) cellular automata (CA) algorithm to enable a more realistic and accurate computation of the ensemble rather than individual particle trajectories that need to be updated from one time step to the next (allowing, as such, a fraction of the collection of particles in any lattice grid cell to be updated in a time step, rather than the entire collection of particles as in the standard LBM-CA algorithm leading to a better representation of the dynamic interaction between the particles and the background flow). Exploitation of the inherent parallelism of the modified LBM-CA algorithm to provide a computationally efficient scheme for computation of particle-laden flows on readily available commodity general-purpose graphics processing units (GPGPUs).
Design/methodology/approach
This paper presents a framework for the implementation of a LBM for the simulation of particle transport and deposition in complex flows on a GPGPU. Towards this objective, the authors have shown how to map the data structure of the LBM with a multiple-relaxation-time (MRT) collision operator and the Smagorinsky subgrid-scale turbulence model (for turbulent fluid flow simulations) coupled with a CA probabilistic method (for particle transport and deposition simulations) to a GPGPU to give a high-performance computing tool for the calculation of particle-laden flows.
Findings
A fluid-particle simulation using our LBM-MRT-CA algorithm run on a single GPGPU was 160 times as computationally efficient as the same algorithm run on a single CPU.
Research limitations/implications
The method is limited by the available computational resources (e.g. GPU memory size).
Originality/value
A new 3D LBM-MRT-CA model was developed to simulate the particle transport and deposition in complex laminar and turbulent flows with different hydrodynamic characteristics (e.g. vortex shedding, impingement, free shear layer, turbulent boundary layer). The solid particle information is encapsulated locally at the lattice grid nodes, allowing for straightforward mapping of the datastructure onto a GPGPU enabling a massive parallel execution of the LBM-MRT-CA algorithm. The new particle transport algorithm was based on the local (bulk) particle density and velocity and provides more realistic results for the particle transport and deposition than the standard LBM-CA algorithm.
Details
Keywords
Esmail Lakzian, Mostafa Ramezani, Sima Shabani, Fahime Salmani, Miroslaw Majkut and Heuy Dong Kim
The purpose of this study is to model steam condensing flows through steam turbine blades and find the most suitable condensation model to predict the condensation phenomenon.
Abstract
Purpose
The purpose of this study is to model steam condensing flows through steam turbine blades and find the most suitable condensation model to predict the condensation phenomenon.
Design/methodology/approach
To find the most suitable condensation model, five nucleation equations and four droplet growth equations are combined, and 20 cases are considered for modelling the wet steam flow through steam turbine blades. Finally, by the comparison between the numerical results and experiments, the most suitable case is proposed. To find out whether the proposed case is also valid for other boundary conditions and geometries, it is used to simulate wet steam flows in de Laval nozzles.
Findings
The results indicate that among all the cases, combining the Hale nucleation equation with the Gyarmathy droplet growth equation results in the smallest error in the simulation of wet steam flows through steam turbine blades. Compared with experimental data, the proposed model’s relative error for the static pressure distribution on the blade suction and pressure sides is 2.7% and 2.3%, respectively, and for the liquid droplet radius distribution it totals to 1%. This case is also reliable for simulating condensing steam flows in de Laval nozzles.
Originality/value
The selection of an appropriate condensation model plays a vital role in the simulation of wet steam flows. Considering that the results of numerical studies on condensation models in recent years have not been completely consistent with the experiments and that there are still uncertainties in this field, further studies aiming to improve condensation models are of particular importance. As condensation models play an important role in simulating the condensation phenomenon, this research can help other researchers to better understand the purpose and importance of choosing a suitable condensation model in improving the results. This study is a significant step to improve the existing condensation models and it can help other researchers to gain a revealing insight into choosing an appropriate condensation model for their simulations.
Details
Keywords
Lucilla Coelho de Almeida, Joao Americo Aguirre Oliveira Junior and Jian Su
This paper aims to present a novel approach for computing particle temperatures in simulations coupling computational fluid dynamics (CFD) and discrete element method (DEM) to…
Abstract
Purpose
This paper aims to present a novel approach for computing particle temperatures in simulations coupling computational fluid dynamics (CFD) and discrete element method (DEM) to predict flow and heat transfer in fluidized beds of thermally thick spherical particles.
Design/methodology/approach
An improved lumped formulation based on Hermite-type approximations for integrals to relate surface temperature to average temperature and surface heat flux is used to overcome the limitations of classical lumped models. The model is validated through comparisons with analytical solutions for a convectively cooled sphere and experimental data for a fixed particle bed. The coupled CFD-DEM model is then applied to simulate a Geldart D bubbling fluidized bed, comparing the results to those obtained using the classical lumped model.
Findings
The validation cases demonstrate that ignoring internal thermal resistance can significantly impact the temperature in cases where the Biot number is greater than 0.1. The results for the fixed bed case clearly demonstrate that the proposed method yields significantly improved outcomes compared to the classical model. The fluidized bed results show that surface temperature can deviate considerably from the average temperature, underscoring the importance of accurately accounting for surface temperature in convective heat transfer predictions and surface processes.
