Proposed Computational Fluid Dynamics Model Research Articles

CFD analysis of Pd-Ag membrane reactor performance during ethylbenzene dehydrogenation process

In this study, the catalytic dehydrogenation of ethylbenzene (EB) to styrene production was investigated in a tubular Pd-Ag membrane reactor (MR) in presence of a commercial iron oxide catalyst. To this purpose, a 2D-axisymmetric, isothermal model based on computational fluid dynamic (CFD) method is presented to investigate the Pd-Ag MR performance during EB dehydrogenation process for styrene and hydrogen production. The proposed CFD model provides the local information of velocity, pressure and component concentration for the driving force analysis. After investigation of mesh independency of CFD model, the validation of model results was carried out by experimental data and a good agreement between model results and experimental data was achieved. It was found that the efficient removal of hydrogen in the Pd-Ag MR could significantly increase the EB conversion. Moreover, using CFD simulation runs, effects of operating parameters such as reaction temperature, pressure and gas hour space velocity (GHSV) values on the Pd-Ag MR performance with two various flow patterns was evaluated in terms of EB conversion and COx-free hydrogen recovery. It can be concluded that the EB conversion realized in Pd-Ag MR with countercurrent flow is higher than the ones achieved for Pd-Ag MR with cocurrent flow and also for traditional reactor (TR) during EB dehydrogenation reaction, in all the studied cases. In particular, under the optimal reaction conditions, 40% enhancement in EB conversion can be obtained in the Pd-Ag MR with countercurrent flow with respect to TR.

CFD analysis of a hybrid sorption-enhanced membrane reactor for hydrogen production during WGS reaction

The main aim of this work is a comprehensive study on a new Hybrid Sorption-Enhanced Membrane Reactor (HSE-MR) concept, in which a Pd-Ag membrane during water gas shift (WGS) reaction was applied. This purpose was performed by integrating both the WGS and CO2 absorption reactions. To avoid the high experimental test costs, for evaluating the HSE-MR performance during WGS reaction, a 2D model based on Computational Fluid Dynamic (CFD) method was developed. The proposed CFD model provides the local information of pressure and component molar fractions for the driving force analysis at unsteady state conditions. The validation of the HSE-MR during WGS reaction was carried out by experimental data and a good agreement between modeling results and experimental data was found. After model validation, the performance of the HSE-MR has been compared with that obtained by both a Pd-Ag MR and a Sorption-Enhanced Reactor (SER). Moreover, the effects of some significant operating parameters, such as reaction temperature, reaction pressure and gas hour space velocity (GHSV), on the performance of the HSE-MR were studied in terms of CO conversion and hydrogen recovery in compared with both MR and SER. The CFD results show that HSE-MR, during WGS reaction, presents better performance with respect to MR and SER. As a special consequence, CFD simulation results also show that the increasing of operating parameters has a positive effects on the HSE-MR performance during WGS reaction.

Theoretical Study of Palladium Membrane Reactor Performance During Propane Dehydrogenation Using CFD Method

This study presents a 2D-axisymmetric computational fluid dynamic (CFD) model to investigate the performance Pd membrane reactor (MR) during propane dehydrogenation process for hydrogen production. The proposed CFD model provided the local information of temperature and component concentration for the driving force analysis. After investigation of mesh independency of CFD model, the validation of CFD model results was carried out by other modeling data and a good agreement between CFD model results and theoretical data was achieved. Indeed, in the present model, a tubular reactor with length of 150 mm was considered, in which the Pt-Sn-K/Al2O3 as catalyst were filled in reaction zone. Hence, the effects of the important operating parameter (reaction temperature) on the performances of membrane reactor (MR) were studied in terms of propane conversion and hydrogen yield. The CFD results showed that the suggested MR system during propane dehydrogenation reaction presents higher performance with respect to once obtained in the conventional reactor (CR). In particular, by applying Pd membrane, was found that propane conversion can be increased from 41% to 49%. Moreover, the highest value of propane conversion (X = 91%) was reached in case of Pd-Ag MR. It was also established that the feed flow rate of the MR is to be the one of the most important factors defining efficiency of the propane dehydrogenation process.

