Coiled Flow Inverter Research Articles

Coiled flow inverter mediated synthesis of activated carbon fiber-supported Ni nanoparticles

A single-stage continuous flow process for the synthesis of Ni nanoparticle-dispersed activated carbon fibers is developed using CFI technology.

Hydrodynamics and Mixing in a Novel Design of Compact Microreactors: Arc Flow Inverters

A novel tubular microreactor to intensify mixing, namely arc flow inverter (AFI) was proposed and the mixing behavior was investigated. The design concept of AFI expanded a design space of mixing/reactor devices consisting of curved tubes and 90 degrees bends compared with conventional coiled flow inverter (CFI). The fabrication difficulties were overcome by using 3D printing technology. Numerical study on hydrodynamics NRe ≤ 400 revealed that the profile of Dean vortices was spatially periodic along the axis of AFI. The narrower residence time distribution in AFI compared to CFI implied an enhanced lateral mixing due to the Dean vortices. Micro-mixing time in AFI was experimentally accessed via Dushman-Villermaux reaction. The AFI outperformed other fluidic devices in the literature in terms of the coefficient of mixedness.

Continuous Synthesis of Uniformly Dispersed Mesoporous SBA-15 Supported Silver Nanoparticles in a Coiled Flow Inverter Reactor.

Mesoporous silica supported nanocatalysts have shown great potential in industrial processes due to their unique properties, such as high surface area, large pore volume, good chemomechanical stability and so on. Controllable and tunable synthesis of supported nanocatalysts is a crucial problem. Continuous synthesis of supported nanoparticles has been reported to get uniformly dispersed nanomaterials. Here, a method for continuous synthesis of uniformly dispersed mesoporous SBA-15 supported silver nanoparticles in a coiled flow inverter (CFI) microreactor is described. Compared to Ag/SBA-15 synthesized in the conventional batch reactor and Ag synthesized in continuous flow, mesoporous silica nanocatalysts synthesized in continuous flow are found to have smaller average size (7–11 nm) and narrower size distribution. The addition of capping agents can effectively change the characteristic of catalysts. Moreover, two kinds of support with different surface area and pore size have been added into the continuous synthesis. This method can provide further understandings for the synthesis of uniformly dispersed supported nanocatalysts in continuous flow, especially for mesoporous nanomaterials, which provides the possibilities of large-scale yield process of supported nanocatalysts in industry.

Ultrasound-assisted synthesis of visible-light-driven Ag/g-C3N4 catalysts in a continuous flow reactor

Size control of supported nanoparticles remains a challenge, especially in the presence of external fields. In this paper, an ultrasound-assisted method was developed for the continuous synthesis of visible-light-driven Ag/g-C3N4 catalysts with controllable sizes and narrow size distributions in a coiled flow inverter reactor. The catalytic performance was characterized by the photocatalytic water splitting, which was considered as a promising method to provide hydrogen fuel. Here, we investigated the synergy effect of output power of ultrasound, residence time, and Ag loading content on the characteristic and catalytic performance of the catalysts. With the increase of ultrasound output power (from 0 W to 120 W) and the decrease of residence time (from 140s to 17.5s), the size of silver nanoparticles becomes smaller, and the distribution is narrower. The higher catalytic activity was achieved for the catalyst under 60 W power, 1.22 times higher than that of the catalyst synthesized without ultrasound. Ag/g-C3N4 catalysts with higher Ag loading exhibited better catalytic activity, despite the bigger size of Ag nanoparticles. The results suggest that 7 wt% Ag/g-C3N4 catalysts synthesized under 60 W ultrasound power for 35s (residence time) exhibited the best photocatalytic activity for water splitting, which was 2.76 times higher than that of using pure g-C3N4.

