Predicted Flow Patterns Research Articles

Modeling and simulation of multi-physics multi-scale transport phenomenain bio-medical applications

We present a short overview of some of our most recent work that combines the mathematical modeling, advanced computer simulations and state-of-the-art experimental techniques of physical transport phenomena in various bio-medical applications. In the first example, we tackle predictions of complex blood flow patterns in the patient-specific vascular system (carotid artery bifurcation) and transfer of the so-called "bad" cholesterol (low-density lipoprotein, LDL) within the multi-layered artery wall. This two-way coupling between the blood flow and corresponding mass transfer of LDL within the artery wall is essential for predictions of regions where atherosclerosis can develop. It is demonstrated that a recently developed mathematical model, which takes into account the complex multi-layer arterial-wall structure, produced LDL profiles within the artery wall in good agreement with in-vivo experiments in rabbits, and it can be used for predictions of locations where the initial stage of development of atherosclerosis may take place. The second example includes a combination of pulsating blood flow and medical drug delivery and deposition controlled by external magnetic field gradients in the patient specific carotid artery bifurcation. The results of numerical simulations are compared with own PIV (Particle Image Velocimetry) and MRI (Magnetic Resonance Imaging) in the PDMS (silicon-based organic polymer) phantom. A very good agreement between simulations and experiments is obtained for different stages of the pulsating cycle. Application of the magnetic drug targeting resulted in an increase of up to ten fold in the efficiency of local deposition of the medical drug at desired locations. Finally, the LES (Large Eddy Simulation) of the aerosol distribution within the human respiratory system that includes up to eight bronchial generations is performed. A very good agreement between simulations and MRV (Magnetic Resonance Velocimetry) measurements is obtained. Magnetic steering of aerosols towards the left or right part of lungs proved to be possible, which can open new strategies for medical treatment of respiratory diseases.

Hydraulic model of steady state multiphase flow in wellbore annuli

Abstract Based on the classification and flow behaviors of two phase flow in wellbore annuli, the hydraulic models for slug flow and annular flow in annuli for vertical or inclined wells were established, and the flow regime transition criteria were also obtained. Based on the flow behavior research of multiphase flow in wellbore annuli, the liquid film zone was used as the control volume, and the effect of the tubing liquid film, casing liquid film and the droplets in gas core area on the mass and momentum transfers were considered. The mass and momentum conservation equations of slug and annular flows were obtained. Then the evaluation criterion of flow pattern transitions were established, including dispersed flow to slug flow, bubble flow to slug flow and slug flow to annular flow. The model prediction results were compared under the experimental conditions from the previous literatures. The predictions of flow pattern, liquid holdup and pressure gradient were compared between the new model and the pipe flow model modified by using the hydraulic diameter. The results show that the flow pattern, liquid holdup and pressure gradient can be predicted by the new model more accurately, and the prediction of liquid holdup and pressure gradient are better.

지진시 산사태 발생 예측 및 산지 내 문화재 영향 분석

문화재가 위치하고 있는 서울특별시 종로구 일대의 산지를 연구지역으로 선정하고 Newmark displacement model을 이용하여 지진으로 유발되는 산사태 위험지 변화와 산사태로 인한 토석류 흐름 양상을 예측하여 연구 지역에 분포하고 있는 문화재에 미치는 영향을 분석하였다. 연구 결과, 지진으로 유발되는 산사태 발생 위험지에는 문화재가 위치하지는 않는 것으로 분석되었으나, 토석류 예상 이동경로 상에 사직단이 위치하고 있어 이에 대한 추가 연구가 필요할 것으로 사료된다. It was selected as the study area where heritage are located on the Mountain in Seoul. The variation of landslide risk induced earthquake by using the Newmark displacement model and the prediction of debris flow pattern due to landslides were performed. And these effects on heritage distributed in the study area were investigated. As a result, it was analyzed that heritage on landslide risk areas induced earthquake does not be placed, however the further research for Sajikdan on the predicted moving path of debris flow would be recommendable.

Prediction of Two-phase Slug Flow Patterns in Microchannel with T-junction

Prediction of Two-phase Slug Flow Patterns in Microchannel with T-junction

Hidden Markov Flow Network Model: A Generative Model for Dynamic Flow on a Network

1 Abstract—In this paper, we propose a generative model that describes the dynamics of flow on a network — the hidden Markov flow network (HMFN) model, which is inspired by the gravity model in traffic engineering. Each node in the network has a dynamic hidden state and the flow observed on links depends on the states of the nodes being connected. For model inference, a collapsed Gibbs sampling algorithm is also proposed. Lastly, the model is applied to synthetic data and real human mobility network generated by GPS data from taxis in Bangkok. The synthetic data example shows that the reconstruction accuracy of the proposed method outperforms compared with the k-means method and the hidden Markov model, which do not consider the network interaction. The results of human mobility data show that the HMFN model can be used for spatio-temporal anomaly detection and prediction of future flow patterns.

