CFD Simulation Of Flow Research Articles

Analysis of the Dispersive and Distributive Mixing Effect of Screw Elements on the Co-Rotating Twin-Screw Extruder with Particle Tracking.

Compounding is an important step in processing base polymers and is used to incorporate various additives into a polymer. For this purpose, different screw elements are used for dispersive and distributive mixing on a co-rotating twin-screw extruder. Optimising the screw configuration requires precise knowledge of the screw elements' mixing properties, which have not been thoroughly investigated. This study analyses the mixing behaviour of individual screw elements regarding dispersive and distributive mixing using 3D CFD flow simulations with subsequent particle tracking. For distributive mixing, the particle distribution behind the screw elements in the XY plane is analysed and the mixing index MQ, which relates the standard deviation and the mean value of the triangular areas between the particles, is calculated. For dispersive mixing, the maximum shear stress on the particle path and the integral of the shear stress over the residence time of each individual particle are determined. The results show that screw element geometry and rotation speed have a significant influence on dispersive and distributive mixing. In addition, better dispersive mixing is achievable with highly viscous materials. These findings enable the optimisation of the mixing zone of a co-rotating twin-screw extruder for the efficient mixing of mineral fillers.

Novel drainage pipeline breakages detection based on MEMS inertial sensor: From mechanism to application

Urban water environment pollution is a global concern, in developing countries, sewage infiltration resulting from urban drainage pipelines breakage is an essential element in the urban groundwater pollution and the recurrence of black odor water bodies, it is crucial to accurately and efficiently detection and localisation of urban drainage pipelines breakage to protect the urban water resources. In this paper, a device for detecting defects in drainage pipelines was developed and assembled using microelectromechanical systems (MEMS) inertial sensors as the core components, and the improved cumulative sum (CUSUM) model was used for anomalous detection of the pitch angle of the device's movement along the course of the pipeline as a method of detecting pipeline breakage. In the laboratory simulation of drainage pipeline tests, the CUSUM peaks (0.709, 1.102, 3.038, 7.990) for the case of external water infiltration rates into the pipeline at the point of pipe breakage (2.9%, 4.6%, 5.8%, 9.2%), and for the cases of sewer exfiltration rates in the pipeline of 4.2% and 6.4% (0.760, 1.382). CFD simulations of the water flow in the laboratory pipeline show a high degree of overlap between the trend of the water surface near the point of breakage and the anomalous fluctuations in the pitch angle of the device motion in the laboratory tests. Finally, the authors tested the device on municipal drains in the city of A. The results demonstrated the reliability and high accuracy of the device. The device enables to improve the ecological quality of urban water environment by accelerating the rate of defect detection in urban drainage pipelines and reducing the detection expenses.

CFD simulation of liquid food flow in a coiled tube UVC reactor

The coiled tube reactor is the most efficient UVC reactor for disinfecting microorganisms in liquid food flow. Thus, it is critical to investigate the effective parameters for designing a coiled tube UVC reactor. In this study, CFD simulation is used to investigate the turbulent and laminar flow of Newtonian and non-Newtonian fluids. In turbulent flow, disinfection in the tube area is nearly uniform, with the exception of regions near internal lamps, where the most disinfection has occurred. The variation of log10 reduction in terms of tube turn number is linear. Increasing the non-Newtonian behavior increases the disinfection of microorganisms in the reactor. Furthermore, the effect of tube diameter on coiled reactor performance is investigated. Reducing the diameter of the reactor's tubes improves its performance. Finally, two correlations are obtained for the influence of the effective parameters on the log10 reduction of this type of reactor.

Development of Correlations Based on CFD Study for Microchannel Condensation Flow of Environmentally Friendly Hydrocarbon Refrigerants

A CFD simulation of the condensation flow of R600a and R290 within microchannels was conducted to explore the effect of mass flux, hydraulic diameter, and vapour quality on heat transfer rate and pressure drop. Data obtained from CFD simulations were used to develop new heat transfer and pressure drop correlations for the condensation flows of R600a and R290, which are climate-friendly refrigerants. Steady-state numerical simulations of condensation flow of refrigerants were carried out inside a single circular microchannel with diameters varying between 0.2 and 0.6 mm. The volume of fluid approach was used in the proposed model, calculating the interface phase change using the Lee model. The CFD simulation model was validated via a comparison of the simulation results with the experimental data available in the literature. It is found that the newly developed Nu number correlation shows a deviation, with an Ave-MAE of 11.16%, compared to those obtained by CFD simulation. Similarly, the deviation between friction factors obtained by the newly proposed correlation and those obtained by CFD simulation is 20.81% Ave-MAE. Widely recognized correlations that are applicable to the condensation of refrigerants within small-scale channels were also evaluated by comparing newly developed correlations. It is concluded that the newly proposed correlation has a higher accuracy in predicting the heat transfer coefficient and pressure drop. This situation can contribute to the creation of a sustainable system via the use of microchannels and climate-friendly refrigerants, like R600a and R290.