Axial dispersion in curved channels in the presence of pulsating flow

A narrow residence time distribution (RTD) is desirable in several chemical engineering processes. However, in systems operating at low Reynolds number, axial dispersion can be significant. To lower it, we utilised two mixing approaches: secondary flow achieved with curved geometries and oscillatory variation of the flow rate. We investigated their combined effect on axial dispersion in millifluidic channels with three geometries: straight tube, helically coiled tube (HCT) and coiled flow inverter (CFI). We studied the influence on axial dispersion of two key parameters of pulsating flows: amplitude and frequency of pulsation; in dimensionless form, these are expressed via the amplitude ratio and Strouhal number, respectively. For unsteady flow, we performed numerical simulations to characterise mixing. The results indicate that pulsation enhances radial mixing significantly. Our experimental studies show that axial dispersion is lower in the presence of pulsation, and increasing amplitude and/or frequency has a positive effect. For the same amplitude ratio and Strouhal number, axial dispersion decreases more in the CFIs than in the HCTs. Comparing two extremes, the straight capillary with steady flow (no RTD enhancement) and the CFI with pulsation (lowest axial dispersion achieved in our work), we observed a 10-fold reduction in the axial dispersion number.

Continuous Cooling Crystallization in a Coiled Flow Inverter Crystallizer Technology—Design, Characterization, and Hurdles

Continuous small-scale production is currently of utmost interest for fine chemicals and pharmaceuticals. For this purpose, equipment and process concepts in consideration of the hurdles for solids handling are required to transfer conventional batch processing to continuous operation. Based on empirical equations, pressure loss constraints, and an expandable modular system, a coiled flow inverter (CFI) crystallizer with an inner diameter of 1.6 mm was designed. It was characterized concerning its residence time behavior, tested for operation with seed crystals or an ultrasonic seed crystal unit, and evaluated for different purging mechanisms for stable operation. The residence time behavior in the CFI corresponds to ideal plug flow behavior. Crystal growth using seed crystals was demonstrated in the CFI for two amino acids. For fewer seed crystals, higher crystal growth rates were determined, while at the same time, secondary nucleation was observed. Feasibility for the interconnection of a sonicated seeding crystal unit could be shown. However, the hurdles are also identified and discussed. Prophylactic flushing combined with a photosensor for distinguishing between solvent and suspension phase can lead to stable and resource-efficient operation. The small-scale CFI technology was investigated in detail, and the limits and opportunities of the technology are presented here.

Nucleation in continuous flow cooling sonocrystallization for coiled capillary crystallizers

Nucleation in continuously operated capillary coiled cooling crystallizers is experimentally investigated under the influence of ultrasound. It was found that there is no sharp boundary but rather a transition zone for nucleation under sonication. For this purpose, a tube with an inner diameter of 1.6 mm and a length of 6 m was winded in a coiled flow inverter (CFI) design and immersed into a cooled ultrasonic bath (37 kHz). The CFI design was chosen for improved radial mixing and narrow residence time distribution, which is also investigated. Amino acid l-alanine dissolved in deionized water is employed in a supersaturation range of 1.10 to 1.46 under quiet and sonicated conditions. Nucleation is non-invasive detected using a flow cell equipped with a microscope and camera.Graphical abstractSince the interest and demand for small-scale, continuous crystallization increases, seed crystals were generated in a coiled tube via sonication and optically investigated and characterized. No distinct threshold for nucleation could be determined in a wide range of supersaturations of l-alanine in water

Numerical modeling of segmented flow in coiled flow inverter: Hydrodynamics and mass transfer studies

A novel CFD modeling approach was developed to investigate the hydrodynamics and mass transfer in a gas–liquid slug flowing through microscale coil and coiled flow inverter channels. One straight slug model was formulated by adding a virtual centrifugal body force. The model was validated in terms of the helicity and secondary flow magnitude. The secondary flow magnitude was shown to be a power function of the Dean number, and a new correlation was proposed. The mass transfer across the interface was compared to that obtained in previous studies. The new model described the temporal and spatial distribution of species in the slug reasonably well. The volumetric mass transfer coefficient kLa in the coil was found to be 1.5 times higher than that in the straight channel, and the enhancement in kLa reached a maximum at a modified Dean number of 1.2.

