Sidewall Region Research Articles

Effects of transverse fire locations on flame length and temperature distribution in a bifurcated tunnel fire

In this paper, a series of experiments were conducted in a 1:10 reduced scale bifurcated tunnel to investigate transverse flame length and temperature field distribution under the ceiling with different transverse fire source locations. Five fire locations were considered and the corresponding distances (D) between the fire source centerline and sidewall are 0.1 m, 0.3 m, 0.5 m, 0.7 m and 0.9 m respectively. It is found that the predicted value by Gao’s model overestimates the ceiling jet flame extension length, thus a modified correlation considering the influence of the branch tunnel is established, which includes a sidewall and non-sidewall region. Moreover, a simplified equation for predicting the dimensionless maximum ceiling jet temperature by taking transverse fire locations into account is developed based on Ji’s model. Besides, the longitudinal temperature decay coefficient in the main tunnel ceiling shows a non-monotonous trend with D, exhibiting a maximum value at the condition for D is 0.3 m. However, there is a linear relationship between the longitudinal temperature decay coefficient and the ratio of the distance from sidewall and tunnel width. Meanwhile, based on Hu’s model, a revised formula for predicting the dimensionless longitudinal temperature rise by considering the effect of transverse fire location is established.

Size segregation of granular materials during Paul-Wurth hopper charging and discharging process

In an ironmaking blast furnace top, raw granular materials such as iron ore and coke are delivered to the parallel Paul-Wurth (PW) hoppers first and then discharged to the furnace. In this work, the effects of variables such as filling positions and filling angles on the size segregation during PW hopper charging and discharging processes are examined. Results illustrate that small particle gathering area appears near the filling points due to the rolling mechanism, and the area size is related to the distance of filling position to the side wall. Trajectory is another main segregation mechanism related to different filling angles. Steep filling angle changes particle trajectories significantly and large particles tend to gather in the side wall region. Increasing flow rate decreases the segregation. During the discharging process, a depression appears and large particles are engulfed in the depression, leading to the segregation at the last stage of discharging.

Effects of Grounding Bottom Oxide Protection Layer in Trench-Gate SiC-MOSFET by Tilted Al Implantation

A trench gate SiC-MOSFET with BPW grounded by tilted Al implantation is developed in order to optimize the cell design and process for grounding the BPW in a more simple manner. From evaluation of static characteristics, the MOSFETs with sidewall region can improve the trade-off relationship between Ron,sp and Vbd by the variation of dSRs, and is superior than that of conventional BPW ground contact structure. From evaluation of dynamic characteristics, the MOSFETs with sidewall region can realize stable p-type ohmic contact for BPW compared with conventional BPW ground contact structure. Furthermore, the trade-off between Ron,sp and tsc of this device is adjusted to optimized layout of the p-type sidewall regions without degradation of the dV/dt dependence of turn-on and turn-off losses.

Numerical analysis of reasons for the CO distribution in an opposite-wall-firing furnace

In practical operations, the carbon monoxide (CO) distribution in an opposite-wall-firing furnace (OWFF) is characterized by a high concentration near the side walls and a low concentration in the center, accompanied by a series of combustion-related issues. To find the reasons for the CO distribution, a numerical study was conducted on a 660 MWe OWFF. The CO concentration profiles, distribution coefficients of coal and air, mixing coefficients, and the aerodynamic characteristics were extracted for analysis. The CO distribution within the furnace greatly depends on the mixing of coal and air. A mismatch between the aerodynamic behaviors of coal and air causes the non-uniform distribution of CO. Taking into consideration that distinctive flow patterns exist within the different regions, the formation mechanisms of the CO distribution can be divided into two components: (1) In the burner region, the collision of opposite flows leads to the migration of gas and particles toward the side wall which, together with the vortexes formed at furnace corners, is responsible for unburned particles concentrated and oxygenized from the furnace center to the side wall. Thus, high CO concentrations appear in these areas. (2) As the over-fire air (OFA) jet is injected into the furnace, it occupies the central region of furnace and pushes the gas from the burner region outward to the side wall, which is disadvantageous for the mixing effect in the side wall region. As a consequence, a U-shaped distribution of CO concentration is formed. Our results contribute to a theoretical basis for facilitating the control of variation in CO concentration within the furnace.

