Coaxial Jet Mixer Research Articles

Insights into the hydrodynamics in the annular pipe of industrial‐scale top‐blown smelting furnace

AbstractThe coaxial jet consisting of swirl jet and axial jet plays a critical role in the industrial processes but is rarely investigated; therefore, it is numerically explored by means of the computational fluid dynamics (CFD) approach in the present work. The force on the swirler, axial and tangential velocity at the annular pipe outlet, and the spatial distribution of swirl number (SN) are selected to evaluate the effect of geometrical parameters on the swirling performance. The results clarify that the velocity and their azimuthal components in the transverse cross‐section can be categorized into six segments based on high/low velocity values. The coaxial jets form a weak swirl with high axial, certain tangential, and low radial velocities. x‐ and y‐vorticity vary within −200 to 200 s−1. Coaxial jet mixing decays the SN. Based on the multi‐objective matrix analysis, swirler height has the largest effect on swirl performance followed by diameter, angle, and number based on analysis. Optimal parameters are 130° vane angle, 240 mm diameter, 10 vanes, and 250 mm height of the swirler.

Effect of velocity ratio and Mach number on thin lip coaxial jet

Abstract The effect of nozzle lip thickness and velocity ratio on coaxial subsonic jet mixing, at different Mach numbers, has been studied experimentally and numerically. Decay of coaxial subsonic jets emanating from coaxial nozzles of lip thickness 0.7, 1.7 and 2.65 mm with velocity ratio (VR) from 0.2 to 1.0 at primary jet exit Mach numbers of 0.6, 0.8 and 1.0 has been studied. Free jet without co-flow (VR0) was also studied for comparison. Jet centerline Mach number decay, turbulence and velocity variation in the radial direction are analyzed. The results show that mixing the coaxial jet at a low-velocity ratio is better than a high-velocity ratio, at all Mach numbers of the present study. The nozzle lip thickness has a significant influence on the secondary jet. Mixing of the jet in the presence of VR0.2 coaxial jet is found to be the highest. Characteristic decay of Mach 0.8 and 1.0 jet for lip thickness 1.7 and 2.65 mm is faster than lip thickness 0.7 mm. For a given lip thickness, increasing of velocity ratio is found to retard the mixing between primary and secondary jets.

Stochastic modeling of multiple scalar mixing in a three-stream concentric coaxial jet based on one-dimensional turbulence

Modeling turbulent mixing is a standing challenge for nonpremixed chemically reacting flows. Key complications arise from the requirement to capture all relevant scales of the flow and the necessity to distinguish between turbulent advective transport and molecular diffusive transport processes. In addition, anisotropic mean shear, variable advection time scales, and the coexistence of turbulent and nonturbulent regions need to be represented. The fundamental issues at stake are addressed by investigating multi-scalar mixing in a three-stream coaxial jet with a map-based stochastic one-dimensional turbulence model. ODT provides full-scale resolution at affordable costs by a radical reduction of complexity compared to high-fidelity Navier–Stokes solvers. The approach is partly justified by an application of the boundary-layer approximation, but neglects fluctuating axial pressure gradients. It is demonstrated that low-order scalar statistics are reasonably but not fully captured. Despite this shortcoming, it is shown that the model is able to reproduce experimental state-space statistics of multi-stream multi-scalar mixing. The model therefore offers physics-compatible improvements in multi-stream mixing modeling despite some fundamental limitations that remain from unjustified assumptions.

Process Robustness in Lipid Nanoparticle Production: A Comparison of Microfluidic and Turbulent Jet Mixing.

