High Injection Velocity Research Articles

Brinkman equation in reactive flow: Contribution of each term in carbonate acidification simulations

This article studies the individual contribution of each term in the Navier-Stokes-Darcy (Brinkman) equation to the fluid linear momentum balance and the consequences of opting for the Darcy or Brinkman equations in 3D reactive flow simulations of a vuggy carbonate. A two-scale continuum model was used to simulate the acidification of a carbonate sample using the Darcy and Brinkman equations. Rock heterogeneity is considered in the initial porosity and permeability fields, which are calculated directly from micro-CT images. Simulations showed that the Darcy equation predicts the acid breakthrough earlier in most cases. The convective acceleration term in the Brinkman equation plays an important role in describing the fluid momentum balance at high injection velocities, and this is a clear evidence against the use of the Darcy equation to model reactive flow in such conditions.

Impact of high mobility III‐V compound material of a short channel thin‐film SiGe double gate junctionless MOSFET as a source

AbstractIn recent years, technology has embraced the use of Junctionless Double Gate Metal‐Oxide‐Semiconductor Field‐Effect Transistors (JL DGMOSFET) to reduce Short Channel Effects (SCEs). This research presents a novel JL DGMOSFET based on a highly doped N‐type SiGe in which an III‐V compound material is used at source regime. The III‐V compound material GaSb with higher mobility and higher injection velocity is used as source material, whereas SiGe is considered for both channel and drain materials to produce a higher output current and low leakage current for the N channel JL DGMOSFET. In addition, high‐k dielectric material HfO2 is employed to improve the controllability of the gate at 20 nm channel length. Different parameters, such as Id, SS, gm, TGF, Ion/Ioff ratio, Cgs, and fT of a Symmetric JL DGMOSFET are studied and compared to existing works. The comparison shows that the proposed JL DGMOSFET outperforms the existing state of knowledge. The analysis is also being extended by including the trap charge for the symmetric JL DGMOSFET. Parametrically, the asymmetrical structure is finally studied. The proposed structure yields a higher Id of 40 mA, SS of 60.25 mV/decade, gm of 0.148 A/V, TGF of 3.69 V‐1, Ion/Ioff ratio of 3.41 × 1013, Cgs of 3.78 × 10−16 F and fT of 1.19 × 1013 Hz, hence indicating an improved RF and DC analysis.

Influence of flame stabilization and fuel injection modes on the flow and combustion characteristics of gas turbine combustor with cavity

The power-weight ratio is an important feature of a gas turbine used in transportation applications. However, while the ultra-compact combustion mode shows good application prospects, achieving high-efficiency and low-resistance combustion in an ultra-compact space at high air velocities remains a major challenge. A new ultra-compact combustion mode was proposed in this paper to further increase the configurable compactness with improvements to the flow and combustion characteristics. The relationships of the flow and combustion characteristics with the combustor configuration were numerically investigated in detail, and the calculation model was verified experimentally. This study focused on the configurable factors of the combustor components related to the major combustion zone, including the mainstream flame holder, the radial cavity, the fuel injector, and the diffusion channel. The results showed that rapid fuel-air blending and high-efficiency combustion were achieved under the condition of an ultra-compact space and a high air injection velocity. The adoption of a streamlined flame holder with a radial cavity and the integration of a simple fuel injector with a flame holder were very effective at simultaneously improving the configurable compactness and combustion characteristics without increasing the flow resistance, and these achievements are significant for improving the power-weight ratio of gas turbines.