Modelling W/O/W double emulsions preparation in static mixers: Accounting for the shear-thinning behaviour of the dispersed phase

The dispersion of a shear-thinning non-Newtonian fluid using in-line mixers to prepare double emulsions is investigated experimentally and numerically in this study. A two-step method is adopted for the preparation of double emulsions, comprising in a first step the preparation of a reverse water-in-oil (W/O) emulsion using a high-shear rotor-stator device. This inner emulsion is dispersed in a second step into an outer aqueous phase by continuous parallel pumping of both phases through a set of static mixers. The second preparation step is modelled using a population balance equation (PBE) accounting for droplet breakage inside the mixers. Since the inner emulsion behaves as a shear-thinning fluid, the breakage efficiency depends on the local shear rate. Using classical turbulent breakage kernels is therefore inappropriate, hence there is a need for a kernel accounting for the shear-thinning character of the dispersed phase. To tackle this issue, single-phase CFD simulations of the fluid flow through the mixers are carried out showing a high shear rate magnitude near the walls of the pipe and the mixer crossbars. To avoid CFD-PBE direct coupling, the probability density function (PDF) of the shear rate is extracted from the CFD simulations. This PDF is then used to develop a volume-averaged PBE, where a classical Ostwald-de Waele model is employed to relate the apparent viscosity of the inner emulsion to the shear rate. Different experimental parameters influencing the quality of the dispersion are investigated, including the fraction of the inner emulsion phase, the oil viscosity and the inner and outer aqueous phase viscosities. In the different cases, the model captures the transient evolution of the droplet size distribution of the W/O/W double emulsions at the outlet of the mixers while the computational time remains very low.

Increasing Computational Efficiency of CFD Simulations of Reactive Flows at Catalyst Surfaces through Dynamic Load Balancing.

We propose a numerical strategy based on dynamic load balancing (DLB) aimed at enhancing the computational efficiency of multiscale CFD simulation of reactive flows at catalyst surfaces. Our approach employs DLB combined with a hybrid parallelization technique, integrating both MPI and OpenMP protocols. This results in an optimized distribution of the computational load associated with the chemistry solution across processors, thereby minimizing computational overheads. Through assessments conducted on fixed and fluidized bed reactor simulations, we demonstrated a remarkable improvement of the parallel efficiency from 19 to 87% and from 19 to 91% for the fixed and fluidized bed, respectively. Owing to this improved parallel efficiency, we observe a significant computational speed-up of 1.9 and 2.1 in the fixed and fluidized bed reactor simulations, respectively, compared to simulations without DLB. All in all, the proposed approach is able to improve the computational efficiency of multiscale CFD simulations paving the way for a more efficient exploitation of high-performance computing resources and expanding the current boundaries of feasible simulations.

CFD simulation of unstable fluid flows in the rotor of a high-speed precipitation centrifuge

The results of a numerical study of unstable fluid flows in the rotor of a high-speed vertical precipitation centrifuge are presented. It is shown that during the operation of a high-speed precipitation centrifuge, a qualitative change in the hydrodynamic regime is possible from conditionally laminar to conditionally turbulent, characterized by large-scale axial and radial pulsations of the liquid phase, accompanied by a significant decrease in sedimentation efficiency. It has been established that the flow pulsations are not random in nature, but the amplitude of these pulsations first increases with increasing rotation rate of the centrifuge rotor, and after passing a certain “critical” rotation rate it begins to decrease. Thus, the “critical” rotor rotation rate can be considered as a resonant rate, at which the frequency of turbulent flow pulsations (natural oscillation frequency) coincides with the rotor rotation frequency (forced oscillation frequency). The dependences of the pitch, frequency, and amplitude of liquid flow pulsations on the edge of the centrifuge overflow disk on the rotor rotation rate were obtained. It has been established that in the “subcritical” and “supercritical” operating modes, the amplitude and step of liquid pulsations on the overflow disk of the centrifuge are increasing and decreasing respectively.

