Mixer Units Research Articles

Hydrogen Production using PEM Electrolyzer

Abstract: This paper presents a simulation study of alkaline electrolysis for H2 production using Aspen Plus. The simulation model incorporates reactor, separators, mixer, and heat exchanger units to accurately represent the AWE process. The model is designed to evaluate the performance of an AWE system under different operating conditions and aims to achieve a reference H2 production rate of 0.179663 kg/hr. The simulation results demonstrate that the AWE system can successfully produce H2 at the specified rate. The model provides a detailed analysis of the system's behavior and H2 production rate, under varying operating conditions. The findings of this study provide valuable insights into optimizing the design and operation of AWE systems for large-scale H2 production

Nanobody-functionalized conduit with built-in static mixer for specific elimination of cytokines in hemoperfusion

Removing excessively produced cytokines is of paramount significance in blood purification therapy for hypercytokinemia-associated diseases. In this study, we devised a conduit that is modified with nanobodies (Nb) and incorporates static mixers (Nb-SMC) to eliminate surplus cytokines from the bloodstream. The low-pressure-drop (LPD) static mixer, with each unit featuring two 90°-crossed blades, was strategically arranged in a tessellated pattern on the inner wall of the conduit to induce turbulent mixing effects during the flow of blood. This arrangement enhances mass transfer and molecular diffusion, thereby assisting in the identification and elimination of cytokines. By utilizing computational fluid dynamics (CFD) studies, the Nb-SMC was rationally designed and prepared, ensuring an optimal interval between two mixer units (H/G = 2.5). The resulting Nb-SMC exhibited a remarkable selective clearance of IL-17A, reaching up to 85 %. Additionally, the process of Nb immobilization could be adjusted to achieve the simultaneous removal of multiple cytokines from the bloodstream. Notably, our Nb-SMC displayed good blood compatibility without potential adverse effects on the composition of human blood. As the sole documented static mixer-integrated conduit capable of selectively eliminating cytokines at their physiological concentrations, it holds promise in the clinical potential for hypercytokinemia in high-risk patients. Statement of significanceHigh-efficient cytokines removal in critical care still remains a challenge. The conduit technique we proposed here is a brand-new strategy for cytokines removal in blood purification therapy. On the one hand, nanobody endows the conduit with specific recognition of cytokine, on the other hand, the build-in static mixer enhances the diffusion of antigenic cytokine to the ligand. The combination of these two has jointly achieved the efficient and specific removal of cytokine. This innovative material is the only reported artificial biomaterial capable of selectively eliminating multiple cytokines under conditions close to clinical practice. It has the potential to improve outcomes for patients with hypercytokinemia and reduce the risk of adverse events associated with current treatment modalities.

Drop rise and interfacial coalescence initiation in Bingham materials

Drop coalescence in viscoplastic materials is present in various industrial applications and the environment. The plasticity of the surrounding material affects drop rise, collision, and film drainage dynamics, and knowledge about these is essential for designing and operating industrial mixer and separator units. Despite its importance, the coalescence of drops in yield stress materials is not entirely understood. In this work, we investigate the effects of the surrounding material plasticity on the rise and interfacial coalescence initiation of Newtonian drops using direct numerical simulations. Plastic effects contribute to the formation of smaller and spherical films, which facilitate the film drainage process on the one hand, but also to an increase in the resistance of the film to flow, which makes the drainage process more difficult on the other hand. The fluids’ interfaces are less deformable for high surface tension regimes, and the flow resistance effects become more significant than the film shape change effects. As a result, the drainage time tends to increase with the level of plasticity. For low surface tension regimes, the fluid interface is more deformable, and film drainage time tends to decrease with an increase in the level of plasticity.

Novel stirring-rod-inspired mixer-integrated printhead for fabricating gradient tissue structures

Conventional methods for creating gradient tissue structures using extrusion-based 3D printing (E3DP) systems involve using mixers to create homogeneous materials. However, commercially available mixers can generate high fluid pressure and shear force that harm cells. Hence, a new mixer-integrated printhead was developed, inspired by stirring-rod-assisted mixing processes. The as-designed mixing system was validated through computational fluid dynamics (CFD) simulations using input parameters including ink viscosity, density, and velocity vector and output parameters including material volume fraction, average fluid pressure, and shear force. Six-stir element mixer units were used to comprehensively analyze material mixing while considering the fluid volume fraction after flowing through the mixers. Printheads integrated with multiple discrete mixers with consistent spiral directions, performing well when introducing gaps, were used to reduce the cell pressure and shear force. The optimal mixer design, with two 1.62-mm gaps and six-stir element mixer units sharing the same spiral structure, reduced the average fluid pressure and shear force by 3.196e+4 Pa and 0.368e+2 Pa, respectively, compared with a commercial static mixer. Finally, a mixer-integrated printhead was manufactured, matching well with the original design. This research could improve E3DP systems and serve as a design reference for 3D printing structures of varying stiffness.