Mechanism study of SiO2 layer formation and separation at the Si die sidewall during nanosecond laser dicing of ultrathin Si wafers with Cu backside layer

Laser dicing of ultrathin dies is promising and is gaining importance because of its cost and quality advantages over mechanical and plasma dicing. However, the effects of laser dicing on the mechanical strength and microstructure of ultrathin Si dies need to be further understood, especially when dicing through Si wafers with backside Cu layer. A critical phenomenon effecting the Si die sidewall strength after nanosecond laser dicing of Si wafers with backside Cu is the formation and separation of a SiO2 layer at the sidewall. The mechanisms behind the SiO2 layer formation and separation were studied in this work. Si wafer samples without and with backside Cu layer were prepared by dicing with nanosecond laser using standard production parameters. The microstructure and phases formed were investigated by energy dispersive spectroscopy and nanobeam diffraction in a transmission electron microscope. In die samples without backside Cu, the sidewall consists of a thin surface layer of amorphous Si, followed by a polycrystalline Si layer, and finally an epitaxial Si layer. In die samples with backside Cu, the sidewall microstructure was observed to be vastly different. At the upper region of the sidewall, a surface layer of polycrystalline Cu was found, followed by a polycrystalline Cu3Si layer, a SiO2 layer mixed with Cu3Si, and finally a thick SiO2 layer. The Cu3Si catalyzes the growth of the SiO2 through an oxidation step of the Cu3Si on the sidewall surface as well as at the SiO2/Si interface. In the lower region of the sidewall, the microstructure is similar to the upper region, but there is a separation of the SiO2 layer from the crystalline Si. The SiO2 undergoes a decomposition reaction at the SiO2/Si interface, releasing volatile SiO which causes microvoids to form and grow laterally at the interface. The growth and coalescence of the microvoids eventually lead to the separation of the SiO2 layer from the crystalline Si, leaving behind a clean and rough crystalline Si surface with a peak-to-peak roughness of 100–200 nm. In the areas where the SiO2 layer has separated from the Si die sidewall, the fracture strength of the sidewall is dependent on the material property and surface roughness of the crystalline Si, and not on the SiO2 layer. In the sidewall region near the die frontside, the SiO2 thickness is more than regions near the die backside, and no microvoiding and separation at the SiO2/Si interface were detected. This is hypothesized to be due to a higher O2 pressure at the upper region of the narrow dicing trench which is open to the atmosphere compared to the lower regions where there could be O2 deprivation and lower O2 pressure.

Statistics of temperature and thermal energy dissipation rate in low-Prandtl number turbulent thermal convection

We report the statistical properties of temperature and thermal energy dissipation rate in low-Prandtl number turbulent Rayleigh-Bénard convection. High resolution two-dimensional direct numerical simulations were carried out for the Rayleigh number (Ra) of 106 ≤ Ra ≤ 107 and the Prandtl number (Pr) of 0.025. Our results show that the global heat transport and momentum scaling in terms of Nusselt number (Nu) and Reynolds number (Re) are Nu = 0.21Ra0.25 and Re = 6.11Ra0.50, respectively, indicating that scaling exponents are smaller than those for moderate-Prandtl number fluids (such as water or air) in the same convection cell. In the central region of the cell, probability density functions (PDFs) of temperature profiles show stretched exponential peak and the Gaussian tail; in the sidewall region, PDFs of temperature profiles show a multimodal distribution at relatively lower Ra, while they approach the Gaussian profile at relatively higher Ra. We split the energy dissipation rate into contributions from bulk and boundary layers and found the locally averaged thermal energy dissipation rate from the boundary layer region is an order of magnitude larger than that from the bulk region. Even if the much smaller volume occupied by the boundary layer region is considered, the globally averaged thermal energy dissipation rate from the boundary layer region is still larger than that from the bulk region. We further numerically determined the scaling exponents of globally averaged thermal energy dissipation rates as functions of Ra and Re.

Size-induced segregation of granular materials during filling a conical hopper

Granular materials often experience segregation due to the differences of particle size, density and shape. In this work, particle size-induced segregation is investigated for one typical device – conical hopper which is widely used in the storage and processing of granular materials. In particular, the fundamentals governing particle size segregation during the hopper filling process are revealed by the analysis of DEM data such as particle velocities, trajectories, coordination number (CN) and mixing index. The results show that during the central charging process, particles with large velocities easily bounce to the side wall region while particles with small velocities are obstructed by their neighbours and stop moving quickly. Large particles tend to roll along the free surface and accumulate in the side wall region. Particle scale mixing index decreases with the increase of hopper height and the distance from the centre, indicating the effect of charging height and segregation occurrence along the radial direction. Further, the effect of friction coefficients is examined, and a contour plot is drawn, illustrating that a combination of sliding friction coefficient larger than 0.5 and a moderate rolling friction coefficient in a range of 0.01dp to 0.1dp leads to pronounced segregation. The concentration distribution of small particles for various feeding mixtures is analysed, and general trends are observed to demonstrate the segregation extent at different hopper radial locations.

