In-line Mixer Research Articles

Effect of structural parameters on the flow field and power consumption of in-line high shear mixer

The effects of three structural parameters on flow field and power consumption of in-line high shear mixer (HSM) were investigated by large eddy simulation (LES). In addition, an artificial neural network (ANN) is used to predict the relationship between the structural parameters and the power consumption, and the effect of dimensionless structural parameters on the power number constant Poz and k1 is studied. The results show that the stator tooth thickness and the tooth tip-base distance have a slight effect on the flow field, and the shear gap width is a key parameter affecting the flow field. As the stator teeth thickness, the tooth tip-base distance and the shearing gap width increases, the power number Po decreases. There is a linear relationship between the constant k1 and the dimensionless structural parameters. With the increase of the dimensionless parameter Ts/Ds-o of the stator tooth thickness, the dimensionless parameter St/H of the tooth tip-base distance, and the dimensionless parameter Sg/DR-o of the shear gap width, the constant k1 decreases. With the increase of the parameter St/H, Sg/DR-o and Ts/Ds-o, the constant Poz first increases and then decreases. There is a linear relationship between the constant Poz and the parameter Ts/h. With the increase of the parameter Ts/h, the constant Poz increases.

Active chaotic mixing in a channel with rotating arc-walls

An active inline mixer, called Rotating Arc-Wall mixer (RAW), suitable for flows at low Reynolds number and high P\'eclet number, is studied. The forcing protocol, imposed by three rotating circular arc-walls, is time periodic. We use simple phenomenological arguments to estimate heuristically the mixing efficiency with two nondimensional control parameters: the frequency of the forcing protocol, and the strength of the cross flow relative to the primary flow. The validity and limitations of the proposed mixing conditions are explained by the transport mechanisms in the mixer, and the beneficial role of chaotic advection for mixing is highlighted.

Stiffening control of cement-based materials using accelerators in inline mixing processes: Possibilities and challenges

In many applications such as grouting, shotcrete, and 3D concrete printing, conflicting material requirements exist between the transportation and fabrication process, as fresh materials should be pumped easily with a low stiffening rate and a high fluidity while a rapid strength gain must occur after placement. In such applications, it is therefore imperative to achieve a stiffening control of the concrete. In this paper, we discuss how the inline mixing process of an accelerator post-pumping can be used to achieve this stiffening control. We begin with a review of the mechanisms of various commonly used accelerators. This is followed by a detailed discussion on the inline mixing process of accelerators. Finally, we also point out the problems and challenges of using accelerators in these applications.

Effect of the stator tooth thickness on flow characteristics of high shear mixer

Due to the complexity of flow field in high shear mixer, it is very difficult to measure the flow field in full three-dimensional. CFD simulation has become a powerful means in mixer research. In this study, large eddy simulation (LES) was used to simulate the single-phase flow field of a pilot scale in-line high shear mixer with ultra-fine teeth. The research results show that with the increase of the stator tooth thickness, the turbulence intensity and eddy current intensity around the outermost stator increase slightly, and the shear rate area with a larger value change slightly. This means that the stator tooth thickness has a slight effect on the flow field. These results provide important guidance for the design and optimization of high shear mixer structure.

Effect of Electrical Load On the Emulsification Methods of Inline Mixing System RTES Produced by The Static Mixer and Ultrasonic on Fuel Consumption and Emission Characteristics