The recent clinical and commercial success of lipid nanoparticles (LNPs) for nucleic acid delivery has incentivized the development of new technologies to manufacture LNPs. As new technologies emerge, researchers must determine which technologies to assess and how to perform comparative evaluations. In this article, we use a quality-by-design approach to systematically investigate how the mixer technology used to form LNPs influences LNPstructure. Specifically, a coaxial turbulent jet mixer and a staggered herringbone microfluidic mixer were systematically compared via matched formulation and process conditions. A full-factorial design-of-experiments study with three factors and three levels was executed for each mixer to compare process robustness in the production of antisense oligonucleotide (ASO) LNPs. ASO-LNPs generated with the coaxial turbulent jet mixer were consistently smaller, had a narrower particle size distribution, and had a higher ASO encapsulation as compared to the microfluidic mixer, but had a greater variation in internal structure with less ordered cores. A subset of the study was replicated for mRNA-LNPs with comparable trends in particle size and encapsulation, but more frequent bleb features for LNPs produced by the coaxial turbulent jet mixer. The study design used here provides a road map for how researchers may compare different mixer technologies (or process changes more broadly) and how such studies can inform process robustness and manufacturing control strategies.

Multi-scalar mixing in turbulent coaxial jets

Although natural and industrial flows often transport and mix multiple scalars, relatively few studies of turbulent multi-scalar mixing have been undertaken. In the present work, a novel three-wire thermal-anemometry-based probe – capable of simultaneously measuring velocity, helium concentration and temperature – is used to investigate the evolution of multiple scalars ($\phi _1$,$\phi _2$,$\phi _3$) and velocity in turbulent coaxial jets. The jets consist of (i) a centre jet containing a mixture of helium and air ($\phi _1$), (ii) an annular jet containing pure (unheated) air ($\phi _2$) and (iii) a coflow of (pure) heated air ($\phi _3$). Axial measurements are made at three different momentum flux ratios ($M=0.77, 2.1, 4.2$). Increasing$M$was observed to result in complex, competing effects. Larger momentum flux ratios cause the potential core of the centre jet to decrease in size, greater scalar fluctuations and more rapid correlation of$\phi _1$and$\phi _2$. However, at the same time, certain statistics, including those describing the velocity field, evolve more slowly. Moreover, the flow near the beginning of the fully merged region appears to be less mixed at higher values of$M$. The present work finally demonstrates that differences can be observed in the evolution and mixing of coaxial jets between those in which$M<1$and those in which$M>1$, thereby presenting an opportunity by which the mixing process in coaxial jets may be controlled.

Chemically reacting mixing in coaxial miscible liquid jets under variable viscosities and reaction rates

We study the mixing and reactions between two fluids with disparate viscosities in a co-axial flow at high Schmidt number, through numerical simulations. The chemical reactions chosen in this work are competitive-consecutive in nature. Numerical implementation of the reactions proceeds as given by Li and Toor (1986), in a Large-Eddy Simulation (LES) framework. The aim of the present study is to investigate the effect of reaction rate constant ratio on the product and byproduct formations under distinct viscosity ratios between the annular and central jets. Flow features promoting mixing and reactions such as turbulence, engulfment, jet instability, waves and break-up are described. The effect of viscosity difference between the jet and co-flow on the mixing and reactions are also delineated. It is found that selectivities of the undesirable product decrease with reducing viscosity ratio as well as increasing reaction rate constant ratio.

Investigation of three-scalar subgrid-scale mixing in turbulent coaxial jets

Abstract

Continuous synthesis of stable ferrocene nanoparticles using a self-aligned coaxial turbulent jet mixer

Ferrocene nanoparticles possess an outstanding characteristic as a drug delivery carrier, in being able to trigger on-demand release of drugs in a specific condition with reactive oxygen species (ROS). However, due to the limitation of the conventional bulk nanoprecipitation method, uniform and highly stable nanoparticles have still been difficult to develop. In this study, we developed device-mediated ferrocene nanoparticles (D-FNPs) with highly controlled uniform size and long-term stability through a flash nanoprecipitation method using a self-aligned coaxial turbulent jet mixer. The self-aligned coaxial turbulent jet mixer could be easily assembled using commercial tube fittings, which enabled the coaxial self-alignment of fluidic parts. In addition, by utilizing diaphragm pumps and pulsation dampers for the control of fluid flow, the coaxial turbulent jet mixer could be operated in a fully continuous manner. Thus, the D-FNPs could be prepared in a continuous manner with a high production rate of 633 mg/min. The D-FNPs were highly stable in aqueous media for 3 months. In addition, after lyophilization without any cryoprotectants, the D-FNPs exhibited stable dispersion in aqueous solution. Importantly, the D-FNPs maintained their original outstanding ROS-responsive characteristics, while showing no cytotoxicity.

