Transient Flow Patterns Research Articles

Evolution of downburst-like flows produced by an active-controlled multi-blade facility

The intricate dynamics of vortex structures within the downburst outflow region present significant challenges in studying flow evolutionary features, which are crucial for understanding the effect of such flow on various structures. This study aims to reveal the evolutionary features of downburst-like winds produced by an active-controlled multi-blade (AMBS) facility, using the particle image velocimetry tests and the large-eddy simulation (LES) studies. The numerical simulation indicates that the wind velocity profiles, nonstationary wind velocity time history, and the transient flow patterns of the downward flow impinging on the ground can be well simulated by the LES method. For stationary winds, a series of columnar vortices are produced, and the vortices tend to be more organized as the maximum velocity appears at a lower height. The proper orthogonal decomposition analysis manifests that the primary vortex region is affected by multiple modes of the fluctuating wind field. In addition, the primary vortex structures of the AMBS-generated flow present apparent evolutionary features. During the downward flow impinging on the ground, the nose-shaped wind velocity profile gradually forms at the turntable center and is well developed when the maximum velocity is reached. This observation is in accordance with the findings in available full-scale measurement campaigns.

The Slump Flow of Cementitious Pastes: Simulation vs. Experiments.

Understanding the transient properties of cementitious pastes is crucial for construction materials engineering. Computational modeling, particularly through Computational Fluid Dynamics (CFD), offers a promising avenue to enhance our understanding of these properties. However, there are several numerical uncertainties that affect the accuracy of the simulations using CFD. This study focuses on evaluating the accuracy of CFD simulations in replicating slump flow tests for cementitious pastes by determining the impact of the numerical setup on the simulation accuracy and evaluates the transient, viscosity-dependent flows for different viscous pastes. Rheological input parameters were sourced from rheometric tests and Herschel-Bulkley regression of flow curves. We assessed spatial and temporal convergence and compared two regularization methods for the rheological model. Our findings reveal that temporal and spatial refinements significantly affected the final test results. Adjustments in simulation setups effectively reduced computational errors to less than four percent compared to experimental outcomes. The Papanastasiou regularization was found to be more accurate than the bi-viscosity model. Employing a slice geometry, rather than a full three-dimensional cone mesh, led to accurate results with decreased computational costs. The analysis of transient flow properties revealed the effect of the paste viscosity on the time- and shear-dependent flow progress. The study provides an enhanced understanding of transient flow patterns in cementitious pastes and presents a refined CFD model for simulating slump flow tests. These advancements contribute to improving the accuracy and efficiency of computational analyses in the field of cement and concrete flow, offering a benchmark for prospective analysis of transient flow cases.

Assessing airflow unsteadiness in the human respiratory tract under different expiration conditions

To enhance the understanding of airflow characteristics in the human respiratory system, the expiratory airflow in a human respiratory tract model was simulated using large eddy simulation and dynamic mesh under different expiration conditions aligned with clinically measured data. The airflow unsteadiness was quantitatively assessed using power spectral density (PSD) and spectral entropy (SE). The following findings were obtained: (1) The airflow is highly turbulent in the mouth-pharynx region during expiration, with its dynamic characteristics being influenced by both the transient expiration flow pattern at mouth piece and the glottis motion. (2) PSD analysis reveals that the expiratory airflow is very unsteady, exhibiting a broad-band attenuation spectrum in the pharynx-trachea region. When only transient expiration or glottis motion is considered, the PSD spectrum changes slightly. When both are ignored, however, the change is significant, with the peak frequency reduced to 10% of the real expiration condition. (3) SE analysis indicates that the airflow transitions into turbulence in the trachea, and there may be multiple transitions in the region of soft palate. The transient expiration or glottis motion alone increases turbulence intensity by 2%–15%, while ignoring both reduces turbulence intensity by 10%–20%. This study implies that turbulence characteristics can be significantly different under different expiratory conditions, and therefore it is necessary to determine the expiratory flow characteristics using clinically measured expiratory data.

Angiographic velocimetry analysis using contrast dilution gradient method with a 1000 frames per second photon-counting detector.

