Static Mixer Elements Research Articles

Applicability and Validity of CFD‐based Compartment Models for One to Multiple Operating Points

AbstractCFD‐based compartment (CPT) models offer a promising modeling method and trade‐off between computational effort and required accuracy. The models combine the relevant fluid dynamics from the computational expensive CFD and the incorporation of complex reaction mechanisms usually used in basic reactor models. However, one criticism is their reliance on specific operating points, rendering them invalid when boundary conditions change. This study explores using a CFD‐based CPT model for static mixing elements across multiple operating points by making use of the creeping flow. The mean age theory facilitates a comprehensive comparison between CFD and CPT models. Results indicate that within this flow region, the CPT model can be extrapolated to other operating points via linear scaling.

Plug‐and‐Play Multimaterial Chaotic Printing/Bioprinting to Produce Radial and Axial Micropatterns in Hydrogel Filaments

AbstractNature abounds with micro‐architected materials containing layered multi‐material patterns that often transition within the very same monolithic piece. Fabricating these complex materials using current technologies is challenging. Multimaterial chaotic printing is presented—an extrusive printing method based on the use of chaotic advection—that can fabricate microstructured hydrogels with well‐defined multimaterial and multilayered micropatterns. Printheads containing internal Kenics static mixing (KSM) elements and top‐ and lateral‐positioned inlets are used to produce a wide repertoire of multilayered hydrogel filaments. In this plug‐and‐play system, the radial and axial micropatterns can be designed ad hoc by defining the printhead configuration (i.e., the number of KSM elements and inlets, and the inlet positions) and the flow program (i.e., activation/deactivation of the ink‐flow through each inlet). Computational fluid dynamics simulations closely predict the microstructure obtained by a given printhead configuration. The application of this platform is illustrated for easy fabrication of fibers with radial microgradients, bacterial ecosystems, structured emulsions, micro‐channeled hydrogel filaments, a pre‐vascularized tumor niche model, and skeletal muscle‐like tissues with axial and radial transitions of bioactive glass compartments. It is envisioned that multimaterial chaotic printing will be a valuable addition to the toolbox of additive manufacturing for the rational fabrication of advanced materials.

Analysis of heat transfer enhancement due to helical static mixing elements inside cooling channels in machine tools

In this contribution, the effectiveness of helical static mixers in different arrangements and flow configurations/regimes is explored. By means of a thorough numerical analysis, the application limits of helical static mixers for the heat transfer enhancement inside cooling channels of machine tools are provided. The numerical simulations were processed with the commercial finite volume Computational Fluid Dynamics (CFD) code, ANSYS Fluent 2020 R2. This study shows that there exists an optimal range of application for static mixers as heat exchange intensifier depending on the flow speed, the transmitted heat flow and the thermal conductivity of the tool. The investigations of this contribution are restricted to single-phase flow in circular cross-sections and straight channel geometries. As a representative application example for a machine tooling, the cooling of a simple injection mold is investigated. The research carried out reveals that the application of static mixing elements for enhancement of heat transfer is very effective, particularly for fluid flow with low to medium Reynolds numbers, close-contour cooling, high values of heat fluxes, and high thermal conductivity of the tooling material.

A novel process to produce stratified structures in food

A method to create stratified structures with static mixing elements initially developed for the plastic polymer industry is investigated here as a new route for structuring food dispersions. Food dispersions of different viscosities were structured with static mixing elements to investigate the potential of the method for foods. Differently coloured chocolates were used as the model products. The viscosity of the chocolate was controlled through the addition of pea fibre. The first step was the formation of 2–8 layers, with the two differently coloured chocolates. Then, the chocolate dispersions were layered into 256 layers with an approximate layer thickness of 60 μm. Layer formation was facilitated when using similar paste viscosity and when slip was induced through wall coating with vegetable oil. Uniaxial cutting tests of the layered chocolate indicated that layering resulted in different mechanical properties, parallel and perpendicular to the layers. Fibre orientation in the direction of flow was observed, resulting in the potential to induce anisotropy, additional to the layers. The higher viscous dispersions, wheat dough and melt cheese, could also be structured into layers, although the force constraints of the experimental set-up were reached. Mid-stream additions were added to produce strand structures instead of layers, resulting in higher hierarchy structures but less uniformity.

