Changes In Flow Patterns Research Articles

Upper mantle and continental crust anisotropy in southeastern Mexico determined from shear-wave splitting measurements using local intraslab earthquakes

Cocos intraslab earthquakes were used to make shear-wave splitting measurements to explore the factors that control seismic anisotropy and to study the mantle wedge flow patterns in southeastern Mexico, where the Cocos plate subducts beneath the North American plate. Cocos intraslab earthquakes reach depths of 250 km, making it possible to sample the mantle wedge. The Silver and Chan (1991) covariance method was used to measure the splitting parameters: the fast polarization direction (φ) and the delay time (δt). The measurements can be divided into three regions: (1) northwest and (2) southeast of the Tehuantepec Ridge extension (i.e., the subducted Tehuantepec Ridge within the Cocos slab) and (3) the region above the subhorizontal Cocos slab. (1) In the first region, northeast of the 100 km isodepth contour of the Cocos slab, the fast axes are trench-perpendicular. This can be explained assuming the development of A-type olivine fabric and the existence of 2-D corner flow driven by the downdip motion of the Cocos slab. Southwest of the 100 km isodepth contour, measurements show trench-parallel fast polarization directions that are also consistent with corner flow, albeit in a serpentinized mantle wedge. Right above the Tehuantepec Ridge extension (northeast of the 100 km isodepth contour of the subducting slab), a change in the fast polarization directions from trench-normal to trench-parallel while going from northwest to southeast is observed and signals a change in the mantle flow pattern possibly through a vertical tear in the Cocos slab. 3-D toroidal flow could drive subslab mantle material around this slab edge and into the mantle wedge. (2) In the second region, the measured fast polarization directions show a trench-parallel orientation that is interpreted to result from southeastward trench-parallel flow through a serpentinized mantle wedge tip and also through a mantle wedge core made up of A- or C-type olivine fabrics with their fast axes oriented parallel to the flow direction. Trench-perpendicular fast polarization directions are observed beneath the fore-arc region of the Central America Volcanic Arc, near Tacaná Volcano, and trench-parallel polarizations are observed beneath the arc. These orientations could be explained by assuming the presence of B-type olivine fabric in the mantle wedge tip, A- or C-type olivine fabric in the mantle wedge core, and trench-parallel flow, so that the orientations of the fast axes become perpendicular to the mantle flow direction beneath the fore-arc and parallel to it beneath the arc. Lastly, (3) in the third region, over the flat slab, the observed delay times (0.04–0.42 s) are consistent with crustal anisotropy magnitudes, and the fast polarization directions seem to be controlled by the orientations of fault systems and alignments in foliations. Therefore, crustal faults and folds seem to be the dominant factors controlling the observed anisotropy.

Numerical investigation of heat transfer performance for rectangular, elliptical, and airfoil shaped pin fin heatsinks through the novel combination of perforation and bulge inserts

There is a desire to improve the forced convection heat transfer for various innovative shaped pin fin heatsink designs. Hence, a numerical investigation is conducted to observe the effect of convection heat transfer for various shaped pin fin heatsinks by changing various parameters on fluid and solid domains. Different shapes of perforations and bulges are added to create more surface area and flow pattern change. Several pin fin configurations are proposed for the design to increase the performance. Navier-Stokes's equations and RANS (Reynolds Averaged Navier-Stokes) based k − ε turbulence model governs the study's modeling. The investigations are performed using the CFD program for Reynolds numbers (Re) ranging from 8547 to 21,367. The results reveal that elliptical shape pin fins play a crucial role in enhancing hydro-thermal performance factor (HTPF). The circular perforated elliptical pin fin provides a maximum HTPF of 1.72 as the Re changes from 8547 to 21,367. A performance improvement of 56% to 72% is found, which merits consideration in the pin fin heatsink design. Furthermore, the heat transfer performance for the elliptical-shaped circular perforation pin fin is examined using copper-diamond composite material. The Cu-diamond composite has a maximum HTPF of 1.75 at a Reynolds number of 21,367.