Analysis and validation of CFD simulations for flow in the large power station flue gas system

Analysis and validation of CFD simulations for flow in the large power station flue gas system

CFD simulation of two-phase flow in a batch-mode electrodialysis of lithium sulphate: Effect of gas evolution

Electrodialysis (ED) of Li2SO4 plays a crucial role in the closed-loop recycling of lithium-ion batteries. The enhanced flexibility and energy efficiency of batch-mode EDs highlight the significance of time-dependent models. The gaseous molecules evolved from electrochemical reactions induce localized turbulence, significantly impacting the velocity, potential, and concentration distributions. This study presents a two-phase model that analyzes the dynamic behaviour of a batch-mode Li2SO4 ED and investigates the bubbles’ impact employing an Euler-Euler model. The finite element method solves time-dependent hydrodynamic, mass conservation, and electrochemical equations. The model shows close agreement with experimental data, and incorporating the two-phase model reduces the concentration error from 20.6% to 10.3%. Bubbles-induced liquid circulation by buoyant and drag forces reduces concentration polarization, increasing transmembrane ionic fluxes and improving ED performance. Although bubbles increase ohmic overpotential, the enhanced ionic concentrations in concentrate channels due to bubble-induced liquid circulation reduce electrolyte resistance. Raising the inlet flowrate reduces the gas fraction and diminishes solution circulation.

Equivalent diffusion ratio distribution in the UGT15000 low pressure compressor

With spatial and temporal periodicity approach the results of steady state CFD simulation of compressible air flow in each blade-to-blade row of low pressure compressor (LPC) of the UGT15000 gas turbine engine (Ukrainian SSR constr. and prod.) are presented. Near the nominal rotation speed compressor map and adiabatic efficiency of each stage and the flow angles at leading and trailing blade edges are predicted and calculated. At the average radius stage flow and stage load coefficients are determined. It has been established that the reason of the low efficiency of the last stage is associated with the low stage reaction (≈0.5) leading to high airflow swirling at outlet. For LPC optimization a calculation of the radial distributions of the equivalent diffuser coefficient was performed. It is shown that the greatest total pressure losses are in the stator rows of stages 9, 8, 5 and in the rotor rows of stage 9. High losses are also shown on the upper half of the 4th, 3rd, 2nd stator blades and the lower half of the 1st rotor blades. The identified potential for increasing the efficiency of the LPC is up to 2% without significant construction changes.

Flow-based stress-blended eddy simulation: A local RANS/LES turbulence model for urban flow CFD simulations

In the present article, we introduce a local hybrid RANS/LES turbulence model, the Flow-based Stress-Blended Eddy Simulation (Fb-SBES). The methodology is applied to urban flow simulations in atmospheric boundary layer. The blending from RANS to LES is performed on the fly with respect to a flow deviation parameter. This makes the model self-adaptive and requires no prior knowledge of the flow contrary to typical zonal LES models. The present methodology enables the RANS equations to be solved in the major part of the computational domain (e.g. on average 88% for a single building). The RANS zone is modelled with a comprehensive RANS turbulence model for ABL simulations that sustains the fully developed inlet conditions until the built environment. In general, Fb-SBES shows better agreement with experimental data on the building and in the wake compared to advanced RANS and DDES simulations.

Numerical Simulation of Turbulent Fluid Flow in Rough Rock Fracture: 3D Case

We investigate both laminar and turbulent flow regimes in a 3D rock fracture via numerical CFD simulations. We construct our realistic fracture model from 3D scan data of a fractured rock sample and implement changes in both shear displacement and contact ratio, examining their effect on fracture permeability and friction factor. While previous studies were investigating either fully viscous Darcy or inertial Forchheimer laminar flow regimes, we chose to cover the wide Reynolds number range of 0.1–106\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^6$$\\end{document}. We introduce CFD simulation of a turbulent flow for realistic 3D fractures, implementing the RANS approach to turbulence modeling. We focus on 3D fracture geometries and implement changes in both shear displacement and contact ratio, systematically examining their effect on fracture permeability and friction factor in a manner similar to the fundamental studies of the flow in rough-walled pipes. Growing Re leads to first stationary–non-stationary and then laminar–turbulent transitions. The presence of contact spots severely disrupts the flow pattern and adversely affects the overall permeability of the fracture. Regardless of shear displacement, ‘no contact’ 3D models can be reasonably approximated by the 2D profiles. Depending on the fracture geometry, Forchheimer β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document} fitting for both laminar and turbulent regimes can be performed either by a single or by two parameter values.

