Mixing Velocity Research Articles

Fast Numerical Optimization of Electrode Geometry in a Two-Electrode Electric Resistance Furnace Using a Surrogate Criterion Derived Exclusively from an Electromagnetic Submodel

The Joule heat generated by current flow between electrodes in a resistance furnace not only melts and heats the charge but also induces mixing of the molten material. Increased mixing promotes improved chemical and temperature uniformity within the bath. This paper presents a novel approach to effectively optimizing electrode geometry in resistance furnaces. The method relies on a surrogate criterion derived exclusively from an electromagnetic submodel, which governs the process hydrodynamics. This criterion is based on the location of the Joule heat generation center in the bath. Its idea is to lower this center as much as possible while keeping it close to the vertical bath axis. Owing to this, the best conditions for the development of natural convection were obtained. The developed methodology was demonstrated through an application to a two-electrode furnace. The results showed that the influence of forced MHD convection is negligible in this furnace (with a Lorentz force of only about 0.0015 N/kg). The validation of the optimized geometry, derived using solely the electromagnetic submodel, was carried out using a full process model, including time-consuming hydrodynamic calculations. The proposed optimization methodology enabled a 10-fold increase in the average mixing velocity (from 0.0008 to 0.0084 m/s). The main significance of the presented study is the introduction of a surrogate criterion that allows for a multiple reduction in the time of numerical optimization of the mixing intensity in electrode resistance furnaces in comparison to the standard solution based on the flow velocity criterion determined from the hydrodynamic model.

Systematic analysis of mixing and segregation patterns of binary mixtures in fluidised beds for multi-functional processes

Fluidized beds are increasingly used in renewable energy and chemical production due to their versatility in handling different solids for multi-functional industrial applications. The diversity in size and density of solid particles impacts fluidization, influencing mixing and segregation behaviours critical for optimizing chemical processes and reactor design. This study investigates the expansion and segregation behaviours of mixed Geldart group powders in binary systems, simulating polydispersed beds with different materials and catalysts. By applying a modified Cheung equation and an adapted Gibilaro-Rowe model, the study analyzes segregation behaviours of Geldart Group A and B materials at varying mixing rates and gas flow velocities. Results show a good match between experimental data and model predictions. Using novel non-invasive X-ray imaging, the study provides real-time analysis of mixing and segregation at different fluidization regimes and temperatures. These findings aid in designing and optimizing advanced thermochemical conversion technologies, enhancing process efficiency and resilience.

Supercritical Carbon Dioxide Mixing Loss Characteristics Near the Critical Point

Abstract This paper aims to study the mixing loss characteristic of sCO2 near the critical point and shed light on the non-ideal fluid effect on the mixing losses. As a simplified model of the mixing process in the trailing edge or tip leakage flow in turbomachines, a case of mixing in a constant area adiabatic duct involving two streams of parallel flows is studied by control volume analysis. Both perfect gas and non-ideal fluid calculations are carried out for comparisons. The isolated and coupled effects of the two mixing streams' temperature, velocity, and pressure differences on the loss are investigated. The study shows that non-ideal fluid mixing produces significantly higher losses when compared to the equivalent perfect gas estimation. It also reveals that the non-ideal fluid mixing loss is sensitive to the average thermodynamic states of the mixing streams. A significant variation of the mixing loss coefficient is reported if the static state of any of the two streams is near the critical point, which is mainly caused by the significant variation of the temperature gradient regarding the entropy along the isobar. The results also show that the change in the mixing loss due to the variation of one property difference between mixing streams is almost independent of the other property difference. The results from this simple case contribute to understanding the mixing loss behaviour differences between perfect gas and non-ideal fluids in sCO2 turbomachinery and hold significance for the development of mean-line models.