Role of Vector Flow Mapping in Evaluating Left Ventricular Diastolic Flow Dynamics in Patients Who Underwent Mitral Valve Repair for Degenerative Mitral Regurgitation.

Mitral valve (MV) morphology after MV repair affects postoperative left ventricular (LV) blood flow pattern and long-term cardiac function. Pilot data suggest that LV diastolic vortex flow pattern changes after operation, but specific quantifiers remain unknown. We aimed to explore the role of vector flow mapping (VFM) in LV diastolic vortex flow pattern in patients who underwent MV repair. A total of 70 patients with degenerative mitral regurgitation were consecutively enrolled and 30 age- and gender-matched controls were recruited. 50 Patients who underwent MV repair were eventually included in our study. LV average energy loss (EL-AVE) during diastole was measured in the MV repair group by VFM one week before and one month after the operation, and compared with that of controls using one-way analysis of variance. The effect of surgical techniques and the extension of leaflet degeneration on postoperative EL-AVE were analyzed using muti-way analysis of variance, and patients were categorized into a resection subgroup (n = 29) and a non-resection subgroup (n = 21). The EL-AVE one month after operation in the MV repair group was decreased (p 0.001) compared to that one week before the operation, and was increased (p 0.001) compared to that in controls. Mitral leaflet resection had a statistically significant effect on postoperative EL-AVE. The EL-AVE of the resection subgroup was higher than that of non-resection subgroup (p 0.001). VFM can be used to evaluate the diastolic blood flow pattern of LV after MV repair, and to observe the changes of LV blood flow pattern caused by different surgical techniques. VFM may be a potential new hemodynamic evaluation method after MV repair.

On the numerical assessment of flow losses and secondary flows in Pelton turbine manifolds

Different methods combining analytical guidelines, numerical simulations, and the manufacturer’s experience are employed to design and optimise the distributor manifold of a Pelton turbine. All these methods have in common to assume undisturbed straight inflow to the manifold, thus neglecting the upstream flow conditions. Our numerical simulations executed with the open-source code OpenFOAM v2012 show that the insufficient consideration of the upstream flow situation may lead to inaccurate predictions of the manifold flow. Five turbulence models were tested in our simulations, and the inflow turbulence intensity was varied from 1% to 10%. The flow quality was assessed by evaluating the head loss coefficient from total pressure drop, the head loss coefficient from the entropy production, the secondary velocity ratio upstream the injectors and the mass flow imbalances in the injectors. The study of turbulence models revealed that the k-ω Shear Stress Transport model predicted the head loss and secondary flows with reasonable accuracy. Also, the computationally less expensive model of Spalart-Allmaras leads to similar results and therefore emerges as an appropriate model for optimisation. The simulations with varying inflow turbulence intensity levels indicate a flow pattern change, if the specified inflow turbulence intensity is less than 4%. Below this value of inflow turbulence intensity, a significant increase of the secondary flow upstream of the injectors was observed.

Numerical Study on Flow and Sludge Sedimentation Pattern Change Depending on the Array and Operation Time of the Propellers Inside the Anaerobic Digester in Jeongeup

Numerical Study on Flow and Sludge Sedimentation Pattern Change Depending on the Array and Operation Time of the Propellers Inside the Anaerobic Digester in Jeongeup

Gas/liquid two-phase flow with perforated hollow filament spacer to enhance the filtration performance in spiral wound membrane module

In brackish water and seawater desalination process, flat sheet and spiral wound membrane modules are commonly used to remove particulate pollutants and/or inorganic ions. In these membrane modules, feed spacer is used to construct the flow channel, enhance the flow field and corresponding filtration performance. However, two negative effects also occur for the spacer. One is the high pressure drop due to flow around the filament. The other is the stagnant zone near the filament, which results in localized fouling. In this paper, a new perforated hollow filament spacer was proposed. Gas/liquid two-phase flow was used to mitigate the membrane fouling. Filtration experiments were performed by microfiltration of SiC suspension. Results showed that compared with conventional spacer, the hollow filament spacer can improve the steady permeate flux by 56 %, with lower pressure drop. Particle deposition on membrane surface was effectively retarded, without localized fouling observed. Gas/liquid Flow patterns in the membrane channel were studied with high-speed photography. With the increase of Gas/liquid ratio, the flow pattern changes from bubble flow, slug flow to churn flow. The best filtration improvement performance was obtained with slug flow pattern. This hollow filament spacer is expected to mitigate the membrane fouling and improve permeate flux in the membrane-based desalination process.