High-speed continuous production of polymeric nanoparticles with improved stability using a self-aligned coaxial turbulent jet mixer

Continuous synthesis of polymeric nanoparticles (NPs) has been intensively studied due to its great potential to produce NPs with the physicochemical properties of reproducibility and controllability. Here, we developed a self-aligned coaxial turbulent jet mixer for high-speed continuous synthesis of polymeric NPs. The coaxial turbulent jet mixer can be constructed using commercial tube fittings and tubes. Since those fluidic components are self-aligned coaxially, leak-free jet mixers can be assembled without the use of tools or specialized skills in robust manner. Using the jet mixer with polystyrene (PS) solution, uniform polymeric NPs can be synthesized in a fully continuous manner, for which diaphragm pumps and pulsation dampers are used for continuous control of the flow. We also improved the dispersion stability of the PS NPs in aqueous solution against centrifugation by introducing polystyrene-poly(ethylene oxide) diblock copolymer (PS-b-PEO) as steric stabilizer. The NPs prepared using the coaxial turbulent jet mixer were smaller and more uniform in size compared to NPs synthesized by a bulk nanoprecipitation method.

Experimental study of confined coaxial jets in a non-axisymmetric co-flow

Confined, turbulent, coaxial jets in a non-axisymmetric co-flow are studied using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) simultaneously. Eight different cases are measured. Two momentum flow ratios of the co-flow are used in the experiment to investigate the effect on the coaxial burner jet behavior and mixing characteristics of the coaxial jet flow and the co-flowing, secondary fluid. In addition, four different momentum flow ratios of the coaxial outer to inner jet are investigated. The objective of the study is to get a deeper understanding of how the flow dynamics affects the entrainment and mixing process in a coaxial jet with a non-axisymmetric, surrounding co-flow. The results show that the introduction of a coaxial stream affects the inner jet and decreases the mixing with the surrounding co-flow; the effect is enhanced as the momentum flow ratio of the coaxial jet increases. The distribution of the secondary, co-flowing fluid controls the shape and direction of the coaxial jet, but does not have a significant impact on the mixing process near the centerline. Practical implications of this investigation are related to the possibility to better control a diffusion flame by introducing a coaxial stream. In this context it is concluded that it is possible to affect the jet development and hence the flame length. The conclusion is based on the assumption that the outer, coaxial stream has a low mass flow, not enough to provide complete combustion, and hence the co-flowing, secondary fluid provides the air needed for the combustion process.Graphic abstract

Influence of jet exit conditions on mixing and statistics of flow fine structures

Mixing in a coaxial jet mixer was investigated at variable initial conditions simultaneously using PIV and PLIF methods. Velocity and concentration fields were measured at two spatial resolutions: across the mixer and in a small area at its axis resolving Kolmogorov's scale. Jet exit conditions were modeled by varying flow rate (3⋅103 ≤ Red ≤ 1.78⋅104) and by applying vortex generators (tabs) at the jet exit. The study was executed within a transition flow region. Nevertheless, it is possible to claim that in the self-similarity flow region mean flow parameters do not depend on the initial conditions but turbulence does. The influence of the initial conditions is manifested in turbulent characteristics measured at a high spatial resolution and in the size of fine structures of the studied flows.

Automated and Continuous Production of Polymeric Nanoparticles.