Tailoring flow behavior and heat transfer in tempering channels for high-pressure die casting—analysis of potentials of commercial static mixers and prospects of additive manufacturing

Additive manufacturing (AM) opens up manifold possibilities to influence the heat transfer between fluid and die in high-pressure die casting (HPDC), eventually allowing to minimize the total cycle time of the process. AM already has been exploited to establish near-contour temperature control systems in industrial applications. However, AM not only allows to influence the position of tempering channels in dies but it also allows to influence the fluid dynamics itself, e.g., by imprinted static mixers. Up to now, such flow-influencing mixing elements have not been considered in metal AM. In the present work, the impact of such metallic static mixers and most relevant processing conditions is investigated experimentally as well by computational fluid dynamics (CFD) simulation. In a first step, conventional static mixer elements are integrated into straight tempering channels to stimulate turbulences of the flowing tempering medium, finally resulting in an increase of the heat transfer up to 33%. In a second step, laser-based powder bed fusion of metals (PBF-LB/M) is applied to realize static mixers. Results obtained reveal that tempering channels without negative influences on the general flow behavior compared to conventional static mixers in straight tempering channels can be realized. In conclusion, the presented results show a positive impact on heat transfer and, thus, allow to further increase the economic efficiency of the HPDC process.

One-Step Bioprinting of Multi-Channel Hydrogel Filaments Using Chaotic Advection: Fabrication of Pre-Vascularized Muscle-Like Tissues.

The biofabrication of living constructs containing hollow channels is critical for manufacturing thick tissues. However, current technologies are limited in their effectiveness in the fabrication of channels with diameters smaller than hundreds of micrometers. It is demonstrated that the co-extrusion of cell-laden hydrogels and sacrificial materials through printheads containing Kenics static mixing elements enables the continuous and one-step fabrication of thin hydrogel filaments (1mm in diameter) containing dozens of hollow microchannels with widths as small as a single cell. Pre-vascularized skeletal muscle-like filaments are bioprinted by loading murine myoblasts (C2C12 cells) in gelatin methacryloyl - alginate hydrogels and using hydroxyethyl cellulose as a sacrificial material. Higher viability and metabolic activity are observed in filaments with hollow multi-channels than in solid constructs. The presence of hollow channels promotes the expression of Ki67 (a proliferation biomarker), mitigates the expression of hypoxia-inducible factor 1-alpha , and markedly enhances cell alignment (i.e., 82% of muscle myofibrils aligned (in ±10°) to the main direction of the microchannels after seven days of culture). The emergence of sarcomeric α-actin is verified through immunofluorescence and gene expression. Overall, this work presents an effective and practical tool for the fabrication of pre-vascularized engineered tissues.

Study of fluid flow movement of biodiesel production with helical static mixing reactor using computational fluid dynamics(CFD)

The simulation was carried out using the computional fluid dynamics method to find out and read the flow pattern in the reactor. Simulations were implemented in nine reactors, which every reactor have 12 helical type static mixer elements. The elements in every static mixer are twisted 180°, and between elements are glued at an angle of 90°. Also performed two scenarios on the modification of the torsion angle of the elements, namely 225° and 270° . Based on the flow velocity and viscosity, the static mixer with 270° torsion angle has a good mixing pattern compared to the torsion angle of 225° and 180° . The viscosity was descresed by 5.4% and the velocity was increased by 3.05%. The concentration of fatty acid methyl ester using static mixer 270° (as much as 97.50%) was higher than the 225° torsion angle (as much as 97.46%) and the 180° torsion angle (as much as 97.41%).

Combining Functional Prototyping of 3D Printed Reactors with a Modular Reactor Setup for Continuous Emulsion Polymerization

AbstractThe potential for fast and specific process optimization by functional prototyping with 3D printed reactors was shown for a known continuous emulsion polymerization in a modular setup. Three tubular reactors, two with static mixing elements and a continuously stirred tank reactor (CSTR) were printed from polylactic acid. Thermal imaging of the reactors allows to map the basically adiabatic progress of the redox‐started radical polymerization in a space‐resolved way. The application of static mixing elements led to a higher conversion stability and a more uniform product, as expected for a better mass transfer. Polymerization in combinations of CSTR and a tubular reactor showed further improvements of process stability and product uniformity in terms of particle size and mol masses.

