Impinging Jet Reactor Research Articles

Experimental study of mixing enhancement of viscous liquids in confined impinging jets reactor at low jet Reynolds numbers

Mixing performance of water and glycerol–water solution in a confined impinging jets reactor (CIJR) with and without excitation was experimentally studied using planar laser induced fluorescence (PLIF) at 100≤Re≤500. The effects of the jet Reynolds number (Re), fluid viscosity and excitation on the oscillation behaviors and mixing performance in CIJR have been qualitatively and quantitatively investigated. Results show that for Re≤100 the flow is segregated with poor mixing; for Re≥150 the flow evolves to an oscillation regime with strong mixing. Compared with the Reynolds number, the fluid viscosity has an insignificant effect on the mixing in CIJR. The mixing in CIJR at low jet Reynolds number can be effectively enhanced by excitation with low frequency, as a periodic oscillation is induced by the pulsed inflow, which further causes the continuous folding and stretching of the impingement plane. The enhancement of mixing is strengthened with the increase of excitation amplitude and is weakened with the increase of excitation frequency.

On the transient flow characteristics in Confined Impinging Jet Mixers ‐ CFD simulation and experimental validation

Confined impinging jet reactors (CIJMs) are very efficient mixing devices. Due to the generation of high turbulent dissipation and, thus, intensive mixing of two colliding liquid flows CIJMs are widely used in laboratory applications. Besides low construction effort, these mixers enable a sensitive control of fast reactions, an efficient initial homogenization of educts and consequently a rapid build-up of supersaturation as the driving force for precipitation and crystallization. The understanding of fluid mechanics and mixing in those CIJMs is of fundamental interest for a proper description of parallel or consecutive processes. Therefore, this paper gives an insight into characteristic procedures, with the main focus on the turbulent flow regime in a T- and Y-CIJM. Experimental investigation on the local mixing behavior of liquid-phase impinging jets in static mixers is carried out by using an optical laser induced fluorescence (LIF) and particle image velocimetry (PIV) setup. In order to avoid optical measurement errors due to the cylindrical geometry, a refractive index correction of fluids with the ionic additive NH4SCN has been carried out. Due to poor information in literature, important properties of the corrected aqueous solution are listed. Another main focus of this work lies in the mathematical modeling of the flow field based on computational fluid dynamics (CFD) methods. The transient hybrid Detached Eddy-SST-k–ω turbulence approach is introduced as a computational cost-efficient highly accurate method to calculate flow conditions in turbulent CIJMs. LIF and PIV as well as pressure drop measurements provide a wide set of data that serve to validate CFD simulations.

Sustainable Formation of Curcumin Nanoparticle: Stirred Tank and Confined Impinging Jet Reactor

Sustainable Formation of Curcumin Nanoparticle: Stirred Tank and Confined Impinging Jet Reactor

Micromixing efficiency in a T-shaped confined impinging jet reactor

Confined impinging jet reactor (CIJR) offers advantages for chemical rapid processes and has become an important new reactor used in the chemical industry. The micromixing efficiency in a T-shaped CIJR for two tubes of inner diameter of 3mm was studied by using a parallel competing iodide–iodate reaction as the working system. In this work, the effects of different operating conditions, such as impinging velocity and acid concentration, on segregation index were investigated. In addition, the effects of the inner nozzles diameter and the distance L between the jet axis and the top wall of the mixing chamber on the micromixing efficiency were also considered. It is concluded that the best range of L in this CIJR is 6.5–12.5mm. Based on the incorporation model, the estimated minimum micromixing time tm of CIJR approximately equals to 2×10−4s. These experimental results indicate clearly that CIJR possesses a much better micromixing performance compared with the conventional stirred tank (micromixing time of 2×10−3 to 2×10−2s). Hence, it can be envisioned that CIJR has more promising applications in various industrial processes.