Determination and optimisation of Resonant Acoustic Mixing (RAM) efficiency in Polymer Bonded eXplosive (PBX) processing

An investigation into how the efficiency (time and energy required for homogeneity) of Resonant Acoustic Mixing (RAM) can be determined and optimised was undertaken. An idealised Polymer Bonded eXplosive (PBX) simulant based on glass microbeads (28.3 μm D50, 62% v/v in binder and plasticiser) was used for mixing. Mixing evolution was monitored using machine output data, whereby the mixer ‘intensity’ (related to power draw) was plotted against time. Experiments were undertaken with three acceleration settings, three mixer units, and three vessel materials of low, medium, and high surface free energy. Different stages of the mixer ‘intensity’ profiles were found to correspond to discrete stages of mixing, as well as further rheological changes due to continued frictional heating, thus viscosity reduction, beyond homogeneity being achieved. Time to mixing completion was found to be repeatable within a standard deviation of ±10%, strongly dependent on acceleration setting, and additionally dependent on vessel material, though additional data is required to confirm this. A significant difference in mixing time was observed between different LabRAM units. Partial vacuum application without degassing was beneficial for mixing. Finally, a paradigm linking the ‘movement modes’ of mixing was constructed, based on literature observations and the experimental results.

A new reactor for enzymatic synthesis of biodiesel from waste cooking oil: A static-mixed reactor pilot study

Nowadays, biodiesel has become a globally accepted renewable liquid fuel. The environmentally friendly enzymatic synthesis process is being widely researched. To solve the problem that production efficiency is low in enzymatic process, we optimized the structure of the static mixer by computational fluid dynamics (CFD) modeling. The optimal static mixer consists of 6 mixer units, and the length-diameter ratio of every mixer unit is 1.5. The enzymatic synthesis of biodiesel was conducted between waste cooking oil (WCO) and methanol by transesterification and esterification. The reaction conditions were also optimized in this designed static-mixed reactor. Under optimal conditions, the reaction time can save half time when compared with the traditional stirred reactor, which indicates that the static mixer has higher production efficiency.

Mixing of Dredging Sludge with Cement Powder in New Continuous M–Y Mixer

The new 2n mixing theory, which is basically based on kneading and lapping mechanism, was originally developed with the concept of Japanese noodle (UDON) making method. With development of prototype mixer, it was experimentally verified that different types of light and heavy materials were possible to be mixed properly achieving the required properties similar to that from conventional mixing method. New continuous mixer “M–Y mixer” was developed to mix various materials for the practical use. This paper describes the mixing of dredging sludge in M–Y mixer using cement paste injection method and cement powder feeding methods at the actual site. Test results showed that the mixing performance of M–Y mixer reached to the nearer level of conventional mixing method in terms of 28 days compressive strength and its variation coefficient while using 15 numbers of M–Y mixer units. However, it did not give any descriptive trend on both compressive strength and its variation coefficient due to non-uniformity of feeding very small amount of cement continuously.

Influence of successive and independent arrangement of Kenics mixer units on light/dark cycle and energy consumption in a tubular microalgae photobioreactor

The design of mixers in tubular photobioreactors is a key part to reduce the cost of microalgal culture. There have been several investigations of the static Kenics mixer in tubular photobioreactors, but how to use it efficiently has been rarely reported. In this work, the efficiency of light/dark cycle enhancement, defined as the ratio of the dimensionless increment of light/dark cycle frequency to the dimensionless increment of energy consumption, is introduced to evaluate economic aspects of adding a mixer. Then, the 4-unit Kenics mixer consisting of four successive left-right-twisting units and 1-unit Kenics mixer consisting of only one unit are compared in terms of the efficiency using computational fluid dynamics, which shows that an increase of the unit number (from 1 to 4) does not bring a considerable improvement (<7.5%) in the L/D cycle frequency, while leads to a much higher pressure drop (>36%), and thus a much lower efficiency. Finally, two approaches to increasing the efficiency are developed. One is to adjust the boundary of light and dark zones in the tube to approximate the high vorticity region, and the other is to adopt more effective types of arrangement of units (e.g., the interval arrangement, instead of the already-existing successive arrangement).