Continuous microfluidic synthesis of zirconium-based UiO-67 using a coiled flow invertor reactor

Metal-organic frameworks (MOFs), particularly Zirconium based, have a wide variety of potential applications, such as catalysis and separation. However, these are held back by traditionally only being synthesised in long batch reactions, which causes the process to be expensive and limit the amount of reaction control available, leading to potential batch to batch variation in the products, such as particle size distributions. Microfluidics allows for batch reactions to be performed with enhanced mass/heat transfer, with the coiled flow inverter reactor (CFIR) setup narrowing the residence time distribution, which is key in controlling the particle size and crystallinity. In this work, a Zirconium based MOF, UiO-67, has been synthesised continuously using a microfluidic CFIR, which has allowed for the product to be formed in 30 min, a fraction of the traditional batch heating time of 24 h. The microfluidicially synthesised UiO-67 is also smaller product with a narrower particle size distribution (≈200 nm to ≈400 nm) than its batch counterpart (~500 nm to over 3 µm).

Continuous Crystallization Processes in Pharmaceutical Manufacturing: A Review

This scientific paper presents an overview of continuous solution crystallization in the pharmaceutical industry. Since the specific knowledge spectrum of precipitation is very broad, topics covering the following were analyzed and assessed in detail: a comparison between batch and continuous crystallizers, their engineering advantages/disadvantages, the introduction of the solid form structuring to continuously oriented chemical production, and the usage of the online process analytical technology (PAT) methodologies in interacting functional systems. Furthermore, mechanistic multiscale modeling, whose understanding is of decisive importance for further control application development, was thoroughly discussed as well. The multiscale modeling section also includes the simulation of processes and the optimization of crystallizers. In the last section, model-based predictive control (MPC) is considered, which also covers the intensification approach methods in the field of crystal formation and the introduction of new, highly potential continuous systems, e.g. the coiled flow inverter (CFI) crystallizer, in industry and academia. In the mentioned main sections, individual theme-related articles are collected, discussed, and compared; therefore, a reader can get acquainted with pieces of research, their found results, which have been developed until now, and various emerging perspectives. With regard to the importance of crystallization in the pharmaceutical industry, a reader can already find literature on continuous crystallization. However, due to the growing tendency toward the synthesis of products with specific properties which cannot be achieved with conventional approaches, more attention has been paid in the present work to the establishment of continuous systems for the production of specific fine chemicals. In addition, continuous crystallization could also enable more efficient and “on-demand” production, modeling for optimization, MPC, and intensification approaches. A review of the literature classifying studies according to the choice of a continuous system and their description was omitted in this study, as such reviews are already available in the literature.

Continuous microfluidic solvent extraction of cobalt from mimicked and real asteroid leaching solutions

This research proposes a pathway for the last step of the asteroid mining process: the purification of the adjacent metals, cobalt and nickel, in the frame of in-situ resource utilization (ISRU) in space. Major technological and economic challenges will need to be overcome, and one main issue to be tackled is the reduction of water usage in this process. Therefore, the leached metal solutions are expected to contain ultra-high metal concentrations, up to 10 mol/l. These solutions will have challenging thermodynamic properties (increased density, viscosity and interfacial tension). As a result, an analysis of dimensionless numbers for fluidics and mass transport was made, showing that some of these are favourable under the constraints of accessible microfluidic operations. Experiments were performed with advanced microfluidic reactors (a coiled-flow inverter (CFI) and an industrial re-entrance flow reactor from Corning®) at high metal concentrations and high nickel to cobalt ratios (3:0.3 mol/l Ni:Co). Using Cyanex 272 as a selective extractant for cobalt, extraction efficiencies of 60% with high separation factors (>1000) were reached in just one extraction stage. The CFI showed high extraction efficiency for low fluid velocities and a residence time of 60 s. For the Corning® reactor, high fluid velocities or the use of many modules (>3) are needed to obtain an emulsion, resulting in high extraction efficiencies at a very short residence time of 13 s. The comparison between the CFI and the Corning® reactor shows that they share the best operation point (at 120 ml/h), but the Corning® reactor performs better at higher flow rates and thus can leverage higher productivity. However, the CFI is easier to operate and has a much lower pressure drop, resulting in low energy input. Finally, an iron meteorite sample was leached and efficiently extracted in both microfluidic reactors.

