Iranian Journal of Chemical Engineering(IJChE)

Transport Phenomena,

Experimental and CFD Studies on the Effect of the Jet Position on Mixing Performance

Volume 6, Issue 3 , July 2009, , Pages 3-12

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Transport Phenomena,

An Experimental and Theoretical Investigation on Thermal Performance of a Gas-Liquid Thermosyphon Heat Pipe Heat Exchanger in a Semi-Industrial Plant

Volume 6, Issue 3 , July 2009, , Pages 13-25

Abstract

  "> Waste heat recovery is very important, because it not only reduces the expenditure of heat generation, but also it is of high priority in environmental consideration, such as reduction in greenhouse gases. One of the devices used in waste heat recovery is heat pipe heat exchanger. An experimental ...  Read More "> Waste heat recovery is very important, because it not only reduces the expenditure of heat generation, but also it is of high priority in environmental consideration, such as reduction in greenhouse gases. One of the devices used in waste heat recovery is heat pipe heat exchanger. An experimental and theoretical research is carried out to investigate heat performance of an air to water thermosyphon heat pipe heat exchanger according to ε-NTU method. The experiments were done according to the following procedure: cold water with 0.1kg/s flows through the condensation section and hot air in a closed cycle is blown into the evaporation section. A blower with varying frequency of current turns in the mass flow rate between 0.14-0.6 kg/s and a temperature range of 125-225°C. The results of the experiments show that as the ratio of C Ch c rises, the rate of heat transfer goes up. The efficiency of the heat pipe heat exchanger remains constant as the temperature of the hot stream goes up, but the amount of heat transferred increases.

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Modeling and Simulation

Mathematical Modeling of Fluorination Reaction of Uranium Dioxide and Evaluation of Existing Gas-Solid Reaction Models

Volume 6, Issue 2 , April 2009, , Pages 63-74

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Modeling and Simulation

Unsteady-State Modeling of the Fluidized Bed Polyethylene Reactor

Volume 6, Issue 1 , January 2009, , Pages 23-39

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Modeling and Simulation

Effect of Hydrocarbon Fluid Characterization on Wax Precipitation Modeling

Volume 6, Issue 1 , January 2009, , Pages 50-65

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Modeling and Simulation

A Study on Liquid-liquid Mixing in a Stirred Tank with a 6-Blade Rushton Turbine

Volume 5, Issue 4 , October 2008, , Pages 12-22

Abstract

  The turbulent flow field generated in a baffled stirred tank was computed by large eddy simulation (LED) and the flow field was developed using the Sliding Mesh (SM) approach. In this CFD study, mixing times and power number have been determined for a vessel agitated by a 6-blade Rushton turbine. The ...  Read More The turbulent flow field generated in a baffled stirred tank was computed by large eddy simulation (LED) and the flow field was developed using the Sliding Mesh (SM) approach. In this CFD study, mixing times and power number have been determined for a vessel agitated by a 6-blade Rushton turbine. The predicted results were compared with the published experimental data. The satisfactory results of comparisons indicate the potential usefulness of this approach as a computational tool for designing stirred reactors.          

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Modeling and Simulation

Determination of the Equilibrium Parameters of Gaseous Detonations Using a Genetic Algorithm

Volume 5, Issue 3 , July 2008, , Pages 3-13

Abstract

  The present work is concerned with the development of a new algorithm for determination of the equilibrium composition of gaseous detonations. The elements balance equations, and the second law of thermodynamics (i.e., the minimization of the Gibbs free energy of products), are used to determine the ...  Read More The present work is concerned with the development of a new algorithm for determination of the equilibrium composition of gaseous detonations. The elements balance equations, and the second law of thermodynamics (i.e., the minimization of the Gibbs free energy of products), are used to determine the equilibrium composition of the detonation products. To minimize the Gibbs free energy with traditional deterministic methods one needs to solve a set of highly nonlinear equations. The numerical methods in the existing equilibrium codes suffer from several drawbacks such as the divergence possibility in some equivalent ratios, and the possibility of converging to a local relative minimum in the minimization process. To overcome these drawbacks, a genetic algorithm is presented in the present study. Converging to the global minimum of Gibbs function in all equivalent ratios, and having a reasonable CPU time are the notable aspects of the proposed algorithm.    