Predicting the effect of biofouling on ship resistance using CFD

This paper proposes a Computational Fluid Dynamics (CFD) based unsteady RANS model which enables the prediction of the effect of marine coatings and biofouling on ship resistance and presents CFD simulations of the roughness effects on the resistance and effective power of the full-scale 3D KRISO Container Ship (KCS) hull.Initially, a roughness function model representing a typical coating and different fouling conditions was developed by using the roughness functions given in the literature. This model then was employed in the wall-function of the CFD software and the effects of a typical as applied coating and different fouling conditions on the frictional resistance of flat plates representing the KCS were predicted for a design speed of 24 knots and a slow steaming speed of 19 knots using the proposed CFD model. The roughness effects of such conditions on the resistance components and effective power of the full-scale 3D KCS model were then predicted at the same speeds. The resulting frictional resistance values of the present study were then compared with each other and with results obtained using the similarity law analysis. The increase in the effective power of the full-scale KCS hull was predicted to be 18.1% for a deteriorated coating or light slime whereas that due to heavy slime was predicted to be 38% at a ship speed of 24 knots. In addition, it was observed that the wave resistance and wave systems are significantly affected by the hull roughness and hence viscosity.

Total resistance prediction of an intact and damaged tanker with flooded tanks in calm water

This paper presents the prediction of the total resistance of an intact and damaged ship model using the computational fluid dynamics (CFD) technique. The study is performed on the model of a tanker with a large hole in the bottom of the hull. The damage is based on statistical data on ship grounding accidents and the chosen hole size and location in the midship area represents its plausible size and location due to grounding. Reynolds-Averaged Navier-Stokes (RANS) equations with the volume of fluid (VOF) surface capturing technique are employed to solve the flow around the steadily advancing model of a damaged ship in calm water. The experiments, both on an intact and a damaged ship model that were carried out in the towing tank of the Brodarski Institute in Zagreb, Croatia, are used to evaluate the results. The numerical results are in a good agreement with the experimentally obtained results. The significant average increase of 27% in total resistance due to the altered flow around the hole and inside the flooded tanks can be observed for the analysed case. The study shows that the proposed CFD model and settings provide a good prediction of the total resistance together with the flow both around the damaged hull and inside the flooded tanks of the damaged tanker.

Evaluation of airflow and thermal comfort in buildings ventilated with wind catchers: Simulation of conditions in Yazd City, Iran

The usage of passive cooling systems such as wind catchers can reduce the energy usage in buildings and provide natural ventilation and comfort to its occupants, particularly in hot and dry regions of Iran and neighboring countries where it was traditionally used. The purpose of this study was to investigate the airflow and thermal comfort in six different designs of wind catchers using computational fluid dynamics (CFD) technique. Simulations of airflow in the wind catcher and the building were done under steady state and turbulent flow regime with boundary conditions based on typical conditions found in Yazd city, Iran. Several commonly used turbulence models were evaluated to assess the accuracy of the simulation. First, the proposed CFD model was validated through comparison of wind tunnel data available in the literature, and then the model was used for design purposes. It was found that the k−ω turbulence model can accurately predict the airflow velocity in the range of parameters studied. The design and performance of wind catcher were evaluated based on the thermal comfort levels using the Center for the Built Environment (CBE) thermal comfort tool and numerical data. Width and height of the wind catcher were varied in the simulations and optimal values were determined. It was found that varying the width of the wind catcher had the greatest impact on the airflow speed and distribution inside the room. Reducing the width from 2.5m to 2m showed that airflow velocity in the middle area was increased up to 34%. While reducing the width from 2m to 1.5m showed an entirely different flow pattern inside the building and also increase airflow speed in the middle area up to 50%. The addition of curved wall at the bottom of the inlet channel showed that it could increase the airflow speed of the inflow stream, however, it also caused the airflow to be directed towards the lower levels of the room and very large rotating flows in the upper levels. Finally, the results showed that the wind catcher may be optimized for improving comfort for various climates using the tools presented in this work.