Study of the Flow in a Vaneless Diffuser at Part Speed Operating Conditions

The aim of the current paper is to investigate the evolution of the flow in the vaneless diffuser of a scaled-up turbocharger compressor using the steady-state viscous calculations. First, the predicted flow patterns are compared with the detailed laser Doppler anemometry (LDA) and probe measurements acquired at different operating conditions. Then, the numerical results are analyzed further to understand the origins of the flow features observed in the measurements. It is shown that, despite the complexity of the flow, the main flow features in the vaneless diffuser can be predicted by computational fluid dynamics (CFD) at different operating conditions using a simple mixing length turbulence model. It is also demonstrated that, in the compressor studied, a vortical flow feature develops near the diffuser shroud at high flow coefficients. This flow feature is generated by strong pressure variations downstream of the impeller trailing edge and disappears at low flow coefficients, where the static pressure gradient becomes almost radial in the vaneless diffuser.

Experimental study on flow patterns for water boiling in horizontal heated tubes

An experimental study on flow patterns for water boiling in horizontal heated tubes was conducted to observe the evolution and transition of flow patterns while controlling various parameters, such as heat flux, mass velocity, and tube diameter. Six boiling flow patterns are observed in the test tubes, namely, bubble, plug, slug, wave, stratified, and annular flows, which can be further classified into three types based on their various characteristics: intermittent, stratified-wave, and annular flows. The evolution of flow patterns for water boiling in horizontal heated tubes was significantly affected by heat flux, mass velocity, and tube diameter. The increment of heat flux pushed the starting point of each flow pattern toward the inlet of the tube. Intermittent and stratified-wave flows occurred at lower mass velocity, and annular flow occurred with an increase in mass velocity. Moreover, annular flow easily appeared in tubes with smaller diameters. Since the heat per unit of mass for the full tube length increases with either an increase in heat flux or a decrease in mass velocity and tube diameter, the transition always occurs at smaller vapor qualities with the increase of the heat per unit of mass during the transition of the three flow patterns. The experimental data in this study were compared with the adiabatic flow pattern maps proposed by Baker, Mandhane, Taitel, and Weisman. Based on the experimental data, a new flow pattern map for water boiling was proposed for predicting flow patterns in horizontal heated tubes.

Flame pattern, temperatures and stability limits of pulverized oxy-coal combustion

The challenges in maintaining a stable oxy-coal flame have been reported in the open literature. In case of pulverized coal combustion, narrower flammable regimes arise not only of differences in the feed gas composition, but also due to changes in the flow dynamics because of reduced volume flow rate through the burners to match similar temperatures and radiative heat transfer within the furnace. The present work focuses on the study of flame structure and stability of pre-dried lignite fired by a staged feed-gas burner. Experimental runs were carried out in a 0.40MWth laboratory facility, with the objective of investigating the effects of swirl strength and feed gas distribution in the burner registers. To assess the experimental data, a numerical study of the non-reacting flow in the near burner region is performed. Predicted flow pattern and flame images show that the primary fuel jet penetrates the internal recirculation zone, forming an annular doughnut reverse flow region for both firing conditions and resembling a type-1 flame pattern. Temperature measurements indicate that the feed gas distribution among the burner registers control the flame temperature in parallel with the swirl number in both air-fired and oxy-fired environments. The oxy-fuel cases exhibite markedly reduced temperatures on the flame axis. This difference in the core arises not just from the more pronounced penetration depth of the primary jet, but also due to reaction mechanisms including pyrolysis and gasification reactions at the higher concentrations of CO2 and water vapor. Flame stabilization is shown to be strongly dependent on an appropriate distribution of the feed gas and strength of swirling flow in the burner front. The results correlated in terms of swirl number, secondary/tertiary flow ratio and secondary/primary axial momentum point to similarities in the stability limits between air-firing and oxy-firing.