Contrast dilution gradient (CDG) analysis is a quantitative method allowing blood velocity estimation using angiographic acquisitions. Currently, CDG is restricted to peripheral vasculature due to the suboptimal temporal resolution of current imaging systems. We investigate extension of CDG methods to the flow conditions of proximal vasculature using 1000 frames per second (fps) high-speed angiographic (HSA) imaging. We performed in-vitro HSA acquisitions using the XC-Actaeon detector and 3D-printed patient-specific phantoms. The CDG approach was used for blood velocity estimation expressed as the ratio of temporal and spatial contrast gradients. The gradients were extracted from 2D contrast intensity maps synthesized by plotting intensity profiles along the arterial centerline at each frame. In-vitro results obtained at various frame rates via temporal binning of 1000 fps data were retrospectively compared to computational fluid dynamics (CFD) velocimetry. Full-vessel velocity distributions were estimated at 1000 fps via parallel line expansion of the arterial centerline analysis. Using HSA, the CDG method displayed agreement with CFD at or above 250 fps [mean-absolute error (MAE): , ]. Relative velocity distributions correlated well with CFD at 1000fps with universal underapproximation due to effects of pulsatile contrast injection (MAE: 4.3cm/s). Using 1000fps HSA, CDG-based extraction of velocities across large arteries is possible. The method is sensitive to noise; however, image processing techniques and a contrast injection, which adequately fills the vessel assist algorithm accuracy. The CDG method provides high resolution quantitative information for rapidly transient flow patterns observed in arterial circulation.

On the Self-Similarity in an Annular Isolator under Rotating Feedback Pressure Perturbations

In this paper, the transient flow simulation in an annular isolator under rotating feedback pressure perturbations simplified from the rotating denotation wave (RDW) is performed. The instantaneous flow characteristics and the self-similarity of the isolator flow-field are investigated in detail. It is found that a helical moving shock wave (MSW) and a quasi-toroidal terminal shock wave (TSW) are induced in the isolator. Hence, the flow-fields on the meridian planes could be classified into three zones, i.e., the undisturbed zone, the terminal shock wave/moving shock wave/boundary layer interaction (TSW/MSW/BLI) zone and the moving shock wave/boundary layer interaction (MSW/BLI) zone. The TSW/MSW/BLI zone is characterized by the coupling of the TSW/BLI and the MSW/BLI due to their small axial distance, which intensifies the adverse pressure gradient on the meridian planes, thus rolling up large separation bubbles developing along the MSW driven by the circular pressure gradient. In the MSW/BLI zone, the shock induces the boundary layer to separate, forming a helical vortex located at the foot of the MSW. During the upstream propagation process, the pattern of the MSWs transforms from a moving normal shock wave to a moving oblique shock wave with decreased strength. Moreover, after the collision with the MSWs, P, Temp and S of the flow elevate with the prompt decrease of va, while vθ increases to a higher level. Despite the deflection effect of the MSWs on the streamlines, the flow direction of the air still maintains an almost axial position at the exit, except in the adjacent region of the MSW. Likewise, three types of zones can be determined in the flow pattern at the exit: the rotating detonation wave/boundary layer interaction (RDW/BLI) zone, the expansion zone, and the vortices discharge zone. Comparing the transient flow patterns at different moments in one cycle and between adjacent cycles, an interesting discovery is that the self-similarity property is observed in the flow-field of the annular isolator under rotating feedback pressure perturbations. The global flow structure of the isolator at different moments shows good agreement despite its rotation with the RDW, and the surface pressure profiles of the corresponding meridian planes all match perfectly. Such a characteristic indicates that the rotation angular velocity of the TSW and the MSW are equal and hold invariant, and the isolator flow could be regarded as a quasi-steady flow. On this basis, the theoretical model of the inclination angles of the MSW by the coordinate transformation and velocity decomposition is developed and validated. The relative errors of the inclination angles between the predicted and measured results are below 3%, which offers a rapid method to predict the shape of the MSW, along with a perspective to better understand the physical meaning of the shape of the MSW.

