Predicted Flow Patterns Research Articles

Experimento didático de Reynolds e conceitos básicos em mecânica dos fluidos

Os escoamentos podem ser caracterizados como: escoamento laminar ou turbulento; uniforme ou transiente e compressível e incompressível. O número de Reynolds é uma grandeza adimensional que caracteriza o movimento de fluidos, sendo definido pela razão entre forças inerciais e forças viscosas. O presente trabalho teve como objetivo utilizar um experimento didático da disciplina de Laboratório de Engenharia Química, especificamente Mecânica dos Fluidos, para evocar os seguintes estes conceitos vistos em sala de aula, bem como: a) diâmetro hidráulico; b) número de Reynolds; c) vazão mássica e vazão volumétrica; d) velocidade média do escoamento; (e) equação da continuidade, e visualizar os diferentes regimes de escoamento: laminar, transição e turbulento. A observação experimental possibilitou uma classificação do escoamento coerente com aquela dos cálculos. Neste experimento, foi confirmada, matematicamente pela análise de propagação de incertezas, usando o programa EES, a contribuição significativa da medida do volume de água nos valores dos erros experimentais. O efeito da temperatura e a contribuição de sua incerteza também foram verificados na determinação do número de Reynolds.

Low-Reynolds number mixing ventilation flows: Impact of physical and numerical diffusion on flow and dispersion

Quality assurance in computational fluid dynamics (CFD) is essential for an accurate and reliable assessment of complex indoor airflow. Two important aspects are the limitation of numerical diffusion and the appropriate choice of inlet conditions to ensure the correct amount of physical diffusion. This paper presents an assessment of the impact of both numerical and physical diffusion on the predicted flow patterns and contaminant distribution in steady Reynolds-averaged Navier–Stokes (RANS) CFD simulations of mixing ventilation at a low slot Reynolds number (Re≈2,500). The simulations are performed on five different grids and with three different spatial discretization schemes; i.e. first-order upwind (FOU), second-order upwind (SOU) and QUICK. The impact of physical diffusion is assessed by varying the inlet turbulence intensity (TI) that is often less known in practice. The analysis shows that: (1) excessive numerical and physical diffusion leads to erroneous results in terms of delayed detachment of the wall jet and locally decreased velocity gradients; (2) excessive numerical diffusion by FOU schemes leads to deviations (up to 100%) in mean velocity and concentration, even on very high-resolution grids; (3) difference between SOU and FOU on the coarsest grid is larger than difference between SOU on coarsest grid and SOU on 22 times finer grid; (4) imposing TI values from 1% to 100% at the inlet results in very different flow patterns (enhanced or delayed detachment of wall jet) and different contaminant concentrations (deviations up to 40%); (5) impact of physical diffusion on contaminant transport can markedly differ from that of numerical diffusion.

Generalized formulation for evaporation rate and flow pattern prediction inside an evaporating pinned sessile drop

When a sessile drop is heated from below, it evaporates and it induces a cooling effect in a zone close to the drop surface. The important evaporation rate at the contact line, the surface tension gradient at the liquid-air interface and the buoyancy generate the liquid motion inside the drop. Several parameters affect the evaporation rate among which the substrate properties, the moisture of the surrounding air and the heating conditions. Therefore, different flow patterns could be observed during the evaporation and they are mainly influenced by the relative importance of the evaporation rate, the thermo-capillarity and the buoyancy. The present study uses a generalized formulation to predict the flow patterns at any time during evaporation taking into account all these effects. The contribution and the relative importance of each effect are analyzed under isothermal and non-isothermal heating and different values of the relative humidity of the surrounding air. The correlation proposed by Hu and Larson for assessment of the evaporation rate is extended to non-isothermal surfaces for any evaporation conditions. Flow pattern maps are elaborated based on the dimensionless height of the drop apex and the evaporation conditions.

Mathematical Analysis and Physical Profile of Blalock-Taussig Shunt and Sano Modification Procedure in Hypoplastic Left Heart Syndrome: Review of the Literature and Implications for the Anesthesiologist.