Mixing characterization in different helically coiled configurations by laser-induced fluorescence

Flow Mixing of two miscible liquids has been characterized experimentally in three different helically coiled reactor configurations of two different lengths in the laminar flow regime at Re = 50…1000. A straight helical coil, a coiled flow inverter, and a new coiled flow reverser have been built, each in a 3-turn and a 6-turn configuration. Laser-induced fluorescence of resorufin has been used to visualize and quantify mixing in cross-sections throughout the reactors. A mixing coefficient is derived from the fluorescence images to allow for a quantitative measure and comparison of the six configurations. It becomes obvious from these experimental results, that an early flow redirection in the helical configuration is beneficial to mixing. The 3-turn reactors achieve nearly the same mixing coefficients as the 6-turn reactors with the double length. This can be explained by the stabilizing effect of the Dean vortices in the helix, which develop during the first two turns. After that, the liquid is trapped inside the vortices and further mixing is inhibited. Accordingly, the coiled flow inverter and coiled flow reverser configurations lead to much higher mixing coefficients than the straight helical coil. The results of these measurements are now used for validation of numerical simulations, which reproduce the geometrical and flow conditions of the experiments. Some exemplary results of these calculations are also shown in this article.Graphic abstractMass fractions of tracer fluid at Re = 500 in the six examined helix configurations.

Mass Transfer Characterization of Ionic Liquid Solvents for Extracting Phenol from Aqueous Phase in a Microscale Coiled Flow Inverter

In this work, the extraction of phenol from aqueous solutions toward the ionic liquids 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [Bmim][NTf2] and 1-hexyl-3-methylimidazolium bi...

Experimental Study of Forced Convective Heat Transfer in a Coiled Flow Inverter Using TiO2–Water Nanofluids

The curved geometry of a coiled flow inverter (CFI) promotes chaotic mixing through a combination of coils and bends. Besides the heat exchanger geometry, the heat transfer can be enhanced by improving the thermophysical properties of the working fluid. In this work, aqueous solutions of dispersed TiO2 nanometer-sized particles (i.e., nanofluids) were prepared and characterized, and their effects on heat transfer were experimentally investigated in a CFI heat exchanger inserted in a forced convective thermal loop. The physical and transport properties of the nanofluids were measured within the temperature and volume concentration domains. The convective heat transfer coefficients were obtained at Reynolds numbers (NRe) and TiO2 nanoparticle volume concentrations ranging from 1400 to 9500 and 0–1.5 v/v%, respectively. The Nusselt number (NNu) in the CFI containing 1.0 v/v% nanofluid was 41–52% higher than in the CFI containing pure base fluid (i.e., water), while the 1.5 v/v% nanofluid increased the NNu by 4–8% compared to water. Two new correlations to predict the NNu of TiO2–water nanofluids in the CFI at Reynolds numbers of 1400 ≤ NRe ≤ 9500 and nanoparticle volume concentrations ranges of 0.2–1.0 v/v% and 0.2–1.5 v/v% are proposed.

Development of an integrated continuous PEGylation and purification Process for granulocyte colony stimulating factor

PEGylation of therapeutic proteins has long been recognized as a safe and effective approach to enhance pharmacokinetic properties of proteins by increasing the in-vivo half-life and thereby the bioavailability. Despite all the benefits linked to PEGylation, high cost of PEGylated products has hindered accessibility of these products to patients. Continuous processing offers a solution to this predicament with its proven capability to improve economics without sacrificing product quality. In this study, we report the development of an integrated continuous PEGylation and purification process for a therapeutic protein, PEG-GCSF. The methodology to achieve this consisted of developing the batch PEGylation and purification protocols followed by their conversion into an integrated continuous process. A batch process involving rapid and highly productive PEGylation (reaction completion within one hour of reaction time) followed by cation exchange chromatography was developed. Enabling technologies like coiled flow inversion reactor, inline concentrator and counter-current chromatography, were utilized for the successful conversion of the batch process to continuous mode. The final integrated continuous process consisted of continuous PEGylation in a coiled flow inverter reactor followed by four column continuous counter-current cation exchange chromatography. Continuous chromatography was performed in a novel displacement mode, wherein all the multi-PEGylated impurities were removed in the loading flow-through and the pure mono-PEGylated protein was obtained in a single step salt elution. In combination with our previously established GCSF manufacturing train, the end-to-end continuous manufacturing process starting from inclusion bodies to unformulated PEG-GCSF drug substance was successfully run for 12 h. All attributes were found to be consistent over the period of operation with product purity > 99 % and high molecular weight impurities < 0.5 %. We hope that the current study will lay the foundation for implementation of continuous processing as a method to improve manufacturability of PEGylated therapeutic proteins.