A combination of large eddy simulation and physics-informed machine learning to predict pore-scale flow behaviours in fibrous porous media: A case study of transient flow passing through a surgical mask

A predictive method using physics-informed machine learning (PIML) and large eddy simulation (LES) is developed to capture the transient flow field through microscale porous media (PSPM). An image processing technique extracts the 3D geometry of the internal layers of the mask from 2D microscopy images, and then the fluid flow is first simulated numerically. The subsequently developed PIML method successfully predicts the transient flow patterns inside the porous medium. For the first time, 3D maps of time-dependent pressure, velocity, and vorticity are predicted across the fibrous porous medium. The results show that, compared to conventional computational fluid dynamics, the PIML method can reduce the computational cost by over 20 times. Further, the LES model can replicate the fine fluctuations caused by the flow passage through the porous medium. Therefore, the developed methodology allows for transient flow predictions in highly complex configurations at a substantially reduced cost. The results indicate that the PIML method can reduce the total computational time (including training and prediction) by 22.5 and 20.7 times over the standard numerical simulation, based on speeds of 0.1 and 0.5 m/s, respectively. Several factors including the inherent differences between CPUs and GPUs, algorithms and software, appear to influence this improvement.

Impact of pressure drop oscillations and parallel channel instabilities on microchannel flow boiling and critical heat flux

Microchannel flow boiling heat sinks that leverage the highly efficient heat transfer mechanisms associated with phase change are a primary candidate for cooling next-generation electronics in electric vehicles. In order to design flow boiling heat sinks for such practical applications, one key obstacle is an understanding of the conditions for occurrence of dynamic two-phase flow instabilities, to which microscale flow boiling is particularly susceptible, as well as their impact on heat transfer performance. While mapping the operational regimes of these instabilities has been well-studied, with numerous stability criteria available, their impact on the heat transfer performance of heat sinks in practical applications is not understood. This work seeks to assess the impact of pressure drop oscillations and parallel channel instabilities on the surface temperature and critical heat flux in parallel microchannel heat sinks. This is achieved through measurement of time-averaged steady-state temperatures and pressures, combined with high-frequency pressure signals and high-speed flow visualization. These data are compared across three controlled flow configurations that comprise a condition of stable flow boiling, a condition where only parallel channel instabilities can occur, and a third where both pressure drop oscillations and parallel channel instabilities can occur. Experiments are performed using the dielectric refrigerant HFE-7100 in 2 cm long parallel microchannel heat sinks with square-cross-section channels (0.25, 0.5, 0.75, and 1 mm widths) at three mass fluxes (100, 400, and 1600 kg/m2s). Across this range of conditions, the time-averaged surface temperature and critical heat flux were remarkably insensitive to the occurrence of these instabilities despite the significant hydrodynamic events and transient flow patterns observed.

The global atmospheric energy transport analysed by a wavelength-based scale separation

Abstract. The atmosphere transports energy polewards by circulation cells and eddies. To the present day, there has been a knowledge gap regarding the preferred spatial scales and physical mechanisms of eddy energy transport. To fill the gap, we separate the meridional atmospheric energy transport in the ERA5 reanalysis by spatial scales and into quasi-stationary and transient flow patterns and latent and dry components. Baroclinic instability is the major instability mechanism in the transient synoptic scales and is responsible for forming cyclones, anticyclones, and small-scale Rossby waves. At the planetary scales, circulation patterns are often induced by other mechanisms such as flow interaction with orography and land–sea heating contrasts. However, a separation between circulation patterns at the synoptic and planetary scales has yet to be established. We find that both baroclinically induced and transient energy transport is predominantly associated with eddies at wavelengths between 2000 and 8000 km. The maxima in both types of transport occur at wavelengths around 5000 km, in good agreement with linear baroclinic theory. Since these results are independent of latitude, we adapt the scale separation of the energy transport to be based on the wavelength instead of the previously used wavenumber. We define the synoptic transport by the wavelength band between 2000 and 8000 km. We analyse the annual and seasonal mean in the energy transport components and their inter-annual variability. The scale-separated transport components are fairly similar in both hemispheres. Transport by synoptic waves is the largest contributor to extra-tropical energy and moisture transport, mainly of a transient character, and is influenced little by seasonality. In contrast, transport by planetary waves depends highly on the season and has two distinct characteristics. (1) In the extra-tropical winter, planetary waves are important due to a large transport of dry energy. This planetary transport features the largest inter-annual variability of all components and is mainly quasi-stationary in the Northern Hemisphere but transient in its southern counterpart. (2) In the sub-tropical summer, quasi-stationary planetary waves are the most important transport component, mainly due to moisture transport, presumably associated with monsoons. In contrast to transport by planetary and synoptic waves, only a negligible amount of energy is transported by mesoscale eddies (< 2000 km).