The Water-in-Diesel emulsion (W/D emulsion) imposed the benefit of alternative fuel by reducing the main emission problems in the diesel engines such as Particulate Matters (PM) and Nitric Oxides (NOx) emissions. However, the main issue of W/D emulsion was dependency on surfactant which creates a huge barrier to commercialize this alternative fuel. Therefore, a new concept namely as the Real-Time Non-Surfactant Non-Emulsification System (RTES) was introduced to eliminate the surfactant in W/D emulsion. However, the effect of the electrical load of RTES operation in diesel engine vehicles is still unknown, especially on fuel consumption. Hence, this paper focussed on the effect of electrical load on the emulsification methods of inline mixing system RTES produced by the static mixer and ultrasonic on fuel consumption and emission characteristics. There are two different methods of emulsification made motor and static mixer (EMS) and motor, ultrasonic and static mixer (EMUS) from the RTES were tested of the light-duty lorry under the engine speed of 2200rpm. It is found that the electrical load from the operation of RTES increased the fuel consumption by 1.0% compared to the B10 fuel but reduced by 1.5% when the EMS emulsion fuel was applied. The EMS and EMUS emulsion exhibit the same pattern of NOx reduction by 7% However, EMS and EMUS increased by 20% and 16.5% for CO emission and 16.9% and 9.7% for HC emission respectively compared to B10 fuel. Overall, the electrical load in the RTES operation slightly consumed fuel consumption but the introduction of the static mixer in the RTES system had successfully be applied without deteriorated the benefit of emulsion fuel.

Multi-material additive manufacturing of functionally graded carbide ceramics via active, in-line mixing

Advanced ceramics are required in many applications including armor, engine components, and wear parts for abrasive, corrosive, and high temperature environments. Heterogeneous structuring in these materials has the potential to unlock extrinsic mechanisms that improve damage tolerance, of vital importance for structural functionality. However, traditional ceramic powder processing and forming techniques limit the design space to simple geometries with chemically homogenous microstructures. Thus, additive manufacturing by direct ink writing (DIW) was applied to fabricate multi-phase carbide specimens with tailored composition and mesostructure. A custom DIW system was developed to allow simultaneous extrusion and mixing of multiple inks, comprised of ceramic particulate suspensions, through a single nozzle. Boron carbide (B4C) and silicon carbide (SiC) were chosen for this study due to their excellent mechanical properties. Aqueous B4C and SiC inks were loaded to 47.5 vol% ceramic content and showed yield-pseudoplastic behavior. The carbide inks were characterized and modified to exhibit similar rheological behavior (yield stress and viscosity), and were used to produce B4C–SiC parts with either discrete or continuous composition variation. Specimens were hot pressed at 35 MPa and 1950 °C, yielding near full density with hardness (Knoop) values of 20–23 GPa. Tailored heterogeneity, achieved via active in-line mixing, is revealed through microstructural characterization. Cracking observed in the specimen with discretely varied composition is the result of thermally-induced residual stress, and is elucidated through analytical calculations.

Analysis of Power Input of an In-Line Rotor-Stator Mixer for Viscoplastic Fluids

In this work, the power draw and shear profile of a novel in-line rotor-stator mixer were studied experimentally and the laminar flow regime was simulated. The power draw of the rotor-stator mixer was investigated experimentally using viscoplastic shear-thinning fluid and the results of the obtained power consumptions were verified through simulations. The power draw constant and Otto-Metzner coefficient were determined from the result of experimental data and through simulations. A new method is suggested for the determination of the Otto-Metzner coefficient for the Herschel–Bulkley model and the term efficiency is introduced. It was shown that the proposed method can be applied successfully for the prediction of the Otto-Metzner coefficient for the mixing of viscoplastic shear-thinning fluids. The effect of geometry and rotor speed on power consumption and shear rate profile in the investigated mixer is discussed from the results of the simulations. It was found that numerical methods are a convenient tool and can predict the power draw of the in-line rotor-stator mixer successfully.

