Static Mixer Research Articles

Comparative analysis of different static mixers performance by CFD technique: An innovative mixer

Abstract The flow and mixing behavior of two miscible liquids has been studied in an innovative static mixer by using CFD, with Reynolds numbers ranging from 20 to 160. The performance of the new mixer is compared with those of Kenics, SMX, and Komax static mixers. The pressure drop ratio (Z-factor), coefficient of variation (CoV), and extensional efficiency (α) features have been used to evaluate power consumption, distributive mixing, and dispersive mixing performances, respectively, in all mixers. The model is firstly validated based on experimental data measured for the pressure drop ratio and the coefficient of variation. CFD results are consistent with measured data and those obtained by available correlations in the literature. The new mixer shows a superior mixing performance compared to the other mixers.

Experimental Study on the Performance of an Innovative Tide-Induced Device for Artificial Downwelling

Hypoxia has been increasingly observed in estuaries and coastal marine ecosystems around the world. In this paper, a tide-powered artificial downwelling device is proposed to potentially alleviate hypoxia in bottom waters. The downwelling device mainly consists of a vertical square tube, a 90° bend sitting on the top of the tube, two symmetrical-guide plates which installed alongside the vertical tube, a static mixer, and an artificial reef. Scale model experiments are performed with respect to different density difference heads, horizontal current velocities, and tube geometries. The results show that the downwelling flow rate is dependent on horizontal current velocity, tube geometry parameters, and the density profile of ambient water. In addition, increasing the equivalent diameter and bend radius of the device can decrease the total loss coefficient in the tube, which in turns enhance the downwelling efficiency. The two symmetrical-guide plates also generate obvious downwelling of surface water which further improves the whole performance of the device. Further work will need to determine the influence of the other parts of the device, such as the static mixer and artificial reef, on the downwelling efficiency.

Design and Validation of an Additively Manufactured Flow Cell–Static Mixer Combination for Inline NMR Spectroscopy

There have been an increasing number of publications on flow chemistry applications of compact NMR. Despite this, there has been so far no comprehensive workflow for the technical design of flow cells. Here, we present an approach that is suitable for the design of an NMR flow cell with an integrated static mixing unit. This design moves the mixing of reactants to the active NMR detection region within the NMR instrument, presenting a feature that analyzes chemical reactions faster (5–120 s region) than other common setups. During the design phase, the targeted mixing homogeneity of the components was evaluated for different types of mixing units based on computational fluid dynamics simulation. Subsequently, the flow cell was additively manufactured from ceramic materials and metal tubing. Within the targeted working mass flow range, excellent mixing properties as well as narrow line widths were confirmed in validation experiments, comparable to common glass tubes.

Short and spaced twisted tapes to mitigate fouling in tubular membranes

Static mixers are an efficient means to mitigate membrane fouling as they deflect the fluid, thus increasing the shear rate at the membrane surface and enhancing back-transport of rejected matter. However, inserting static mixers in the flow channel of a membrane imposes an additional pressure drop. To decrease this detrimental effect of static mixers, we shorten twisted tape mixers and investigate how this shortening translates into a reduction of fouling mitigation. We follow two approaches known from heat transfer enhancement: i) shorten the total length of the twisted tape and ii) use regularly spaced short twisted tape elements which are kept at their position by smooth rods placed in between the twisted elements. Computational fluid dynamics (CFD) is applied to analyze the flow pattern, the shear rate at the membrane and the resulting pressure drop. The results allow for the selection of modified twisted tape mixers with lower pressure loss, but sufficient flow properties for fouling mitigation. The most promising mixer designs were selected according to the CFD study, 3D-printed, and their fouling mitigation effect experimentally investigated using silica suspensions. Additionally, the effect of foulant concentration in this system is analyzed. For low silica concentrations (0.03g/L) the short and spaced twisted tapes mitigate fouling as efficiently as the full-length twisted tape. At high silica concentrations and fluxes, the full-length mixer mitigates fouling more strongly than the short and spaced twisted tapes. However, the modified twisted tapes prove to be more energy-efficient up to a certain fouling exposure.

Optimization of supercritical CO2-assisted spray drying technology for the production of inhalable composite particles using quality-by-design principles

The main goal of this work was to assess if the Supercritical CO2-Assisted Spray Drying (SASD) is a competitive technology for the production of inhalable trehalose and leucine composite particles with advantageous properties and aerodynamic performance while ensuring a high process throughput and yield. For that purpose, a systematic Quality-by-Design approach using the design of experiments tool, followed by a statistical analysis were implemented.A full-factorial design was used to assess the impact of the static mixer pressure, inlet drying gas temperature and feed flowrate on the powder physical properties and in vitro aerodynamic performance.The powders were produced through SASD with yields up to 70%, while enabling the optimization of the overall throughput. Improved in-vitro aerodynamic performance was driven by the successful manipulation of the process parameters, namely by decreasing the feed flowrate and increasing the inlet drying temperature, yielding powders with fine particle fraction values up to 86%.