Thermohydraulic management coupled with flow pattern distinction for concentrating solar direct-steam-generation technology

Concentrating solar direct-steam-generation (DSG) technology is favored for tying solar energy and water to directly power the energy loop, which is positive in achieving a zero-carbon future. Whereas, the external intermittence of the meteorological irradiation and internal instability of flow boiling pose challenges to the thermohydraulic operation and management. Herein, a light-heat-flow-pattern transient coupled analysis model of parabolic trough collector direct-steam-generation (PTC-DSG) loop was established to figure out the action among the irradiance, thermohydraulic and two-phase flow pattern. The transient flow patterns along the loop were investigated under different irradiance (I), mass flowrate (min) and inlet temperature (tin) of the loop. The results showed that increasing I and tin temporarily reduces the probability of stratified flow and increasing tin permanently reduces the probability of stratified flow. In all cases, the proportion of intermittent flow to evaporation stage remains almost unchanged (about 11%.), and the heat transfer in superheating stage still needs a long time (253s ∼ 3646s) to recover after the flow stages distribution is stable. More importantly, a quantified management strategy for irradiance -thermohydraulic-flow pattern is built. To achieve a favorable operating state, the inlet mass flow rate min should be lower than the superheated line ((1.25·I – 6.25)✕10−3 kg s−1) to obtain the superheated steam, and higher than 0.35 kg s−1 to get out of the stratified flow in evaporation stage. When the irradiation is lower than 285 W m−2 for a long time, the start-up and operation is not recommended.

Experimental study on transient flow patterns in simplified saccular intracranial aneurysm models using particle image velocimetry

Experimental study on transient flow patterns in simplified saccular intracranial aneurysm models using particle image velocimetry

Transient flow patterns of start-up flow in round microcavities

Transient flow patterns of start-up flow in round microcavities

Arbitrary Lagrangian-Eulerian discrete velocity method with application to laser-induced plume expansion

We propose a direct arbitrary Lagrangian-Eulerian (ALE) variant of the previously developed discrete velocity method to solve the kinetic equation with the Bhatnagar–Gross–Krook (BGK) model collision integral. The effectiveness and robustness of the new scheme are demonstrated by computing the axisymmetric plume expansion into a low pressure gas due to evaporation from the solid surface caused by a nanosecond laser pulse. The numerical studies show that the new numerical scheme provides a very significant reduction of the required computing time as compared to the discrete velocity method on a fixed mesh. Cross-comparisons with the direct simulation Monte Carlo (DSMC) approach further confirm the accuracy of the new scheme and model kinetic equations as applied to plume expansion studies. Finally, the good parallel scalability of the new ALE scheme as implemented into the in-house code Nesvetay is demonstrated. The use of two very different approaches to numerical prediction of the transient flow pattern allows us to obtain a reliable numerical solution, which can be regarded as a new transient benchmark test.

Generation of Local Diffusioosmotic Flow by Light Responsive Microgels.

Here we show that microgels trapped at a solid wall can issue liquid flow and transport over distances several times larger than the particle size. The microgel consists of cross-linked poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-AA) polymer chains loaded with cationic azobenzene-containing surfactant, which can assume either a trans- or a cis-state depending on the wavelength of the applied irradiation. The microgel, being a selective absorber of trans-isomers, responds by changing its volume under irradiation with light of appropriate wavelength at which the cis-isomers of the surfactant molecules diffuse out of the particle interior. Together with the change in particle size, the expelled cis-isomers form an excess of the concentration and subsequent gradient in osmotic pressure generating a halo of local light-driven diffusioosmotic (l-LDDO) flow. The direction and the strength of the l-LDDO depends on the intensity and irradiation wavelength, as well as on the amount of surfactant absorbed by the microgel. The flow pattern around a microgel is directed radially outward and can be maintained quasi-indefinitely under exposure to blue light when the trans-/cis-ratio is 2/1, establishing a photostationary state. Irradiation with UV light, on the other hand, generates a radially transient flow pattern, which inverts from inward to outward over time at low intensities. By measuring the displacement of tracer particles around neutral microgels during a temperature-induced collapse, we can exclude that a change in particle shape itself causes the flow, i.e., just by expulsion or uptake of water. Ultimately, it is its ability to selectively absorb two isomers of photosensitive surfactant under different irradiation conditions that leads to an effective pumping caused by a self-induced diffusioosmotic flow.