Durability prediction of an ultra-large mining truck tire using an enhanced finite element method

Ultra-class mining trucks used for material haulage in rugged surface mining terrains experience premature tire fatigue failure in operation. Typical failures include belt edge separation, ply turn-up separation, and tread base and sidewall cracking. The use of reinforcing fillers and processing aids in tire compounds result in the formation of microstructural in-homogeneities in the compounds. This article presents an application of the critical plane analysis technique for predicting the fatigue life of the belt package of an ultra-large mining truck (CAT 795F) tire of size 56/80R63 in a surface coal mine. Experimental data obtained from extracted specimens (sidewall, tread, and belt edge region) of the tire are used to characterize the stress–strain and fatigue behavior of the modeled tire. The tire’s duty cycle stresses and strains were obtained from finite element analysis of the rolling tire in Abaqus. Fatigue life calculations were performed in the rubber fatigue solver Endurica CL. Effects of inflation pressure, tire speed, and axle load on the fatigue life of the belt package under strain-crystallizing and non-crystallizing conditions of the belt compound are discussed. Specifically, the results show the belt edges to be critical regarding crack nucleation.

The effect of the diffusion creep behavior on the TSV-Cu protrusion morphology during annealing

As through-silicon vias (TSVs) are key structural elements of 3D integration and packaging, creep deformation, which causes TSV-Cu protrusion, is critical for TSV reliability. Here, the effect of the diffusion creep behavior on the TSV-Cu protrusion morphology is analyzed using experiment and simulation. The protrusion morphology of TSV-Cu after annealing treatment is examined using a white light interferometer. The diffusion creep mechanism of TSV-Cu is determined by observation of the TSV-Cu microstructure using a scanning electron microscopy and a focused ion beams. The TSV-Cu grain size is measured using an electron backscatter diffraction system. The diffusion creep rate model of TSV-Cu is deduced based on the energy balance theory and is introduced into the finite element model to clarify the influence of diffusion creep on TSV-Cu protrusion. It is determined that the diffusion creep of TSV-Cu is mainly caused by grain boundary diffusion and grain boundary sliding. The diffusion creep strain rate is positively correlated with the ambient temperature and the external load but negatively correlated with the grain size. The amount of TSV-Cu protrusion increases with decreasing grain size. The simulation results show that the “donut”-shaped protrusion morphology is more likely to occur in TSV-Cu with smaller grain sizes near the sidewall region of the via.

Numerical and experimental investigation of three-dimensionality in the dam-break flow against a vertical wall

The three-dimensionality extent of the dam break flow over a vertical wall is investigated numerically and experimentally in this paper. The numerical method is based on Reynolds averaged Navier-Stokes (RANS) equation that describes the three-dimensional incompressible turbulent flow. The free surface is captured by using the unstructured multi-dimensional interface capturing (UMTHINC) scheme. The equations are discretized on 2-D and 3-D unstructured grids using finite volume method. The numerical simulations are compared with newly conducted experiment with emphasis on the effect of three-dimensionality on both free surface and impact pressure. The comparison between the numerical and experimental results shows good agreement. Furthermore, the results also show that 3-D motion of the flow originates at the moment of impact at the lower corners of the impact wall and propagates to the inner region as time advances. The origin of the three-dimensionality is found to be the turbulence development as well as the relative velocity between the side wall region and the inner region of the wave front at the moment of impact.

Flow loss and structure of circular arc blades with different leading edges

Due to much lower cost of development and production, circular arc blades are often applied to axial flow fans. However, compared with NACA 65 profile, circular arc blades have higher losses, which are caused by the formation of separation bubbles or complete separation at the leading edge. Therefore, it is necessary to identify a specific geometry of leading edge, which can reduce the separation bubbles or complete separation. In this article, circular arc blades with different leading edges are examined by numerical method. The numerical investigations were performed with Reynolds numbers of [Formula: see text] and [Formula: see text]. All examinations were performed for different incidence angles. The influence of the sidewall on the flow loss and behavior is taken into account. In this article, the influence of leading edge geometry and Reynolds number on the flow losses is shown. The occurrence of flow behavior such as separation bubbles at the leading edge, secondary flow, and corner stall is shown and discussed. The flow structure on the blade and the corresponding sidewall region is illustrated with numerical streamline figures.