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Modeling and Simulation

Multi-objective Genetic Optimization of Ethane Thermal Cracking Reactor

Volume 5, Issue 3 , July 2008, , Pages 29-39

Abstract

  An industrial ethane thermal cracking reactor was modeled assuming a molecular mechanism for the reaction kinetics coupled with material, energy, and momentum balances of the reactant-product flow along the reactor. To carry out the multi-objective optimization for two objectives such as conversion and ...  Read More An industrial ethane thermal cracking reactor was modeled assuming a molecular mechanism for the reaction kinetics coupled with material, energy, and momentum balances of the reactant-product flow along the reactor. To carry out the multi-objective optimization for two objectives such as conversion and ethylene selectivity, the elitist non-dominated sorting genetic algorithm was used. The Pareto optimum set was obtained successfully and finally the effect of the decision variable was discussed.    

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Modeling and Simulation

Multidimensional Dynamic Modeling of Milk Ultrafiltration Using Neuro-Fuzzy Method and a Hybrid Physical Model

Volume 5, Issue 2 , April 2008, , Pages 3-22

Abstract

  Prediction of the dynamic crossflow ultrafiltration rate of a protein solution such as milk poses a complex non-linear problem as the filtration rate has a strong dependence on both the solution physicochemical conditions and the operating conditions. As a result, the development of general physics-based ...  Read More Prediction of the dynamic crossflow ultrafiltration rate of a protein solution such as milk poses a complex non-linear problem as the filtration rate has a strong dependence on both the solution physicochemical conditions and the operating conditions. As a result, the development of general physics-based models has proved extremely challenging. In this study an alternative dynamic neuro-fuzzy model for milk ultrafiltration that describes the variation in dynamic permeate flux decline with temperature, transmembrane pressure (TMP), fat percentage, pH and molecular weight cut off (MWCO) has been developed with the experimental data of the pilot spiral wound membrane test rig. By increasing the temperature, TMP, and pH the permeate flux is increased, and by increasing fat concentration the permeate flux is decreased. The MWCO variation indicates a paradoxical permeate flux. Additionally, a hybrid physical model for dynamic prediction of total resistance in the milk ultrafiltration by combination of two neuro-fuzzy (ANFIS) models and a physical model (BLA model) is developed. By increasing the TMP and fat concentration, the total resistance is increased. But by increasing the pH and temperature, the total resistance is decreased. Also, MWCO variation indicates a paradoxical total resistance value.

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Transport Phenomena,

An NLP Approach for Evolution of Heat Exchanger Networks Designed by Pinch Technology

Volume 5, Issue 1 , January 2008, , Pages 13-21

Abstract

  Common methods to design heat exchanger networks (HENs) by pinch technology usually need an evolutionary step to reduce the number of heat transfer units. This step is called loop breaking and is based on the removal of exchangers that impose minimum increase on utility consumption. Loops identification ...  Read More Common methods to design heat exchanger networks (HENs) by pinch technology usually need an evolutionary step to reduce the number of heat transfer units. This step is called loop breaking and is based on the removal of exchangers that impose minimum increase on utility consumption. Loops identification and breaking is a tedious task and becomes more complicated in large networks. This paper presents a rapid nonlinear programming (NLP) formulation for the evolution of HENs in which loop identification is not required. The objective of the NLP is the minimization of HENs annual cost, which is not considered in current methods. In this method a search is done to find the best units elimination of which improves HENs annual cost. The search continues until the minimum number of units (MNU) is achieved and the exchangers that must be removed from the network are specified. The method was applied to some networks reported in the literature and better results were obtained. Also, the convergence of the presented method is very fast and it can be applied to different networks designed by pinch technology.