On turbulent flow and aerodynamic noise of generic side-view mirror with cell-centred finite difference method

This paper investigates the turbulent flow and aerodynamic noise of a half-cylinder body mounted on a flat plate at using high-order cell-centred finite difference method with delayed detached-eddy simulation (DDES) and large-eddy simulation (LES). Transient flow patterns from the two simulations are found to be very different in consideration of the small-scale structures. The profiles of mean velocity, resolved turbulent kinetic energy and resolved Reynolds shear stress are found to be similar among all the simulations, indicating mean quantities are relatively insensitive to turbulence modelling and grid resolution. The power spectra density of the pressure fluctuations show that LES is more capable of resolving energies in high-frequency range than DDES. After computing the normalised wavenumber-frequency spectra of fluctuating pressure on the window, we further carried out the wavenumber-frequency decomposition to separate the acoustic and the hydrodynamic components from the pressure fluctuations. The energy distribution shows that the acoustic energy has a much slower decaying rate in the high-frequency range than the hydrodynamic energy. In addition, the space-averaged sound pressure levels of pressure fluctuations on the window indicate that the present simulation with a high-order method is able to improve the accuracy in predicting pressure spectra. Finally, we carry out proper orthogonal decomposition to extract the dominating features of the decomposed acoustic and hydrodynamic components of pressure fluctuation. Patterns of multi-scale turbulence in hydrodynamic modes and propagating wavefronts of cylinder shape in acoustic modes are identified. The present research indicates that a relatively coarse grid is still capable of resolving fluctuating quantities of energy-containing structures, and LES is suggested against DDES when near-wall aerodynamic noise is the main concern.

Study on the impacting performance of a self-excited oscillation pulsed jet nozzle

The pulsive jet nozzle, which converts the continuous jet into a pulsive jet, is widely used in downhole well operations, such as drilling and perforation. In this paper, a self-excited oscillation pulsed jet nozzle is proposed basing on the Coanda effect. The effects of nozzle design, inlet flow rate, and target distance on the jet dynamics, such as the pulsive characteristics and impacting performance, were investigated. The transient flow pattern was studied with a high-speed camera, which showed a good agreement with the numerical results. Furthermore, with the increase of the inlet flow, the pulsation amplitude of impacting pressure of the Coanda nozzle increased. Based on the obtained data, the relationship between the pulsive frequency and Reynolds number and that between Strouhal number and Reynolds number was revealed. Under a confining pressure of 30 MPa, a target distance of 70 mm, and an inlet flow rate of 15 m/s, the error between the numerical impacting pressure and the experimental value was 9.7%, which confirmed the numerical approach could be used to predict the transient jet process. The obtained results can guide the design of a self-excited oscillation pulse jet nozzle and its oilfield application. • A self-excited oscillation pulsed jet nozzle with Coanda effect is proposed. • Computational fluid dynamics was applied to simulate the pulsive behavior. • Process parameters shown significant influence on the pulsive characteristics. • An error of 9.3% was achieved between numerical and experimental results.

Experimental visualization of two-phase flow inside a real-size piston of a crosshead-type marine engine

ABSTRACT The oscillating cooling method is one of the most effective cooling solutions to improve the piston cooling ability for diesel engines. Most of the experimental studies were focused on the simplified model, and few were based on the actual complex piston cooling cavities. To give a better insight into the flow mechanism inside the actual cavities, a flow visualization test rig was built based on a real-size piston model with a stroke of 1550 mm and a cylinder diameter of 350 mm. The model replicates the piston and cooling cavities of a typical low-speed two-stroke crosshead marine engine MAN B&W 6S35ME. The test rig ensures that the coolant supply mode, the coolant flow path, and the kinematic curve of the piston head are consistent with the real machine. The piston model is an exact replica of the original scale made of PC material. A high-speed camera was used to capture the transient flow patterns of the gas-liquid two-phase flow inside the cooling cavities during the reciprocating motion of the whole stroke. More accurate boundary conditions are thus provided for the numerical simulation method, which significantly improves the accuracy of previous simulations under the same research topic. Analysis of the piston’s oscillatory cooling method is beneficial to optimizing the thermal management of engines in the future.

