Computational Fluid Dynamics Modeling Study Research Articles

Evaluating airflow dynamics in common vertical circulation spaces of a multi-floor apartment building for mitigating airborne infection risks: A CFD modeling study

As more people increasingly inhabit indoor spaces, the importance of interior environment design has grown significantly. The focus of this research is to assess the air flow and air change per hour (ACH) within common service vertical circulation spaces in apartment buildings, emphasizing the potential role of these spaces in mitigating airborne infections. The intricate relationships between the design parameters of these spaces and variables related to air circulation are examined. To achieve this goal, the investigation employed a simulation-based approach, utilizing computational fluid dynamics (CFD) analysis to scrutinize the prevalent design of common vertical circulation spaces. The simulation outcomes unequivocally reveal that the design of these spaces has a direct impact on air circulation patterns, often influencing suboptimal conditions. Armed with these insights, this research advocates for a reevaluation of design considerations of common service vertical circulation in forthcoming housing projects. Furthermore, this research proposes innovative design solutions and strategies aimed at enhancing natural ventilation and overall air flow within common service vertical circulation spaces while evaluating their performance.

Effects of SDS surface-active agents on hydrodynamics and oxygen mass transfer in a square bubble column reactor: Experimental and CFD modeling study

This work examined experimentally and numerically the effects of sodium dodecyl sulfate (SDS) surfactant agent on mass transfer coefficients kLaL and kL in a high-aspect square bubble column reactor. To this end, SDS aqueous solutions at concentrations between 5 ppm and 30 ppm were prepared. Superficial gas velocity was varied from 0.74 cm.s−1 to 9.44 cm.s−1 covering all flow regimes to analyze the interaction between different phases and the effect of liquid surface tension on gas-liquid interfaces. Experimental data indicated that the presence of the SDS in the liquid phase augmented the overall gas holdup up to 25% at a constant gas velocity (Ug = 7.3 cm.s−1) in the transition regime, which is due to the role of SDS in bubble interactions. The impact of SDS addition on the mass transfer is twofold. Firstly, it reduced kL because the SDS molecules migrate towards the bubble-liquid interface thanks to the lower O2 diffusivity in water, thus hindering the O2 transfer from one phase to the other. Secondly, it increased aL owing to the inhibition of bubbles coalescence and, therefore, the lower mean bubble size. Among these two effects, the latter is prevailing, which led to an increase in kLaL in contaminated systems. In the second part of this work, a population balance model (PBM) was coupled with a computational fluid dynamics (CFD) model based on large-eddy simulation (LES) to analyze the effect of both tap water and SDS contaminated systems on the breakage phenomena, local flow pattern, and the resulting hydrodynamics and mass transfer features in the reactor. Ultimately, experiments and numerical simulations agreed well in terms of global gas holdup and kLaL coefficient. In particular, the transition points in the case of the SDS media (except for foam formation) provided the model with adequate PBM definitions for the dispersed phase.

Optimizing pressure retarded osmosis spacer geometries: An experimental and CFD modeling study

Existing desalination plants face the challenges of high energy costs and environmental impacts from brine disposal. Pressure retarded osmosis (PRO) is a membrane-based technology that could mitigate these issues by capturing the potential energy in the salinity gradient between brine and dilute (e.g., freshwater/wastewater) solutions. Currently, a major challenge facing PRO is concentration polarization (CP), which is the reduction of the salinity gradient caused by the buildup of solutes along both the brine side of the membrane surface (external) and within the membrane support structure (internal). CP can be reduced using membrane spacers, but they have the drawback of increasing the pressure drop along the length of the feed channel. Therefore, it is important to design a membrane spacer that can minimize the effects of both CP and the internal pressure drop. In this study, we simulated the effect that membrane spacer geometries have on CP and the internal pressure drop via computational fluid dynamics (CFD) using the open-source software, OpenFOAM. Simulations were validated using experimental results for five physical spacer geometries on a bench-scale PRO system. The highest performing physical spacer geometry was a 47 mil (1.41 mm) thick parallel oriented spacer (47P), which was then improved upon through integrated CFD-based optimization using the open-source optimization toolkit, DAKOTA. Single-objective genetic algorithms were used to iteratively modify the spacer geometry by increasing the linearity of the thinner cross-strand and decreasing the linearity of the thicker parallel strand, which created a more hexagonally shaped cross-section. This modification was able to increase overall system performance, which was represented by the ratio of the mass flux density of the feed permeate through the membrane to the pressure drop across the length of the feed channel, by 16.3%. This suggests that a membrane spacer with a parallel hexagonal configuration allows the fluid to flow with minimal internal pressure drop while still creating the necessary back-mixing from the membrane surface to the bulk fluid needed to promote mass transfer and reduce the impacts of CP. Implementing these improvements in spacer design would cause the feed pump to consume less energy, which would increase the net energy generation potential and overall sustainability of PRO systems.