Gas‐Liquid Flow Patterns in a Rectangular Milli‐Structured Channel with Static Mixing Elements

AbstractThe gas‐liquid flow behavior through a milli‐scaled channel provided with a staggered herringbone‐like static mixer was investigated using high‐speed recordings. For three different substance systems consisting of water, 5 wt % acetic acid in aqueous solution, and propylene glycol as liquid phase and nitrogen as gas phase, flow patterns and their transitions were determined by analyzing image sequences of the flow and summarized in flow pattern maps. Surge flow, slug flow, and bubbly flow were observed at different flow rates. The flow distribution and transitions between flow patterns mainly depend on the viscosity and surface tension of the liquid phase. By just reducing the surface tension, slug flow is not observed, and thus an early transition into a bubbly flow regime takes place. An increase in viscosity counteracts this effect.

Mathematical modelling of hydrothermal performance for Kenics type static mixer using power law obeying fluids

AbstractIn this study, analytical, numerical, and experimental works are presented to demonstrate hydrothermal characteristics of a flow choosing non‐Newtonian behaviour through a Kenics type static mixer. Experiments are conducted by varying the superficial fluid velocities of the heterogeneous mixture oil with Sudan dye and water, as well as for the homogeneous aqueous system, consisting of CMC (2 wt%) in water. Six static mixing elements are placed in series, and the corresponding wall temperatures of the inline pipe are varied over a range of 293–363 K. In the context of hydrodynamic study, analytical models are solved using the Bessel function and Laguerre function and validated with the in‐house experimental results and numerical results. In the thermal performance study, mathematical models are formulated based on differential transformation method (DTM) and homotopy perturbation method (HPM), and have been validated with the numerical results. The deviation among the experimentally measured average pressure drops estimated from our experiment and that predicted by analytical models is found to be as low as ±8.1%. The deviation between the analytical results obtained from the HPM and DTM method and numerical results based on the finite volume method solution of the same equation is observed as low as ±4%. Additionally, both proposed analytical methods used are compared with each other to evaluate the dimensionless swirl flow velocity and temperature gradient of the inline Kenics Static mixer. In the thermal performance study, we observe that the DTM is in good agreement with the numerical method as compared to HPM.

Numerical simulation study on performance optimization of desuperheater

In order to make the superheated steam flowing at high speed complete the desuperheating process in the pipeline with limited distance, so as to save the production cost, this paper makes structural innovation on the existing equipment, a solution to install static mixing elements in the pipeline downstream of the nozzle of the desuperheater is proposed to improve the performance of the desuperheater without increasing the cost of nozzle atomization. Based on Fluent software, the working process of the new desuperheater is numerically simulated, and its working mechanism and desuperheating effect are visually analyzed. Compared with the traditional desuperheater, the desuperheating range of the new desuperheater in the pipeline with the same distance is increased by about 70.8%, and the temperature non-uniformity coefficient is reduced by about 75.5%. Furthermore, the validity of the above simulation results is verified by experiments.

One‐step creation of hierarchical fractal structures

AbstractRelatively recently, we advanced a route to create, in a controlled fashion, combined horizontal and vertical stratified structures by simple and energy‐efficient processing operations employing static mixing elements. While in state‐of‐the‐art static mixing the focus is on layer multiplication, here the aim is to create hierarchical fractal structures. Therefore, the main question addressed in this article is how structures, rather than layers, can be multiplied. The key aspect is the addition of layers on the sides or in the midplane of the flow during the process; every addition step increases the hierarchy by one level. This article derives the general formalism for forming fractal structures with controlled hierarchy, and we develop the language required to design and construct the dies. The main part of the article addresses this main topic and is based on the splitting serpentine static mixer geometry that can be easily made on the parting surfaces of a mold on both the micro‐ and the macroscale. The second part of the article addresses the strategy to minimize the number of mirroring steps, eventually avoiding mirroring completely, and is based on the rotation‐free multiflux static mixer geometry. With the design language derived, complex hierarchical fractal structures can be generated simply by changing the number and sequence of operators within extrusion dies or molds, providing a one‐step solution to produce material structures for potential use in diverse applications ranging from advanced mechanical systems to photovoltaic devices, where controlled assembly of dissimilar materials, and the realization of huge interfaces and genuine cocontinuity throughout the cross section, is critical.