Deposition of Smoke Particles in Human Airways with Realistic Waveform

Exposure to toxic particles from smoke generated either from bush fire, stable burning, or direct smoking is very harmful to our health. The tiny particles easily penetrate deep into the lungs after exposure and damage the airways. Tobacco smoking causes the direct emission of 2.6 million tons of CO2 and 5.2 million tons of methane annually into the atmosphere. Nevertheless, it is one of the significant contributors to various respiratory diseases leading to lung cancer. These particles’ deposition in the human airway is computed in the present article for refining our understanding of the adverse health effects due to smoke particle inhalation, especially cigarette smoke. Until recently, little work has been reported to account for the transient flow pattern of cigarette smoking. Consideration of transient flow may change the deposition pattern of the particle. A high-resolution CT scan image of the respiratory tract model consisting of the oral cavity, throat, trachea, and first to sixth generations of the lungs helps predict cigarette smoke particle (CSP) deposition. With the same scan, a realistic geometric model of the human airways of an adult subject is used to simulate the transport of air and particle. The CSP deposition is determined at different locations from the oral cavity to the sixth generation of the bronchi. In addition, an unsteady breathing curve indicative of realistic smoking behavior is utilized to represent the breathing conditions accurately. The discrete phase model (DPM) technique is used to determine smoke particle deposition in the human airways. It is found that the deposition increases with the size of the smoke particle. Particles tend to deposit in the oral cavity around the bifurcation junction of the airways. The deposition fraction of CSP with the realistic waveform of smoking is found to be smaller compared to that during the stable flow condition. It is also observed that the fine particles (0.1–1.0 micron) escape to lower generations, leading to higher deposition of fine particles in the deeper airways. The outcome of the study is helpful for understanding smoke-related pulmonary complications.

Micro-macro model for the transient heat and fluid transport in solidification structure evolution during static casting processes

The current work used micro-macro model to study the transient fluid flow patterns, heat transfer and solute segregation during the solidification of eutectic binary Al-4%Cu alloy in a static casting process. Custom codes in the form of user defined functions (UDFs) for Nucleation and growth kinetics, thermo-physical properties, and other transport terms including boundary conditions specifically developed for this study were interfaced to ANSYS Fluent. Solidification kinetics was coupled to macroscopic heat transfer equation through the latent heat evolution. The pressure-velocity coupling in the momentum equations were handled by Semi-Implicit Method for Pressure-Linked Equations Consistent (SIMPLEC). The energy and species conservation equations were also solved with similar algorithm. The transient terms of the transport equations were evaluated using fully implicit scheme. Three cases were simulated to evaluate the effect of cooling conditions on the transient evolution of fluid flow, heat transfer and macro-segregation. The results obtained show significant variations in the pattern of fluid flow, heat transport and solute segregation for the three cases. Different thermal regions were reported for the three cases studied. Thickness of the slurry region was observed to be a function of cooling condition. Severity of macro-segregation varied significantly due to imposed boundary conditions. The results obtained provide evidence that choosing cooling orientations arbitrarily can lead to either overestimation or underestimation of casting defects. Therefore, thermal design and process parameters should be optimized for improved product quality and production output.

Determination of Transient Flow Pattern in Steel Continuous Casting Molds Using Nail Board Measurement and Onsite Top Flux Observation

Determination of Transient Flow Pattern in Steel Continuous Casting Molds Using Nail Board Measurement and Onsite Top Flux Observation

Large Eddy Simulation of Transient Flow, Particle Transport, and Entrapment in Slab Mold with Double‐Ruler Electromagnetic Braking

To study the transient transport and capture of inclusions and argon bubbles simultaneously in slab mold with double‐ruler electromagnetic braking (EMBr), a transient large eddy simulation model coupling molten steel flow, solidification, electromagnetic field, and particle motion is constructed. In this model, momentum transfer between argon bubbles and molten steel is implemented by two‐way coupling. The results indicate that the EMBr changes the molten steel transient flow pattern in the liquid pool. Due to the braking effect, the asymmetry and instability of the molten steel transient flow are weakened. Moreover, EMBr changes the transient particle (inclusion and argon bubble) transports inside the liquid pool. The particle motions inside the liquid pool are constrained, and the dispersion of the particles inside the liquid pool is weakened by EMBr. In addition, the contents of particles within the slab surface layer are decreased under the application of EMBr. Nevertheless, in the slab interior, the contents of the particles under the application of EMBr are higher than those in the absence of EMBr.