Microfluidic sputum homogenizer driven by water-head pressure

Homogenizing organism distribution in sputum samples is an initial, yet crucial step to diagnose pulmonary diseases with the samples. Although a homogenization platform for a diagnostic system needs to be system-compatible and efficient, it is rarely implemented. Here, we present a pulsatile micromixer for sputum homogenization that is efficient and does not use dynamic external controllers. The device consists of three oscillator and one mixer units. The oscillator unit autonomously converts a constant input of water-head pressure to a pulsatile pressure, and the mixer unit utilizes this pressure to homogeneously mix two solutions. The mixing performance is analyzed with different oscillation frequencies and width of mixer membranes. The device implemented homogeneous micromixing with a 9 Hz pulse for a flow rate up to 350 μL/min and approximately 200 μL/min for 1 cP and 10 cP viscosity solutions, respectively. Importantly, the device demonstrated successful homogenization of sputum samples with cell viabilities similar to those of the standard method for the flow rate up to 100 μL/min, thereby exhibiting biocompatibility with clinical samples. Our device is potentially useful for various lab-on-a-chip applications that require the compatibility of system integration without sacrificing mixing efficiency.

Pulsatile micromixing using water-head-driven microfluidic oscillators

This study presents a pulsatile micromixer which does not use any dynamic off-chip controllers to achieve homogeneous mixing. The micromixer system consists of oscillator and mixer units that include microfluidic valves and elastomeric membranes. The oscillator unit autonomously generates pulsatile pressure using the constant input of water head pressure. Driven by the pulsatile pressure, periodic fluidic bands are generated in the mixer unit and are mixed within a short channel length. In this way, the oscillator unit controls fluidic switching frequency and the mixer unit regulates flow rate, separately. The mixing performance for various channel widths, switching frequencies, and flow rates is analyzed. The micromixer shows homogenous mixing with a mixing index of ∼90% for a flow rate of up to 20μL/min and switching frequency in the range of 14–20Hz.

A "twisted" microfluidic mixer suitable for a wide range of flow rate applications.

This paper proposes a new “twisted” 3D microfluidic mixer fabricated by a laser writing/microfabrication technique. Effective and efficient mixing using the twisted micromixers can be obtained by combining two general chaotic mixing mechanisms: splitting/recombining and chaotic advection. The lamination of mixer units provides the splitting and recombination mechanism when the quadrant of circles is arranged in a two-layered serial arrangement of mixing units. The overall 3D path of the microchannel introduces the advection. An experimental investigation using chemical solutions revealed that these novel 3D passive microfluidic mixers were stable and could be operated at a wide range of flow rates. This micromixer finds application in the manipulation of tiny volumes of liquids that are crucial in diagnostics. The mixing performance was evaluated by dye visualization, and using a pH test that determined the chemical reaction of the solutions. A comparison of the tornado-mixer with this twisted micromixer was made to evaluate the efficiency of mixing. The efficiency of mixing was calculated within the channel by acquiring intensities using ImageJ software. Results suggested that efficient mixing can be obtained when more than 3 units were consecutively placed. The geometry of the device, which has a length of 30 mm, enables the device to be integrated with micro total analysis systems and other lab-on-chip devices.

Prototyping a calorimeter mixing cell with direct metal laser sintering

Herein we demonstrate the inherent strengths of an additive manufacturing method in the fabrication of a continuous-flow static mixing cell. The mixing cell was designed for the measurement of the enthalpy change related to mixing of fluids. The manufactured mixing cell consists of a single continuous structure and contains a highly tortuous internal channel, the construction of which would have been impossible using more conventional techniques. The design of the mixing cell is analyzed through both theoretical calculations as well as experimental testing. The manufactured calorimeter cells were tested with two well-known reference systems and were found to be fully functional and comparable to commercial ones. Inclusion of laminating mixer units inside the mixing cell was found to facilitate the mixing of the incoming streams.