Load distribution by zones of frame sub-constructions of D2 class buggy racing car

In this paper, the authors consider the loading of the buggy car system under the most typical loading modes: the mode of approach of the front wheel to the obstacle, the mode of the rear wheel approach to the obstacle, the mode of diagonal loading, as well as the mode of twisting the frame around the longitudinal axis. For the convenience of analysis, the frame of the buggy car is divided into substructures, which, in turn, are divided into zones. For each of the zones of each sub-structure, the bar graph shows the proportion of the perceived load for each type of loading. The presented graphs make it easy to analyze overloaded and underloaded areas. For example, the rods of the upper zone of the rear subframe take a very small load, given the proportion of their volume. The reverse situation is observed in the sidewall region: in this zone much lower load is accounted for by a much smaller volume of material. At the same time, the areas of the floor and the middle perceive a load share, consistent with its volume fraction, which can be considered the optimal indicator of load distribution by volume. In this connection, it is important to note that the presented diagrams of the distribution of medium stresses over zones of substructures can be used as a starting point for optimizing of existing or for developing of such structures “from scratch”. Calculation of the load applied to the substructure was carried out by summing the average stresses on the elements constituting the considered subconstruction. In addition, with the help of the appropriate coefficient, an estimate was made to the correspondence of the proportion of the volume of the zone of a particular subconstruction to the proportion of the load applied to it. This information can then be used to optimize the design or used as a starting point for the design of similar structures. All the presented calculations were performed in the SolidWorks software using the finite element method.

Application of local optical flow methods to high-velocity free-surface flows: Validation and application to stepped chutes

The entrainment of air on a high-velocity spillway leads to a rapid bulking in flow depth and developments of complex flow patterns downstream of the inception point of aeration. This study examines the feasibility of two local optical flow techniques – the Lucas-Kanade method and the Farneback method – applied to high-velocity air-water skimming flows above a stepped chute. Such methods are not widely known to the multiphase flow community. Experimental studies were undertaken in a relatively large-size stepped spillway model. Validation test cases were performed using a synchronised ultra-high-speed camera and phase-detection probe setup. The optical flow technique detected changes in brightness due to reflectance difference associated with passages of air-water interfaces. The standard deviation of luminance correlates with void fraction and bubble count rate, and may be used asa predictor for uncertainties in optical flow estimation. The streamwise optical flow properties were in close agreement with those determined by the phase-detection probe next to the sidewall, with increasing differences for void fraction greater than 50% (C>0.5). In the sidewall region, however the bubble count rate and interfacial velocity distributions were underestimated compared to the channel centreline's interfacial properties. The tests demonstrated that the optical flow methods can provide useful qualitative and quantitative information on complex air-water flow patterns.

Prediction of velocity-dip-position over entire cross section of open channel flows using entropy theory

An analytical model to predict the velocity-dip-position is presented in this study. Unlike the previous studies where empirical or semiempirical models were suggested, in this study the model is derived by using entropy theory. Using the principle of maximum entropy, the model for dip-position is derived by maximizing the Shannon entropy function after assuming dimensionless dip-position as a random variable. No estimation of empirical parameter is required for calculating dip-position from the proposed model. The model is capable of predicting the velocity-dip-position at any section from sidewall region (along lateral direction) of an open channel with any aspect ratio. The ratio of mean to maximum value of dip-position is analyzed from data, and it is found that ratio is almost constant for narrow open channels and it increases with aspect ratio for wide open channels. A relation is also proposed to predict this ratio in case of wide open channels. The developed model of velocity-dip-position is tested with existing experimental data for a wide range of aspect ratio and is also compared with other empirical models. The present model shows good agreement with the observed data and is comparable with the existing models.

Raman mapping of hexagonal hillocks in N-polar GaN grown on c-plane sapphire

A large amount of huge hexagonal hillocks were observed on the surface of N-polar GaN film grown on c-plane sapphire substrate by MOCVD. The distribution of residual stress and dislocation density in a typical hexagonal hillock was investigated by the mapping measurement of Micro-Raman and Cathodoluminescence (CL) spectroscopy. It is found that the residual stress at the top region of the hillock is much smaller than that of the sidewall region and the region around the hillock. Meanwhile, the CL images confirmed that the dislocation density around the hexagonal hillock is higher than the top region of the hillock. The bending and annihilation of the dislocations during the growth of the hexagonal hillock result in the relaxation of residual stress which should be responsible for the spatial variation of dislocation density and residual stress.