Approximation of acoustic black holes with finite element mixed formulations and artificial neural network correction terms

Wave propagation in elastodynamic problems in solids often requires fine computational meshes. In this work we propose to combine stabilized finite element methods (FEM) with an artificial neural network (ANN) correction term to solve such problems on coarse meshes. Irreducible and mixed velocity–stress formulations for the linear elasticity problem in the frequency domain are first presented and discretized using a variational multiscale FEM. A non-linear ANN correction term is then designed to be added to the FEM algebraic matrix system and produce accurate solutions when solving elastodynamics on coarse meshes. As a case study we consider acoustic black holes (ABHs) on structural elements with high aspect ratios such as beams and plates. ABHs are traps for flexural waves based on reducing the structural thickness according to a power-law profile at the end of a beam, or within a two-dimensional circular indentation in a plate. For the ABH to function properly, the thickness at the termination/center must be very small, which demands very fine computational meshes. The proposed strategy combining the stabilized FEM with the ANN correction allows us to accurately simulate the response of ABHs on coarse meshes for values of the ABH order and residual thickness outside the training test, as well as for different excitation frequencies.

Computational fluid dynamics study on first reaction chamber of internal circulation anaerobic reactor

This study aims to investigate the characteristics of gas–liquid-solid three-phase flow in an Internal Circulation (IC) anaerobic reactor during the treatment of wastewater. Through computational fluid dynamics (CFD) simulations of the gas–liquid-solid three-phase in the first reaction chamber and based on the anaerobic granule swarms drag coefficient model, the study investigates the effects of superficial liquid velocity and superficial gas velocity on granules distribution, uniformity index, gas holdup, flow velocities of each phase, and the dimensionless variance of residence time distribution. In addition, the relationship between the fully mixed superficial velocities of gas and liquid in the first reaction chamber is also determined.

Investigating the convective flow of ternary hybrid nanofluids and single nanofluids around a stretched cylinder: Parameter analysis and performance enhancement

Within this research, we examined the convective flow of a blend of ternary hybrid nanofluids and single nanofluids with a stagnation point caused by a stretched cylinder. The purpose of this study is to investigate the effect of using a ternary hybrid nanofluid instead of a single nanofluid. Water is used as the base fluid in this investigation. The single nanofluid is made of copper and the ternary hybrid nanofluid is made of Molybdenum disulfide, copper, and silver. The impact of the curvature parameter, nanoparticle volume fraction, mixed convection parameter, velocity ratio, shape factor, conjugate number and Eckert number parameters on temperature and velocity profiles has been investigated. Differential equations with partial derivatives were transformed to equations of ordinary differential type. The ODEs were then solved using the RK5th method. The ternary hybrid nanofluid has greater advantages than the single nanofluid and enhances the velocity and temperature compared to the single nanofluid, according to this study. Furthermore, the results showed that when curvature parameter, volume fraction and shape factor improved, so did the velocity and temperature profile. The results showed that moving from a single nanofluid to a ternary hybrid nanofluid at shape factor equal to 16.2 (Lamina) boosts the velocity by 20 %. Also, in Eckert number equal to 0.45, and substituting the ternary hybrid nanofluid boosts the temperature tenfold.

A total three-dimensional evaluation method to analyze the loss mechanism of film cooling on turbine guide vane

In view of the situation that the secondary flow in the passage deflects the coolant from film cooling holes and changes heat transfer, a total three-dimensional evaluation method is developed based on the HS1A high-pressure turbine guide vane to take a new insight into the loss mechanism. Film cooling holes are placed on the suction surface with compound angles to obtain different blade models. After satisfying the requirement of film cooling effectiveness, TTDM, a new total three-dimensional evaluation method where both mainstream and coolant are treated in three dimensions is established. Then, loss mechanism is analyzed by controlling the temperature ratio, changing the exit Mach number and blowing ratio. The entropy creation due to mixing is used as the evaluation basis to analyze different models within the high film cooling effectiveness range. It is believed that the mixing temperature and velocity need to be elaborated and distinguished in high subsonic environments. Compared with the original model within a certain range, the increase of the film cooling effectiveness can be found under the application of different compound angles in a short distance on suction surface. A slight increase of entropy is also noticed. By lessen the loss of secondary flow within a certain range of blowing ratio and exit Mach number conditions, the total loss can be reduced with reasonable setting of compound angle. Finally, the loss with film cooling is evaluated more accurately by the total three-dimensional evaluation method considering the effects of secondary flow.