Experimental study of oscillation behaviors in confined impinging jets reactor under excitation

Dynamic behaviors in a three‐dimensional confined impinging jets reactor (CIJR) under excitation were experimentally studied by a flow visualization technique at 75 ≤ Re ≤ 150. The effects of inlet Reynolds numbers (Re), excitation frequencies and excitation amplitudes on the oscillation behaviors in CIJR have been investigated by a particle image velocimetry (PIV) and a high‐speed camera. Results indicate that the excitation in the inflow of the opposed jets can induce periodic oscillation of the impingement plane along the axis, whose oscillation frequency is equal to the excitation frequency. At Re ≤ 100, the induced axial oscillation can further cause a deflective oscillation with a frequency nearly equal to the excitation, and the scale of the vortex in the impingement plane is well regulated by the excitation frequency. At Re = 150, the excitation of amplitude less than 20% has insignificant effect on the deflective oscillation existing in CIJR. A semiempirical formula has been proposed to predict the oscillation amplitude of the impingement plane in CIJR under excitation. © 2014 American Institute of Chemical Engineers AIChE J, 61: 333–341, 2015

Experimental study of flow regimes in three‐dimensional confined impinging jets reactor

Dynamic behaviors in a three‐dimensional confined impinging jets reactor (CIJR) were experimentally studied by a flow visualization technique at 100 ≤ Re ≤ 2000 and 2 ≤ D/d ≤ 12 (where D is the reactor diameter and d is the nozzle diameter). The effects of inlet Reynolds numbers (Re) and geometry configurations of the CIJR on the flow regimes have been investigated by a particle image velocimetry and a high‐speed camera. Results show that with the increasing Re, a segregated flow regime, a radial deflective oscillation, an axial oscillation and a vortex shedding regime emerge in turns in CIJR. A map of parameter space formed by the inlet Reynolds number (Re) and the normalized reactor diameter (D/d) has been presented. The effects of jet instability and confined boundary of the chamber on the flow regimes and their transition are also investigated and discussed. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3033–3045, 2014

Particle Image Velocimetry (PIV) Investigation of Flow Characteristics in Confined Impinging Jet Reactors

The flow characteristics in confined impinging jet reactors (CIJRs) were investigated, using particle image velocimetry. The effects of Reynolds number (Re), jet velocity ratio (u1/u2), jet diameter (d), and the factor L (defined as the distance between the axes of two jets and the top wall of the CIJR chamber) on the flow characteristics of CIJRs were discussed. The similarity of the turbulent flow in CIJRs was extended to the operating conditions with high Reynolds numbers, ranging from Re = 10 620 to Re = 21 210. The position of the stagnation point in CIJR is closely related to u1/u2, but independent of d. The decrease of the ratio of the factor L to impinging jet diameter (L/d) from 4 to 1.5 can increase the values of turbulent kinetic energy and intensify momentum transfer and mixing in the impinging region of CIJR. The present study shows that CIJRs are ideal reactors for rapid chemical reactions, and optimized parameters are helpful for the design and operation of such reactors.

Flow Field and Turbulence Characterization of a Counter Impinging Jet Reactor Using Particle Image Velocimetry

We characterize the three dimensional structure and quantify turbulence quantities in a counter-impinging jet reactor with trapezoidal cross-section to test the feasibility of achieving stratified mixing. Dye flow-visualization and particle image velocimetry (PIV) velocity field measurements are made in the inlet section of the reactor. Two-component velocity measurements are made on three sets of orthogonal planes for Rej = 1000, 1800, 2600, and 3700; the overall structure of the flow field is found to be qualitatively similar for the Reynolds numbers studied, but the precise trajectory of the mean flow is found to be sensitive to inflow boundary conditions. Reynolds stresses and anisotropic invariants are calculated; the turbulent kinetic energy decreases linearly with increasing distance downstream in the reactor and it decreases at the same relative rate for all Reynolds numbers studied; anisotropic invariants and Reynolds stress maps indicate a turbulent stress state that tends toward isotropy downstream of the inlets. Turbulent stress maps indicate that the Reynolds stress components are stratified in the reactor channel, becoming uniform as a function of z by y/Dh = 4.