Terahertz hot electron bolometer waveguide mixers for GREAT

Supplementing the publications based on the first-light observations with the German Receiver for Astronomy at Terahertz frequencies (GREAT) on SOFIA, we present background information on the underlying heterodyne detector technology. We describe the superconducting hot electron bolometer (HEB) detectors that are used as frequency mixers in the L1 (1400 GHz), L2 (1900 GHz), and M (2500 GHz) channels of GREAT. Measured performance of the detectors is presented and background information on their operation in GREAT is given. Our mixer units are waveguide-based and couple to free-space radiation via a feedhorn antenna. The HEB mixers are designed, fabricated, characterized, and flight-qualified in-house. We are able to use the full intermediate frequency bandwidth of the mixers using silicon-germanium multi-octave cryogenic low-noise amplifiers with very low input return loss. Superconducting HEB mixers have proven to be practical and sensitive detectors for high-resolution THz frequency spectroscopy on SOFIA. We show that our niobium-titanium-nitride (NbTiN) material HEBs on silicon nitride (SiN) membrane substrates have an intermediate frequency (IF) noise roll-off frequency above 2.8 GHz, which does not limit the current receiver IF bandwidth. Our mixer technology development efforts culminate in the first successful operation of a waveguide-based HEB mixer at 2.5 THz and deployment for radioastronomy. A significant contribution to the success of GREAT is made by technological development, thorough characterization and performance optimization of the mixer and its IF interface for receiver operation on SOFIA. In particular, the development of an optimized mixer IF interface contributes to the low passband ripple and excellent stability, which GREAT demonstrated during its initial successful astronomical observation runs.

Approximate mapping method for prediction of chaotic mixing in spatial-periodic microchannel

The use of approximate Poincaré maps for prediction of chaotic mixing in spatial-periodic channel is investigated in this article. The maps are constructed based on the corresponding distribution of discrete tracers on two successive Poincaré sections. Three methods are analysed including the triangular weighted interpolation, Shepard's method and weighted-least-square polynomial fitting (WLS-PF). Their application to a three-dimensional (3D) chaotic micromixer is demonstrated. Relevant results show that all the schemes can provide reliable predictions of the mixing quality within a limited number of mixer units. Among the three, the WLS-PF is less influenced by the grid-sizes. The mapping approach provides an alternative way to examine the performance of the spatial-periodic chaotic micromixer. It will greatly reduce the enormous efforts involved in 3D computational fluid dynamics (CFD) analysis.

Dynamic modelling of copper solvent extraction mixer–settler units

The copper Leaching, Solvent Extraction and Electrowinning circuit (LX–SX–EW) is one of the most effective processes for extracting copper from low grade ores. This work focuses on the liquid–liquid extraction SX sub-process, since many difficult to handle operational problems within LX–SX–EW circuits are related to SX malfunction. Controlling these problems better can reduce operational costs and increase recovery and copper production. Realistic dynamic simulation is a standard tool nowadays to design and assess more effective control strategies. In this work we present a general dynamic model for SX mixer–settlers, and applied it to two different units, one located in an extraction stage and the other in a stripping stage of a copper plant. The model includes a non-trivial settler hydrodynamics represented by a set of nonlinear differential equations for both mixer and settler units. The mixer is modelled as a continuous stirred tank reactor and the settler as a hydrodynamic circuit combining series and parallel connections of continuous stirred tank and plug flow reactors. The model was calibrated with industrial plant data, resulting in realistic simulations of outlet copper concentrations. Using the proposed model, we obtained better fitting than that achieved with simpler settler models that include only a time delay. The model fitting parameters provide sufficient flexibility to accurately reproduce the dynamics of different units in industrial plants.

Design tools to control transients in solvent extraction plants

The design of solvent extraction plants has been generally based on the assumption of steady operating conditions in both the settler and the mixer units. However, recent experience in both large and small plants has shown this not to be the case. Mixer transients include start up aqueous locking and partial phase separation in secondary mixers, which both lead to reduced plant capacity or overflow of upstream mixers. Analysis of the hydraulic pressure profiles has generated new design methods to eliminate the effects of the partial or complete phase separation. Changes to the method of specification and selection of primary and secondary mixers have been made to eliminate the onset of partial separation during operation. The observation of settler operation has shown that it is also a dynamic process, even under “steady-state” conditions. Four transient phenomena have been identified that lead to internal circulating flows, poor disengagement affine secondary haze and erratic and high entrainment levels in the discharges. A first approximation analysis has shown that there are significant pressure differentials within settlers, and these change along the length and with the phase separation rates. A technique to control the effects of these transients was developed that allows plant performance to be improved beyond “tstandard” expectations. The design and selection of the settler internals is described.