Mechanistic modeling of peracetic acid wastewater disinfection using computational fluid dynamics: Integrating solids settling with microbial inactivation kinetics

While the impact of suspended solids on chemical disinfection kinetics has been widely recognized, a detailed modeling framework for assessing their contribution on disinfection efficiency in municipal contact tanks is yet unavailable. In this paper, we conducted experimental and modeling studies to mechanistically describe the interplay between suspended solids (not removed by gravity settling in secondary clarifiers) and disinfection performance of an emerging disinfectant, peracetic acid, operated in a municipal contact tank. Specifically, we developed an integrated computational fluid dynamics (CFD) model to simultaneously predict the fate and transport of suspended solids, Escherichia coli and peracetic acid in a hypothetical reactor using an exposure-based (i.e., CT-based) inactivation rate expression. The integrated CFD model, calibrated against laboratory data, was used to gain insights on the vertical distribution and local PAA decay effect associated with solids settling and their impact on disinfectant decay and microbial inactivation. Results indicated that: (a) solids settling in contact tanks is a significant phenomenon that cannot be neglected, which can substantially impact disinfection efficiency under low flow conditions; (b) vertical solids distribution and stratification in contact tanks can strongly affect Escherichia coli inactivation by peracetic acid, as highlighted by the CFD modeling studies; (c) Escherichia coli settling is experimentally measurable, and strongly correlated with solids settling. These phenomena can be successfully integrated into a CFD model to obtain a comprehensive description of the PAA disinfection process in presence of changes in secondary effluent quality and flow, a situation typically encountered in municipal contact tanks operated in full scale wastewater treatment plants.

Comparative Study of CFD and LedaFlow Models for Riser-Induced Slug Flow

The goal of this study is to compare mainstream Computational Fluid Dynamics (CFD) with the widely used 1D transient model LedaFlow in their ability to predict riser induced slug flow and to determine if it is relevant for the offshore oil and gas industry to consider making the switch from LedaFlow to CFD. Presently, the industry use relatively simple 1D-models, such as LedaFlow, to predict flow patterns in pipelines. The reduction in cost of computational power in recent years have made it relevant to compare the performance of these codes with high fidelity CFD simulations. A laboratory test facility was used to obtain data for pressure and mass flow rates for the two-phase flow of air and water. A benchmark case of slug flow served for evaluation of the numerical models. A 3D unsteady CFD simulation was performed based on Reynolds-Averaged Navier-Stokes (RANS) formulation and the Volume of Fluid (VOF) model using the open-source CFD code OpenFOAM. Unsteady simulations using the commercial 1D LedaFlow solver were performed using the same boundary conditions and fluid properties as the CFD simulation. Both the CFD and LedaFlow model underpredicted the experimentally determined slug frequency by 22% and 16% respectively. Both models predicted a classical blowout, in which the riser is completely evacuated of water, while only a partial evacuation of the riser was observed experimentally. The CFD model had a runtime of 57 h while the LedaFlow model had a runtime of 13 min. It can be concluded that the prediction capabilities of the CFD and LedaFlow models are similar for riser-induced slug flow while the CFD model is much more computational intensive.

The influence of wind in secondary settling tanks for wastewater treatment - A computational fluid dynamics study. Part II: Rectangular secondary settling tanks.