Two-Phase Flow in a Coiled Flow Inverter: Process Development from Batch to Continuous Flow

The transfer of batch processes to continuous flow is a major driver for the application of microreactors. Here, we present a methodology for the transfer of (bio-)chemical reactions in batch mode ...

Comparative assessment of mixing in compact coiled flow inverters under diffusion free laminar flow condition

Mixing characteristics in two innovative variants of coiled flow inverter, namely, symmetrical compact coiled flow inverter (SCCFI) and asymmetrical compact coiled flow inverter (ACCFI) are assessed against that of standard coiled flow inverter (CFI), through experimental and numerical analysis conducted under diffusion-free laminar flow condition (2.35≤NDe≤11.5;7.55≤NRe≤36.96). The experimental study involves the comparison of step input residence time distribution (RTD) curves to examine (i) the narrowing effects with the increase in Dean number until a unique RTD is achieved, and (ii) the effect of bends on narrowing of RTD. Results show that maximum narrowing of RTD is achieved in SCCFI, followed by ACCFI and standard CFI, and the unique RTDs obtained comply with the narrowing trends: SCCFI at NDe=5.3, ACCFI at NDe=3.5 and standard CFI at NDe=3. The experimental trends are interpreted through an elaborate CFD analysis that predicts the secondary flow features as well as RTD curves. The CFD results show Dean vortices and flow inversion intensifying with Dean number that explains the narrowing effect with the increase in Dean number. RTDs obtained at intermediate bends in all the geometries, show the sequential narrowing with increasing number of bends, thus establishing the beneficial role of complete flow inversion on radial mixing.

Intensified tailoring of ZnO particles in a continuous flow reactor via hydrothermal synthesis

ZnO micro-particles of narrow size distribution were successfully produced by the continuous hydrothermal synthesis of zinc nitrate in a coiled flow inverter reactor at different [OH−/Zn2+] molar ratios and flow rates. Results revealed that an increase in mixing intensity and [OH−/Zn2+] molar ratio yields an increase in particle size due to an enhancement in mass transfer between the reacting phases, while the particle size distribution analysis showed that the particles synthesized are monodisperse with polydispersity index below 0.21 and polydispersity P-parameter below 12.3% for all the flow rates tested. The obtained results are a consequence of a dampening effect in axial dispersion due to the formation of a secondary flow and inversion of the velocity profile. Moreover, no significant variation in particle size was obtained by increasing the [OH−/Zn2+] molar ratio at Dean numbers of 20. The experimental results suggest that the coiled flow inverter is an attractive alternative for carrying out the hydrothermal synthesis of metal oxides offering production flexibility with a high quality product if mixing throughout the system meets the hydrodynamic criteria discussed in this work.

Numerical study of flow mixing and heat transfer in helical pipes, coiled flow inverters and a novel coiled configuration

Liquid mixing is compared in different helical configurations, i.e. straight coils, coiled flow inverters (CFI), and newly introduced coils (Coiled Flow Reversers, CFR). The considered ranges of Reynolds and Dean numbers are 10 ⩽ Re ⩽ 3,000 and 3 ⩽ De ⩽ 900, respectively. Two orientations for the liquids interface at the inlet were applied (parallel or perpendicular interface to the coil axis). The parallel interface leads to significantly higher mixing, due to an optimal alignment with Dean vortices. The use of CFI or CFR could reduce the strong influence of the inlet interface. For Re ⩾ 500, mixing in the CFR is best despite the strongly reduced residence time. When heat transfer is compared to the straight coil, the CFR shows about 5% increase in outlet temperature, compared to less than 4% increase in the CFI for Re ⩾ 1,000. Nevertheless, the CFR has a slightly higher pressure drop.

Mixing of Viscoelastic Fluid Flows in a Coiled Flow Inverter

Despite having the advantage of a secondary flow pattern in coiled tubes, a very high Dean number is required to induce significant mixing in helical coils, usually implying high shear rates. At ve...