Polymeric nanoparticles (NPs) are increasingly used as therapeutics, diagnostics, and building blocks in (bio)materials science. Current barriers to translation are limited control over NP physicochemical properties and robust scale-up of their production. Flow-based devices have emerged for controlled production of polymeric NPs, both for rapid formulation screening (~μg min−1) and on-scale production (~mg min−1). While flow-based devices have improved NP production compared to traditional batch processes, automated processes are desired for robust NP production at scale. Therefore, we engineered an automated coaxial jet mixer (CJM), which controlled the mixing of an organic stream containing block copolymer and an aqueous stream, for the continuous nanoprecipitation of polymeric NPs. The CJM was operated stably under computer control for up to 24 h and automated control over the flow conditions tuned poly(ethylene glycol)-block-polylactide (PEG5K-b-PLA20K) NP size between ≈56 nm and ≈79 nm. In addition, the automated CJM enabled production of NPs of similar size (Dh ≈ 50 nm) from chemically diverse block copolymers, PEG5K-b-PLA20K, PEG-block-poly(lactide-co-glycolide) (PEG5K-b-PLGA20K), and PEG-block-polycaprolactone (PEG5K-b-PCL20K), by tuning the flow conditions for each block copolymer. Further, the automated CJM was used to produce model nanotherapeutics in a reproducible manner without user intervention. Finally, NPs produced with the automated CJM were used to scale the formation of injectable polymer–nanoparticle (PNP) hydrogels, without modifying the mechanical properties of the PNP gel. In conclusion, the automated CJM enabled stable, tunable, and continuous production of polymeric NPs, which are needed for the scale-up and translation of this important class of biomaterials.

Flow‐based reactor design for the continuous production of polymeric nanoparticles

AbstractPolymeric nanoparticles (NPs) are versatile and effective drug delivery systems (DDS) that can be produced via nanoprecipitation of block copolymers. Yet, translation into clinical products has been limited. Thus, methods for NP production that enable rapid formulation screening and continuous production are needed. Toward this end, we engineered a coaxial jet mixer (CJM) for controlled and continuous nanoprecipitation in flow. The CJM enabled continuous assembly of poly(ethylene glycol)‐block‐polylactide NPs with various co‐solvents and was compared to batch nanoprecipitation. Other fabricated microfluidic devices were suitable for small scale formulation screening but more limited in scalable and continuous processes. In contrast, the CJM was tolerant to all water‐miscible solvents tested, enabled formulation screening, and scalable production of NPs and DDS. In total, the CJM provides a complementary approach to the process engineering of polymeric NP formation that can be used broadly for formulation screening and production.

Numerical investigation of passive scalar transport and mixing in a turbulent unconfined coaxial swirling jet

This paper presents the numerical results of a study on passive scalar mixing in coaxial jets under the influence of swirl. Two cases with different swirling strengths are considered and compared to a non-swirling case. Each jet is injected with an individual scalar to better understand the mixing between jets. The case with intermediate swirling strength exhibits faster centerline decay and radial spread in the mean streamwise velocity in the downstream region when compared to the non-swirling case. The case with strong swirling exhibits the formation of an internal recirculation zone. The mean scalar distributions indicate a better spreading rate of scalars in the intermediate swirling case in the far downstream region, whereas the strong swirling case exhibits maximum spread far upstream. These results are confirmed based on entropy, which is a measure of the diffusion of scalars. Furthermore, the ambient fluid reaches the centerline earlier with the introduction of swirl as a result of an increase in the entrainment rate caused by swirl. The enhanced presence of ambient fluid is observed to influence scalar fluctuations. Otherwise negligible turbulent azimuthal fluxes of both scalars exhibit higher values in the swirling cases. The positive correlation between scalar fluctuations is more evident farther upstream in the intermediate swirling case compared to the non-swirling case. This phenomenon is a result of the enhanced presence of ambient fluid. However, in the strong swirling case, this process takes place far upstream based on additional effects of the internal recirculation zone. The joint probability density function of scalar fluctuations at the leading centerline stagnation point of the internal recirculation zone contains two distinct peaks, indicating the presence of flapping between inner and outer jet scalars caused by the oscillating stagnation point.