Energy efficient turbulence promoter flux-enhanced microfiltration for the harvesting of rod-shaped bacteria using tubular ceramic membrane

Substitution of synthetic agrochemicals with bio pesticides, due to the hazards of pollution, has put attention on the development of cost-effective solutions for their production. Membrane fouling remains an immense problem for cross-flow microfiltration implementation in bio-control agent production. The shear-induced arrangement of rod-shaped bacterial cells results in the creation of the brick-like wall layer in filtration cake that has denser packing, and a higher tortuosity, which leads to higher cake resistance. From this perspective, applying turbulent flow by increasing cross-flow velocity is a possible method for the reduction of cake resistance, controlling the filtration performance, which in turn results in higher energy consumption. Turbulence promoters can be positioned into a channel of tubular membranes to reduce cake resistance and consequently increase permeation flux. Radial mixing caused by the turbulence promoter has contributed to disturbance of the shear-induced arrangement of cells and the flux improvement was in the range between 50% to approximately 300%, depending on experimental conditions. Static mixer i.e. turbulence promoter caused higher permeate fluxes at same specific energy consumption, without loss of cell viability due to an increase in shear rate. Microfiltration parameters were optimized using response surface methodology and genetic algorithm.

CFD modeling of immiscible liquids turbulent dispersion in Kenics static mixers: Focusing on droplet behavior

The present study is concerned with the computational fluid dynamics (CFD) simulation of turbulent dispersion of immiscible liquids, namely, water–silicone oil and water–benzene through Kenics static mixers using the Eulerian–Eulerian and Eulerian–Lagrangian approaches of the ANSYS Fluent 16.0 software. To study the droplet size distribution (DSD), the Eulerian formulation incorporating a population balance model (PBM) was employed. For the Eulerian–Lagrangian approach, a discrete phase model (DPM) in conjunction with the Eulerian approach for continuous phase simulation was used to predict the residence time distribution (RTD) of droplets. In both approaches, a shear stress transport (SST) k − ω turbulence model was used. For validation purposes, the simulated results were compared with the experimental data and theoretical values for the Fanning friction factor, Sauter mean diameter and the mean residence time. The reliability of the computational model was further assessed by comparing the results with the available empirical correlations for Fanning friction factor and Sauter mean diameter. In addition, the influence of important geometrical and operational parameters, including the number of mixing elements and Weber number, was studied. It was found that the proposed models are capable of predicting the performance of the Kenics static mixer reasonably well.

Salt-enhanced permeabilization for monoclonal antibody precipitation and purification in a tubular reactor with a depth filtration membrane with advanced chromatin extraction

Non-protein A-based purification technology is increasingly needed in that protein A chromatography possesses mang inherent problems, such as the high material and operational costs, limited productivity, and leaching of the protein A ligand. In this study, antibody purification was first achieved by precipitation of the antibody from the cell culture supernatant (CCS) in a tubular reactor with a static mixer. The protein precipitates were efficiently intercepted by incorporating a depth filtration membrane directly after the mixer. Chromatin-directed cell culture clarification was shown to enable the full usage of the load of the filter membrane and also significantly reduced the burden of the subsequent purification step. The addition of NaCl to the CCS significantly increased the permeabilization of the filter membrane by increasing the loading capacity by up to 20%. The re-dissolved and eluted antibodies were further polished using single multimodal chromatography, which supported direct sample loading. The content of non-histone host cell protein (n-h-HCP) in the final product was less than 20 ppm, DNA was less than 1 ppb, and the aggregates was less than 0.05%. The overall antibody recovery was ˜82%. This method is a feasible alternative to the current protein A-dominant antibody purification platform and has high value and potential for widespread implementation.

How thermally efficient are chaotic advection mixers? An experimental assessment

Chaotic Laminar Mixers (CLMs) are static mixers whose concept uses chaotic advection based on the baker's transformation. The present work is an attempt to study CLMs from the viewpoint of heat transfer efficiency and global energy efficiency, and to compare them with helical heat exchangers with the same exchange surface. In the present work, we propose two new CLM geometries alongside two classical geometries. The influence of the number of bends and of the orientation of curvature planes was studied to detect the role of regular and alternate Dean flow. An experimental investigation using water as the inner hot fluid was carried out. It is shown that for the studied range of Reynolds numbers (100–2000), CLMs have a heat transfer efficiency two-times better than helical heat exchangers. However taking into account pressure losses, helical exchangers have global energy efficiency comparable to CLMs. For laminar flows, CLMs might be good heat exchangers when only mixing and heat transfer are required.