The first stage of surgical treatment for hypoplastic left heart syndrome (HLHS) includes the creation of artificial systemic-to-pulmonary connections to provide pulmonary blood flow. The modified Blalock-Taussig (mBT) shunt has been the technique of choice for this procedure; however, a right ventricle-pulmonary artery (RV-PA) shunt has been introduced into clinical practice with encouraging but still conflicting outcomes when compared with the mBT shunt. The aim of this study is to explore mathematical modeling as a tool for describing physical profiles that could assist the surgical team in predicting complications related to stenosis and malfunction of grafts in an attempt to find correlations with clinical outcomes from clinical studies that compared both surgical techniques and to assist the anesthesiologist in making decisions to manage patients with this complex cardiac anatomy. Mathematical modeling to display the physical characteristics of the chosen surgical shunt is a valuable tool to predict flow patterns, shear stress, and rate distribution as well as energetic performance at the graft level and relative to ventricular efficiency. Such predictions will enable the surgical team to refine the technique so that hemodynamic complications be anticipated and prevented, and are also important for perioperative management by the anesthesia team.

Numerical analysis of a Pelton bucket free surface sheet flow and dynamic performance affected by operating head

The present paper aims to find out the influence of operating head on the rotating bucket free surface sheet flow and hydrodynamics performance for a Pelton turbine. Three-dimensional unsteady air-water two-phase flow simulations in the rotating buckets were performed by adopting the shear stress transport curvature correction turbulence model and homogenous model. The sensitivities of the unsteady simulation results to moving mesh resolution and computational fluid dynamics solver time-step have been evaluated to discuss the effect of Courant–Friedrichs–Lewy conditions on the two-phase flow simulation. The accuracy of the numerical predicted flow pattern and the hydrodynamic performance results are reasonable when compared with the experimental data. The simulation results indicate that the remaining kinetic energy carried by the outflow under the nondesigned water head is the main reason for the efficiency loss in the Pelton turbine. Under low water head conditions, jet distortion caused by the Coanda effect and flow interference will lead to more severe efficiency deterioration.

CFD simulation of horizontal oil-water flow with matched density and medium viscosity ratio in different flow regimes

Simulation of horizontal oil-water flow with matched density and medium viscosity ratio (μo/μw=18.8) in several different flow regimes (core annular flow, oil plugs/bubbles in water and dispersed flow) was performed with the CFD package FLUENT in this study. The volume of fluid (VOF) multiphase flow modeling method in conjunction with the SST k-ω scheme was applied to simulate the oil-water flow. The influences of the turbulence schemes and wall contact angles on the simulation results were investigated for a core annular flow (CAF) case. The SST k-ω turbulence scheme with turbulence damping at the interface gives better predictions than the standard k-ε and RNG k-ε models for the case under consideration. The flow regime of density-matched oil-water flow with medium viscosity ratio, or more generally speaking, the flow regime of fluids where the surface tension is playing a prevailing role is sensitive to the wall contact angle. Simulation results were compared with experimental counterparts. Satisfactory agreement in the prediction of flow patterns were obtained for CAF and oil plugs/bubbles in water. The simulation results also demonstrated some detailed flow characteristics of CAF with relatively low-viscosity oil (oil viscosity one order higher than the water viscosity in the present study compared to the extensively studied CAF with oil viscosity being two to three orders higher than the water viscosity). Different from the velocity profiles of high-viscosity oil CAF where there is sharp change in the velocity gradient at the phase interface with velocity across the oil core being roughly flat, there is no sharp change in the velocity gradient at the phase interface for CAF with relatively low-viscosity oil.

Advanced neural network prediction and system identification of liquid-liquid flow patterns in circular microchannels with varying angle of confluence

The flow pattern map for liquid-liquid system in a circular microchannel of 600μm was experimentally investigated for a varying confluence angle (10–170 degree) of inlet fluids. The experimental results showing distinguishing nature of transition boundaries were established using graphical interpretation. Investigations were carried out to find a better objective flow pattern indicator for a vast flow pattern observations. Studies on advanced feed-forward back-propagation networks and radial basis networks such as CFN, ANN-FF, ANN-PR, PNN, GRNN and ANFIS showed that GRNN (Generalized Regression Neural Network) showed a better prediction over other prediction techniques with a R2 value of 0.988. The relative impact of input variables such as confluence angle, superficial velocity of dodecane and superficial velocity of water on flow pattern formation was found to be 17.78%, 43.30% and 38.92% respectively. The discrete and continuous time state space models for the system was also developed and interpreted in detail using system identification technique for the better understanding of the system.