Identification of nucleation rate parameters with MD and validation of the CFD model for polymer particle precipitation

We present a new approach to calculate the precipitation of polymer nanoparticles in confined impinging jets reactors (CIJRs) obtained by coupling together the computational fluid dynamics (CFD) model, accounting for turbulent mixing, nucleation, growth and aggregation, and the molecular dynamics (MD) description of polymer molecules. A new expression for the nucleation rate is adopted and the MD simulations are used to identify all the missing parameters involved. Different operating conditions are investigated in order to assess the reliability of the model. Its predictions, in terms of mean particles size, are compared with experiments, resulting in good agreement.

An economic and scalable approach to synthesize high power LiFePO4/C nanocomposites from nano-FePO4 precipitated from an impinging jet reactor

A novel, economic and scalable method is proposed in this context using an impinging jet reactor to continuously precipitate FePO4 (FP) nanoparticles with high purity. The LiFePO4/C (LFP/C) nano-composites synthesized from the FP, lithium and carbon sources show fast charge capability and excellent power performance. The generated FP and LFP/C are characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and inductively coupled plasma (ICP) spectrometry. The LFP/C nano-composites are cycled at various C-rates to explore the electrochemical performance. When the pH of the working solution is 1.3, the molar ratio of Fe to P equals 1 in the obtained amorphous FP. In addition, the precipitation mechanism is discussed. Compared to the amorphous FP, the hexagonal FP obtained after calcining the former one is preferred to synthesize high power LFP/C. It is proved that 2 mol% excess LiOH is needed to compensate for the possible loss of Li during calcination. With 4.4 wt% of in situ carbon coating, the LFP/C nano-composites exhibit 145 mA h g−1 at 10 C (1.7 A g−1, 6 min) charge (without floating charge) and discharge, without obvious capacity loss up to 100 cycles, which is among the best high power performances reported so far. This strategy offers an inexpensive and easy control method to mass-produce high quality LFP/C nano-composites which might be suitable for powering hybrid electric vehicles and plug-in hybrid electric vehicles.

Synthesis of superior fast charging–discharging nano-LiFePO4/C from nano-FePO4 generated using a confined area impinging jet reactor approach

LiFePO4/C nanocomposites with excellent electrochemical performance is synthesized from nano-FePO4, generated by a novel method using a confined area impinging jet reactor (CIJR). When discharged at 80 C (13.6 Ag(-1)), the LiFePO4/C delivers a discharge capacity of 95 mA h g(-1), an energy density of 227 W h kg(-1) and a power density of 34 kW kg(-1).

Micromixing Efficiency in an Asymmetric Confined Impinging Jet Reactor

Micromixing Efficiency in an Asymmetric Confined Impinging Jet Reactor

Turbulence measurements in a rectangular mesoscale confined impinging jets reactor

Mesoscale chemical reactors capable of operating in the turbulent flow regime, such as confined impinging jets reactors (CIJR), offer many advantages for rapid chemical processing at the microscale. One application where these reactors are used is flash nanoprecipitation, a method for producing functional nanoparticles. Because these reactors often operate in a flow regime just beyond transition to turbulence, modeling flows in these reactors can be problematic. Moreover, validation of computational fluid dynamics models requires detailed and accurate experimental data, the availability of which has been very limited for turbulent microscale flows. In this work, microscopic particle image velocimetry (microPIV) was performed in a mesoscale CIJR at inlet jet Reynolds numbers of 200, 1,000, and 1,500. Pointwise and spacial turbulence statistics were calculated from the microPIV data. The flow was observed to be laminar and steady in the entire reactor at a Reynolds number of 200. However, at jets Reynolds numbers of 1,000 and 1,500, instabilities as a result of the jets impinging along the centerline of the reactor lead to a highly turbulent impingement region. The peak magnitude of the normalized Reynolds normal and shear stresses within this region were approximately the same for the Reynolds numbers of 1,000 and 1,500. The Reynolds shear stress was found to exhibit a butterfly shape, consistent with a flow field dominated by an oblique rocking of the impingement zone about the center of the reactor. Finally, the spatial auto- and cross-correlations velocity fluctuations were calculated and analyzed to obtain an understanding of size of the coherent structures.