Numerical simulation study on hydrogen ammonia mixed combustion in a swirl combustion chamber

Abstract The NO x emissions and combustion performance of pure ammonia and hydrogen-doped combustion (90% NH3 volume fraction and 10% H2 volume fraction) in the cyclone combustion chamber were comprehensively analyzed through numerical simulations under varying thermal operating conditions. The findings reveal that the flame characteristic length in hydrogen-doped combustion surpasses that in pure ammonia combustion, indicating an extended migration of the high-temperature zone after hydrogen doping. Furthermore, the addition of hydrogen results in an elevated exhaust temperature within the combustion chamber, while the Outlet Temperature Distribution Function (OTDF) decreases, signifies an enhancement in the uniformity of temperature distribution at the outlet. Moreover, the reflux zone experiences less impact, and the mixed gas velocity increases following hydrogen doping. Notably, NO x emissions demonstrate a significant decrease after the addition of hydrogen. The average NO emission concentration in pure ammonia combustion, under various operating conditions, is measured at 212.47 mg/m3, representing a 3.51-fold increase compared to hydrogen-doped combustion.

Study on the Flow Characteristics of Heavy Oil-Water Two-Phase Flow in the Horizontal Pipeline.

Aiming at the problem of transportation for heavy oil during the middle-later development stages of the Lvda oilfield, based on the self-developed design of a visual circulating flow experimental apparatus for heavy oil-water two-phase flow-the flow regime characteristics and corresponding drag properties of the two-phase flow of Lvda viscous oil, which is simulated by 500# industrial white oil and water in a horizontal pipeline are investigated experimentally. According to the Kelvin-Helmholtz instability theory, the flow pattern transition criteria from stratified flow to annular flow (AF) are proposed. The effects of 0.11-0.90 m/s oil superficial velocities, 0.06-1.49 m/s water superficial velocities, and 0.09-0.93 input water cuts on the drag reduction effect of different flow regimes are analyzed. The experimental results indicated that with the increase of mixing velocity and water volume fraction, stratified flow, AF, oil plug flow, and dispersed oil lump flow are successively observed in the horizontal heavy oil-water two-phase flow, in which AF is the main flow pattern. As the Froude number increases to 4.0, the input water volume fraction does not change any more and remains at about 10% of the total flow rate in the process of converting from stratified flow to AF. The four delivery approaches can archive the reduction of transportation resistance for heavy oil at different degrees, in which the transportation of heavy oil surrounded by a water ring has the best effect of drag reduction. At the optimal working conditions of 0.61 m/s oil superficial velocity, 0.07 m/s water superficial velocity, and 0.10 input water cut, the pressure drop of water annulus conveying for heavy oil is only 1/62.54 of that of separate transport for pure heavy oil under the same oil flow rate.

Mixing performance of cohesive particles in a double barrel with differential velocity based on DEM

The double barrel with differential velocity (DBDV) was proposed to improve the mixture quality. However, the mixing mechanism of cohesive particles in the DBDV is unclear. So, the mixing performance of cohesive particles in the DBDV was studied. The cohesive force between particles was simulated using a viscous contact model. The effects of linear velocity, inclination and cohesive force on the mixing performance were studied. The mixing process of particles was analyzed through mixing uniformity, mixing time, velocity, and contact forces. The results show that excessive cohesion cannot promote the dispersion of particles in the mixture, affecting production efficiency. The motion intensity of particles in the differential region is stronger than that in the non-differential region. The differential zone is suitable for particle motion with high cohesion. This study reveals the detailed mixing behavior of cohesive particles in DBDV, which provides operational guidance for the actual road material mixing process.

Reduced-Order Model for Supersonic Transport Takeoff Noise Scaling with Cruise Mach Number

The recent interest in the development of supersonic transport raises concerns about an increase in community noise around airports. As noise certification standards for supersonic transport other than Concorde have not yet been developed by the International Civil Aviation Organization, there is a need for a physics-based scaling rule for supersonic transport takeoff noise performance. Assuming supersonic transport takeoff noise levels are dominated by the engine mixed jet velocity and the aircraft-to-microphone propagation distance, this paper presents a reduced-order model for supersonic transport takeoff noise levels as a function of four scaling groups: cruise Mach number, takeoff aerodynamic efficiency, takeoff speed, and number of installed engines. This paper finds that, as cruise Mach number increases, supersonic transport takeoff noise levels increase while their thrust cutback noise reduction potential decreases. Assuming constant aerodynamic efficiency, takeoff speed, and number of installed engines, the takeoff noise levels and noise reduction potential of a Mach 2.2 aircraft are found to be ∼15.3 dB higher and ∼19.2 dB less compared to a Mach 1.4 aircraft, respectively. This scaling rule can potentially yield a simple guideline for estimating an approximate noise limit for supersonic transport, depending on their cruise Mach number.