Computational fluid dynamics (CFD) model is used to study the effect of wind on the performance of a rectangular secondary sedimentation tank (SST) in a wastewater treatment plant (WWTP). Unlike most of the previous CFD modeling studies which evaluated the wind effect on the sedimentation tank in only water treatment plants, this study evaluates a rectangular SST in a WWTP at different wind speeds and directions, and under different inflow loading conditions. The wind is qualitatively and quantitatively analyzed for a range of wind speeds and directions as well as loading rates. The net effect is to change the three-dimensional hydrodynamics profiles, effluent suspended solids, and sludge blanket height. The simulation results show that the wind deteriorates overall clarification performance of the rectangular SST and has little effect on the sludge thickening under mild wind conditions until the speed increases an extreme windy condition. These CFD simulation results suggest that in strong windy climates, covering SSTs or protecting them from strong winds may be justified. PRACTITIONER POINTS: This is the first comparison of wind effects on a rectangular secondary sedimentation tank The effects of varied flow conditions, wind directions, and velocities are compared Wind-induced currents in the settling tank negatively affect removal efficiency Winds have strong negative impact on the performance of sedimentation tanks.

CFD and kinetic modelling study of methane MILD combustion in O2/N2, O2/CO2 and O2/H2O atmospheres

To deepen the understanding of combining moderate or intense low-oxygen dilution (MILD) combustion with oxy-fuel combustion for enhancing flame stability while realizing carbon capturing and storage, this paper presents a numerical study of methane MILD combustion in three atmospheres, i.e.: O2/N2, O2/CO2 and O2/H2O, with both computational fluid dynamics (CFD) and kinetic calculation approaches. Firstly, CFD predictions for the three conditions were performed following a systematic validation of the numerical method against experimental measurement from methane/air MILD combustion in a laboratory-scale closed furnace. Subsequently, kinetic calculations with a well-stirred reactor model was used to quantitatively identify the operating ranges of MILD combustion in the three atmospheres for methane. Moreover, the kinetic calculation provided additional insight into the fuel oxidation pathway. The results reveal that replacing N2 with either CO2 or H2O would help to establish MILD combustion mode from the viewpoint of lower temperature increase, due to both physical and chemical property discrepancies among the diluents. Specifically, the chemical effect and physical effect are responsible to the lower temperature rise for CO2-diluted case and H2O-diluted case, respectively. Inside the MILD combustion furnace, the negative heat release region disappears in regardless of atmospheres, indicating the eliminated fuel pyrolysis process under MILD combustion mode. Detailed analysis of the flame structure suggests that the combustion regimes inside the furnace in the three atmospheres are all in well-stirred combustion regime, and CO2-diluted case has the most extended reaction zone. Kinetic calculation indicates that CO2 or H2O dilution would result in a wider MILD combustion operating range compared to N2 dilution, while it is more pronounced for CO2. These observations all imply that MILD combustion will be more easily established with CO2 dilution than N2 or H2O dilution. However, higher CO formation is obtained in O2/CO2, forcing more attention to be paid on CO emission under CO2-diluted MILD combustion. Furthermore, the hydrocarbon recombination route is negligible under MILD combustion in spite of the atmospheres, implying lower sooting tendency as compared with conventional combustion.

Computational Fluid Dynamics (CFD) Modelling and Application for Sterilization of Foods: A Review

Computational fluid dynamics (CFD) is a powerful tool to model fluid flow motions for momentum, mass and energy transfer. CFD has been widely used to simulate the flow pattern and temperature distribution during the thermal processing of foods. This paper discusses the background of the thermal processing of food, and the fundamentals in developing CFD models. The constitution of simulation models is provided to enable the design of effective and efficient CFD modeling. An overview of the current CFD modeling studies of thermal processing in solid, liquid, and liquid-solid mixtures is also provided. Some limitations and unrealistic assumptions faced by CFD modelers are also discussed.