Prediction of Flow Patterns of Rotating Inclined Reactors by Using a Modified Permeability Approach

AbstractA new inclined rotating tubular fixed bed reactor was recently suggested for process intensification of heterogeneous catalytic multiphase reactions. Favorable operating conditions can be achieved by operating the reactor in a wetting intermittency mode by periodic catalyst immersion in a stratified gas‐liquid flow. This flow pattern adjustment, which requires the careful selection of reactor inclination and rotation, eventually enhances the reaction rate. To predict the flow patterns by means of computational fluid dynamics, a 3D model based on the relative permeability approach was developed, in which gas and liquid phases flow concurrently downwards through the inclined rotating tubular fixed bed reactor. The model can clearly predict the four evolving patterns, depending on the operating conditions. The model was capable of correctly predicting the hydrodynamics for aqueous liquid mixtures with varying viscosity and surface tension.

Comparison of CFD Simulations with Experimental Measurements of Nozzle Clogging in Continuous Casting of Steels

Measurements of clog deposit thickness on the interior surfaces of a commercial continuous casting nozzle are compared with computational fluid dynamics (CFD) predictions of melt flow patterns and particle–wall interactions to identify the mechanisms of nozzle clogging. A submerged entry nozzle received from industry was encased in epoxy and carefully sectioned to allow measurement of the deposit thickness on the internal surfaces of the nozzle. CFD simulations of melt flow patterns and particle behavior inside the nozzle were performed by combining the Eulerian-Lagrangian approach and detached eddy simulation turbulent model, matching the geometry and operating conditions of the industrial test. The CFD results indicated that convergent areas of the interior cross section of the nozzle increased the velocity and turbulence of the flowing steel inside the nozzle and decreased the clog deposit thickness locally in these areas. CFD simulations also predicted a higher rate of attachment of particles in the divergent area between two convergent sections of the nozzle, which matched the observations made in the industrial nozzle measurements.

Prediction of oil-water flow patterns, radial distribution of volume fraction, pressure and velocity during separated flows in horizontal pipe

Flow of two immiscible fluids gives rise to variety of flow patterns, which influence transportation process. In this work, we present detailed analysis on the prediction of flow pattern maps and radial distribution of volume fraction, pressure and velocity of a pair of immiscible liquids through a horizontal pipeline by computational fluid dynamics (CFD) simulation using ANSYS FLUENT 6.3. Moderately viscous oil and water have been taken as the fluid pair for study. Volume of fluid (VOF) method has been employed to predict various flow patterns by assuming unsteady flow, immiscible liquid pair, constant liquid properties, and co-axial flow. From the grid independent study, we have selected 47 037 number of quadrilateral mesh elements for the entire geometry. Simulation successfully predicts almost all the flow patterns (viz., plug, slug, stratified wavy, stratified mixed and annular), except dispersion of oil in water and dispersion of water in oil. The simulated results are validated with experimental results of oil volume fraction and flow pattern map. Radial distribution of volume fraction, pressure and velocity profiles describe the nature of the stratified wavy, stratified mixed and annular flow pattern. These profiles help to developing the phenomenological correlations of interfacial characteristics in two-phase flow.

Numerical simulation of flow field characteristics in a gas-liquid-solid agitated tank

Computational fluid dynamics simulation was carried out to investigate flow field characteristics in a gas-liquid-solid agitated tank. The Eulerian multifluid model along with standard k-e turbulence model was employed in the simulation. A multiple reference frame approach was used to treat the impeller rotation. Liquid velocity, gas holdup and solid holdup distributions in the agitated tank were obtained. The effect of operating conditions on gas and solid distributions was investigated. The predicted flow pattern was compared with results in literature. The simulation results indicate that local hydrodynamic behaviors such as velocity, gas and solid holdup distribution, are strongly influenced by operating conditions. Within the scope of our study, increasing gas inlet rate caused liquid circulation to be weakened and was not in favor of gas dispersion. Solid holdup in the upper part of the tank, especially near the wall region decreased. Adding solid loadings resulted in liquid mean velocity near the surface region decreased, gas dispersion and solid suspension becoming worse.