Model validation for precipitation in solvent-displacement processes

In this work a model for precipitation of polymer nanoparticles in solvent-displacement processes is presented and validated. The model is based on computational fluid dynamics coupled with a population balance model. The standard k–ε turbulence model in combination with the enhanced wall treatment approach is used to describe mixing and particle formation in a confined impinging jets reactor. The interaction between turbulent fluctuations and particle formation (i.e., micro-mixing) is modelled with the so-called direct quadrature method of moments coupled with the interaction and exchange with the mean approach, whereas the population balance model is solved by using the quadrature method of moments. The model is used here for the first time to model the precipitation of polymer nanoparticles of poly-ε-caprolactone via solvent-displacement with acetone and water as solvent and anti-solvent. Particle formation is described with the classical nucleation, molecular growth and aggregation steps and a discussion on the effect of the polymer molecules behaviour in the system is presented and its effect on the results of the models is shown. The relevant rates are derived from first principles and most of the parameters appearing in the model are identified through independent measurements or from theory. Results show good agreement with experimental data and prove that the approach is very interesting, but further work is needed because, as shown, molecular characteristics of the polymer molecules cannot be neglected and need to be linked with the macroscopic description of the system obtained by computational fluid dynamics. Strategies to assess the value of some missing model parameters via multi-scale modelling are also discussed.

Visualization of turbulent reactive mixing in a planar microscale confined impinging-jet reactor

Turbulent reactive mixing in a rectangular microscale confined impinging-jet reactor was investigated using the pH indicator phenolphthalein in this study for three different jet Reynolds numbers Rej = 25, 1000 and 1500. Laminar flow was observed at Rej = 25 whereas the flow was turbulent at Rej = 1000 and 1500. An image processing technique was applied to instantaneous images to extract quantitative mixing data by identifying regions with pH ⩾ 9.3 and regions with pH < 9.3. Ensemble averages were computed using these thresholded images to compare mixing performance between different Reynolds numbers. Finally, the spatial auto-correlation fields of the thresholded image fluctuations were evaluated, based on which large-scale turbulent structures were analyzed.

Preparation of Poly(MePEGCA-co-HDCA) Nanoparticles with Confined Impinging Jets Reactor: Experimental and Modeling Study

In this work, the biodegradable copolymer poly(methoxypolyethyleneglycolcyanoacrylate-co-hexadecylcyanoacrylate) is used to prepare nanoparticles via solvent displacement in a confined impinging jets reactor (CIJR). For comparison, nanoparticles constituted by the homopolymer counterpart are also investigated. The CIJR is a small passive mixer in which very fast turbulent mixing of the solvent (i.e., acetone and tetrahydrofuran) and of the antisolvent (i.e., water) solutions occurs under controlled conditions. The effect of the initial copolymer concentration, solvent type, antisolvent-to-solvent ratio, and mixing rate inside the mixer on the final nanoparticle size distribution, surface properties, and morphology is investigated from the experimental point of view. The effect of some of these parameters is studied by means of a computational fluid dynamics (CFD) model, capable of quantifying the mixing conditions inside the CIJR. Results show that the CIJR can be profitably used for producing nanoparticles with controlled characteristics, that there is a clear correlation between the mixing rate calculated by CFD and the mean nanoparticle size, and therefore that CFD can be used to design, optimize, and scale-up these processes.

A comparative study for nanoparticle production with passive mixers via solvent-displacement: Use of CFD models for optimization and design

Active and passive mixers, including a considerable variety of micro-devices, are nowadays widely used for the production of nanoparticles. Polymer nanoparticles for controlled drug delivery applications are investigated in this work with two specific objectives. The first one is to experimentally quantify the efficiency of confined impinging jets reactors and Tee-mixers in the production of nanoparticles constituted by two polymers: poly-ɛ-caprolactone and poly(methoxypolyethyleneglycolcyanoacrylate- co-hexadecylcyanoacrylate). The second objective is the development of a simple and reliable mathematical model to be used for the design, optimization and scale up of mixers for polymer nanoparticle production. Although the behaviour of the polymers investigated is quite different, it is possible to conclude that confined impinging jets reactors are more efficient than Tee-mixers, in converting the pressure drop into turbulent kinetic energy and as a consequence in producing smaller particles. The very simple modelling approach proposed here (based on the evaluation of the mixing time) seems to be able to correlate well experimental data obtained under different operating conditions, independently on the type of device used. Moreover, in the case of poly-ɛ-caprolactone it was also possible to successfully quantify the particle formation time with a simple power law, further exploiting the model.