New insights of foam flow dynamics in a high-complexity 2D micromodel

In this work, we present direct observation of foam flow through a 2D porous microfluidic device. Through a specially designed image processing workflow, we perform individual bubble tracking and establish flow dynamics within the micromodel structure. In addition to our experimental data, we provide 2D and 3D numerical Newtonian flow simulations on equivalent digitized versions of the model, carried out using Lattice Boltzmann simulation codes for comparison. The results show that foam flow in our experimental conditions, low gas fraction and high injection velocity, demonstrate a high degree of similarity to the flow of a Newtonian fluid in both 2D and 3D simulations, in aspects of large-scale flow distribution homogeneity and specific flow passage activation. However, the foam data shows a larger spread of pore-scale flow velocities, spanning from blocked off areas of quasi-zero flow, to zones of high velocity, with velocities well above the Newtonian counterparts. For our model depth and characteristics, the 2D simulation demonstrates slightly more flow heterogeneity and is closer to the foam case. Detailed bubble tracking gives access to other characteristics of the foam flow inside the medium such as the dichotomy between the flow patterns of the smallest bubbles, typically dispersing and accessing most regions available, and the largest bubbles, which travel in long straight preferential paths exclusively. We show that intrinsically tied to these different flow patterns is the relationship between bubble velocity and bubble size, as we demonstrate distinct populations of trapped and flowing bubbles with distinct sizes. Finally, we explore the relationships between microstructural parameters and flow intensity and note a weak correlation to local structural parameters. Our study, which combines high spatial and time resolution, small network dimensions, high network complexity and efficient bubble tracking, therefore sheds new light on the study of foam flow in porous media.

Modelling of multispecies reactive transport on pore-space images

We present a new model, named poreReact, to simulate multispecies reactive transport on pore space images. We solve the Navier–Stokes equations and the advection-diffusion equation for concentration on an unstructured grid using the finite volume method implemented in OpenFOAM. We couple it with the chemical model Reaktoro, which we use to calculate the chemical equilibrium of homogeneous reactions in each grid cell, considered as a completely mixed batch reactor. We validate the model against analytical solutions and experimental data, and investigate, for a range of Péclet numbers, the interplay between transport and reaction for multispecies reactive transport in a 3D bead pack where two streams of reactants at different pH are injected in parallel. We analyse the distribution of species and the rates of formation and consumption in the pore space and find that, despite the relative homogeneity of the bead pack and symmetry in injection conditions, the concentration fields of the products can be asymmetric because of the interplay between transport and chemical equilibrium. For different Péclet numbers, we calculate relative yields (the ratio between the observed change in concentration and the change that would be obtained if the reactants were completely mixed). We observe that lower Péclet numbers give rise to higher relative yields because of increased transverse mixing by diffusion. However, higher absolute yields are obtained at higher injection velocities because of the larger amount of matter available for reaction in a given time. Reaction is more favoured in the faster-flowing regions of the pore space. However, this effect is more marked for species for which advection is the dominant mechanism of transport to reactive sites, as opposed to diffusion-mediated reactions where the full velocity distribution is sampled before reaction occurs.

Calculation of Stall Margin Enhancement With Micro-Tip Injection in an Axial Compressor

Although steady micro-injection is experimentally validated as an attractive method in improving the stall margin of axial compressors, up to now a fast prediction of stall boundary remains some way off. This investigation is to propose such a prediction model. A flow stability model is developed to further consider the effect of high-speed micro-injection. After the base flow field is calculated by steady computational fluid dynamics simulation, a body force model is applied to reproduce the effect of blade on the flow turning and loss. A group of homogeneous equations are obtained based on linearized Navier–Stokes equations and harmonic decomposition of small flow disturbance. The stall onset point can be judged by the imaginary part of the resultant eigenvalue. After the existing experimental results are summarized, an unsteady numerical simulation reveals that the computed characteristics and radial profile of pressure rise coefficient are almost unchanged. The unsteady response of compressor to the micro-injection is preliminarily verified based on the observation of the disturbed spillage of tip leakage flow. It is verified that this approach can provide a qualitative assessment of stall point with acceptable computational cost. Both high injection velocity and short axial gap between injector and rotor leading edge are beneficial for the stall margin extension. These theoretical findings agree well with experimental measurements. It is inferred that the spillage of tip clearance flow, which is inward pushed by higher speed injection with shortened distance away from rotor, could lead to further stable flow field.