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Transport Phenomena,

An Efficient Coupled Genetic Algorithm-NLP Method for Heat Exchanger Network Synthesis

Volume 5, Issue 1 , January 2008, , Pages 22-33

Abstract

  Synthesis of heat exchanger networks (HENs) is inherently a mixed integer and nonlinear programming (MINLP) problem. Solving such problems leads to difficulties in the optimization of continuous and binary variables. This paper presents a new efficient and robust method in which structural parameters ...  Read More Synthesis of heat exchanger networks (HENs) is inherently a mixed integer and nonlinear programming (MINLP) problem. Solving such problems leads to difficulties in the optimization of continuous and binary variables. This paper presents a new efficient and robust method in which structural parameters are optimized by genetic algorithm (G.A.) and continuous variables are handled due to a modified objective function for maximum energy recovery (MER). Node representation is used for addressing the exchangers and networks are considered as a sequence of genes. Each gene consists of nodes for generating different structures within a network. Results show that this method may find new or near optimal solutions with a less than 2% increase in Hen annual costs.

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Modeling and Simulation

Determination of the Kinetic Parameters and Dynamic Modeling of the Reactor for the Direct Conversion of Synthesis gas to Di-methyl ether

Volume 3, Issue 4 , October 2006, , Pages 23-34

Abstract

  "> In the present study the reaction kinetic and dynamic modeling of the reactor for syngas transformation into dimethyl ether using a mixture of a metallic oxides (CuO, ZnO, Al2O3), and an acidic component (γ-Al2O3) as the catalyst has been investigated. A combination of the Graff kinetic model ...  Read More "> In the present study the reaction kinetic and dynamic modeling of the reactor for syngas transformation into dimethyl ether using a mixture of a metallic oxides (CuO, ZnO, Al2O3), and an acidic component (γ-Al2O3) as the catalyst has been investigated. A combination of the Graff kinetic model for methanol synthesis and the Bercic model for methanol dehydration was correlated with the experimental results obtained in this study. Activity and kinetic measurements were carried out using a catalytic fixed bed micro reactor. The operating temperature range was 230-300 °C and the pressure was 8 barg. The experimental runs were performed applying a wide range of catalyst to feed ratios. A simple dynamic model for the reactor performance was developed and tested with the experimental data. The mean absolute deviation, concerning the data for the steady state conditions, was less than 8%.

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Modeling and Simulation

A hybrid neural–genetic algorithm for predicting pure and impure CO2 minimum miscibility pressure

Volume 3, Issue 4 , October 2006, , Pages 44-59

Abstract

  "> Accurate prediction of the minimum miscibility pressure (MMP) in a gas injection process is crucial to optimizing the management of gas injection projects. Because the experimental determination of MMP is very expensive and time-consuming, searching for a fast and robust mathematical determination ...  Read More "> Accurate prediction of the minimum miscibility pressure (MMP) in a gas injection process is crucial to optimizing the management of gas injection projects. Because the experimental determination of MMP is very expensive and time-consuming, searching for a fast and robust mathematical determination of CO2-oil MMP is usually requested. This paper presents a new model based on a hybrid neural-genetic algorithm for predicting pure and impure CO2-oil MMP. The CO2-oil MMP of a reservoir fluid was correlated with the reservoir temperature, the composition of the oil, and that of the solution gas. The developed model is able to reflect the impacts on the CO2–oil MMP of the molecular weight of the C5+ fraction, reservoir temperature, and solution gas in the oil. The validity of this new model was successfully approved by comparing the model results to the calculated results for the common pure and impure CO2-oil MMP correlations. The new model yielded the accurate prediction of the experimental slim-tube CO2-oil MMP with the lowest mean absolute percentage error (MAPE), the standard deviation of error (SD), the root mean square error (RMSE), and the highest correlation coefficient among tested impure and pure CO2-oil MMP correlations. The results demonstrate that the hybrid neural-genetic model can be applied successfully and provide high accuracy and reliability for MMP forecasting.