Effect of outer secondary-air vane angle on the flow and combustion characteristics and NOx formation of the swirl burner in a 300-MW low-volatile coal-fired boiler with deep air staging

Small-scale laboratory experiments of airflow through a single burner model and industrial-scale experiments on the centrally fuel-rich, low NOx swirl burner on a 300-MW wall-fired subcritical boiler burning low-volatile coal under deep air staging were performed. The aerodynamic characteristics, flue gas temperature, and gas concentrations were measured for various vane angles of outer secondary air in the burner nozzle region. The results show that a stable, symmetric central reverse-flow zone forms close to the exit of the burner nozzle region under deep air staging. With decreasing vane angle, i) the maximum axial, radial, and tangential velocities and swirl intensity of the airstream increase; ii) the decaying rate of velocity increases between X/D = 0 and X/D = 0.8; iii) the maximum diameter, length, and the jet divergence angle of the central reverse-flow zone increase; and iv) the relative reverse-flow rate increases. While the primary air concentration decreases slightly, the maximum primary air concentration decreases rapidly with decreasing vane angle. In contrast, the maximum axial relative mixing rate increases in the initial stage along the airstream direction. A decrease in vane angle increases the flue gas temperature, the rate of increase indicating a closer ignition position of the anthracite and lean coal along the airstream direction of the burner. The O2 consumption rate and NOx formation rate increase in the initial stage of combustion, whereas in the later stage the CO concentration increases notably and the O2 concentration remains almost constant below 1%. The CO concentration can exceed 20,000 ppm, which restrains the NOx formation and reduces the NOx concentration notably, but beyond X′ = 0.8 m, the NOx concentration remains almost constant. The flue gas temperature varies slightly for different vane angles in the side-wall region. The O2 concentration exceeds 4% near the location of the water-cooled wall. The O2 concentrations are below 2% and the CO concentrations are above 5000 ppm along the radial direction 1.8375 m ≤ R′≤2.3375 m from the centerline of the burner in the side-wall region. With decreasing vane angle, the CO concentration increases while the NOx concentration decreases.

Novel technique and simple approach for supra-alar region and supra-alar crease correction by supra-alar cinching.

This technical report describes a simple and innovative surgical technique for supra-alar sidewall region constriction and supra-alar crease attenuation by cinching technique through intraoral approach.

Experimental study on influence of boundary on location of maximum velocity in open channel flows

The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.

Formation of PtSi Schottky barrier MOSFETs using plasma etching

PtSi Schottky barrier (SB) MOSFETs were fabricated and their device performance was characterized. PtSi was selected instead of NiSi to form the p-type SB junction since such a configuration would be easy to fabricate through SF6 based plasma etching. The addition of He-O2 in SF6 decreases the etching rate of PtSi while the etching rate of Pt remains unchanged. The retardation in the etching rate of PtSi in He-O2/SF6 is attributed to the formation of a metal oxide on the etched PtSi surface, as evidenced by the x-ray photoelectron spectroscopy results. Optical emission spectroscopy was conducted to establish the endpoint where the wavelength from the feed gas was traced instead of tracing the etching by-products since the by-products have little association with the plasma reaction. The IDS–VDS curves at various VG–VTH indicate that plasma etching resulted in the successful removal of the Pt on the sidewall region, with negligible damage to the S/D area.

Suppression of the sidewall effect in pillar array columns with radially elongated pillars

An important bottleneck of pillar array columns designed for liquid chromatography is that small deviations of the target ‘magical distance’ at the sidewall region leads to detrimental sidewall effects, due to local differences of linear velocities at the sidewall region versus other locations in the pillar bed. In the present study, we demonstrate that a lateral elongation of the pillar significantly increases the tolerance for offsets of the magical distance. By shifting the sidewall distance 600nm for 2 pillar aspect ratio (AR) designs (AR=3 and 9), only minor sidewall effects on the measured plate heights could be observed for the AR=9 columns, while the plate height was roughly doubled when using the wrong versus the correct sidewall distance for the AR=3 columns. Technologically, this constitutes a huge advantage because small deviations (order of 100nm) between the set and the finally achieved value for the inter-pillar distance are very common using mid-UV lithography based etching processes.