A Comparative Study of CFD Models of a Real Wind Turbine in Solar Chimney Power Plants

A solar chimney power plant consists of four main parts, a solar collector, a chimney, an energy storage layer, and a wind turbine. So far, several investigations on the performance of the solar chimney power plant have been conducted. Among them, different approaches have been applied to model the turbine inside the system. In particular, a real wind turbine coupled to the system was simulated using computational fluid dynamics (CFD) in three investigations. Gholamalizadeh et al. simulated a wind turbine with the same blade profile as the Manzanares SCPP’s turbine (FX W-151-A blade profile), while a CLARK Y blade profile was modelled by Guo et al. and Ming et al. In this study, simulations of the Manzanares prototype were carried out using the CFD model developed by Gholamalizadeh et al. Then, results obtained by modelling different turbine blade profiles at different turbine rotational speeds were compared. The results showed that a turbine with the CLARK Y blade profile significantly overestimates the value of the pressure drop across the Manzanares prototype turbine as compared to the FX W-151-A blade profile. In addition, modelling of both blade profiles led to very similar trends in changes in turbine efficiency and power output with respect to rotational speed.

Comparative study of CFD models of the air flow produced by an air-assisted sprayer adapted to the crop geometry

A computational fluid dynamics (CFD) model for simulating the air flow produced by an air-assisted sprayer can be developed according to any one of several sets of criteria and for various specific applications. Thus far, most CFD models have focused on the characterization of the air flow generated by the sprayer. However, such models may not be the best when assessing the effectiveness of air-assisted sprayers adapted to crop geometry, such as those used in vineyards. In this study, the air flow produced by an air-assisted sprayer adapted to the geometry of a vineyard was simulated using four CFD models: Model 1 was designed to simulate air velocity measurements at the outlets; Model 2 was designed to simulate air velocity measurements at a certain distance from the outlets; Model 3 was dedicated to the modelling of the internal geometry of the air ducts rather than the characterization of the air flows generated by the sprayer; and Model 4, which was developed as a variant of Model 3, was created to perform the same calculation in several stages. The models were validated with actual measurements of the air velocity near the sprayer outlets. The results showed that although Models 1 and 2 (both of which have been used in most existing studies) simplified the calculation, they are impractical for simulating different air flows. By contrast, Models 3 and 4 provided complex meshes that complicate the convergence of the calculation and require a suitable treatment of both the viscosity and the flow near the walls. Model 3 showed the smallest error (16%) in the air velocity estimated in the treatment plane. Model 4 showed potential for future implementation of the dispersed phase and crop-air interaction because it mitigated the problems arising from the complexity of the meshes. It should also be noted that there are errors inherent to the implementation of the CFD model, errors related to inaccuracies in the geometry of the air ducts, inaccuracies related to the measurement of the air velocities, inaccuracies in the quantification of the air flow, and simplifications linked to the turbulent model.

Thermal performance analysis of solar parabolic trough collector using nanofluid as working fluid: A CFD modelling study

In this work, forced convection heat transfer turbulent fluid flow inside the receiver tube of solar parabolic trough collector is numerically simulated. The CuO-water and Al2O3-water nanofluids are used in this study as working fluid. The Computational Fluid Dynamics (CFD) commercial code is employed to find hydrodynamic and heat transfer coefficients by means of Finite Volume Method (FVM). This analysis is carried out based on k–ε RNG turbulent model for different heat flux conditions. The effect of nanoparticles volume fraction (ϕ) on thermal performance of the solar parabolic collector is studied. Results show that nanofluid enhances the heat transfer characteristics of the parabolic trough collector in comparison with pure water. Also, the results indicate that by increasing of the nanoparticle volume fraction, the average Nusselt number increases for both nanofluids. Furthermore, the heat transfer coefficient was found to be enhanced up to 28% and 35% by using Al2O3-water and CuO-water nanofluids (ϕ=3%), respectively.