Direct numerical simulation of primary breakup for power-law biodiesel sprays

Abstract Biodiesel is a very promising alternative fuel in internal combustion engines. Fragmentation of the fuel injection has a fundamental influence on engine performance. The influence factors for the spray breakup process, including near nozzle fields, are still unclear. In this study, the primary of fuel sprays occurring with turbulence perturbation is devoted to simulation. The evolutionary processes of biodiesel fuels atomization affected by turbulence are investigated in present models. A validated single-phase fully developed turbulent flow is generated first to store time-varying outlet velocity database. Then, the database is mapped as the two-phase model inlet velocities boundary. A modified VOF (Volume of Fluid) coupled with DNS (direct numerical simulation) method is applied to study the evolution of fuel spray. It is found that wavy surface, ligaments, and droplets with various scales and shapes turn up gradually in jet evolution process. Meanwhile, after being sheared, distorted and stretched, different ligaments separation patterns are captured. Larger Reynolds number and higher gas densities accelerate the jet break-up process. Higher injection velocities and lower power-law indexes (n 1) fuel jet. What’s more, similar breakup patterns are detected in shear-thinning fluid (n

Research on Coatings and Infiltration to Strengthen Ceramic Lost Cores Used in High-Pressure Die Casting Processes

Lost cores used to manufacture complex aluminium components through high-pressure die casting (HPDC) processes need to withstand very high injection velocities and pressures. The conventional sand cores used in other casting processes, such as sand casting or low-pressure die casting, do not support the aggressive process parameters of the HPDC, so advanced ceramic cores must be used. These cores must be strong enough not to get broken during the casting process, but, at the same time, they must have a minimum porosity to be easily removed from the casting to obtain the finished part. Due to this porosity, the aluminium penetrates the core surface during the casting process. So, the criterion here is to find the necessary compromise between strength and porosity and to protect the core surface from the aluminium penetration. In this work, two research lines have been followed to address these challenges. On the one hand, different refractory coatings have been applied to the ceramic core surface with the aim of sealing it. Amongst the coatings analysed, boron nitride-based one has been found to be the most suitable and cost-effective solution to avoid aluminium penetration. On the other hand, silica has been proved to be a suitable infiltration agent to increase the strength of the core.

Electrical Properties of Vertical InAs/InGaAs Heterostructure MOSFETs

Vertical InAs/InGaAs nanowire MOSFETs are fabricated in a gate-last fabrication process, which allows gate-lengths down to 25 nm and accurate gate-alignment. These devices demonstrate high performance with transconductance of 2.4 mS/μm, high on-current, and off-current below 1 nA/μm. An in-depth analysis of the heterostructure MOSFETs are obtained by systematically varying the gate-length and gate location. Further analysis is done by using virtual source modeling. The injection velocities and transistor metrics are correlated with a quasi-ballistic 1-D MOSFET model. Based on our analysis, the observed performance improvements are related to the optimized gate-length, high injection velocity due to asymmetric scattering, and low access resistance.

Solvent diffusion and dispersion in partially saturated porous media: An experimental and numerical pore-level study

Recent research on unlocking the solvent dispersion as a physical blending process in porous media has been mainly focused on core-scale observations. Pore-level studies of multiphase displacements can help to develop models that correlate rock macro-scale characteristics with its small-scale features, particularly for unsaturated rocks where the intricate fluid arrangements cause dynamic events to be localized in preferential pathways. In this work, to draw new insights into the physics of pore-level interfaces and crystallize the role of small-scale phenomena on the efficiency of solvent-aided bitumen recovery processes, numerical simulations coupled with experiments are conducted in pore-level domains. We simulate fluid flow and transport phenomena through millimeter-sized three-dimensional slabs of consolidated and unconsolidated packings of grains representing the geological rock types of the McMurray formation. We propose a robust numerical workflow for simulation of miscible-floods in unsaturated porous media and investigate the impact of matrix heterogeneity, connate water, cementation, and injection velocity on the longitudinal dispersion coefficient. In particular, primary drainage is simulated at low capillary numbers resulting in two-phase fluid occupancies through pore space domains. Finite element simulations are then carried out in order to solve the mixing advection-diffusion equations within the water-free pore space, and lastly, the effluent history is analyzed to predict the dispersion coefficient in both fully- and partially-saturated conditions and evaluate the efficiency of miscible displacements in the presence of microheterogeneities. A new analytical model for calculation of dispersivity, together with the numerical simulation results, is utilized to adjust a general model for the prediction of longitudinal dispersion coefficient in unsaturated sandy porous media of either uniform or non-uniform grains. Moreover, miscible-flood experiments at low to high injection velocities are conducted in a transparent glass micromodel. According to the results, rock micro-heterogeneities and immobile water both increase the longitudinal dispersion coefficient, and two-phase equilibria control the velocity field by creating connected regions of brine and low resistance oil-filled channels and consequently influence the solute transport and mixing processes. The effect of viscosity contrast on the longitudinal dispersion coefficient is also noteworthy, as the viscous fingering at unfavorable viscosity ratios widens the mixing zone.