Originality/value
The proposed approach offers a physically more consistent simulation without imposing a significant increase in computational cost. The improved lumped formulation can be easily and inexpensively integrated into a typical DEM solver workflow to predict heat transfer for spherical particles, with important implications for various industrial applications.
Details
Keywords
Chiara Biscarini, Silvia Di Francesco and Matteo Mencattini
The purpose of this paper is to prove the validity of the front‐tracking variant of the lattice Boltzmann method (LBM) to simulate free surface hydraulic flows (i.e. dam break…
Abstract
Purpose
The purpose of this paper is to prove the validity of the front‐tracking variant of the lattice Boltzmann method (LBM) to simulate free surface hydraulic flows (i.e. dam break flows).
Design/methodology/approach
In this paper, an algorithm for free surface simulations with the LBM method is presented. The method is chosen for its computational efficiency and ability to deal with complex geometries. The LBM is combined to a surface‐tracking technique applied to a fixed Eulerian mesh in order to simulate free surface flows.
Findings
The numerical method is then validated against two typical cases of environmental‐hydraulic interest (i.e. dam break) by comparing LBM results with experimental data available in literature. The results show that the model is able to reproduce the observed water levels and the wave fronts with reasonable accuracy in the whole period of the transient simulations, thus highlighting that the present method may be a promising tool for practical dam break analyses.
Originality/value
Even if the main philosophy of the proposed method is equal to the volume of fluid technique usually coupled to Navier‐Stokes models, no additional differential equation is needed to determine the relative volume fraction of the two phases, or phase fraction, in each computational cell, as the free‐surface tracking is automatically performed. This results in a method very simple to be coded with high computational efficiency. The results presented in this paper are the first, to the best of the authors' knowledge, in the field of hydraulic engineering.
Details
Keywords
Zhiyi Yu, Baoshan Zhu and Shuliang Cao
Interphase forces between the gas and liquid phases determine many phenomena in bubbly flow. For the interphase forces in a multiphase rotodynamic pump, the magnitude analysis was…
Abstract
Purpose
Interphase forces between the gas and liquid phases determine many phenomena in bubbly flow. For the interphase forces in a multiphase rotodynamic pump, the magnitude analysis was carried out within the framework of two-fluid model. The purpose of this paper is to clarify the relative importance of various interphase forces on the mixed transport process, and the findings herein will be a base for the future study on the mechanism of the gas blockage phenomenon, which is the most challenging issue for such pumps.
Design/methodology/approach
Four types of interphase forces, i.e. drag force, lift force, virtual mass force and turbulent dispersion force (TDF) were taken into account. By comparing with the experiment in the respect of the head performance, the effectiveness of the numerical model was validated. In conditions of different inlet gas void fractions, bubble diameters and rotational speeds, the magnitude analyses were made for the interphase forces.
Findings
The results demonstrate that the TDF can be neglected in the running of the multiphase rotodynamic pump; the drag force is dominant in the impeller region and the outlet extended region. The sensitivity analyses of the bubble diameter and the rotational speed were also performed. It is found that larger bubble size is accompanied by smaller predicted drag but larger predicted lift and virtual mass, while the increase of the rotational speed can raise all the interphase forces mentioned above.
Originality/value
This paper has revealed the magnitude information and the relative importance of the interphase forces in a multiphase rotodynamic pump.
Details
Keywords
Reza Azadbakhti, Farzad Pourfattah, Abolfazl Ahmadi, Omid Ali Akbari and Davood Toghraie
The purpose of this study is simulation the flow boiling inside a tube in the turbulent flow regime for investigating the effect of using a porous medium in the boiling procedure.
Abstract
Purpose
The purpose of this study is simulation the flow boiling inside a tube in the turbulent flow regime for investigating the effect of using a porous medium in the boiling procedure.
Design/methodology/approach
To ensure the accuracy of the obtained numerical results, the presented results have been compared with the experimental results, and proper coincidence has been achieved. In this study, the phase change phenomenon of boiling has been modeled by using the Eulerian–Eulerian multi-phase Rensselaer Polytechnic Institute (RPI) wall boiling model.
Findings
The obtained results indicate using a porous medium in boiling process is very effective in a way that by using a porous medium inside the tub, the location of changing the liquid to the vapor and the creation of bubbles, changes. By increasing the thermal conductivity of porous medium, the onset of phase changing postpones, which causes the enhancement of heat transfer from the wall to the fluid. Generally, it can be said that using a porous medium in boiling flows, especially in flow with high Reynolds numbers, has a positive effect on heat transfer enhancement. Also, the obtained results revealed that by increasing Reynolds number, the created vapor phase along the tube decreases and by increasing Reynolds number, the Nusselt number enhances.
Originality/value
In present research, by using the computational fluid dynamics, the effect of using a porous medium in the forced boiling of water flow inside a tube has been investigated. The fluid boiling inside the tube has been simulated by using the multi-phase Eulerian RPI wall boiling model, and the effect of thermal conductivity of a porous medium and the Reynolds number on the flow properties, heat transfer and boiling procedure have been investigated.
Details