Experimental and Numerical Study on Flow Resistance and Bubble Transport in a Helical Static Mixer

Flow resistance and bubble transport in a helical static mixer were studied experimentally and numerically. The inline mixer increases the volume fraction of gas in liquids by breaking bubbles into smaller sizes with a micrometer size in the flow experiments. The gas–liquid flow was simulated by a combination of computational fluid dynamics and Taylor expansion methods of moments. The friction factor of the helical static mixer is much smaller than that of the Kenics static mixers. The pressure drop increases with the Reynolds number, and the increment is larger when the Reynolds number is higher. The equidistant pressure drop increases with the argument of Reynolds number, and increases when the pitch decreases from upstream to downstream. The energy expenditure increases significantly when the variable-pitch coefficient is too small. The bubble geometric mean diameter decreases and the geometric standard deviation increases when the gas–liquid fluid flows through the mixer. The variable pitch structure enhances the bubble breakup effectively. The change of the bubble size decreases with the argument of the Reynolds number. The effect of the mixer has a limitation on breaking the bubbles.

Comparison of image-based methods for determining the inline mixing uniformity of pesticides in direct nozzle injection systems

Seven image-based methods to determine mixing uniformity in inline mixers by image processing were compared using viscous pesticides mixtures with gradually increasing uniformity. After obtaining initial optimal methods and calculation parameters, they were further evaluated by a jet mixer and a layered mixer. Results showed that quantitative descriptions for uniformity inside the tube by grey level co-occurrence matrix (GLCM) and concentration difference within time sequence (CVT) failed to reflect accurately the changing-trends in uniformity. A histogram information entropy (HIE)-based method tended to underestimate changes, while coefficient of variance based on each single frame (CVS) which calculated differences in pixel values underestimated it when mixtures showed stratification, indicating that both methods were not suitable. However, the accuracy of methods using explicit features such as second-order moments of grey-scale histogram (HSM) and optimised area-weighted uniformity index (OAU), as well as implicit methods such as principal components analysis (PCA) were suitable, and the normalised index > 80% can be suitable because no non-scattered pesticide remained. Single-viewing images were adequate for evaluating the uniformity produced by mixers although small errors between horizontal and vertical-viewing images existed. During evaluations by mixers, OAU and PCA proved to be more advantageous than HSM because these methods do not only rely on pixel probability distributions of grey-scale histograms, but the positional information of the pesticide distribution, even though the HSM is more time-efficient than them.

Evaluation of Mixing Uniformity for Inline Mixers by Image Processing

HighlightsFour inline mixers with different structures are designed and tested for DNIS applications.A new method for evaluating inline mixing uniformity by image processing is presented.While higher carrier flow rates cause better uniformity, changes due to higher mixing ratios are complicated.The multi-injection jet mixer has simplified structure and relatively satisfactory mixing efficacy.Abstract. Effective and specialized mixing devices that can achieve pesticide injection and inline mixing simultaneously are required to achieve better mixing efficacy in direct nozzle injection systems (DNISs), especially when high-viscosity pesticides are used. To evaluate the inline mixing efficacies of four inline mixers with different structures under various application conditions and to propose optimized structures for those inline mixers, a new method for evaluating uniformity based on image processing is presented. The results of experiments show that the proposed method is adequate for determining mixing uniformity. The mixing uniformity of each mixer increased with carrier flow rates (Q) ranging from 800 to 2,000 mL min-1, but the variations were less significant than those achieved by varying the mixing ratio (P) from 1:100 to 10:100. The mixing uniformity in the jet mixer (mixer A) clearly decreased with an increase in P at different values of Q because the pesticide gradually concentrated on one side of the detection tube. The layered mixer (mixer B) performed better than mixer A, especially at high P. The extension tube installed downstream of mixer B to improve uniformity was shorter than that of mixer A. Mixer C, whose structure was a combination of mixers A and B, had optimal mixing efficacy and the most complicated structure. The uniformity of the multi-injection jet mixer (mixer D) (Haverage = 12.46) obtained by simplifying mixer C was superior to that of mixers A (Haverage = 15.35) and B (Haverage = 14.65) but inferior to that of mixer C (Haverage = 4.08). With a relatively simple structure, mixer D may generally meet the uniformity requirements, thus resulting in advantages for practical use in DNISs, although further structural optimization of mixer D seems necessary. Keywords: Direct nozzle injection system, Image processing, Inline mixers, Mixing uniformity, Principal component analysis, Various application conditions.