بررسی تحلیلی تاثیر ضرایب پراکندگی و هدایت حرارتی شکاف در مخازن زمین گرمایی شکاف دار

Renewable energy is defined as sort of energy whose producing resources possess the capability to renew through nature during a short period of time. The analytical model of water injection into geothermal reservoirs process which is used to describe more complex matters, can explain the heat transfer processes in the porous media better. The presented corresponding studies so far are based on numerical and semi-analytical methods while here, a fully exact analytical solution is introduced considering phenomena of convection, conduction and dispersion inside fractures, conduction inside matrix blocks, and matrix-fracture heat transfer. In this regard, geothermal fractured reservoir related heat transfer equations are solved, ignoring fracture dispersion and heat conduction phenomena, which appears to be an appropriate assumption in high injection velocity values and then the effects of injection water velocity and distance from injection well parameters on the amount of error percent of these two models are investigated. Moreover, thermal recovery efficiency is employed to investigate cold water flooding into such reservoirs followed by a comparison to a numerical model for the purpose of validation.

Mitigation of source term in suppression pools: Large uncertainties in predictability

The Fukushima accident has revived the interest of suppression pools as a passive way to scrub radioactivity from the gas reaching the aqueous volume in case of a severe accident. However, modeling of pool scrubbing is far from being mature. This paper focuses on the scrubbing occurring at the nearby of the injection point and, by illustrating how far from observations prediction can be, it highlights the importance of developing proper models at this region of the pool. To do so, a specific simple ASTEC model has been set-up and a jet scrubbing database has been gathered from the open pool scrubbing literature by picking suitable tests in which all the key initial and boundary conditions were recorded and reported. In particular, low-submergence experiments with high injection velocity experiments have been chosen to address what is known as jet scrubbing (i.e., scrubbing at the inlet region when particles are carried in the pool by a gas submerged jet).

Investigation on jet scrubbing in nuclear reactor accidents: From experimental data to an empirical correlation

The Fukushima accident stressed the significance of suppression pools as passive systems for fission product trapping. Even though pool scrubbing was extensively investigated in the past, there are gaps in the existing data base and modeling that need to be addressed, particularly those relative to high gas injection velocities in the pool. In this paper, the main results of an experimental campaign (PSP tests) on particles scrubbing at the pool inlet region when the carrier gas forms a submerged jet (“jet scrubbing”), are presented and discussed. The tests have been conducted in the PECA-PS facility of the Laboratory for Analysis of Safety Systems (LASS) and the experimental conditions have been based on two non-dimensional variables: the Weber non-dimensional number, which has been set to values over the threshold from globule to jet regime; and the gas saturation ratio, which has ranged from under saturation to over-saturation. Jet scrubbing efficiency at the pool inlet has been measured to be over 90% whenever the gas enters the pool within the jet regime (Wetest ≥ Wec), regardless thermal boundary conditions. Analysis of gas steam content, though, has not shown any clear trend. Based on the PSP experiments and some others gathered from the open literature, a tentative correlation dependent on non-dimensional Stokes number (Stk), which accounts for inertial impaction, and saturation ratio (S), which captures diffusiophoretic deposition, has been proposed as a first step to empirically model jet scrubbing. Finally, some lessons learned for forthcoming experiments have been withdrawn, particularly concerning the high impact of hydrodynamics.This work has been done within the framework of the 7th FWP of EURATOM through the EU-PASSAM project (Grant agreement No. 323217 – Euratom 7FP).