Flow-induced phase inversion in the intensive processing of concentrated emulsions

Flow-induced phase-inversion (FIPI) phenomenon is applied to the emulsification of highly viscous (polymeric) epoxide resins to obtain concentrated colloidal emulsions. It is shown that the phase inversion of a W/O emulsion can be achieved not only through changes in thermodynamic state variables but also by the imposition of ultra-high deformation (extensional) rates under constant thermodynamic conditions. Phase inversion is carried out using a model static mixer (multiple expansion contraction static mixer, MECSM) which is essentially a series of short capillaries with flow dividers. The degree of phase inversion is dependent on the rate of deformation and number of mixer units. The effects of temperature, surfactant concentration and composition and mean hydrophile-lipophile balance on phase inversion behaviour are investigated. The properties of the emulsions produced by this FIPI-emulsification are evaluated through particle size and viscosity measurements and optical and electron microscopy studies. Mechanisms of phase inversion and subsequent emulsion droplet size reduction are proposed which are based on the behaviour of microstructured fluids under converging and diverging flows. The significance of the type of surfactant system used in the experiment is discussed in facilitating the flow-induced phase inversion and subsequent emulsion droplet size reduction, as well as emulsion stability.

The use of slow pseudo-first-order reaction to estimate the size of micro-mixed volume in a flow system

The pseudo-first-order hydrolysis reaction of acetic anhydride in water is employed as a chemically reacting tracer to measure the size of a flow system's micro-mixed volume. Unlike previous attempts to use chemical reactions for measuring the effectiveness of mixing, the present method is based on a relatively slow first-order reaction, with the reaction time and residence time distribution enabling an indirect evaluation of a micro-mixed volume without using any specific flow model. Using an electrolyte conductivity meter, a series of steady-state output concentrations of the reaction product, acetic acid, are measured at different operating temperatures. After plotting the conversion vs reaction rate constant, the slope at the zero reaction rate represents the space time that reactant spent in a micro-mixed volume. This method was demonstrated using a 0.0206 m i.d. pipe with commercial motionless mixer units inserted in the front section of the pipe. The results for Re = 5000 showed that the fraction of micro-mixed region increased from 0.87 with no mixer unit to 0.96 with two mixer units, and to 1.0 with 14 mixer units, thus providing a valuable information on the extent of usage of the internal volume.

Turbulent dispersion of aqueous drops in organic liquids

AbstractDrops sizes for turbulent dispersion of aqueous solutions in organic liquids were determined and correlated for three types of dispersion devices: small‐diameter tubes, motionless mixer units, and a rotating annular disperser with Couette flow. Empirical correlation based on dimensional analyses were useful for application of these devices to gel‐sphere processes. The results support the Kolmorogoff theory of turbulence as a dispersion mechanism for a range of 104 for the rate of energy dissipation.

Mixing and homogenizing of granular bulk material in a pneumatic mixer unit

Especially with the plastics that are produced on a large scale in these days, it is important to have constant product qualities such as the melt index, the color values and the number of additives during long production periods. In order to compensate for any fluctuations of those product qualities which can be caused during production, the manufacturers use high capacity mixers of a capacity of 1000 m 3 max. on an increased scale. The fluidized bed mixer units which are often used for plastic powders with particle size of less than 500 (μm) are uneconomical as concerns the mixing of plastic granules because of the high velocity of more than 0.5 m/s necessary for loosening the material. With the new circulation mixer unit, the bulk material is extracted from a silo with a conical bottom into different circular zones and circulated pneumatically by means of a central rising pipe. The mixer works without moving parts and can be operated by a single-stage radial fan because of the low working pressure of about 20 – 120 mbar. An air volume of about 300 m 3 in standard is necessary for the mixing of 1 t of plastic granules. The air flow depends on the necessary mixing time. After the description of the mixer, the experiences already found with the industrial application are published and details concerning the mixing qualities obtained are given.