Numerical Modeling of Interstitial Fluid Flow Coupled with Blood Flow through a Remodeled Solid Tumor Microvascular Network

Modeling of interstitial fluid flow involves processes such as fluid diffusion, convective transport in extracellular matrix, and extravasation from blood vessels. To date, majority of microvascular flow modeling has been done at different levels and scales mostly on simple tumor shapes with their capillaries. However, with our proposed numerical model, more complex and realistic tumor shapes and capillary networks can be studied. Both blood flow through a capillary network, which is induced by a solid tumor, and fluid flow in tumor’s surrounding tissue are formulated. First, governing equations of angiogenesis are implemented to specify the different domains for the network and interstitium. Then, governing equations for flow modeling are introduced for different domains. The conservation laws for mass and momentum (including continuity equation, Darcy’s law for tissue, and simplified Navier–Stokes equation for blood flow through capillaries) are used for simulating interstitial and intravascular flows and Starling’s law is used for closing this system of equations and coupling the intravascular and extravascular flows. This is the first study of flow modeling in solid tumors to naturalistically couple intravascular and extravascular flow through a network. This network is generated by sprouting angiogenesis and consisting of one parent vessel connected to the network while taking into account the non-continuous behavior of blood, adaptability of capillary diameter to hemodynamics and metabolic stimuli, non-Newtonian blood flow, and phase separation of blood flow in capillary bifurcation. The incorporation of the outlined components beyond the previous models provides a more realistic prediction of interstitial fluid flow pattern in solid tumors and surrounding tissues. Results predict higher interstitial pressure, almost two times, for realistic model compared to the simplified model.

A Simplified Mechanistic Model for an Oil/Water Horizontal Pipe Separator

Summary A new methodology for oil/water horizontal pipe separator (HPS) design and performance prediction is developed. The separator diameter is determined on the basis of oil/water flow-pattern prediction. A batch separator model is adopted and modified for pipe flow to predict the separator length for achieving a desired separation quality. An experimental program is carried out to validate the proposed model.

El-Nino/Southern Oscillation (ENSO): Recent Evolution and Possibilities for Long Range Flow Forecasting in the Brahmaputra-Jamuna River

The El Nino-Southern Oscillation is the dominant pattern of short-term climate variation, and is therefore of great importance in climate studies. Some recent studies showed the teleconnection between stream flow and the El-Nino Southern Oscillation (ENSO) of the equatorial Pacific Ocean. This paper presents an overview of the relationship between ENSO and stream flow in the Brahmaputra-Jamuna and the potential for wet season flow forecasting. This seasonal forecast of stream flow is very invaluable to the management of land and water resources, particularly in Bangladesh to improve the predictability of severe flooding. Over the years, large investments have been made to build physical infrastructure for flood protection, but it has been proved that it is not feasible, both economically and technically, to adopt solely structural mitigation approach. The choice of non-structural measures in this country focused mainly on flood forecasting because many of the nonstructural measures including flood plain zoning, compulsory acquisition of flood prone land, relocation etc have also been proved inappropriate for Bangladesh. The aim of this research is to find out an effective and long-lead flow forecasting method with lead time greater than hydrological time scale, using El Nino-Southern Oscillation index. Some studies indicate that SST can be predicted one to two years in advance using several ocean/ coupled ocean atmosphere models, therefore the ability to predict flow patterns in rivers will be highly enhanced if a strong relationship between river discharge and ENSO exists, and is quantified. With this view, to assess the strength of teleconnection between river flow and ENSO, at first correlation analyses between ENSO indices of any year and wet season flow of that year have been done. Here sea surface temperature (SST) has been used as ENSO index. This correlation analysis demonstrates a noteworthy relationship between natural variability of average flow of the months July-August-September (JAS) of the Brahmaputra-Jamuna River with SST of the corresponding months. Then discriminant prediction approach, also known as “Categoric Prediction” has been used here for the assessment of long range flood forecasting possibilities. This approach will be able to forecast the category of flow (high, average or low) using the category of predictor (predicted SST) at a sufficient lead time. In order to judge the forecast skill, a synoptic parameter “Forecasting Index” has also been used. This discriminant approach will improve the forecasting lead-time while the hydrologic forecast through rainfall-runoff modeling could provide a lead time on the order of the basin response time, which is several days or so. As the Ganges–Brahmaputra river basin is one of the most populous river basins of the world and is occupied by some developing countries of the world like Bangladesh, any reduction in the uncertainty about the flood in the Brahmaputra-Jamuna River would contribute a lot to the improvement in flow forecasting as well as to the economic development of the country.

3D imaging of flow patterns in an internally-pumped microfluidic device: redox magnetohydrodynamics and electrochemically-generated density gradients.