Effect of injection velocity on the structure and mechanical properties of micro injection molded polycarbonate/poly(ethylene terephthalate) blends

A method of investigating the relationship between morphological evolution and mechanical properties of blends prepared by Micro injection moulding through regulating the process conditions was presented in this paper. The microstructure and microscopic mechanical properties of polycarbonate/poly (ethylene terephthalate) (PC/PET) microparts prepared by micro injection moulding were investigated with respect to the effects of the injection velocity. The PC/PET microparts exhibited typical “skin–core” morphology. Thickness of the skin layer is greater than that of the core layer near the gate of micropart. With an increase in the injection velocity, the core layer became thicker. It was detected that the PET microdomains were selectively located in the core layer in preference to the shear layer with high injection velocity. In addition, the degree of orientation for main chain and pendant group in the PC/PET molecular chains increased first and then decreased with an increase in the injection velocity. Nanoindentation testing showed that the modulus decreased along the flow direction and increased with an increase in the injection velocity, except at very high values. Among the different layers, the highly oriented shear layer had the highest indentation modulus.

Oxy-fuel combustion of methane in a swirl tubular flame burner under various oxygen contents: Operation limits and combustion instability

Oxy-fuel combustion of methane was conducted in a rapidly mixed tubular flame burner, as oxygen content (mole fraction) was varied from 0.25 to 1.0. The fuel and oxidizer were injected from individual slits, and the slit widths were varied to promote mixing. Temporal variation of flame structure and acoustic pressure fluctuations were simultaneously measured by using a high speed video camera and a microphone respectively to examine unsteady combustion. Detailed results show that when the oxygen mole fraction was below 0.5, a steady flame can be established in a wide range from lean to rich; above 0.6, combustion-driven oscillation occurred by increasing the equivalence ratio to around 1.0. By reducing fuel slit width to half of the oxidizer slit and assigning CO2 to both fuel and oxidizer slits to maintain the same, high injection velocities, steady tubular combustion range was much expanded. However, when the oxygen mole fraction exceeded 0.7, steady combustion evolved into periodic oscillations by gradually increasing equivalence ratio; around stoichiometry the flame became steady, and thereafter evolved into unsteady state in the rich condition. Based on pressure fluctuation measurements and frequency spectral analyses, high frequency (around 2000Hz) combustion-driven oscillation was observed. This study shed lights on the operation limits of steady oxy-methane tubular combustion under various oxygen contents. For combustion under ultrahigh oxygen contents (0.7–1.0), the inlet width should be much thinner, and the fuel and oxidizer streams be maintained at the same, high injection velocities to achieve steady tubular flame around the stoichiometry.

Influence of solids outlets and the gas inlet design on the generation of a gas-solids rotating fluidized bed in a vortex chamber for different types of particles

Two design aspects of vortex chambers for the generation of gas-solids rotating fluidized beds are experimentally studied for different types of particles: the solids outlet(s) and the gas inlets. Efficient solids retention and minimal solids losses via the chimney are aimed at so that the gas and solids residence times can be controlled independently. The importance of a strong vortex in the central particle bed freeboard region is demonstrated. It is shown that separate, well-dimensioned and -positioned solids outlets prevent a significant presence of particles in the freeboard region, increasing the vortex strength in this region. This is found to be particularly important when fluidizing small/light particles. The ratio centrifugal force-to-radial gas-solid drag force that is generated by the gas injection is shown to also have an important impact. Theoretically it is shown that this ratio strongly depends on the particle characteristics and to what extent it can be increased by increasing the gas injection velocity, preferentially by reducing the gas inlet slot size and otherwise the number of gas inlet slots. Experiments with different vortex chambers and particles qualitatively confirm the theoretical expectations, but show that limitations are encountered. A very high gas injection velocity prevents efficient penetration of especially fine/light particles in the gas inlet jets which is detrimental for the transfer of tangential momentum between the gas and the particle bed. Slots smaller than the particle size are also shown to be inefficient, as they generate rotational motion of the particles around their own center of gravity.