Active Control of Coaxial Jet Mixing and Combustion with Axisymmetric and Non-axisymmetric Mode Excitations

Coaxial jet mixing and combustion are actively controlled through manipulation of the vortical structures and the associated mixing with twelve micro jet actuators installed on the annular nozzle. The different azimuthal mode examined here are the fundamental axisymmetric mode and the alternative mode. In the alternative mode, six adjacent micro jets are driven out-of-phase with the other six. The alternative mode provides a phase difference in the generation of the left and right side vortices and avoids interference between these vortices, so that larger vortices are developed if compared to the axisymmetric mode. The effect of the different azimuthal modes on the mixing and the exhaust gas characteristics are discussed.

Numerical investigation of turbulent reactive mixing in a novel coaxial jet static mixer

In the fast reaction category, the turbulent reactive mixing strongly affects the reaction products yield and distribution. The present work adopts a high-efficiency vortex structure induced by a novel static mixer – hollow cross disk (HCD) to enhance the turbulent reactive mixing within the tubular turbulent flow. Specifically, the direct quadrature method of moments (DQMoM) coupled with the interaction-by-exchange-with-the-mean model (IEM) is utilized to simulate the consecutive competitive reactions system in this tubular turbulent flow. In order to quantitatively evaluate the enhanced mixing effect of the HCD, the turbulent reacting flows in the Kenics static mixer and coaxial jet mixer have also been studied. A combining analysis of turbulent flow field and the chemical species distribution indicates that the turbulent mixing enhancement mechanisms of these two static mixers. The simulation suggests that the sinusoidal wave structure in the HCD generate an important flow structure-counter vortex pairs (CVPs), which increases the momentum exchange between the near-wall region and the flow core. Moreover, the spatial distribution of the mixture fraction and reaction product concentration in these configurations agrees well with its turbulent flow field characteristics. The improved turbulent mixing initially is located at the jet periphery when at 0<z/D<2, which fits well with the HCD's longitudinal evolution of turbulent energy dissipation. Whereas at z/D>2, CVPs of the HCD ameliorate the near-wall area's turbulent mixing and thus increase the reaction productivity and selectivity. Additionally, the effects of flow rate on segregation index are studied to suggest that the improvement of Xs for HCD is of about 35% relative to the original tubular flow.

Experimental investigation of the effects of mean shear and scalar initial length scale on three-scalar mixing in turbulent coaxial jets

In a previous study we investigated three-scalar mixing in a turbulent coaxial jet (Caiet al.J. Fluid Mech., vol. 685, 2011, pp. 495–531). In this flow a centre jet and a co-flow are separated by an annular flow; therefore, the resulting mixing process approximates that in a turbulent non-premixed flame. In the present study, we investigate the effects of the velocity and length scale ratios of the annular flow to the centre jet, which determine the relative mean shear rates between the streams and the degree of separation between the centre jet and the co-flow, respectively. Simultaneous planar laser-induced fluorescence and Rayleigh scattering are employed to obtain the mass fractions of the centre jet scalar (acetone-doped air) and the annular flow scalar (ethylene). The results show that varying the velocity ratio and the annulus width modifies the scalar fields through mean-flow advection, turbulent transport and small-scale mixing. While the evolution of the mean scalar profiles is dominated by the mean-flow advection, the shape of the joint probability density function (JPDF) was found to be largely determined by the turbulent transport and molecular diffusion. Increasing the velocity ratio results in stronger turbulent transport, making the initial scalar evolution faster. However, further downstream the evolution is delayed due to slower small-scale mixing. The JPDF for the higher velocity ratio cases is bimodal at some locations while it is always unimodal for the lower velocity ratio cases. Increasing the annulus width delays the progression of mixing, and makes the effects of the velocity ratio more pronounced. For all cases the diffusion velocity streamlines in the scalar space representing the effects of molecular diffusion generally converge quickly to a curved manifold, whose curvature is reduced as mixing progresses. The curvature of the manifold increases significantly with the velocity and length scale ratios. Predicting the observed mixing path along the manifold as well as its dependence on the velocity and length scale ratios presents a challenge for mixing models. The results in the present study have implications for understanding and modelling multiscalar mixing in turbulent reactive flows.