Can a quantitative means be used to predict flow patterns: Agreement between visual inspection vs. flow index derived flow patterns

Uroflowmetry is a first-line tool in the evaluation of children with lower urinary tract symptoms. Unfortunately, there is a tremendous amount of intra- and interobserver variation in defining the shape of curves. Regrettably, one observer can see one flow as a tower and the other can call it a bell. Here lies the major flaw with the interpretation of uroflow shapes. Previously, we have shown that there is a good correlation between the calculated flow index (FI) and the shape of a flow curve (bell, tower and plateau) in normal children. Our hypothesis was to show that the FI-defined shapes were as good or better than the present system of grading flow curves. If so this would help remove subjectivity from the field of uroflow assessment and make studies objective and easily compared. Consecutive uroflows of children who were being evaluated for lower urinary tract symptoms from two centers were reviewed and compared alongside those of presumed normal voiders; the shape of the curves were read by the same experienced readers at each institution. Only curves that were read as bell, plateau, and tower were compared with the curve patterns derived from the quantitative methods derived by one of the authors. FI was derived by taking the actual Qmax/estimated Qmax. There were 591 males and 1039 females who had uroflow studies, of these 409 and 819, respectively were read as either bell, towers, or plateaus The highest kappa value for males was 0.71 (CI 0.64-0.79) using a 3×3 matrix indicating substantial agreement. In females the highest kappa was 0.52 (CI 0.46-0.59) in the group 2 patients using the receiver operating characteristic cutoffs but the 1 SD cutoff was close with a kappa value of 0.51, which indicates moderate agreement (Table). Using the FI method we saw that there was substantial to moderate agreement using a quantitative method to define flow shapes based on the kappa values that were obtained in this study. The one fundamental flaw with shape determination in both visual and FI-derived methods is that the cutoffs are arbitrary since the visual defined shapes are the basis for the FI shapes. Our findings clearly showed that a FI-derived method of defining shapes is as accurate as visual inspection or more depending on the study. The greatest disagreement occurs in those grey or transition zones between plateau, bell and tower. This system could be useful in removing much of the ambiguity and difficulty in reading flows.

Flow modelling of quasi-Newtonian fluids in two-scale fibrous fabrics

Permeability is the fundamental macroscopic material property needed to quantify the flow in a fibrous medium viewed as a porous medium. Composite processing models require the permeability as input data to predict flow patterns and pressure fields. In a previous work, the expressions of macroscopic permeability were derived in a double-scale porosity medium for both Newtonian and generalized Newtonian (shear-thinning) resins. In the linear case, only a microscopic calculation on a representative volume is required, implying as many microscopic calculations as there are representative microscopic volumes in the whole fibrous structure. In the non-linear case, and even when the porous microstructure can be described by a unique representative volume, a large number of microscopic calculations must be carried out as the microscale resin viscosity depends on the macroscopic velocity, which in turn depends on the permeability that results from a microscopic calculation. An original and efficient offline-online procedure was proposed for the solution of non-linear flow problems related to generalized Newtonian fluids in porous media. In this paper, this procedure is generalized to quasi-Newtonian fluids in order to evaluate the effect of extensional viscosity on the resulting upscaled permeability. This work constitutes a natural step forward in the definition of equivalent saturated permeabilities for linear and non-linear fluids.