Mixing Characteristics Of Gas-Liquid Flow In A Static Mixer: A Numerical Study

Mixing characteristics of gas-liquid co-current upward flow inside a vertical pipe equipped with a helical static mixer element were numerically investigated. The results from computational fluid dynamics (CFD) simulations with Euler-Euler model of three different length to diameter ratio (L/D) of the static mixer elements were compared. All simulated static mixers provide a better mixing condition in the comparison with the one without a static element. The sudden increase of rotational strength indicated by the liquid velocity curl was observed once the gas-liquid flows enter the static-mixer element zone. The smallest L/D static mixer provides the highest liquid velocity curl in the smallest axial distance providing the most effective mixing process among the tested elements. The best mixing characteristics shown by radial gas distribution was achieved with the static mixer with a smallest L/D.

Improving mixing performance by curved‐blade static mixer

AbstractThis article addresses design modification to a flat‐blade static mixer to enhance mixing performance. The static mixer elements used in this work consist of four blades with curvature made to intensify turbulent‐like flow, while reducing the pressure drop. The blades were mounted on a cylindrical housing with 45° rotation relative to the axial direction. The mixer assembly was used in three different arrangements of 8, 10, and 14 elements for a range of Reynolds number between 600 and 7,000. The coefficient of variance (COV) of samples was used to measure the mixing quality. The curved‐blade mixer provides considerable improvement in mixing quality compared with the flat‐blade mixer and comparable to the SMX mixer. Compared with the flat‐blade static mixer, the new design reduces the COV by up to about 50%. This effect is more pronounced when the number of mixing elements increases. Furthermore, the friction factors for the modified mixer, obtained at a wide range of Reynolds number, were apparently smaller than those for the flat‐blade, SMX, and SMV mixers. The correlation presented for the friction factor, when all mixer arrangements and aspect ratios were considered, supports the experimental data with ±15% deviation.

Ir/Ni Photoredox Dual Catalysis with Heterogeneous Base Enabled by an Oscillatory Plug Flow Photoreactor

Continuous flow reactor technology has a proven track record in enabling photochemical transformations. However, transfer of a photochemical batch process to a flow protocol often remains elusive, especially when solid reagents or catalysts are employed. In this work, application of an oscillatory plug flow photoreactor enabled a heterogeneous MacMillan-type C(sp2)–C(sp3) cross-electrophile coupling. Combination of an oscillatory flow regime with static mixing elements imparts exquisite control over the mixing intensity and residence time distribution, pinpointing a mindset shift concerning slurry handling in continuous flow reactors. The C(sp2)–C(sp3) cross-electrophile coupling was successfully transferred from batch to flow, resulting in an intensified slurry process with significantly reduced reaction time and increased productivity (0.87 g/h).

Enhanced Dispersive Mixing in Twin-Screw Extrusion via Extension-Dominated Static Mixing Elements of Varying Contraction Ratios

Abstract Twin screw extruders (TSE) are widely used in polymer blending and compounding operations, since the relatively high stresses they impart on melts and controllable residence times make the...

A Holistic View on Urea Injection for NOx Emission Control: Impingement, Re-atomization, and Deposit Formation

The injection of urea-water solution (UWS) sprays into engine-close selective catalytic reduction (SCR) systems faces developers with complex challenges regarding two-phase flow and deposit formation. Potential spray impact on the static mixing elements inside the exhaust duct can lead to accumulation of liquid film and solid deposits, which may result in detachment of large UWS droplets at the trailing edges of the mixer blades. Present work focuses on the mechanisms of film and deposit formation within the scope of a joint study on spray preparation in the mixing section of SCR systems. A production type SCR exhaust system is used for optical investigations on gas flow and UWS droplets at the mixing element using Laser Doppler Anemometry (LDA) and Long Distance Microscopy (LDM) with a high-speed camera. Measured shear flows inside the mixing element are up to three times higher than the flow velocity upstream the mixer. Here, a decrease of droplet diameters of detached droplets is revealed with increased shear flow velocity. Characteristic urea deposits are created in a laboratory test bench and their surface structure is measured by use of Confocal Microscopy. Results show highly rough surface structures, which are used as input parameters together with the flow measurements to define the computational domain at the trailing edge of the mixer blades. Smoothed Particle Hydrodynamics (SPH) method is adopted for the numerical simulation of the transient two-phase flow and validated by LDM high-speed recordings of droplet detachment. Comparisons reveal a distinct influence of solid depositions on the re-atomization of the liquid film at the rear edge of the mixer blade. By interface resolving simulations with a phase-field method, the wall impingement of a sequence of large secondary droplets and associated film formation are studied. The results indicate that UWS film formation at the exhaust pipe wall may be reduced by hydrophobic surfaces and high gas velocities near the wall.