Water Inrush Mechanism of Karst Collapse Column in Coal Seam Floor Based on a Variable Mass Seepage Mechanical Model

Water inrush of collapse column in the coal seam floor in the karst area is a frequent hydrogeological disaster, and it is becoming one of the significant hidden dangers threatening the safety of coal mine production in China. Based on the self-developed variable mass seepage test system of broken rock mass, different Talbot gradation seepage tests are carried out in the laboratory. A three-flow field coupled nonlinear seepage model is established based on the variable mass seepage theory and fluid mechanics theory of fractured rock mass. The three flow fields are Darcy laminar flow in the aquifer, variable mass seepage in the collapse column, and Navier-Stokes turbulent flow in the roadway. Combined with a project, a numerical calculation model is established to study the water-conducting channel’s formation process and the fluid flow pattern change. The research achievements indicate that the pore pressure gradient and seepage velocity are both 95% fit with the Forchheimer equation, and the seepage of the broken rock mass conforms to the Forchheimer equation. The seepage and migration of particles caused changes in pressure and flow rate, the pressure at the boundary between the aquifer and the collapse column decreased by 0.26 MPa, and the flow rate increased from 0.01 mm/s to 0.064 mm/s. The formation of the water-conducting channel can be divided into two stages, the seepage channel stage and the water-conducting channel stage. The initial fractures continue to develop with the seepage and migration of particles until the water-conducting channel is formed. At the bottom of the collapse column, the Forchheimer number increases from 0.72 to more than 1, and the flow changes from laminar flow to nonlinear seepage. The Forchheimer number at the center of the collapse column fluctuates between 7.5 and 55 at the top of the collapse column. The research results can be treated as an essential basis and reference for the water inrush control of the collapse column and the reasonable prediction of the water inrush amount.

Numerical studies on aerodynamic forces and flow control regimes of square cylinder with four surface ribs

Façade ribs attached to building surface are effective in mitigating wind-induced effects. In this paper, LES approach is adopted to explore the impact of four surface ribs on aerodynamic forces and flow structure around a square cylinder with width D. ANSYS Fluent is used to carry out the simulations at Re=2.2 × 104, the standard sub-grid scale (SGS) model is used. Simulation results indicate that small vortices formed near ribs can remarkably suppress flow separation, and reduce the shear layer's curvature and periodic flapping. Facade ribs accelerate the vortex shedding process, and clearly reduce the wake vortices’ intensity. The change of the flow field clearly mitigates surface pressure with increase in rib extension depth dr, resulting in a clear reduction in wind forces. When the depth dr is greater than 0.06D, the variation trends of drag coefficient C¯D and lift coefficient C’L are relatively complex with change of rib location br. This is due to the significant changes of flow patterns with different rib configurations. The maximum reduction rates of C¯D and C’L are 61% and 82%. It is found that extension of rib dr from around 0.08D to 0.1D with distance to the corner br from about 0.16D to 0.2D may show the best performance in reducing wind load.

Prediction of Critical Heat Flux for Subcooled Flow Boiling in Annulus and Transient Surface Temperature Change at CHF

The ability to predict critical heat flux (CHF) is of considerable interest for high-heat equipment, including nuclear reactors. CHF prediction from a mechanistic model for subcooled flow boiling in rod bundles still remains unsolved. In this paper, we try to predict the CHF in an annulus, which is the most basic flow geometry simplified from a fuel bundle, using a liquid sublayer dryout model. The prediction is validated with both water and R113 data, showing an accuracy within ±30%. After the CHF in an annulus is calculated successfully, a near-wall vapor–liquid structure is proposed on the basis of the liquid sublayer dryout model. Modeling of heat transfer modes over the heating surface at CHF is performed, and predictions of the changes in liquid sublayer thickness and heater surface temperature at the CHF occurrence point are carried out by solving the heat conduction equation in cylindrical coordinates with a convective boundary condition, which changes with the change in flow pattern over the heating surface. Transient changes in the liquid sublayer thickness and surface temperature at the CHF occurrence point are reported.