Study on Flow Field Optimization for SCR System of Coal-fired Power Plants

Coal-fired power plants are undergoing ultra-low emission retrofits. When the flue structure of the SCR denitrification system of the existing unit is fixed, the internal baffles and static mixers need to be optimized to ensure the flow field uniformity, thus ensuring the denitrification efficiency and controlling the ammonia escape rate. For a 660 MW SCR system, numerical simulation of flue gas flow uniformity and cold state test of physical model were carried out. The results show that the uniformity of the flow field distribution and the mixing effect of ammonia and gas in the SCR denitrification system are effectively improved by adding deflectors and optimizing the static mixers. The research in this paper provides reference for similar engineering design and construction in the future.

The M Number: A Novel Parameter to Evaluate the Performance of Static Mixers

Static mixers (SM) have become standard equipment in the process industries. They are widely used in applications that involve chemical reactions, heat transfer, blending of fluids, or a combination of these. Compared to mechanically agitated vessels, SMs consume less energy, require less maintenance, and can provide mixing with shorter residence time. Assessment of the performance of SM provides a means to categorize and rank the available devices and new designs, which in turn facilitates selection for specific applications. Applying the second law efficiency (SLE) principle, we derived and proposed a novel mixing parameter, the M number, which is a dimensionless ratio of mixing level to energy loss. The parameter is compared to an industry-standard method of mixing evaluation that relies on the coefficient of variation (CoV) change across the mixer. Both CoV and the M number are used to evaluate mixing performance from computational fluid dynamics (CFD) results for a static mixer for various inlet conditions. Unlike the CoV-based parameters considered, the M number offers the advantages of accounting for energy loss and the natural mixing effects of the system. In addition, an empirical relationship is obtained that relates the M number to the Reynolds number (Re). Potential applications for the M number are discussed and its limitations are noted. Work in progress includes investigation with other SM.

Automation of process of manufacturing products from a mixture of fluids fast polymerized in air using the jet centrifugal method

The developed method provides the extraction of each component from the transported agents into flexible vessels followed by blending in a dosing unit, mixing in a static mixer, spraying the mixture on the surface of ellipsoidal drums, while ensuring the required thickness of the gel coating transported to the line of formation.

A swirl static mixer with diluent for reducing the flammable extent of venting gases in a low-flashpoint fueled vessel

Analyses on the gas dispersion from a vent mast have been conducted using fire dynamics simulator (FDS) for a 50000 dead weight tonnage (DWT) gas-fueled bulk carrier, under the assumption that methane and propane gases are discharged through a pressure relief valve in the vent system of the fuel storage tank. To assess the transient flammable extents for representative vent scenarios, the initial conditions of venting gases were selected as propane at–30 °C and methane at–150 °C, when wind velocity was set to 2 m/s in the ship exterior. The same ship layout was applied in each of these scenarios with different configurations of the inner components of the vent mast outlet. As a result, the cases with a plate head in the current vent mast outlet did not satisfy international code requirements for the safety distance of the vent mast location in ships powered by low-flashpoint fuels. However, the flammable extents of the venting gases could be significantly reduced by a novel vent system in which a swirl head and nitrogen diluent at 20 °C were adopted. Therefore, a safety design procedure considering gas dispersion characteristics was required to determine the location of the vent mast outlet in the gas-fueled vessel to satisfy the minimum requirements of the international code.

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.

Efficient preparation of macroporous poly(methyl methacrylate) materials from high internal phase emulsion templates

Thermo- and photo-initiated polymerization of emulsion templates for making macroporous poly(methyl methacrylate) materials both suffer from low energy efficiency and require tedious sample preparation (removal of inhibitors, inert atmosphere) or specialized equipment to be used. Here, an easy and efficient method for the preparation of such open pore materials with up to 93% porosity is demonstrated by using redox-initiated polymerization in the oil phase of high internal phase emulsion templates. The method eliminates the need of heating/irradiation and monomer purification, thus reducing the preparation costs without sacrificing the mechanical properties of the porous materials. It also allows of two component HIPE curing systems to be made, stored and used in the field for a rapid preparation of open pore monoliths in spaces with complex geometry. This is demonstrated by the in situ preparation of a filter and a static mixer for foam generation. The proposed method has a considerable potential for further practical exploitation in filtration, separation, microfluidics, chromatography and other fields where porous materials are used.