Calculation of the Mass Transfer Coefficient for the Dissolution of Multiple Carbon Dioxide Bubbles in Sea Water under Varying Conditions

Underwater weapon systems with reforming fuel cells have been developed to increase the number of possible days that the former can be submerged. Reforming hydrocarbons generate a large quantity of carbon dioxide gas that must be completely dissolved in water and released. In this study, the mass transfer coefficient was derived experimentally while changing the process variables that affect mass transfer, such as bubble size, presence/absence of an inline mixer, retention time, pressure, and solvent type. It was found that retention time was most affected, followed by type of solvent, presence/absence of the inline mixer, and bubble size. In addition, by reducing bubble size and retention time and applying an inline mixer, the effect can be like that dissolved at high pressure even at low pressure. Applications of this study are expected to reduce the size of underwater weapon systems. Therefore, further studies on increasing the power consumption of underwater weapon systems due to reduction of bubble size and the application of inline mixers should be conducted.

Development of an autonomous solvent extraction system to isolate astatine-211 from dissolved cyclotron bombarded bismuth targets

Cyclotron-produced astatine-211 (211At) shows tremendous promise in targeted alpha therapy (TAT) applications due to its attractive half-life and its 100% α-emission from nearly simultaneous branched alpha decay. Astatine-211 is produced by alpha beam bombardment of naturally monoisotopic bismuth metal (209Bi) via the (α, 2n) reaction. In order to isolate the small mass of 211At (specific activity = 76 GBq·µg−1) from several grams of acid-dissolved Bi metal, a manual milliliter-scale solvent extraction process using diisopropyl ether (DIPE) is routinely performed at the University of Washington. As this process is complex and time consuming, we have developed a fluidic workstation that can perform the method autonomously. The workstation employs two pumps to concurrently deliver the aqueous and organic phases to a mixing tee and in-line phase mixer. The mixed phases are routed to a phase settling reservoir, where they gravity settle. Finally, each respective phase is withdrawn into its respective pump. However, development of a phase boundary sensor, placed in tandem with the phase settling reservoir, was necessary to communicate to the system when withdrawal of the denser aqueous phase was complete (i.e., the intersection of the two phases was located). The development and optimization of the autonomous solvent extraction system is described, and the 211At yields from several ~1.1 GBq-level 211At processing runs are reported.

Experimental and numerical studies on the flow characteristics and separation properties of dispersed liquid-liquid flows

The local dynamics of spatially developing liquid-liquid dispersed flows at low superficial velocities, ranging from 0.2 to 0.8 m s−1, are investigated. The dispersions are generated with an in-line static mixer. Detailed measurements with laser-based diagnostic tools are conducted at two axial pipe locations downstream of the mixer, namely, at 15 and 135 equivalent pipe diameters. Different flow patterns are recorded, and their development along the streamwise direction is shown to depend on the initial size and concentration of the drops as well as the mixture velocity. The drop size is accurately predicted by an empirical formula. The variations in drop concentration over the pipe cross-section along the pipe result in local changes of the physical properties of the mixture and consequently in asymmetrical velocity profiles, with the maxima of the velocity located in the drop-free region. Computational fluid dynamics simulations based on a mixture approach predict the experimental results close to the experimental uncertainties for the majority of the cases. The simulation results reveal that gravity and lift forces, as well as shear-induced diffusion are the most important mechanisms affecting the drop migration. It is found that the drops behave as suspensions of rigid spheres for the conditions investigated, despite the deformation effects, which are found experimentally to be stronger at the densely packed region.

Continuous Solvent/Detergent Virus Inactivation Using a Packed-Bed Reactor.