Effects of moisture release and radiation properties in pulverized fuel combustion: A CFD modelling study

Pulverized fuels (PF) prepared and fired in utility boilers always contain some moisture. For some fuels with high moisture contents (e.g., brown coals), the share of the evaporation enthalpy is quite significant compared to the heat released during combustion, which often needs to be reclaimed to improve the plant efficiency and is also expected to affect the combustion process. Thermal radiation is the principal mode of heat transfer in combustion. In PF furnaces, radiation consists of contribution from both participating gases and solid particles, in which gas and particle radiation properties play an important role. There are different methods or models in the literature to address fuel moisture release and radiation properties, some of which may be inappropriate and can produce misleading results. This paper compares the different methods and models and demonstrates their implementation and impacts via a computational fluid dynamics (CFD) study of a 609MWe pulverized coal-fired utility boiler. Overall speaking, it is suggested to add the free moisture in the fuel to the primary air stream while lump the bound moisture with volatiles in PF combustion modelling, although different methods for fuel moisture release may not induce distinct difference in combustion of PF with relatively low moisture content. For radiation, it has to be emphasized that particle radiation largely overwhelms gas radiation in PF combustion. The current tide of radiation research that over-focuses on gas radiation while over-simplifies particle radiation or even neglects particle radiation needs to be turned. For gaseous fuel combustion in which particle radiation is negligible, more generic model for gas radiative properties that can naturally and correctly accommodate the changes in combustion condition (e.g., oxy-fuel or air–fuel), account for the variations in CO2 and H2O concentrations in a flame, and include the impacts of other participating gases (e.g., CO and hydrocarbons) needs to be derived for combustion CFD community.

Investigation of film cooling from cylindrical hole with plasma actuator on flat plate

This paper reports the Computational Fluid Dynamics modeling studies on the effect of plasma aerodynamic actuation on combustor film cooling performance. By comparing Case (i.e. film cooling hole with plasma actuator) result to Base (i.e. film cooling hole without plasma actuator) result, the mechanism of improving film cooling performance by using plasma actuator was analyzed. The results show that the Counter Rotating Vortex Pairs in Base are weakened by a new pair of vortex in Case, which is induced by the plasma-actuator-generated arc-shape-distributed electric body force. This leads to less interaction and less mixing between the main flow and the jet flow. Then it causes enhancement of the stability and the steadiness of the jet flow. Finally the average film cooling effectiveness in Case is higher than that in Base. For Case, the uniformity of temperature distribution along spanwise wall surface is improved as the actuator electrode radian increases, so does the average film cooling effectiveness. The film cooling effectiveness is higher when actuator is closer to the exit of hole.

CFD modeling and experimental study of carbon dioxide removal in a lab-scale spray dryer

In a co-current lab-scale spray dryer absorber fitted with a two-fluid nozzle, the removal of carbon dioxide through chemical absorption with NaOH solution as absorbent was investigated experimentally and theoretically. Experimental results showed that in selected ranges of operating parameters, increasing the inlet gas temperature and absorbent concentration has the increasing–decreasing effect on the overall removal efficiency. Also increasing L/G ratio (liquid to gas flow rate), decreasing inlet CO2 concentration and decreasing the droplet mean diameter had favorable effects on overall removal efficiency. Process modeling was done through Computational Fluid Dynamics (CFD) method and using Ansys Fluent 13.0 software. In the three dimensional model of the process the gas phase was modeled as a continuum using the Euler approach and the droplet/particle phase was modeled by the Lagrange approach. An empirical correlation for reaction rate was obtained through experimental data and added to the CFD model of the process as a surface reaction via a user defined function. Predictions of the CFD model were compared to the experimental data. The model prediction in comparison to the experimental trends is fair.

Air and air contaminant flows in office cubicles with and without personal ventilation: A CFD modeling and simulation study

The paper is aimed at building an appropriate computational fluid dynamics (CFD) model for simulating the flow field in the office cubicle with and without personalized ventilation (PV) and using it to investigate the flow field in the cubicle. A computational model was first constructed by using a commercial CFD code (STAR-CCM). In this process, different approaches to represent manikins, boundary conditions, geometries, and gridding were tested, and a proper approach was selected for simulating the air and contaminant movement in the cubicles and their interactions with the remaining room space. A comparison between the simulation and the experimental results are made to show how accurate the CFD model can be. A brief evaluation of the environmental quality was conducted for both cases with PV and underfloor air diffuser (UFAD). This comparison showed a significant advantage in the PV system, indicating how the PV system performed under different airflow rates. This verified CFD model will be utilized in the future to investigate the performance of the partitioned cubicle collaborating with personalized ventilation systems.