Measurement of steam dryness using one-dimensional acoustic waves in pipelines

Heavy oil, extra-heavy oil and bitumen exceed 6 trillion barrels, roughly three times the world total Conventional oil and gas reserves. Thermal-chemical flooding (TCF) is an effective alternative to enhance heavy oil recovery after steam injection. In the steam injection and extraction process of oil, the accurate measurement of water steam dryness can provide a strong guarantee for the efficient exploitation of oil fields. The traditional steam dryness measurement device is affected by the steam flow state, and the error generated will affect the enthalpy calculation of the injected steam, which affects the judgment of energy efficiency of oil well injection in the field. Firstly, this paper proposes a mathematical model for calculating water steam dryness using mixed sound velocity and operating temperature, which is based on the mathematical relationship between water steam dryness and gaseous volume fraction, combined with Wood's formula and the density and sound velocity calculation formula for each region in the IAPWS-IF97 model to derive the monotonic correspondence function of sound velocity and dryness. Secondly, the one-dimensional acoustic wave model of the pipeline is applied to establish a set of sound velocity equations for the frequency-domain data of the array sensors, and the traversal iteration method is used to solve the mixed sound velocity of water steam. Finally, the dryness of steam injection under the operating condition of 270°C∼290°C at the wellhead was measured in the experimental area H33 in Xinfanguan of Liaohe Oilfield, and compared with the standard dryness value, the relative error of the experiment was -3.33% and the repeatability was 1.24%, the accuracy met the requirements of energy efficiency calculation, which verified the feasibility of the sound velocity method to measure the dryness of water steam. Therefore, it is of great engineering guiding significance to utilize sound velocity method to realize the measurement of dryness in the thick oil steam injection process.

Oil-Water Two-Phase Flow with Three Different Crude Oils: Flow Structure, Droplet Size and Viscosity

The study focuses on the flow patterns and pressure drop characteristics of three crude oils and water in a horizontal pipe. The experimental results showed that the transformation boundary of the flow pattern and phase inversion water fraction were related to the flow parameters. Comparing the three oils, it was found that the viscosity and composition of the oil also significantly influence the flow performance, which can be explained by the adsorption properties of the asphaltenes at the oil-water interface. In particular, the droplet size in water-in-oil dispersion flow was observed and measured. It showed that the water droplet size decreased with the increase of oil viscosity, the decrease of water content, the drop of temperature, and the growth of mixing velocity, probably due to higher shear stress and lower frequency of collision and coalescence between droplets. The apparent viscosity of water-in-oil emulsions was calculated by the rheological model, and the qualitative relation between flow parameters and interfacial area concentration on apparent viscosity was obtained. Taking the influence of interfacial area concentration into consideration, a simple and accurate viscosity model was established based on dimensional analysis, which is of great significance for process design in gathering and transportation systems.

A visualization study on characteristics of severe slugging in the S-shaped riser with a kilometer-scale pipeline

Severe slugging is a hazardous multiphase flow phenomenon in the process of offshore oil and gas transportation. Few visualization image data are obtained in experimental riser systems with kilometer-scale pipelines. Therefore, the interface distribution characteristics of severe slugging are visually investigated in a 29.1 m high S-shaped riser connecting a 1657 m long horizontal pipeline. Based on the image data of the gas–liquid interface structure and the pressure fluctuation of the riser, the flow pattern map is plotted. The high riser increases the accumulation space of severe slugging and prolongs the cycle period. A new prediction correlation of the slugging period suitable for experimental systems with different pipeline lengths is proposed. The long pipeline provides sufficient gas compression space and intensifies the blowouts of liquid slugs. The maximum velocity of the slug blowout in the riser reaches 23 times the gas–liquid mixed velocity. The gas expands sharply during the gas blowdown stage of severe slugging, which causes the instability of the gas–liquid interface in the horizontal pipeline and induces a large number of liquid slugs to flow into the riser; thus, the continuity blowdown of slugs appears in the riser.