A unified model to predict flow pattern transitions in horizontal and slightly inclined two-phase gas/shear-thinning fluid pipe flows

Flow pattern transitions in two-phase gas/shear-thinning fluid pipe flows represent a key aspect during oil transportation and in chemical industry. In this paper a unified model to build a complete flow pattern map is proposed and models to predict flow patterns are provided. The transitions from stratified flow regime are investigates performing a linear stability and well-posedness analyses, and a non-linear stability analysis. The steady and fully developed two-fluid model for the annular flow is proposed and validated; the flow pattern transition from the annular flow is discussed considering, also, the structural stability. The transition to dispersed flow, the slug stability approach, and criteria to obtain the slug/plug and the bubbly/plug boundaries are considered. A sensitivity analysis on the effect of the rheology of the shear-thinning fluid on flow pattern boundaries is carried out and, then, the complete flow pattern maps are validated with data taken from the literature showing a good agreement.

Numerical modeling of two-phase fluid flow in deformable fractured porous media using the extended finite element method and an equivalent continuum model

In the present paper, a numerical model is developed based on a combination of the extended finite element method and an equivalent continuum model to simulate the two-phase fluid flow through fractured porous media containing fractures with multiple length scales. The governing equations involve the linear momentum balance equation and the flow continuity equation for each fluid phase. The extended finite element method allows for an explicit and accurate representation of cracks by enriching the standard finite element approximation of the field variables with appropriate enrichment functions, and captures the mass transfer between the fracture and the matrix. Due to the high computational cost of X-FEM, this technique is only used to model large fractures. The pre-existing short fractures, which are distributed randomly in the porous medium, contribute to the increase of the effective permeability tensor and are modeled with an equivalent continuum model. Finally, the robustness of the proposed computational model is demonstrated through several numerical examples, and the effects of crack orientation, capillary pressure function, solid skeleton deformation, and existence of short cracks on the pattern of fluid flow are investigated. It is shown that the developed model provides a correct prediction of flow pattern for different crack configurations.

Numerical modelling of two-phase oil–water flow patterns in a subsea pipeline

The concurrent flow of oil and water in pipelines is a common occurrence in offshore oil production systems. The internal structure of the oil–water flow, known as the flow pattern, and the distribution of water have a great influence on the design of the pipeline. However, due to the complex nature of oil–water flows, predicting flow patterns under different operating conditions is a challenging task. The present study is an attempt toward using a computational fluid dynamics model for predicting the flow patterns under different working conditions. To this end, an Eulerian–Eulerian model along with appropriate closure laws was employed to model two-phase oil–water flows through a horizontal pipe. The standard k–epsilon model was adopted to account for the turbulence effects. Furthermore, a brief description of the main interfacial forces namely the drag, lift, and turbulent dispersion forces has been presented. The numerical model was used to predict the flow patterns under different operating conditions ranging from low to high velocities and water cuts, respectively. A comparison among the obtained numerical results and published experimental data showed reasonable agreement.

Working fluid charge reduction, part 1: CO2 fin-tube evaporator designed for light commercial appliances utilizing flow pattern based phenomenological prediction models

The present study focused on improving the thermal performance of CO2 evaporators while reducing their volume and thus significantly reducing the working fluid charge. To achieve this, the leading two-phase flow pattern and physically-based prediction models for flow boiling of CO2 and void fraction were selected from the literature, together with the leading air-side flow and heat transfer methods, and finally those for modelling oil effects on CO2 flow boiling. The effects of tube size, shape and wettability for significant performance improvements, miscible oil concentration, etc., were addressed while staying within the beverage industry's fabrication and operational limits. Compared to an actual existing design, the volume and refrigerant charge of the CO2 evaporator were reduced by 50% and 58.7%, respectively. The adverse influence of oil was found to reduce the mean CO2 side heat transfer coefficient and to increase the CO2 pressure drop by up to 11% and 94%.

Analysis of Two-Phase Flow and Bubbles Behavior in a Continuous Casting Mold Using a Mathematical Model Considering the Interaction of Bubbles

A new mathematical model considering the process of bubbles interaction has been developed to simulate the transient fluid flow, dispersed bubbles motion and transport process in the slab continuous casting mold. Rather than prescribing a constant bubbles size in previous work, this model allow us to calculate the constantly changed daughter particles size distribution after the process of bubbles collision and breakup. In this paper, using the new model to study the effect of some parameters such as gas flow, casting speed, and the depth of submerged entry nozzle (SEN) on the fluid flow pattern, the gas volume fraction, the distribution of bubbles and so on. The predictions of gas bubble distribution and fluid flow pattern are in good agreement with the water model experimental observations. Meanwhile, the model has successfully reproduced many known phenomena and other new predictions, including the process of bubbles collision and breakup. The simulation results show that the important factors that influence the size and quantity distribution range of bubbles are casting speed and argon gas flow rate and depth of SEN. Through the statistical analysis of bubbles behavior, the effects of blowing argon on porosity defects under different operating conditions can be obtained.