Wavenumber lock-in and spatial parametric resonance in convection

Analysis of convection driven by spatial periodic heating shows a wealth of responses due to Prandtl number dependence. The primary convection is delineated by the heating wavenumber and the secondary convection is characterized by the critical wavenumber established by an instability process. The resulting two-wavenumber dynamical system involves spatial parametric resonance leading to the wavenumber lock-in and the Rayleigh–Bénard (RB) instability producing unlocked states. Heating conditions leading to the co-existence of both types of states have been identified. Transition from the locked to the unlocked states produces states with a wide range of wavelengths and diverse patterns of movement. The possible secondary states are driven by a competition between the RB mechanism and the spatial parametric resonance. The relative strengths of these mechanisms change with Prandtl number $Pr$ resulting in four types of system responses. In the type A response occurring for $Pr>0.4$ , parametric resonance dominates for the heating wavenumber $\alpha < 4.5$ resulting in the pattern lock-in between the primary and secondary convections whereas RB occurs for $\alpha > 10$ . There is a wealth of possible convection patterns in the in-between zone where a small change of $\alpha$ results in a major change of flow pattern. In the type B response, which occurs for $0.19< Pr< 0.4$ , the RB effect dominates eliminating the lock-in. The type C response, which occurs for $0.08 < Pr< 0.19$ , is similar to type A but stronger spatial modulation extends the range of dominance of parametric resonance up to $\alpha =7$ while the RB effect dominates for $\alpha >10$ as in the type A response. A wealth of possible patterns occurs in the transition zone ( $7<\alpha <10$ ). In the type D response, which occurs for $Pr<0.08$ , the strong spatial modulation results in the formation of two separate critical stability curves, one resulting from the dominance of the spatial parametric resonance leading to the lock-in effect, and the other one corresponding to the dominance of the RB effect producing unlocked states. No continuous transition between both states can occur. Conditions where both distinct states can arise simultaneously were identified. Morphing between different patterns of secondary convection may occur in response to small changes in the heating pattern in types A and C, while such processes are not possible in types B and D.

Effective stress effect and slippage effect of gas migration in deep coal reservoirs

The deep coal reservoir is in a high in-situ stress regime, and the drop in pore pressure during the coalbed methane extraction can induce significant slippage effect and effective stress change. Both of them play a competitive role in permeability evolution. In our research, coal seepage experiments under variable bulk stress and pore pressure paths are performed to investigate the slippage effect and effective stress effect during gas migration in deep coal seams. The results show that the gas flow pattern changes from effective stress–control to slippage effect–control during the increase of bulk stress. Because of the dual pore structure and rich clay, coal presents microscopically inhomogeneous assemblage in mechanical and seepage properties. It makes the effective stress coefficient (ESC) for permeability, κ, always greater than 1, up to 1.94–2.64. By substituting the elastic modulus of the bedding for that of the clay in the coal, the clay-particle model can be used to explain the κ > 1. The linear-Klinkenberg equation is no longer applicable to the correction of gas slippage effect in deep coal reservoir, but conforms to the double-slip-Klinkenberg equation. Slippage effect weakens the stress sensitivity of permeability. As the effective stress increases, the slippage coefficient b increases accordingly, and the slippage effect becomes more pronounced. The gas flow pattern in deep coal reservoir is basically in the region of slippage flow, and the slippage effect cannot be ignored in gas migration. Furthermore, the anisotropy of κ is weakened in deep coal reservoirs, and the intrinsic permeability of coal, k∞, has the strongest stress sensitivity to σ3.