Redox magnetohydrodynamics (MHD) is a promising technique for developing new electrochemical-based microfluidic flow devices with unique capabilities, such as easily switching flow direction and adjusting flow speeds and flow patterns as well as avoiding bubble formation. However, a detailed description of all the forces involved and predicting flow patterns in confined geometries is lacking. In addition to redox-MHD, density gradients caused by the redox reactions also play important roles. Flow in these devices with small fluid volumes has mainly been characterized by following microbead motion by optical microscopy either by particle tracking velocimetry (PTV) or by processing the microbead images by particle image velocimetry (PIV) software. This approach has limitations in spatial resolution and dimensionality. Here we use fluorescence correlation spectroscopy (FCS) to quantitatively and accurately measure flow speeds and patterns in the ~5-50 μm/s range in redox-MHD-based microfluidic devices, from which 3D flow maps are obtained with a spatial resolution down to 2 μm. The 2 μm spatial resolution flow speeds map revealed detailed flow profiles during redox-MHD in which the velocity increases linearly from above the electrode and reaches a plateau across the center of the cell. By combining FCS and video-microscopy (with PTV and PIV processing approaches), we are able to quantify a vertical flow of ~10 μm/s above the electrodes as a result of density gradients caused by the redox reactions and follow convection flow patterns. Overall, combining FCS, PIV, and PTV analysis of redox-MHD is a powerful combination to more thoroughly characterize the underlying forces in these promising microfluidic devices.

Numerical study of gas–solid flow in a coal beneficiation fluidized bed using kinetic theory of granular flow

Modeling the dynamic behavior of gas -solid flow in a pilot scale coal beneficiation fluidized bed (CBFB) model was performed in this work, a transient two-dimensional simulation was done based on the Eulerian model together with the kinetic theory of granular flows. Three steps were conducted to testify the choices of sub-models in CBFB modeling, including gas -solid exchange drag models, gas phase turbulence models, granular temperature models and wall boundary condition models for solid phase. Instantaneous and time-averaged results of particle volume fraction, bubble number and size, particle velocity distributions and vortices, as well as bed density distributions were obtained. The impacts of the sub-models on the flow characteristics in the dense CBFB were illustrated in detail and suitable models with better predictions of CBFB flow pattern were then demonstrated. The Syamlal -O'Brien drag model predicted better results in bed characteristics. The dispersed k-ε turbulence model should be used to describe the gas turbulence in the dense CBFB flow regime. The partial slip wall condition for particles had a slight influence in the small model. The partial differential equation granular temperature model could predict the inter-phase surfaces more clearly and the flow pattern more accurately.

Prediction of flow pattern of gas–liquid flow through circular microchannel using probabilistic neural network

The present study attempts to develop a flow pattern indicator for gas–liquid flow in microchannel with the help of artificial neural network (ANN). Out of many neural networks present in literature, probabilistic neural network (PNN) has been chosen for the present study due to its speed in operation and accuracy in pattern recognition. The inbuilt code in MATLAB R2008a has been used to develop the PNN. During training, superficial velocity of gas and liquid phase, channel diameter, angle of inclination and fluid properties such as density, viscosity and surface tension have been considered as the governing parameters of the flow pattern. Data has been collected from the literature for air–water and nitrogen–water flow through different circular microchannel diameters (0.53, 0.25, 0.100 and 0.050mm for nitrogen–water and 0.53, 0.22mm for air–water). For the convenience of the study, the flow patterns available in literature have been classified into six categories namely; bubbly, slug, annular, churn, liquid ring and liquid lump flow. Single PNN model is unable to predict the flow pattern for the whole range (0.53mm–0.050mm) of microchannel diameter. That is why two separate PNN models has been developed to predict the flow patterns of gas–liquid flow through different channel diameter, one for diameter ranging from 0.53mm to 0.22mm and another for 0.100mm–0.05mm. The predicted map and their transition boundaries have been compared with the corresponding experimental data and have been found to be in good agreement. Whereas accuracy in prediction of transition boundary obtained from available analytical models used for conventional channel is less for all diameter of channel as compared to the present work. The percentage accuracy of PNN (∼94% for 0.53mm ID and ∼73% for 0.100mm ID channel) has also been found to be higher than the model based on Weber number (∼86% for 0.53mm ID and ∼36% for 0.05mm ID channel).