Self-assembly of colloidal lignin particles in a continuous flow tubular reactor

A scalable tubular flow reactor was designed and developed for the continuous formation of colloidal lignin particles (CLPs). The reactor consists of a series of tubes, inside which many static mixing elements are equipped to aid in the formation of a homogeneous dispersion of CLPs. The colloids were formed instantaneously through self-assembly upon the addition of the lignin solution into water. The effects of flowrate, length of the tubes and static mixing elements on the particle size, stability and CLP yield after drying were determined. It was found that a higher flowrate of lignin solution within the testing range of 32−240 mL/min resulted in smaller sized CLPs. Optimizations of the mixing length and the static mixing elements to 3 m and at least 1 m, respectively, could ensure an efficient mixing, thus resulting in CLP dispersions with smaller size of lignin particles (200 nm–400 nm) and high lignin concentrations (up to 2.8 wt. %) along with yields up to 95 %. The TEM images indicated that the formed colloids are composed of lignin particles of regular sphere shape and with good stability. The tubular reactor offers better control of particle size which ensures the formation of colloidal dispersions with narrower particle size distribution in comparison to a stirred mixer reactor. Furthermore, using a tubular reactor enables the continuous production of CLPs, making it suitable for scale up and industrial applications.

Digital and lean development method for 3D-printed reactors based on CAD modeling and CFD simulation

The compatibility of computer-aided design (CAD) with computational fluid dynamics (CFD) softwares was used to establish a digital and lean development method for 3D-printed reactors which allows for shorter development cycles and targeted process setup. CAD modeling, as the starting point of an additive manufacturing process, creates 3D-designs, which can be directly evaluated by CFD simulation. Thus, challenging assumptions or issues regarding the performance of a tubular reactor can be visualized and redefined to create iteratively new strategies and solutions in a cost- and time-effective way. Our approach enables to build and deliver reactor designs incrementally and faster as it can be performed digitally and tailored to specific requirements. The developed reactor design subsequently can be fabricated directly by 3D printing techniques. The method is based on an established 3D-printed tubular bended reactor for emulsion polymerizations, without being limited to a specific case and enabled the lean fabrication of a tubular reactor being developed to proactively use Dean vortices by reducing dead zones in a more compact design. Optimized flow patterns were further obtained by the tailor-made implementation of static mixing elements at targeted positions of the reactor design.

Inline gas/liquid flow measurement using sequential static mixing elements

This work explores the use of two sequential static mixers for the determination of mass flow and density of an effervescent two-phase mixture where compressibility effects remain relevant. The upstream static mixer exhibited a non-standard two-phase pressure drop correction factor (KL) due to flow homogenization dynamics, while the downstream static mixer exhibited more traditional KL vs. gas fraction trends. Through combination of the two mixers, mass flow rate was estimated to within ± 5 kg/h for the majority of conditions up to 100 kg/h and 70% gas fraction. Density estimates were comparable to those obtained from an in-line commercial Coriolis meter, with relative error consistently within ± 100 kg/m3 of actual bulk-phase densities. The configuration resulted in predictions comparable to an inline commercial Coriolis meter over a broad range of flow conditions, and represents a relatively inexpensive flow metering approach provided sufficient gas expansion is achieved to cause a variation in KL. Topic points•Use of sequential static mixers to normalize flow patterns in gas-liquid systems.•Introduction of a sudden expansion to induce gas fraction variation and a corresponding change in the 2-phase flow modifier, KL.•Comparison of calibrated results to a commercial Coriolis meter.