Flow modeling of linear and nonlinear fluids in two scale fibrous fabrics

The fundamental macroscopic material property needed to quantify the flow in a fibrous medium viewed as a porous medium is the permeability. Composite processing models require the permeability as input data to predict flow patterns and pressure fields. As permeability reflects both the magnitude and anisotropy of the fluid/fiber resistance, efficient numerical techniques are needed to solve linear and nonlinear homogenization problems online during the flow simulation. In a previous work the expressions of macroscopic permeability were derived in a double-scale porosity medium for both Newtonian and rheo-thinning resins. In the linear case only a microscopic calculation on a representative volume is required, implying as many microscopic calculations as representative microscopic volumes exist in the whole fibrous structure. In the non-linear case, and even when the porous microstructure can be described by a unique representative volume, microscopic calculation must be carried out many times because the microscale resin viscosity depends on the macroscopic velocity, which in turn depends on the permeability that results from a microscopic calculation. Thus, a nonlinear multi-scale problem results. In this paper an original and efficient offline-online procedure is proposed for the efficient solution of nonlinear flow problems in porous media.

Technology Focus: Production and Facilities (December 2015)

Technology Focus Advances in technologies for production and facilities are being driven by the development of unconventional resources and the need for more-efficient and -reliable operations. Considerable progress is being made, for example, on the design and performance of wellbore-inflow-control devices. The objective of this technology is to control both the volume and the character of fluids entering an extended-length wellbore. Both passive and autonomous devices are now available from a number of suppliers. Field experience with this technology was the subject of 10% of the papers in this year’s survey of publications and presentations. Pipeline technology continues its rapid evolution with a focus on the safe operation of, and the early detection of breaks and leaks in, long-distance lines. The environmental hazards associated with unplanned fluid losses from material failures or unwelcome human intervention make the deployment of acoustic monitoring technologies increasingly desirable and economically viable. In some geographical areas, strong environmental and safety concerns about pipelines will most likely favor the installation of such technologies on any line passing through urban or other sensitive environments. With low oil and gas prices being a continuing drag on our industry, a significant amount of work was reported on field-optimization and operations-improvement (i.e., cost-reduction) technology. Authors worldwide described their efforts to reduce unplanned shutdowns, lower maintenance costs, improve operational reliability, and squeeze more barrels out of existing wells by developing field-optimization models. One interesting development associated with production optimization is the use of nanotechnologies to address issues ranging from the control of rock wettability characteristics to the development of fluids with improved heat-transfer characteristics. These applications are moving the field of nanomaterials from the character of “science projects” to emerging or commercial technologies. Finally, the trend toward the increased use of modeling and simulation technologies, which was identified in this feature last year, continues unabated. More than 25% of the papers reviewed for this year’s feature were concerned with the development of models and simulations or were associated with their use and validation. The emphasis was heavy on the generation of models and simulations that were simple to use, were computationally efficient, and that generated short-term realizable cost savings. One interesting paper described the development of a “fuzzynistic” model for more accurate predictions of flow patterns and pressure losses in pipelines, a critical topic for the design and operational control of surface facilities. JPT Recommended additional reading at OnePetro: www.onepetro.org. IPTC 17977 Performance of Autonomous- Inflow-Control Completion in Heavy-Oil Reservoirs by Eltazy Eltaher, Heriot-Watt University, et al. SPE 174812 Fuzzynistic Models for Multiphase-Flow-Pattern Identification by Florentina Popa, Halliburton, et al. SPE 174746 CFD Study for Heat Transfer and Flow Characteristics of Nanofluid in a Flat-Tube Heat Exchanger by Mohamed Elsebay, Gempetco, et al.