Groundwater Modeling: A Tool for Groundwater Management to Support Urban Water Supply and Food Security

Faisalabad is the 3rd largest city of Pakistan where underlying aquifer mostly contains saline water. Heavy population of the city needs huge quantity of fresh water. Water requirements for the existing Faisalabad city are being met by installation of well-fields along Jhang Branch canal, where groundwater is fresh. The increasing population pressure requires more water and identify more suitable sites for installation of well-field on sustainable basis. It was deemed imperative to elevate the existing well field. The MODFLOW, a numerical groundwater model developed by United States Geological Survey (USGS) for simulation and future prediction of aquifer behavior in response to pumping by various well fields was developed, calibrated and validated satisfactorily. A groundwater decomposition approach was also developed to tune various coefficients used in estimation of inflow and outflow components of groundwater system. The calibrated model was used to predict the future response of aquifer under different scenarios of pumping by existing and future/proposed wellfields. Calibrated flow model revealed that a sink has already been developed at the center of existing well-field of Water and Sanitation Agency (WASA) due to excessive pumpage. Future predictions of model indicate that there is no conspicuous change in regional groundwater flow pattern, even with all the existing tubewells remain in operation. However, the sink in the WASA well field area further deepens, and flow gradients become comparatively steep showing increase in groundwater flow velocity. Depth to watertable has already increased from 12 m in 2005 to 16 m in 2011 in the critical area of WASA well field. Model has predicted that this depth will further increase to 24 m in 2018. It has also been observed that groundwater quality along the river is fresh and becomes saline towards Faisalabad city. Due to pumpage in the freshwater zone model predicts that saline water will rush towards well fields deteriorating the quality of fresh water along Jhang Branch Canal. Therefore, it has been suggested that site for further pumping should be moved towards upstream of Jhang Branch Canal at least up to RD 180-187 and possibly on right side of the canal instead of left side

Wake galloping energy harvesting in heat exchange systems under the influence of ash deposition

Since the fluid flows in heat exchange systems contain hydrokinetic energies, flow-induced vibration (FIV) energy harvesting technology can be potentially applied to collect electrical energy. Different from the applications in traditional scenarios, cylinder bluff bodies implemented in the heat exchange systems will inevitably suffer from ash deposition. This study proposes a wake galloping energy harvester to be used in heat exchange systems and focuses on investigating the effects of different ash deposition types on the energy harvesting performance. According to different ash deposition types, bell-shaped and horn-shaped cylinder bluff bodies are designed to consider the ash deposition effect. Wind tunnel experiments are conducted to investigate the performance of the wake galloping piezoelectric energy harvester (PEH) with different upstream ash deposit cylinders, at various space distances and under different wind speeds. The experimental results reveal that compared to the horn-shaped cylinder, the bell-shaped cylinder is more beneficial for energy harvesting. Among all tested cases, the optimal configuration is determined: the upstream cylinder is attached by bell-shaped ash deposition; and the space ratio between the upstream and the downstream cylinders is 1.5. The threshold wind speed of the optimal configuration is reduced and the maximum voltage output is improved by over 111%. It is learned that the two types of upstream ash deposit cylinders can both cause the quenching phenomenon to deteriorate the performance of the energy harvester. Guidelines based on the experimental results are provided to avoid the occurrence of the quenching phenomenon. Computational fluid dynamics (CFD) studies are conducted to reveal the underlying mechanisms to explain the experimental results. The CFD results corroborate that different ash deposit cylinders produce different wake vortices and the flow pattern changes with the space distance, which determines the dynamic response of the downstream cylinder.

A Pilot Study Characterizing Flow Patterns in the Thoracic Aorta of Patients With Connective Tissue Disease: Comparison to Age- and Gender-Matched Controls via Fluid Structure Interaction