A hydrological study of on-site soil absorption systems

The use of on-site soil absorption systems (OSASs) to dispose of domestic wastewater is common in rural and semi-rural areas in Australia as well as in many other developed and developing countries. A need exists for an improved method of evaluating OSAS performance and predicting potential impacts of OSASs on public health and environmental quality. This paper focuses on the hydrological prediction of saturated and unsaturated moisture flow patterns of wastewater dispersed into soil adjacent to OSAS disposal trenches. It presents field and laboratory measurements obtained during an extensive investigation conducted at eight OSAS sites on predominantly silty soil in Victoria, Australia. A numerical moisture flow model was also employed to predict how the hydrological performance of OSAS might be affected by a variety of site specific conditions including soil properties, climatic data, and hydraulic loading rates. The model was fine-tuned using both published data and data from the eight study sites. The predictions show that over 50%, and in some instances over 80%, of water received by an OSAS is lost by way of evapotranspiration. This highlights the importance of evapotranspiration in determining soil absorption capacity and moisture flow patterns around an OSAS, something that is not accounted for in existing OSAS design guidelines.

Large Eddy Simulation for Dispersed Bubbly Flows: A Review

Large eddy simulations (LES) of dispersed gas-liquid flows for the prediction of flow patterns and its applications have been reviewed. The published literature in the last ten years has been analysed on a coherent basis, and the present status has been brought out for the LES Euler-Euler and Euler-Lagrange approaches. Finally, recommendations for the use of LES in dispersed gas liquid flows have been made.

Measurement of Lipid Bilayer Viscosity by Microfluidic Shear Transmission

We use an experimental method for measuring shear transmission through an anchored hemispherical vesicle to estimate the viscosity for several different lipid membranes. We also validate predicted flow patterns and confirm a recently calculated universal ratio [1] for the flow geometry. Comparing experimental with calculated results provides insight about how membrane viscosity contributes to flow patterns in biological configurations, such as characean algae cells, where a lipid membrane experiences strong shear flow [2]. We apply a similar flow to vesicles containing an electrostatically coupled actin cortex in order to observe the effects of external flow on reorganization of proteins inside the vesicle.

High-resolution 3-D full-loop simulation of a CFB carbonator cold model

This work focuses on the 3D full-loop CFD isothermal simulation of a transparent plexi-glass small-scale CFB carbonator built by IFK for the hydrodynamic investigation of the CFB reactor, utilized for the investigation of the calcium looping (Ca-L) process. This work couples the state of the art TFM approach with the advanced EMMS scheme for the calculation of drag coefficient exerted in the solid phase by the gas one. The CFB loop is discretized by 286,753 elements. In contrast to the majority of the published work, the flow characteristics of the re-circulation system of the unit, i.e. cyclone, downcomer and the pneumatic valve type of loop seal working as a flow regulator, is as well simulated and allows for the in-depth investigation and understanding of the whole CFB operation by means of CFD. In order to achieve this, the new proposed Pitman–Schaffer–Gray–Stiles yield criterion forms the basis, upon which the stresses exerted in the particulate phase within the loop-seal are calculated. The numerical results are averaged over a time period of 120 QUOTE s and the predicted flow patterns are compared against corresponding visual observations. Simulation results agree quite well with the experimental data, regarding the re-circulation flux and the pressure profile along the full-loop.

Two-phase flow pressure drops in U-tubes: Towards more accurate measurement methods and prediction models

In this study, flow pattern observations and pressure drop measurements in a U-bend and contiguous straight tubes are presented. The flow pattern observations were made with R134a at an inlet saturation temperature of 5 °C flowing at a mass flux of 300 kg s−1 m−2 inside a horizontal test section with an internal and bend diameters of 13 and 66 mm, respectively. The experimental data were obtained for the same experimental conditions, but with two test sections with one internal diameter of 11.7 mm and two bend diameters (31.7 and 54.8 mm) for different U-bend orientations. The experimental data was compared to the predictions of a new multi-orientation flow pattern based frictional pressure drop method for U-bends of Silva Lima and Thome (2012c) showing that the model predicts 97% of the database within an error window of ±30%. An extensive discussion was made on the benefits of using a data reduction method that allows obtaining the pressure drops effectively occurring in the U-bend and reducing the errors associated with that measure.

Application of VOF Interfacial Tracking Model to Condensation Heat Transfer

Condensation heat transfer used to the condenser as an important way of heat transfer is a phenomenon that involves flowing and heat and mass transfer of both gas and liquid phases. Thus, the development of its numerical prediction helps to the design of the condenser. At the present work, a VOF model was used to numerically simulate condensation heat transfer in a V-shape tube, obtaining volume fraction of vapor, location of liquid film and parameters of heat transfer. Results show that the VOF model may predict flow pattern of condensation and mass flux of condensation of vapor on the liquid film well. From computations, mass flux of condensation of vapor on the liquid film increases along vapor flowing, however, it tends to steady at the back part of the condenser tube. Flow pattern of condensation develops from annular flow at the inlet of the condenser tube to stratified flow, finally to plug flow at its back part. Velocity decreases along the tube length.