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Process Control and Engineering, Process Safety, HSE

A Study of Flow and Mixing in Bubbly Gas-Liquid Pipe Flow Generated by a Grid

Volume 3, Issue 4 , October 2006, , Pages 60-75

Abstract

  The spreading of a tracer in a bubbly two-phase grid-generated turbulent flow system is studied. In this work both particle image velocimetry (PIV) and planer laser-induced fluorescence (PLIF) are used to study the effect of the dispersed phase flow rate on the mixing characteristics of the tracer. The ...  Read More The spreading of a tracer in a bubbly two-phase grid-generated turbulent flow system is studied. In this work both particle image velocimetry (PIV) and planer laser-induced fluorescence (PLIF) are used to study the effect of the dispersed phase flow rate on the mixing characteristics of the tracer. The turbulent intensity of the continuous phase in the bubbly two-phase grid-generated turbulent flow is close to isotropic, and increasing the gas void fraction reduces the degree of non-isotropicity. The self-similarity of mean and RMS values of the cross-stream concentration distribution is observed. A new mathematical model is suggested to describe the self-similarity of the cross-stream profiles of the mean concentration based on two separate Gaussian curves into the central and outer region of the flow. The turbulent diffusivity is calculated using the Taylor hypothesis, which is based on the growth of the variance of the cross-stream profiles of the mean concentration, with a position along the direction of the flow. An increase in the void fraction does not affect the diffusivity of the superimposed distribution of the plume in the central region, however it did increase in the outer region.

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Modeling and Simulation

Asymptotic Analysis of Binary Gas Mixture Separation by Nanometric Tubular Ceramic Membranes: Cocurrent and Countercurrent Flow Patterns

Volume 3, Issue 3 , July 2006, , Pages 3-16

Abstract

  Analytical gas-permeation models for predicting the separation process across  membranes (exit compositions and area requirement) constitutes an important and necessary step in understanding the overall performance of  membrane modules. But, the exact (numerical) solution methods suffer from ...  Read More Analytical gas-permeation models for predicting the separation process across  membranes (exit compositions and area requirement) constitutes an important and necessary step in understanding the overall performance of  membrane modules. But, the exact (numerical) solution methods suffer from the complexity of the solution. Therefore, solutions of nonlinear ordinary differential equations that govern the performance of the membrane modules for gas separations by approximate and asymptotic methods are useful in the design and comparison of processes. In this work, the asymptotic methods were applied for predicting the performance of nanometric tubular ceramic membranes in the separation of binary gas mixtures with cocurrent and countercurrent flow patterns. Also, the exact (numerical) solutions of the governing equations using the fourth order Rung-Kutta technique were proposed. The comparison of the results showed a good agreement between the exact solution and asymptotic analysis methods over the whole range of selectivities (). Because, the asymptotic curves into the former () and latter () boundaries had a suitable overlap with each other to cover the whole range of selectivities. The accuracy of this method was verified by a comparison of the predicted results with different literature experimental data and mathematical models. This result suggests the use of the asymptotic analysis method to provide excellent shortcut, preliminary design information.      

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Modeling and Simulation

A Model For The Residence Time Distribution and Holdup Measurement in a Two Impinging Streams Cyclone Reactor/Contactor in Solid-Liquid Systems

Volume 3, Issue 3 , July 2006, , Pages 17-28

Abstract

  In this paper a two impinging streams cyclone contacting system suitable for handling of solid-liquid systems has been studied. Certain pertinent parameters such as: solid holdup, mean residence time and Residence Time Distribution (RTD) of solid particles have been investigated. A stochastic model based ...  Read More In this paper a two impinging streams cyclone contacting system suitable for handling of solid-liquid systems has been studied. Certain pertinent parameters such as: solid holdup, mean residence time and Residence Time Distribution (RTD) of solid particles have been investigated. A stochastic model based on Markov chains processes has been applied which describe the behavior of solid particles in the contacting system. From this model the RTD data were estimated and compared with the experimental results. The RTD data were obtained at different Dt and compared with those estimated from the model. At Dt = 0.362 s a good correlation has been observed between the predicted and experimental data. The RTD data may be used to determine certain pertinent characteristic parameters of physical and chemical apparatuses such as conversion in chemical reactors.    