Prior computational and imaging studies described changes in flow patterns for patients with Marfan syndrome, but studies are lacking for related populations. This pilot study addresses this void by characterizing wall shear stress (WSS) indices for patients with Loeys-Dietz and undifferentiated connective tissue diseases. Using aortic valve-based velocity profiles from magnetic resonance imaging as input to patient-specific fluid structure interaction (FSI) models, we determined local flow patterns throughout the aorta for four patients with various connective tissue diseases (Loeys-Dietz with the native aorta, connective tissue disease of unclear etiology with native aorta in female and male patients, and an untreated patient with Marfan syndrome, as well as twin patients with Marfan syndrome who underwent valve-sparing root replacement). FSI simulations used physiological boundary conditions and material properties to replicate available measurements. Time-averaged WSS (TAWSS) and oscillatory shear index (OSI) results are presented with localized comparison to age- and gender-matched control participants. Ascending aortic dimensions were greater in almost all patients with connective tissue diseases relative to their respective control. Differences in TAWSS and OSI were driven by local morphological differences and cardiac output. For example, the model for one twin had a more pronounced proximal descending aorta in the vicinity of the ductus ligamentum that impacted WSS indices relative to the other. We are optimistic that the results of this study can serve as a foundation for larger future studies on the connective tissue disorders presented in this article.

Significant Differences in the Value of the Void Fraction in Various Types of Low-Viscosity Two-Phase Flow Patterns in Capillary Tubes with a Particular Slope

A two-phase flow is the simplest form of multi-phase flow. Two-phase flow has basic parameters, including flow behavior, flow pattern, void fraction, pressure gradient, or pressure drop. The development and application of fluid flow in small channels (mini and micro) are in the Micro Electromechanical System (MEMS). In general, the application of two-phase flow can be found in various applications in the industrial world, such as boilers, cores, and steam generators in nuclear reactors, petroleum transportation, electronic cooling, and different other types of chemical reactors. One of the most common challenges is void fractions and flow patterns in horizontal and vertical pipelines. The purpose of this study was to find out the significant difference in the characteristic value of fundamental parameters, primarily void fractions and flow patterns that occur in capillary pipes with a slope of 15o to horizontal. The fraction value and shape of this flow pattern are essential because it determines the pressure drop value, which means determining the level of danger that can occur if the pressure drop value reaches the extreme value. The fluid used a mixture of air-water and glycerin with 0, 10, 20, and 30% concentrations. To determine the void fraction is used digital image processing method with MATLAB R2014a application. A 1200 fps high-speed camera and 640 x 480-pixel resolution are used for video shooting. The experiment was conducted at superficial gas (JG) velocities of 0.025 - 66.3 m/s and superficial fluid velocities (JG) intervals of 0.033 – 4.935 m/s. The experiment results showed a significant difference between the void fraction value for the bubbly flow pattern and the churn flow pattern, which has not been widely discussed in previous studies. The analysis concluded that the higher the velocity of superficial gases, the void fraction value increases. This increase in the void fraction is why there is a significant change in flow patterns from bubble flow patterns to churn. In addition, it was also found that the increased viscosity of the fluid significantly affected changes in flow patterns, incredibly bubbly and plug, but its velocity decreased. It is also the result that the higher homogeneous void fraction (β) value affects the increase in the length of bubbly flow patterns and plugs.

The effect of pulsating air injection on the development of two-phase flow instabilities in an airlift pump

This paper aims at characterizing the instabilities created by the dynamic redistribution of air liquid two-phases through the pump to allow for utilizing a pulsating air injection as a new mode to control and optimize the pump performance. Baseline performance experiments for the pump operating under continuous air injection and for three submergence ratios of 0.5, 0.7 and 0.9 are used in the present analysis. The most efficient operating points of the pump were recorded at a range of air flow rates between 1.1 and 2.3 kg/hr. The characteristics of non-developing two-phase flow were evaluated using both flow pattern visualization using high speed imaging system and instantons void fraction using capacitance sensors at the points with the highest pump efficiency. In these experiments, the dynamics void fraction signals were collected at seven different locations along the pump riser. Both the fast Fourier transform, and power spectral density functions of the void fraction signals were used to identify the effective frequency range at which to perform the pulsation air injection experiments. At lower submergence ratios, the void fraction signals along the pump riser found to take a longer time to reach quasi-fully developed values. Also, pulsating mode of injected air was found to improve the pump performance for all submergence ratios. This is mainly due to the significant changes in the two-phase flow pattern in the pump riser when air pulsating used. In this case, pulsating the air injection at the optimum frequency allowed for maintaining a slug flow pattern during the pump operation and the best pump performance was achieve. Pulsating air injection at different offset frequencies were also evaluated for a dual injection airlift pump. It was found that an overlapping offset frequency or an alternating frequency between the two air injection ports can achieve a better pump performance for high submergence ratios while synchronous pulsation mode was found to be the most effective at improving the pump performance at low submergence ratios.