Evaluation of dense Pd–Ag membrane reactor performance during methanol steam reforming in comparison with autothermal reforming using CFD analysis

This study presents a 2D-axisymmetric computational fluid dynamic (CFD) model to investigate the performance of dense Pd–Ag MR during methanol steam reforming (MSR) in comparison with methanol autothermal reforming (MATR) reaction for hydrogen production. The proposed CFD model provided the local information of velocity, pressure and component concentration for the driving force analysis. After investigation of mesh independency of CFD model, the validation of dense Pd–Ag MR during MSR reaction was carried out by experimental data and a good agreement between modeling results and experimental data was achieved. In the MR model, a dense Pd–Ag membrane with 50 μm thickness and also a commercial Cu/ZnO/Al2O3 catalyst in reaction zone were considered. The effects of the some important operating parameters (temperature, pressure and sweep gas ratio) on the performances of Pd–Ag MR were studied in terms of methanol conversion and hydrogen recovery. The CFD results showed that the Pd–Ag MR during MATR reaction presents higher performance in term of the methanol conversion and hydrogen recovery with respect to once obtained in the MSR reaction. In particular, in the best operating condition, hydrogen production rate in reaction zone show an enhancement around 11% in the MATR reaction over once achieved in the MSR reaction.

Injection pressure and velocity of impact-driven liquid jets

Purpose – The purpose of this paper is to describe a procedure to simulate impact-driven liquid jets by computational fluid dynamics (CFD). The proposed CFD model is used to investigate nozzle flow behavior under ultra-high injection pressure and jet velocities generated by the impact driven method (IDM). Design/methodology/approach – A CFD technique was employed to simulate the jet generation process. The injection process was simulated by using a two-phase flow mixture model, while the projectile motion was modeled the moving mesh technique. CFD results were compared with experimental results from jets generated by the IDM. Findings – The paper provides a procedure to simulate impact-driven liquid jets by CFD. The validation shows reasonable agreement to previous experimental results. The pressure fluctuations inside the nozzle cavity strongly affect the liquid jet formation. The average jet velocity and the injection pressure depends mainly on the impact momentum and the volume of liquid in the nozzle, while the nozzle flow behavior (pressure fluctuation) depends mainly on the liquid volume and the impact velocity. Research limitations/implications – Results may slightly deviate from the actual phenomena due to two assumptions which are the liquid compressibility depends only on the rate of change of pressure respected to the liquid volume and the super cavitation process in the generation process is not taken into account. Practical implications – Results from this study will be useful for further designs of the nozzle and impact conditions for applications of jet cutting, jet penetration, needle free injection, or any related areas. Originality/value – This study presents the first success of employing a commercial code with additional user defined function to calculate the complex phenomena in the nozzle flow and jet injection generated by the IDM.

Numerical investigation of gas channel shape effect on proton exchange membrane fuel cell performance

A three-dimensional, single-phase model of a proton exchange membrane fuel cell with both the gas distribution flow channels and the membrane–electrode assembly has been developed. A single set of conservation equations which are valid for the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region is developed and numerically solved using a finite volume-based computational fluid dynamics (CFD) technique. In this research, some parameters such as oxygen consumption, water production, temperature distribution, ohmic losses, anode water activity, cathode over potential and the fuel cell performance for straight single cell were investigated in more detail. The numerical simulations reveal that these important operating parameters are highly dependent on each other and the fuel cell efficiency is affected by the kind of species distribution. So for especial uses in desirable voltages, for preventing the unwilling losses, these numerical results can be useful. The important goal of this research is the investigation of serpentine channel performance compared with the conventional straight channels, which is highlighted in the results section with more details. Finally, the numerical results of proposed CFD model have been compared with the published experimental data that represent good agreement.