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Modeling and Simulation

Mathematical modeling of a fixed bed chromatographic reactor for Fischer Tropsch synthesis

Volume 3, Issue 3 , July 2006, , Pages 51-64

Abstract

  In this research, Fischer Tropsch synthesis (FTS) has been modeled in the fixed bed chromatographic reactor for the first time by applying a rather complex dispersed plug flow model for fluid phase and linear driving force (LDF) model for adsorbent. Model equations are dynamic, multi-component, non-linear ...  Read More In this research, Fischer Tropsch synthesis (FTS) has been modeled in the fixed bed chromatographic reactor for the first time by applying a rather complex dispersed plug flow model for fluid phase and linear driving force (LDF) model for adsorbent. Model equations are dynamic, multi-component, non-linear and heterogeneous including reaction and adsorption simultaneously Complex kinetics for FTS and water-gas shift (WGS) reaction and the multicomponent Langmuir adsorption isotherm is used in the model. A set of partial differential and ordinary differential equations with algebraic equations have been converted into a set of ordinary differential equations by using the orthogonal collocation technique. Then this set of equations has been solved by multi-step methods of Numerical Differentiation Formulae (NDF) or Backward Dif-ferentiation Formulae (BDF) Known as the Gear’s method. Consequently, results for dynamic model and effects of modeling parameters have been analyzed. Through this fixed bed chromatographic reactor model, one may develop a suitable configuration of simulated moving bed chromatographic reactors.      

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Process Control and Engineering, Process Safety, HSE

A Detailed Investigation of Particulate Dispersion from Kerman Cement Plant

Volume 3, Issue 3 , July 2006, , Pages 65-74

Abstract

  The aim of this study was to investigate the particulate dispersion from Kerman Cement Plant. The upwind – downwind method was used to measure particle concentration and a cascade impactor was applied to determine particle size distribution. An Eulerian model, Gaussian plume model and an artificial ...  Read More The aim of this study was to investigate the particulate dispersion from Kerman Cement Plant. The upwind – downwind method was used to measure particle concentration and a cascade impactor was applied to determine particle size distribution. An Eulerian model, Gaussian plume model and an artificial neural network have been used to compute and predict concentration of PM10 from Kerman Cement Plant. Eulerian model incorporates source related factors, meteorological factors, surface roughness and particle settling to estimate pollutant concentration from continuous sources. The measured data have been used to create an artificial neural network for predicting suspended particle concentration from Kerman Cement Plant. The data includes particle concentration, distance from source, mixing height, lateral and vertical dispersion parameters and 10 meters wind speed. The performance of these models has been compared with the measured data. The AAPD (Average Absolute Percent Deviation) parameter for the results of the Eulerian model, Gaussian model and ANNs was 25.53%, 15.38% and 5.91% respectively.          

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Modeling and Simulation

nonlinear modeling and cascade control design for multi effect falling film evaporators

Volume 3, Issue 2 , April 2006, , Pages 52-63

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Modeling and Simulation

modeling of controlled particle deposition on to electronically conducting surfaces

Volume 3, Issue 1 , January 2006, , Pages 3-12

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Modeling and Simulation

development of an explicit eulerian method for treating particle laden turbulent flow in dust collectors

Volume 3, Issue 1 , January 2006, , Pages 13-28

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Modeling and Simulation

sequential formulation for compositional reservoirs simulation using peng robinson equation of state