Validation of CFD Modeling and Simulation of a Simplified Automotive Model

In the early design phase of automotive sector, the flow field around the vehicle is important in decision making on design changes. It would consume a lot of money and time for multiple prototypes development if adopt traditional testing method which is wind tunnel test. Thus, numerical method such as Computational Fluid Dynamics (CFD) simulation plays an important role here. It is very often simulation results been compared with wind tunnel data. However, with various mesh types, meshing methodology, discretization methods and different solver control options in CFD simulation, users may feel low confidence level with the generated simulation results. Thus, a robust modeling and simulation guideline which would help in accurate prediction should be developed due to the industry’s demand for accuracy when comparing CFD to wind tunnel results within short turnaround time. In this paper, a CFD modeling and simulation study was conducted on a simplified automotive model to validate with wind tunnel test results. The wind tunnel environment was reproduced in the simulation setup to include same boundary conditions. Meshing guidelines, turbulence model comparisons and also the best practice for solver setup with respect to accuracy will be presented. Overall, CFD modeling and simulation methods applied in this paper are able to validate the results from experiment accurately within small yaw ranges.

Flow in a symmetrically filled whirlpool: CFD modelling and experimental study based on Particle Image Velocimetry (PIV)

This study presents Computational Fluid Dynamics (CFD) simulation analyses and Particle Image Velocimetry (PIV) experimental research on two-sided (symmetrical) filling of whirlpool separator’s tank and swirling the liquid. This innovative approach enables flow symmetrization and more efficient use of the secondary flow, which causes the hot trub cone formation. The results of the CFD analyses were verified during the experimental research incorporating image anemometry (PIV) and a laboratory scale model. The results were compared to the data obtained from the CFD and PIV performed on a typical model with single-sided filling. The comparison clearly proved the advantage of the two-sided filling in terms of timing and position of the secondary flow, which causes the hot trub cone formation in a whirlpool separator.

Experimental and CFD Modeling Study of Inulin-Type Fructan Purification from a Model Solution by Diafiltration on a Pilot-Scale Unit

Nanofiltration of a model inulin-sucrose solution has been studied using a pilot cross-flow unit. The aim of this work was to evaluate two operation modes: total recycle nanofiltration and diafiltration. Experiments were performed at transmembrane pressures from 0.4 to 1.45 MPa and two inlet flow rates. It was found that inulin purification is feasible within the range of the process conditions set. Furthermore, the sucrose retention coefficient is highly affected by the transmembrane pressure but the inlet flow rate does not affect this parameter significantly. Experimental results were simulated by Computational Fluid Dynamics (CFD) and a good agreement was observed between the predicted and the experimental values.

CFD modelling study of heat transfer in a coiled agitated vessel

Computational fluid dynamics (CFD) modelling of heat transfer studies in a helical coiled agitated vessel with varying heat input has been carried out using commercial CFD code FLUENT (Version 6.3.26). The study using two agitators namely propeller and disk turbine is proposed to evaluate the CFD predictions of heat transfer performances as well as to provide a detailed insight into the process. The simulations have been performed for the three-dimensional and time-independent flow. The standard k-e model was adopted to capture the turbulent nature. The temperature contours in both axial and radial directions are also discussed. The CFD predicted Nusselt number agrees well with the experimentally reported value and the discrepancy is found to be less than ±7%.

CFD Modeling and Experimental Study of a Spray Dryer Performance

Abstract The performance of a pilot-scale spray dryer is investigated experimentally and theoretically. The governing equations for flow field, heat and mass transfer, and particle trajectory are solved by applying computational fluid dynamics (CFD). The effects of inlet air temperature and initial particle diameter on the outlet humidity and particle residence time are examined. These parameters should be considered carefully in proper designing of spray dryers especially for the heat-sensitive products. The model is validated with an error of 5.5%.