Effect of residence time and energy dissipation on drop size distribution for the dispersion of oil in water using KMS and SMX+ static mixer

The Planar Laser Induced Fluorescence technique was used to determine the drop size distribution of oil dispersed in water at the inlet and outlet of two static mixer geometries (KMS and Sulzer_SMX+) equipped with either 6 or 12 elements. A mineral oil (Lytol®), three times more viscous than the water continuous phase, was used as the dispersed phase. The oil flow rate was kept constant through all experiments forcing the drop detachment from the secondary inlet. The L–L system was very dilute (˜0.05–0.0007% v/v O/W) to avoid coalescence phenomena. The flowrate of the continuous phase (water) was altered giving values of Reynolds number from 2000 to 12,000, covering high transitional and turbulent flow regimes. Increasing the flow rate of the continuous phase, the detached oil drops from the secondary inlet decreased in size as expected. However, same drops after flowing a length of 0.4m of an empty pipe reached a constant size. To investigate a wider range of energy dissipation and residence time, the presence of static mixers has been investigated. Pressure drops, hence energy consumed, were measured to compare the different set ups and drop size distributions. The results show that by increasing the flow rate, the drop size decreased up to a critical point, beyond which oil droplet size reduction became inefficient. The collected data were then used to derive a methodology to identify the optimal flow conditions and choice of static mixer device to achieve best drop size reduction with less energy per unit mass.

Numerical simulation of granular mixing in static mixers with different geometries

A static mixer is a fidelity engineered device for the continuous mixing of fluid/solid materials. To meet the requirements for mixing purpose, a proper design of the static mixer is important. In this study, we proposed various designs of static mixer based on the blade geometry. Six blade patterns including four twisted blades, four elliptical blades and other four combined geometries of two twisted blades and two elliptical blades are chosen to investigate its mixing performance. Mathematical model of the two-phase flow with fluid/solid interaction in the static mixer is presented. Numerical solution of the flow patterns of particulate solids, and the velocity and the pressure fields of the fluid in the static mixer with different blade geometries are carried out. To evaluate the quality of the mixing performance, the results obtained from six blade designs are compared via the relative standard deviation and the amount of pressure drop along the mixing path.

Performance Characterization of Static Mixers in Precipitating Environments

This work investigates the application of static mixers (SMs) in precipitating environments as present in certain pharmaceutical processes, in which the undesired side effect of precipitation of th...

Improved premixing in-line injection system for variable-rate orchard sprayers with Arduino platform

To reduce the tank mixture leftover problem associated with variable-rate orchard sprayers, an experimental automatic premixing in-line injection system was developed with Arduino platform. This system primarily consisted of a precision fluid metering pump, a water pump, a static mixer, a premixing tank and a buffer tank. The required amounts of water and chemical concentrates were accurately pumped into the premixing tank through a static mixer. The mixture was then transferred into a buffer tank for additional mixing process and for the spray pump to discharge to variable flow-rate nozzles. When the buffer tank neared empty, this process was repeated automatically to maintain the same chemical ratio for all nozzles regardless of their spray output differences and variations. Accuracy of the metering pump was verified with simulated pesticide concentrates (tap water, turpentine oil, prime oil, and four different viscous sucrose solutions) at viscosities between 0.9 and 32.0 mPa·s. With addition of a fluorescent tracer, the sucrose solutions were also used to evaluate the uniformity of spray mixtures discharged from the premixing in-line injection system. Test results demonstrated that the fluid metering pump could accurately dispense desired volume (10–300 mL) of simulated pesticides at different pump rotational speeds with relative errors between measured and desired volumes below 5%. The uniformity of spray mixtures at different chemical-to-water ratios (0.1%–2.0%) was consistent, and the highest relative error and coefficient of variation were 7.6% and 4.5%, respectively. The experimental premixing in-line injection system was proven to have stable and accurate performance, and thus would have great potentials to improve spray application efficiency with minimized tank mixture leftovers for future variable-rate sprayers.

On the mixing enhancement in concentrated non-colloidal neutrally buoyant suspensions of rigid particles using helical coiled and chaotic twisted pipes: A numerical investigation

Nevertheless the huge amount of numerical and experimental works on non-colloidal suspension flows, most studies in the literature were limited to the dynamics in different geometries like in channels and pipes. To author's knowledge, mixing enhancement quantification and suspension mixing behavior in static mixers has been rarely studied before. In the present contribution, the mixing enhancement in isothermal monodisperse neutrally buoyant non-Brownian suspensions is investigated through transient 3D CFD simulations. It is quantified for suspension Reynolds (ReS) numbers varying between 50 and 150, for spheres’ diameters (dp) between 25 and 400 μm and for initial volume fractions of particles (ϕ) between 0.25 and 0.45. The influences of dp, ReS and ϕ on the overall mixing enhancement and on pressure drop are quantified for a suspension flow in a chaotic and helical separate pipes (static mixers of equal lengths). It is found that for all cases, the chaotic flow configuration has better mixing performances than the helical pipe flow with almost no significant increase in pressure losses. Moreover, good mixing quality is observed in both static mixers (better at larger particles) where the mixing index ranges between 10 and 75% relative to the initial unmixed particles leaving the straight pipe.