Volume 3, Issue 1 , January 2006, , Pages 52-64

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Modeling and Simulation

Reactor Modeling of a Non-Catalytic OCM Process

Volume 2, Issue 2 , April 2005, , Pages 3-14

Abstract

  ge-newline"> One method for conversion of methane to more valuable products is by non-catalytic gas-phase oxidative coupling of methane (OCM), through which methane is converted into ethylene. The product of this process is ethylene, accompanied by acetylene, ethane, a small quantity of three carbon ...  Read More ge-newline"> One method for conversion of methane to more valuable products is by non-catalytic gas-phase oxidative coupling of methane (OCM), through which methane is converted into ethylene. The product of this process is ethylene, accompanied by acetylene, ethane, a small quantity of three carbon compounds as coupling products, and carbon oxides due to complete oxidation of hydrocarbons. The kinetic model proposed for the OCM process consists of 75 elementary reactions and 23 chemical species. In previous studies, the reactor-kinetic modeling of this process, was implemented in a laboratory micro-reactor at constant temperature and pressure. Considering that this process proceeds with severe variation in the enthalpy, in the present study, in addition to isothermal, the operation of the system has also been modeled for the adiabatic state. The modeling has been carried out in a tubular reactor system. Comparison of the qualitative and quantitative results of the model with experimental data at constant temperature shows that the proposed kinetic model predicts the experimental results properly. Furthermore, in the present study, the effect of various parameters on the operation of the system has also been examined. These studies have been performed in the following ranges of pressure, temperature and CH4/O2 ratio respectively: 1≤ P ≤ 10 (bar), 950≤ T≤ 1100 (K), 4 ≤ CH4/O2 ≤ 10. It has been shown that, by increasing the temperature, the reaction rate increases. Raising the total pressure of the system causes an increase in methane conversion and selectivities of desired products as well as the reaction rate. On the other hand, increasing the residence time in the reactor will result in conversion of desired products to undesirable ones. Finally, it is shown that by decreasing the ratio of methane to inlet oxygen, conversion of methane increases, selectivities of the desired products decrease and the heat released during the reaction rises.

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Modeling and Simulation

Numerical Simulation of the Hydrodynamics of a Two-Dimensional Gas—Solid Fluidized Bed by New Finite Volume Based Finite Element Method

Volume 2, Issue 2 , April 2005, , Pages 22-36

Abstract

  n this work, computational fluid dynamics of the flow behavior in a cold flow of fluidized bed is studied. An improved finite volume based finite element method has been introduced to solve the two-phase gas/solid flow hydrodynamic equations. This method uses a collocated grid, where all variables are ...  Read More n this work, computational fluid dynamics of the flow behavior in a cold flow of fluidized bed is studied. An improved finite volume based finite element method has been introduced to solve the two-phase gas/solid flow hydrodynamic equations. This method uses a collocated grid, where all variables are located at the nodal points. The fluid dynamic model for gas/solid two-phase flow is based on the two fluid model where both phases are continues and fully interpenetrating. For the gas and solid phases the Navier-Stokes equation based on the concept of local average is obtained. Results are verified against experimental data reported in the literature.

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Modeling and Simulation

The effect of wall strengtheners on the performance of double-stage electrostatic precipitators

Volume 2, Issue 2 , April 2005, , Pages 37-48

Abstract

  The presence of wall strengtheners in double-stage electrostatic precipitators affects gas velocity, electrical field and particle movement over the ESP. In this work we have used our previous mathematical model for double-stage ESP {Talaie et. al (2001) [10]] to study the effect of wall strengtheners ...  Read More The presence of wall strengtheners in double-stage electrostatic precipitators affects gas velocity, electrical field and particle movement over the ESP. In this work we have used our previous mathematical model for double-stage ESP {Talaie et. al (2001) [10]] to study the effect of wall strengtheners on the performance of double-stage ESP. One of the important findings was that, due to the fact that wall strengtheners increase the degree of turbulence, the effect of gas turbulence on particle movement can not be ignored. The results of the calculations show that the simple Lagrangian model in which this effect is neglected is not suitable, whereas using an Eulerian approach provides much better results. The results of this model also revealed that the collection efficiency for small particles increases while that for large particles decreases when a baffle is used as wall strengthener.

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