Continuous virus inactivation (VI) remains one of the missing pieces while the biopharma industry moves toward continuous manufacturing. The challenges of adapting VI to the continuous operation are two-fold: 1) achieving fluid homogeneity and 2) a narrow residence time distribution (RTD) for fluid incubation. To address these challenges, a dynamic active in-line mixer and a packed-bed continuous virus inactivation reactor (CVIR) are implemented, which act as a narrow RTD incubation chamber. The developed concept is applied using solvent/detergent (S/D) treatment for inactivation of two commonly used model viruses. The in-line mixer is characterized and enables mixing of the viscous S/D chemicals to ±1.0% of the target concentration in a small dead volume. The reactor's RTD is characterized and additional control experiments confirm that the VI is due to the S/D action and not induced by system components. The CVIR setup achieves steady state rapidly before two reactor volumes and the logarithmic reduction values of the continuous inactivation process are identical to those obtained by the traditional batch operation. The packed-bed reactor for continuous VI unites fully continuous processing with very low-pressure drop and scalability.

A comparison of power and flow characteristics between batch and in-line rotor-stator mixers

Rotor-stator mixers are used in many industries to perform emulsification and de-agglomeration processes. Despite previous research, different modes of operation have not been compared in terms of flow and power characteristics. The aim of this study was to use CFD to investigate power and flow characteristics of a Silverson L5M mixer operating in batch and in-line mode. MRF was used along with the standard k-∊ turbulence model for the simulations. Results suggest that batch mixers can be characterised in the same was as in-line mixers, and for a given mixing head design, the characterisation is independent of the mode of operation. A new way of the calculating flow number is proposed, which explains some discrepant results from previous studies. Overall, this work enhances our understanding of rotor-stator mixers and allows for better design choices of mixer.

Analysis of the variability of pesticide concentration downstream of inline mixers for direct nozzle injection systems

The injection of pesticide directly into spray nozzles results in concentration variations, both periodic discontinuities and pulses, caused by the use of injection pumps and solenoid valves. Such variations can lead to inaccurate application of pesticide. To avoid using long pipelines, long lag times and inaccurate application, efficient mixers are required to shorten the distance between the injection point and the spray nozzle. To analyse concentration variations and periodic pulses, a set of methods based on image processing were proposed and were tested using three inline mixers, a jet mixer (A), a layered mixer (B) which was specially designed, and simplified layered-jet mixer (C) which was developed as combination of mixer A and some simplified structures of mixer B. Results showed the characteristics of concentration variability for three mixers were generally different. The application conditions, carrier flow rate, mixing ratio, and injection frequency, need to be comprehensively considered to achieve improved concentration consistency and improve spraying accuracy. Concentration variability was the most obvious for mixer A with the average Coefficient of Variation (CV) as high as 4.12%. Using auto-correlation and complexity analysis, the concentration series exhibited strong periodicity and relatively lower complexity. Concentration variability for mixer B was less prominent with an average CV value 1.25% and concentration periodicity sometimes being indeterminable. Mixer C showed moderate concentration variability (CV 2.26%) although pulsation was still detectable. Mixers with similar structures to mixer C could be applied for direct nozzle injection systems to improve the spraying accuracy.

Design and characterization of a Low‐pressure‐drop static mixer

Four‐blade static mixer was designed for inline mixing of Newtonian fluids at Reynolds numbers from 700 to 6800. The mixer consists of four equally spaced blades mounted on cylindrical housing with 45° rotation relative to the circumference. It was tested in three different compartments of 6, 8, and 10 mixing elements; each element rotated 45° relative to the adjacent one. Multipoint sampling was used to measure concentration downstream the mixer. The mixing quality was measured by the coefficient of variance (CoV). The CoV decreases as the energy input per unit mass increases. This effect is more pronounced when the number of mixing elements increases. For the case of 10 mixing elements, a good mixing performance (typically more than 95% mixedness or CoV < 0.05) achieved, although a marginally good mixing performance could also be achieved by eight mixing elements. The friction factors were correlated as f = C1/Re + C2/Ren with an average deviation of ±10% from experimental data. Furthermore, experimental friction factors were compared with existing models. For a wide range of Reynolds numbers, the friction factors are apparently smaller than those from SMV, KMX, and baffle‐type static mixers. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1126–1133, 2019