Flow pattern evolution and flow-induced vibration response in multiphase flow within an M-shaped subsea jumper

The subsea jumper, a crucial pipeline connector facilitating liquid transport between underwater structures, experiences dynamic alterations in flow direction, rate, and phase volumes owing to its distinctive design. These complex flow characteristics can trigger flow-induced vibrations, potentially causing fatigue damage to the jumper. This paper explores the multiphase flow patterns (oil, gas, and water) in a rigid M-shaped subsea jumper under varied mixing velocities (2–4 m/s) and different volume fractions of each phase (0.1–0.7). It analyzes the factors influencing structural vibration response. The findings reveal diverse flow patterns within the jumper, each exhibiting distinct characteristics based on flow parameters. Concurrently, spatiotemporal oscillations from fluid dynamics impact each bend. Pressure on jumper walls gradually diminishes with changing flow direction. Furthermore, the study performs structural modal and frequency domain analyses of pulsating pressure to evaluate potential resonance conditions. The results of this paper contribute to a deeper understanding of the multiphase flow characteristics in jumpers, offering valuable insights to enhance the reliability of underwater oil and gas production.

Study on mixing performance of atmospheric entrained flow gasification burner using fine ash as feedstock

A burner structure suitable for atmospheric entrained-flow gasifiers using fine ash as feedstock was proposed. The study investigates the impact of the burner structure on the mixing characteristics through 0.75:1 (geometry reduction) single-phase airflow experiments. Additionally, numerical simulations were conducted to study of the gasification process of fine ash in a 10,000 Nm3/h atmospheric entrained flow gasifier. The results indicate that a larger residual temperature near the burner outlet was observed when the diameter of the burner's gasification agents channel was 10 mm or 15 mm, approximately 0.7–0.8. Additionally, the mixing degree of the two airflows at the burner outlet was high, and the distance required for complete mixing was short. When the diameter of the gasification agent channel was 15 mm, the mixed syngas flow velocity was appropriate. This resulted in a maximum temperature of 2500 °C, an 80 % carbon conversion rate, and an outlet effective syngas (CO + H2) concentration of 62 %.

Entropy analysis of double diffusion in a Darcy medium with tangent hyperbolic fluid and slip factors over a stretching sheet: Role of viscous dissipation

This study aims to numerically investigate entropy optimization for a time-independent tangent hyperbolic fluid flowing past a porous sheet that is stretching linearly. The fluid motion is generated by stretching surfaces and buoyancy forces. The analysis includes momentum, energy, and mass transport associated with mixed convection, thermal radiation, velocity, thermal, and concentration slip factors. Heat dissipation is also considered in energy transport through the viscous dissipation effect. The mathematical formulation leads to a set of non-linearly coupled partial differential equations. To obtain a similarity solution, similarity variables are introduced. The numerical solution of the leading differential equations is obtained using the fourth-order Runge-Kutta method with the shooting technique. The graphical results are presented to show the physical significance of the relevant parameters. The main objective of entropy optimization is achieved by increasing the magnitude of the Darcy dissipation parameter. Entropy generation is directly proportional to the Brinkmann number, Reynolds number, and radiation parameter. The second law of thermodynamics is fulfilled by introducing slip conditions over the porous medium. The use of a tangent hyperbolic fluid over a porous medium has practical applications in various porous geometries, such as oil/gas reservoir simulation, enhanced oil recovery, carbon dioxide sequestration, and water soil infiltration. Therefore, optimizing entropy generation in these mechanical systems is crucial.

Effect of flow patterns and velocity field on oil-water two-phase flow rate in horizontal wells

In a wellbore, any change in flow rate will result in a change in flow pattern and velocity. The flow pattern and velocity are the key parameters that determine the pressure gradient and liquid holdup. To study the effect of the flow pattern and velocity field on the flow rate of oil-water flow in horizontal wells, we apply the commercial software package ANSYS Fluent 2020 R2 to predict the flow patterns, water holdups, pressure gradients, flow rates, and velocity fields of horizontal wells. Trallero’s flow pattern chart and existing experimental data are used to verify the reliability of the model. We develop a simplified mathematical model of water holdup and compare it with existing models. This mathematical model may be limited to the range of fluid properties in the simulated method. The water holdup of the numerical simulation has a definite correlation with the experimental data. By comparing the numerical simulation results of the Nicolas model, the relationship between the slip velocity and water holdup is verified, and the reliability of the simulation results is verified. The simulation results demonstrate that the change in flow pattern is highly sensitive to the change in flow rate. When the flow pattern is stratified flow, the relative error of the simulated flow is small. When the flow pattern is dispersed flow, the relative error of the simulated flow is slightly larger. The oil is mainly concentrated in the high-velocity core area. At a higher total mixing velocity, the flow pattern is that of dispersed flow, with one phase uniformly mixed in the other phase. The simulation results have good qualitative and quantitative agreement with the experimental results.