Manipulation of Large-Scale Vortical Structures and Mixing in a Coaxial Jet with Miniature Jet Actuators Toward Active Combustion Control

Manipulation of large-scale vortical structures and associated mixing in a methane-air coaxial jet is carried out by using miniature jet actuators installed on the inner surface of the annular nozzle. The periodic radial miniature jet injections are achieved with a rapid-response servo-valve. The spatio-temporal primary jet structures are investigated through phase-locked 2C-PIV (2 Component Particle Image Velocimetry) and stereoscopic-PIV. It is found that intense ring-like vortices are produced perfectly in phase with the periodic miniature jet injections regardless of the valve-driven frequency fv examined. When the Strouhal number Stv, which is defined with fv, is larger than unity, the ring-like vortices are densely formed and thus methane/air mixing is prompted with low periodic fluctuation. The diameter of the vortices becomes small as Stv is increased, so that the transport range of the inner methane and outer air fluids can be controlled by changing Stv. In addition, the evolution of counter-rotating vortex pair is also observed in the cross-sectional plane. These streamwise vortices are directly formed as a result of the radial miniature jet injection, which leads to entrainment of the ambient fluid near the primary jet shear layer, and they also contribute to the mixing enhancement. Moreover, it is demonstrated that coaxial jet flame characteristics such as carbon monoxide (CO) emission and flame holding can be drastically improved under different equivalence ratios by the present jet control scheme.

Numerical Simulation of Hydrogen Air Supersonic Coaxial Jet

In the present study, the turbulent structure of coaxial supersonic H2–air jet is explored numerically by solving three dimensional RANS equations along with two equation k–e turbulence model. Grid independence of the solution is demonstrated by estimating the error distribution using Grid Convergence Index. Distributions of flow parameters in different planes are analyzed to explain the mixing and combustion characteristics of high speed coaxial jets. The flow field is seen mostly diffusive in nature and hydrogen diffusion is confined to core region of the jet. Both single step laminar finite rate chemistry and turbulent reacting calculation employing EDM combustion model are performed to find the effect of turbulence-chemistry interaction in the flow field. Laminar reaction predicts higher H2 mol fraction compared to turbulent reaction because of lower reaction rate caused by turbulence chemistry interaction. Profiles of major species and temperature match well with experimental data at different axial locations; although, the computed profiles show a narrower shape in the far field region. These results demonstrate that standard two equation class turbulence model with single step kinetics based turbulence chemistry interaction can describe H2–air reaction adequately in high speed flows.

Numerical study of hydrogen–air mixing in turbulent compressible coaxial jets

Numerical simulations are carried out to study the space development of hydrogen–Air mixing jets discharging in to a confined environment. The full Navier-Stokes equations are solved with a high order Godunov's scheme piecewise parabolic method (PPM) with the approximate Riemann solver of Roe. The case considered in this study is based on the experimental work of Eggers (1971). A great attention has been paid to the computation of the dynamic and mixture field, in order to analyse deeply by means of flow visualizations and statistics the characteristics phenomena of the turbulent mixing. Hydrogen species is seeded in the inner jet and the air in the supersonic co-flow. The aim is to comprehend the turbulent structures effect on the mixing process of hydrogen and air. The approach is mainly based on Monotone Integrated Large Eddy Simulations (MILES). The study shows the MILES ability to track mixing process in such configuration as the grid resolution is important.Furthermore, it is found that the turbulent mixing activity is subjected to an intermittent specificity of the coherent vortices: ring structures with intermittent mushroom-type structures characterizing the ejection phenomena due to the longitudinal counter-rotating vortices. The H2 is quasi-completely dissipated as it is entrained outward the rings and transported by the irrotational stream (air). To overcome this situation, it is recommended to lock the inner jet by an outer jet. The studies with and without confinement display the same results even in 2D as the convective Mach number is subsonic Mc=0.44.