An Economical Approach to Cold Spray Using In-line Nitrogen–Helium Blending

The cold gas dynamic spraying process provides an advantageous solution to the deposition, and additive manufacturing, of metals. Namely, it provides a reduced reactive environment, simple operation, and high deposition rates. It is known that the deposition efficiency of the cold spray process can be substantially increased using helium instead of nitrogen as the process gas. However, the use of pure helium can be cost prohibitive and commercially available helium recovery systems constitute a major capital investment and cannot be used with portable systems. This work focuses on the development and use of a novel, in-line gas mixing system, designed to provide a blend of nitrogen and helium at any ratio. Deposits produced with different gas ratios are investigated through particle velocity measurements, deposition efficiency, coating porosity, and coating hardness. The experimental results show that helium, even in lower percentages, can have a significant effect on deposition efficiency and coating quality. From the results, a cost model is presented which, when provided experimental values and user costs, can be used to identify the nitrogen–helium ratio that will produce the lowest overall coating cost.

On-Board Ultrasonic Water-in-Diesel Emulsion (WiDE) Fuel System for Low-Emission Diesel Engine Combustion

Water-in-diesel emulsion (WiDE) fuel is a promising alternative fuel capable of reducing nitrogen oxides (NOX) and particulate matter (PM) in diesel engine exhaust while simultaneously preserving combustion efficiency of the engine. However, the instability of WiDE fuel—and the high costs of production and transportation—hinder its commercialization and widespread use. An on-board ultrasonic WiDE fuel supply system is proposed as a solution to this challenge. This system allows diesel fuel and water to be continuously emulsified on-board a diesel vehicle. Diesel fuel and water, stored in individual reservoirs, are conveyed in specific ratios to an in-line mixing chamber and are rapidly homogenized by ultrasonic cavitation before entering the fuel injectors. The produced emulsion fuel is then supplied to the engine. A proof-of-concept study was conducted to compare exhaust emissions between emulsion fuels and conventional fuels. Open-flame combustion experiments were conducted using a lab-scale burner to test the system with both diesel and biodiesel fuels. Unique optical diagnostics and image-processing techniques were used to estimate PM emission levels. Results showed a reduction of PM with the use of the on-board WiDE system compared to traditional diesel fuels. PM emissions from biodiesel fuel were reduced by 58% when water-in-biodiesel emulsion was combusted with 2% water. Additionally, a PM emission reduction of 35% was achieved through emulsification of diesel fuel with 2% water. This prototype demonstrates the potential for the on-board WiDE fuel supply concept to both overcome the traditional barriers hindering the commercialization of WiDE fuel and preserve its low-emission and superior combustion efficiency characteristics.

Strain-based approach for measuring structural build-up of cement pastes in the context of digital construction

As a first step toward characterising structural build-up of high-strength, printable concrete mixes, the structural build-up of cement pastes of varying compositions and rheological properties is investigated. It is demonstrated that applying low shear rates over short measurement periods does not always result in the achievement of flow-onset in stiffer cementitious materials, commonly used in digital construction. For such materials, a characteristic delay exists before the effective shear rate reaches the applied shear rate. This leads to effective strains in the materials tested and consequently to the erroneous characterisation of structural build-up. A strain-based approach is suggested here as a more appropriate method for characterising structural build-up in the case of stiff materials. Maintaining a low, constant shear rate among various measurements is not necessary if the total effective strain is kept constant. Investigations on pastes with different compositions show that pastes in which a portion of the cement was replaced with micro-silica and fly ash exhibited high structuration rate. The use of secondary cementitious materials (SCM) appears to be similarly appropriate measure to make cementitious materials ‘printable’ when compared to using set-accelerators, in the absence of inline mixing of accelerators in the printhead.