Numerical Simulation of Turbulent Fluid Flow in Rough Rock Fracture: 2D Case

We investigate both laminar and turbulent flow regimes in a rough-walled rock fracture via numerical CFD simulations. While previous studies were limited to either fully viscous Darcy or inertial Forchheimer laminar flow regimes, we chose to cover the widest possible Reynolds number range of 0.1–10^6. We introduce CFD simulation of a turbulent flow for rough-walled fractures, implementing RANS approach to turbulence modeling. We focus on 2D fracture geometries and implement changes in both shear displacement and wall roughness, systematically examining their effect on fracture permeability and friction factor in a manner similar to the fundamental studies of the flow in rough-walled pipes. For a curvilinear fracture, laminar flow becomes non-stationary between Re , {sim } , 10^2–10^3, earlier for larger shear displacement and wall roughness. Laminar–turbulent transition starting at Re_{textrm{cr}} , {sim } , 2300 may lead to a sharp drop in permeability depending on the fracture geometry; this gap vanishes for larger shear displacement and wall roughness. Depending on the fracture geometry, bottlenecks closing with shear become a major negative factor for the overall permeability.

2D CFD simulations of flow and reaction during carbon dioxide methanation: A spatially resolved channel plate reactor study

Carbon dioxide methanation is a way of storing excess electrical energy as grid compatible gas. Spatially resolved channel plate reactor experiments were used to validate competing reactor (1D, 2Dx-z) models. Parallel exothermic carbon dioxide methanation and endothermic reverse water gas shift reactions were considered. The kinetic model, where the rate determining step is between an oxygenated complex (HCOO*) and an active site (*), was used in 2Dx-z CFD simulations for six laminar inflow conditions and variations in pressure, temperature, H2/CO2 ratio, methane, and steam co-feeds. The performance is improved by decreasing flowrate, and increasing H2/CO2 ratio, pressure, and temperature. Co-feeding methane has a negligible effect on reactor performance. However, co-feeding steam significantly reduces performance. At relatively high conversions, differential rates are obtained. This is due to the negligible dependence of the rate of carbon dioxide conversion with the equilibrium term of the reverse water gas shift reaction. With these studies, a link between the reaction mechanism and reactor performance is established at conditions relevant to power-to-gas applications.

Numerical Simulation of Liquid–Liquid Dispersion Characteristics in Screen-Type Static Mixers by Two Simplified Zero-Dimensional Models

In this work, two different zero-dimensional (0D) modeling approaches as well as PLIF measurements were adopted to analyze liquid–liquid dispersion characteristics in screen-type static mixers. On the framework of the population balance model (PBM), the 0D lumped model based on the volume-averaged turbulent dissipation rate (εAvg) was solved by the fixed pivot technique to predict the evolution of the droplet size distribution (DSD). The 0D homogeneous model accounts for the spatial inhomogeneity behind screens by coupling a probability density function of ε, which was obtained by two-phase flow CFD simulations. Different breakage kernels were applied and compared. Predicted results indicate that the 0D homogeneous model is more predictive to the evolution of the DSD with high prediction accuracy. Both simplified 0D models are computationally cheap compared with time-consuming CFD simulations. The effects of the screen geometry, oil volume fraction, and operating conditions on the dispersion performance were also investigated.

CFD modeling of the multiphase flow in an SKS furnace—The effect of melt density and viscosity

A previously reported numerical method using the multi-fluid VOF model to simulate an SKS furnace multiphase flow was further verified to provide a good reference for the macroscopic flow field simulation of industrial vessels with similar geometry. Using the verified numerical model, CFD simulation of a full-scale SKS furnace multiphase flow was conducted, targeting the agitation performance with different melt densities and viscosities, under constant furnace operating conditions. According to this simulation, the melt density and viscosity in a common applied range in industry is not able to significantly affect the bath agitation efficiency like other parameters, such as the tuyere diameter and bath depth. More specifically, the results indicate that an increased melt density or viscosity slightly weakens the melt flow motion, and increases the wall shear stress. Since variation in melt density and viscosity is common in industry, the results from this simulation offer a good basis for the estimation of SKS furnace operating performance and the adjustment of the physical properties of the melt in SKS furnaces or other similar industrial vessels.