A localized subdomain smoothing MMALE particle method for efficient modeling FSI problems

Fluid–structure-interaction (FSI) phenomena with multi-phase flow dynamics and structural damage commonly exist in engineering practice, which however bring great challenges to nowadays numerical FSI algorithms. A novel localized subdomain smoothing MMALE particle method (ls-ALEPM) is proposed in this paper for efficient and accurate simulations of large scale FSI problems. The MMALE method and the MPM are strongly coupled by immersing the MPM particles into the MMALE grid. In order to avoid the spurious strain induced by the mixed FSI velocity field, a decoupled stress updating scheme is proposed to update the stress of solid particles by introducing a virtual velocity field in the vicinity of FSI interface. And specifically, the highly accurate polyhedron intersection based method is employed for its remapping phase, which however is time-consuming. Thus, the localized subdomain smoothing method (LSSM) is put forward to accelerate the remapping phase which only involves the distorted regions of computational grid. The LSSM is composed of a distorted subdomain determination step and a combinated mesh smoothing step. Each iteration of the combinated mesh smoothing step consists of the modified GETMe and the weighted average method, and the transfinite interpolation method is adopted if the quality criteria is still not satisfied after prescribed maximum number of iterations. The validity and efficiency of ls-ALEPM is verified by several benchmark numerical examples and practical engineering simulations.

Tracer concentration mapping in a stream with hyperspectral images from unoccupied aerial systems

The release of anthropogenic chemicals to streams, stemming from contaminated sites, agriculture, urban sources, or accidental input, represents a significant threat to water resources and thus the health of humans and aquatic ecosystems. Predicting the transport and fate of chemicals is critical to quantifying contaminant concentrations and developing environmental quality standards (EQS). Tracer tests are a well-established tool for such hydrological investigations in various aquatic systems. In stream settings, the experiments have predominantly investigated longitudinal mixing and flow velocities by measuring the tracer concentration in a few discrete locations; few studies have focused on the transverse mixing properties. Recent progress in hyperspectral remote sensing from Unoccupied Aerial Systems (UAS) allows advancing the two-dimensional monitoring of tracer tests, by mapping the tracer concentration with a high spatial resolution in narrow streams with difficult accessibility. So far, such methods have mainly been demonstrated in controlled settings or in ocean waters, but rarely in optically complex streams. In this study, we evaluated the performance of a miniaturized hyperspectral imaging system and a consumer grade camera onboard a UAS, to map the concentration of the fluorescent tracer Rhodamine WT in a stream impacted by a contaminated site. In order to estimate tracer concentrations from the remotely sensed data, a ratio of the red and blue band was used for the RGB camera, while a vector-based method, estimating the spectral angle in regards to a reference spectrum, was applied for the continuum-removed hyperspectral data. The RGB camera performed well only in sections of the stream exposed to direct sunlight (R2: 0.83; nRMSE: 10.2%), failing to map the concentration in all locations, which included areas where direct sunlight was blocked by riparian trees (R2: 0.17; nRMSE: 26.19%). In contrast, the advanced spectral information allowed the hyperspectral- system to map the concentration well in all sections of the stream (R2: 0.78; nRMSE: 13.35%), regardless of illumination changes. This demonstrated the advantage of hyperspectral imaging systems for measuring water-leaving irradiance in hundreds of contiguous narrow spectral bands that also allow detecting finer absorption and emission features. The approach described here could help to improve the knowledge of contaminants mixing in streams, i.e. to predict the location of fully transverse mixing for contaminated sites discharging to streams via groundwater-surface water interactions, as well as general assumptions behind mixing and dilution models.