Effect of water entrainment on the coolability of a debris bed surrounded by a by-pass: Integral reflood experiments and modelling

To assess the severe accident management strategy, the question of debris coolability has to be resolved. In this framework, large scale debris bed reflood tests have been performed in the PEARL facility. The debris bed, 500mm in height and 450mm in diameter, was made of 4mm stainless steel balls surrounded by a 45mm-thick bypass filled with 8mm quartz balls. Bottom-reflood tests have been successfully conducted under pressure (1–2–3–5bar) with different water injection velocities (2–5–10m/h) and initial temperatures (150–400–700°C). For each tests, the bed has been cooled down and the quench front progression was mainly axial from the bottom to the top and homogeneous in most of the experimental bed. The experimental results show that the reflood time tends to a lower limit when the water injection velocity or the pressure is increased. To interpret this result, an analytical model has been developed. It shows that, for high injection velocities (>5m/h) or low pressure (<2bar), water can flow faster in the bypass: this phenomenon limits the reflood efficiency as some of the injected water is not used for bed cooling. Calculations have been made with the severe accident code ICARE-CATHARE V2 as a complement to the interpretation of experimental data. The calculated steam and water velocity fields confirm the experimental observations and the analytical model interpretation, showing the entrainment of water in the bypass under some conditions.

Lower pressure heating steam is practical for the distributed dry dilute sulfuric acid pretreatment

Most studies paid more attention to the pretreatment temperature and the resulted pretreatment efficiency, while ignored the heating media and their scalability to an industry scale. This study aimed to use a relative low pressure heating steam easily provided by steam boiler to meet the requirement of distributed dry dilute acid pretreatment. The results showed that the physical properties of the pretreated corn stover were maintained stable using the steam pressure varying from 1.5, 1.7, 1.9 to 2.1MPa. Enzymatic hydrolysis and high solids loading simultaneous saccharification and fermentation (SSF) results were also satisfying. CFD simulation indicated that the high injection velocity of the low pressure steam resulted in a high steam holdup and made the mixing time of steam and solid corn stover during pretreatment much shorter in comparison with the higher pressure steam. This study provides a design basis for the boiler requirement in distributed pretreatment concept.

Numerical Study on the Effect of Lambda Value (Oxygen/Fuel Ratio) on Temperature Distribution and Efficiency of a Flameless Oxyfuel Combustion System

The flameless oxyfuel combustion technology has been proven to be a promising new method to reduce the fuel consumption and pollutants in industrial applications [...]

A New Direction for III–V FETs for Mobile CPU Operation Including Burst-Mode: In0.35Ga0.65As Channel

In this letter, we show that conventional III–V MOSFETs with moderate/high In content channels (In0.53Ga0.47As or In0.70Ga0.30As) at scaled nodes are incompatible with mobile SoC designs, which often operate at intermediate/high ${V_{{\mathrm {dd}}}}$ (0.7 V to $\geq 1$ V) to achieve high frequency including during burst-mode. The incompatibility is due to conventional III–V FETs having too small bandgap, and thus too high leakage when operated at the increased voltages. We show that FETs with a more optimal lower In content, In0.35Ga0.65As, have the necessary combination of larger bandgap (~Si) and sufficiently high injection velocity (~2.5 times Si) to enable both low leakage and high performance (versus Si), across the entire ${V_{{\mathrm {dd}}}}$ range of mobile SoC operation. We report for the first time the growth and characterization of ultra-thin In0.35Ga0.65As FETs with a standard 1nm EOT gate dielectric. Calibrated models show that In0.35Ga0.65As enables the highest performance at very low leakages at intermediate/high ${V_{{\mathrm {dd}}}}$ in short channel FETs.