Variable nozzle turbocharger: gas-dynamic calculation, 3D modeling, CFD analysis, characteristics

Introduction (problem statement and relevance). The environmental requirements for vehicle engines becoming more stringent require development and introduction of high-performance turbo chargers. Transition from external to internal varying, namely to the variable nozzles of the turbine, is caused by the necessity to reduce the transient process time during operation of the engine and the vehicle itself.The purpose of the study is development and confi rmation of the methodology (general strategy) for designing and modernization of radial-axial turbines with variable nozzles.Methodology and research methods. The study used the combination of calculation models for the engine itself with preliminary verifi cation based on the results of tests on the engine test bench (AVL BOOST, CRUISE M), gas-dynamic calculation of the turbine stage with determination of geometric parameters of the blade ring, housing (volute) and blade drive mechanism, their geometric modeling (Siemens NX) followed by 3D models export, CFD simulation of the stage fl ow including taking into account the transfer element (with impeller rotation) and generation of the stage curves (AVL FIRE).Scientific novelty and results. Combination (synthesis) of calculation models of different levels makes it possible to determine geometric parameters of the turbocharger turbine with variable nozzles providing high effi ciency (performance factor) of the turbine stage with a simultaneous shift of the maximum torque mode of the engine itself to the area of lower crankshaft rotation rate (along the full-load curve).Practical signifi cance of the paper consists in reduction of the time of design and subsequent refi nement (experimental) works during creation and modernization of turbines with variable nozzles of small-sized turbochargers. The obtained values of relative geometric parameters can be used at the design stage

CFD simulation and experimental validation of multiphase flow in industrial cyclone preheaters

A hybrid multiphase model (Dense Discrete Phase Model, DDPM) coupled with a k-ω sst turbulence model, which includes gas–solid heat exchange was developed for the simulation of industrial-scale cyclone preheaters operating under high solid loadings. The model results are validated by experimental measurements from an industrial cyclone preheater with a diameter of 1.6 m, with respect to the pressure drop, gas and particle exit temperature, local gas velocity profiles, measured using the LDA, and gas temperature profiles, measured using thermocouple and FTIR. Reasonable agreement between the data from experiments and simulations was obtained. In addition, the major trends, such as changes in the pressure drop, overall heat transfer rate, and flow pattern, caused by the changes in the operating parameters can be captured accurately by the model.

Numerical simulation of the fluid flow and heat transfer of the supercritical water in the 64-element Canadian SCWR fuel bundle

ABSTRACT Canada has participated in the Generation IV nuclear energy systems focusing on the Supercritical Water-cooled Reactor (SCWR) system. The 64-element fuel rods channel is used in the Canadian SCWR. There are few publicly available experimental studies for the flow in the fuel channels with multiple fuel rods. To date, the CFD simulation reported in open literature for rod bundle flow in the 64-element SCWR is relatively scarce. The cladding surface temperature is of key importance in assessing the safety of the reactor. Since the inhomogeneities in the bundle cross-section can present complex flow phenomena, a CFD study can provide substantial insight into the flow physics. In this work, the full-scale CFD simulation of the supercritical water flow in the 64-element rod bundle was performed. The results suggest the possibility of the presence of gap vortices in the flow subchannels. Higher streamwise velocities and normal Reynolds stresses always exist at the center subchannel regions. The circumferential cladding surface temperature distribution is extremely non-uniform and there is a large difference between the maximum cladding surface temperatures for different fuel rods.

ENGINE INTAKE AIRBOX CFD OPTIMISATION AND EXPERIMENTAL VALIDATION TESTS

The effective power of an internal combustion engine is determined by the amount of air that is drawn into the cylinder. One of the basic requirements for the intake is the even filling of all cylinders. This paper deals with the design of an airbox 4-cylinder 2.2 liter naturally aspirated SI engine. The CFD simulation of the air flow through the serial airbox was performed. This showed an uneven filling of the cylinders. With the help of CFD simulations, the shape of the airbox was optimized to improve the uniformity of the cylinders filling. The validation tests of the real airboxes on the flow bench were performed. The standard airbox and the airbox with the optimized shape were compared. The results confirmed the CFD simulations outputs. Furthermore, it has been shown that the air filter chamber can contribute to the uniform filling of the cylinders. The research resulted in the optimization of the engine's intake tract airbox shape.