Investigation of the flow field in a three-dimensional Confined Impinging Jets Reactor by means of microPIV and DNS

Micro-mixer devices, such as the Confined Impinging Jets Reactor (CIJR) are currently under study, in particular for precipitation processes of micro- and nano-particles, employed in a variety of applications that include pharmaceuticals, cosmetics, dyes and pesticides. In this work, with the purpose of gaining a better understanding of the main mixing mechanisms occurring in a CIJR, the flow field was studied at four inlet flow rates ranging from Re = 62 to Re = 600. These conditions correspond to regimes with incipient turbulence in the chamber. Micro-Particle Image Velocimetry (microPIV) experiments and Direct Numerical Simulations (DNS) were performed and compared. MicroPIV is an innovative experimental technique that allows measurement of the instantaneous velocity fields in microfluidic devices. The coupled numerical-experimental approach was found to be essential in understanding and explaining the flow behaviour and the development of turbulence, in particular with respect to the important effects of the inlet boundary conditions. Oscillations present in the inlet flow of the device are in fact primarily responsible for the chaotic and turbulent effects in the reactor. These results provide insights that are important in the development of appropriate computational models for this type of micro-reactor or mixers.

Validation of LES predictions for turbulent flow in a Confined Impinging Jets Reactor

This work focuses on the prediction of the turbulent flow in a three-dimensionial Confined Impinging Jets Reactor with a cylindrical reaction chamber by using Large Eddy Simulation. Three-dimensional unsteady simulations with different sub-grid scale models, numerical schemes and boundary conditions were performed for various flow rates, covering different flow regimes. First, a qualitative analysis of the flow field was carried out and then predictions of the mean and fluctuating velocities were compared with micro Particle Image Velocimetry data. Good agreement was found both for the mean velocity components and the fluctuations. For low to moderate Reynolds numbers the sub-grid scale model was found not to be very relevant, since small scales are of less importance, as long as scalar transport and chemical reaction are not in play. An important finding is the good prediction of the high velocity fluctuations detected in particular at higher Reynolds number due to the natural instability of the system, strongly enforced by the jets unsteadiness.

The effect of stabilizer addition and sonication on nanoparticle agglomeration in a confined impinging jet reactor

Reactive precipitation is a convenient synthesis route for production of submicron metal oxide particles. In this study, the effects of feed flow rate, feed concentration, stabilizer addition, and sonication on the size of precipitate particles in a confined impinging jet reactor were investigated using the iron oxide model system. Five stabilizers (TEG, DEG, sec butylamine, dextran, and polyacrylamide) were tested to determine optimum performance. The effects of in situ and post-reaction sonication on hard agglomerate size were also investigated. The agglomerate size varies with both feed flow rate and feed concentration. Mixing effects are more pronounced at high feed concentrations. The smallest agglomerates were obtained at a high flow rate and high feed concentration. Stabilizers added in situ reduced agglomeration. Triethylene glycol (TEG) was the most effective, causing the agglomerate size to drop by a factor of three at 5% (v/v) dosage for high feed concentrations and high flow rates. Neither the flow rate nor the TEG additive quantity had any significant influence on agglomerate size at low feed concentrations. Dextran addition leads to the smallest primary particles but the largest hard agglomerates. Post-reaction sonication disperses soft agglomerates, but in situ sonication had a negligible effect on agglomerate size, with or without the addition of stabilizer. CFD simulations indicate that the geometry modified with the in situ sonication probe has a similar energy dissipation field to the original geometry. In situ sonication energy is dominant over turbulent energy dissipation at low flow rates but the latter is comparable to or dominates above a flow rate of 165 mL/min. The second observation is supported by iodide–iodate experiments where the product yield is independent of flow rate above 165 mL/min.