Hydraulic Losses in Systems of Conduits with Flow from Laminar to Fully Turbulent: A New Symbolic Regression Formulation

Separate flow friction formulations for laminar and turbulent regimes of flow through pipes are in common use in engineering practice. However, variation of different parameters in a system of conduits during conveying of fluids can cause changes in flow pattern from laminar to fully turbulent and vice versa. Because of that, it is useful to unify formulations for laminar and turbulent hydraulic regimes in one single coherent equation. In addition to a physical interpretation of hydraulic friction, this communication gives a short overview of already available Darcy’s flow friction formulations for both laminar and turbulent flow and additionally includes two simple completely new approximations based on symbolic regression.

Flow profile and wall normal stress characteristics in pattern-transformable flow silos

This paper describes an experimental investigation on the flow profile and wall normal stress characteristics in pattern-transformable flow silos, where the flow pattern changes from the funnel flow to the mass flow during discharge. The flow zone evolutions in this kind of silo are observed and discussed. The applicability of the existing funnel flow zone prediction model to this flow type is accessed. The distributions and dynamic characteristics of the wall normal stresses are obtained and analyzed. The reasons for the overpressure decrease and stress fluctuation weakening in pattern-transformable flow silos are discussed. A method to calculate the forces acting on the stagnant zone is proposed, and the force analysis is made at the moment when the flow pattern transforms. The unbalance of forces acting on the stagnant zone as a whole plays an important role in the flow pattern transformation. The findings offer a possibility to improve the pattern-transformable flow silo design.

A geometrical criterion for the dynamic snap-off event of a non-wetting droplet in a rectangular pore–throat microchannel

In porous media, non-wetting phase droplets snapping off in a constricted microchannel are one of the most common phenomena in two-phase flow processes. In this paper, the application range of the classic quasi-static criterion in rectangular cross section microchannels is obtained. For three different droplet breakup phenomena—total breakup, partial breakup, and non-breakup—observed in experiments when a non-wetting phase droplet passes through a microchannel constriction, the breakup is caused by the droplet neck snapping off in a channel constriction. A critical criterion for the dynamic snap-off event in a two-phase flow is proposed considering the effect of viscous dissipation by mechanical analysis, energy dissipation analysis, and many microfluidic experiments. When the droplet front flows out of the constriction, snap-off will occur if the surface energy release exceeds the required energy for viscous dissipation and kinetic energy conversion. The unique partial breakup phenomenon is affected by droplet surfactant distribution and the acceleration effect in the constriction center. This partial breakup phenomenon in experiments is an essential evidence for the non-uniform distribution of surfactants in the droplet surface. The results of this study contribute to understanding pore-scale mass transfer and flow pattern changes within porous media.

최대 수축기 및 이완기 동안의 왼쪽 심장 혈류에 대한 수치해석

The left heart performs a circulatory function in which containing oxygen blood moves from the Left Atrium (LA) to the Left Ventricle (LV) and is delivered to the human body. Analysis of LA and LV flow can be Indicators of abnormal heart. Numerical analysis was performed using Computational Fluid Dynamics (CFD) to analyze changes in velocity and flow patterns. As a result, the velocity of the Pulmonary Vein (PV) increased as diastolic progressed, but the movement of blood flow in the LA was lower than that of the systolic blood flow. Also, as the systolic progressed, the velocity of Aortic Valve (AV) and Mitral Valve (MV) increased, showing that the movement of blood flow in the LV increased. In this paper, we propose a standard indicators for a normal heart by analyzing the characteristics of velocity and flow patterns through a heart model implemented close to the human heart.