Computational fluid dynamics (CFD) modeling of VUV/UV photoreactors for water treatment

Abstract Vacuum-UV/UV process, an incipient catalyst/chemical-free advanced oxidation process (AOP), is potentially a cost-effective solution for the treatment of persistent micropollutants from water sources. In this study, a computational fluid dynamics (CFD) model for the simulation of VUV/UV photoreactors used for water treatment was developed and evaluated experimentally. The developed model integrated hydrodynamics, species mass transport, more than 40 reactions, along with the irradiance distribution at 185 nm VUV and 254 nm UV wavelengths within the reactor. The 185 nm VUV and 254 nm UV emissions from an ozone-generating lamp were experimentally measured and fed to the model. The evaluation showed that the proposed CFD model successfully predicted the degradation rate of a model pollutant in a prototype flow-through VUV/UV reactor. The developed model was also able to trace the main by-products of the target micropollutant resulting from 185 nm and 254 nm photolysis as well as OH oxidation. Detailed analysis of the direct-photolysis of the model contaminant at 254 nm and 185 nm vs. OH radical based degradation of the contaminant revealed the latter one as the most dominant degradation pathway. The performed analysis confirmed that degradation rates of micropollutants in the VUV/UV photoreactors are strongly limited by mass transfer in proximity of the quartz sleeve.

Simulation and experimental validation of the flow field at the entrance and within the filter housing of a production spark-ignition engine

The paper aims to analyse the flow field at the entrance and within the filter housing of a production four-cylinder, spark-ignition engine during the intake phase. To this purpose a computational fluid dynamic (CFD) analysis was carried out adopting a finite volume code, while an experimental activity was performed at a steady flow rig to validate the computational model.The comparison between numerical data and experimental measurements showed a good agreement and it demonstrated the capabilities of the proposed CFD model to predict in detail the flow field within a complex production automobile component that largely influences the efficiency and reliability of actual internal combustion engines (ICEs).

CFD modeling of hydrophobic pervaporation process: ethanol/water separation

ABSTRACT The computational fluid dynamics (CFD) approach was employed to model the pervaporation separation of ethanol from its aqueous solutions with polydimethylsiloxane (PDMS) membrane. The proposed CFD model was also used to describe the influences of feed flow rate, temperature, and ethanol concentration on the membrane performance. This approach is based on solving the conservation equations including continuity and momentum equations that were disceritized using finite element method for ethanol in the membrane module. The model was then validated using the experimental data obtained from pervaporation experiments. The simulation results were in good agreement with the experimental data for different values of feed concentration, feed temperature, and Reynolds number (feed flow rate). The CFD results also indicated that as feed temperature and ethanol concentration in the feed solution increased, the ethanol flux enhanced. The feed flow rate was shown to have no significant effect on ethanol flux w...

Computational Analysis of Closed Wet Cooling Towers

The thermal and hydraulic performance of plain and oval tubes closed wet cooling tower (CWCT) are investigated numerically. Computational fluid dynamics (CFD), ANSYS Fluent 12.1, is implemented for the numerical solution. Species transport without reactions is adopted to simulate the mass transfer from the air-deluge water interface to the air. Different turbulence models and near-wall treatments are used to assess which model fits the data better. The mass transfer Colburn factor j m , and friction factor f are presented and compared with experimental data. The proposed CFD model is also applied to predict the mass transfer coefficient of another CWCT and compares well with the experimental data.

Computational fluid dynamics (CFD) modeling of UV disinfection in a closed-conduit reactor

The use of ultraviolet (UV) disinfection in water treatment is governed by several factors, including flow field, fluence rate field, and microbial inactivation kinetics. In this study, a computational fluid dynamics (CFD) model was developed for UV disinfection in a closed-conduit reactor where an improved low-Reynolds number k– ε model was used to calculate flow field and a modified P-1 model was employed to obtain the fluence rate field. The Chick–Watson model was adopted to characterize the inactivation of microorganisms. Commercial CFD software FLUENT 6.3 was employed to solve the governing equations. The predicted flow field agreed well with experimental data obtained by digital particle image velocimetry (DPIV) ( Liu et al., 2007) in terms of velocity field. The proposed CFD model was also evaluated by comparing current predictions to bioassay test data, and reasonable agreement was obtained in terms of effluent log inactivation. The impact of wall reflection of the light on the fluence rate field and the viable microorganism concentration field was investigated. The effect of wall reflection of the light on effluent log inactivation was also investigated under different water qualities and lamp power conditions. The results showed that at higher inactivation levels, the effect of wall reflection was more influential.