Screw Mixer Research Articles

Mixing screw design and high density polyethylene toughening modification for recycled polypropylene based on screw 3D printing

AbstractThe recycling of waste plastics primarily involves physical modification and the addition of modifiers, often utilizing equipment such as twin‐screw extruders for miscible modification. Considering the widespread use of single‐screw 3D printing, improving the mixing efficiency of the single‐screw is crucial to achieve a “one‐stop” recycling modification that is suitable for 3D printing. This paper introduces a 3D printer equipped with a mixing screw (MS) and compares it with a conventional screw (CS). We conduct numerical simulations to investigate the pressure build‐up capacity, velocity streamline distribution, and the mixing effect of the MS. The mechanical properties, thermal characteristics, and molecular orientation of the recycled Polypropylene (rPP) and high density polyethylene (HDPE) mixture are investigated through experiments. The results show that the MS provides more effective elongational flows compared to the CS by breaking down the reinforcing materials into smaller particles. Additionally, toughening and modification experiments are performed on rPP and HDPE. The composites treated with the MS showed improved elongation at break (increased by ~111%), a stable melt crystallization temperature, and an enhanced mixing effect. This study on single‐screw 3D printers lays the groundwork for streamlining the plastic recycling process and increasing the reuse rate of recycled plastics.

Coating powder beds with liquids and foams based on viscous formulations using a twin screw mixer: A continuous process study

Coating with viscous formulations has been essential in numerous industries as it can be a means for providing functionalization, additional properties, as well as other benefits. However, there have been scarce studies that have investigated and proposed methodologies in literature. Continuous coating of powders with viscous liquids poses as a promising technology, which has been mentioned in some studies, but has not yet been thoroughly investigated. This paper employs the use of image processing and analysis, in combination with statistical analysis of particles to evaluate the effectiveness of foams and liquids as a means of coating powder beds. Two different sizes of twin screw mixers that are working in continuous operation are employed, and a new continuous foaming device is fabricated and used for the experiments of coating. The effect of materials and process parameters (as for example rotational speed, and flowrate) on the quality of coating are investigated. Image analysis is used to assess the coating quality. The results clearly showcase the potential of using twin screw mixers for coating purposes and not only for mixing. The hypothesis that using large bubble foams to improve the coating of viscous liquids on particles is proven correct, as they provide higher quality coatings compared to their equivalent liquids, when used in the twin screw mixer. Surprisingly, using a larger scale twin screw mixer, does not show a substantial effect on the mixing, regarding quality, however there is still a requirement for mix optimization for achieving scale-up of this process. These results provide a new pathway for coating powders with viscous formulations in industrial applications, requiring less energy and effort in this process, and can pave the way towards introducing more sustainable industrial methodologies for coating.

The Choice of a Promising Design of a Fertilizer Mixing Unit Using Computer Simulation Technologies

The article deals with applying solid mineral fertilizers within the framework of the precision farming system. The use of complex mineral fertilizer compositions in the fields with an uneven demand for macroelements leads to the bigger amount of fertilizer applied, which has a detrimental effect on the ecology, the physical condition of the soil and the crop itself. It is proposed to use fertilizer mixtures the composition of which has been adjusted in fertilizer mixing units. The existing mixers have been analyzed, the processes occurring during operation of the screw, drum and centrifugal mixers were simulated. The results of the simulation showed that the unevenness coefficient kс for the drum-type mixer was 8.6%, for the blade-type mixer 17.3, and for the centrifugal mixer 3.5%.

Kinematics-Based Design Method and Experimental Validation of Internal Meshing Screw for High-Viscosity Fluid Mixing

The challenge of mixing high-viscosity materials is a common issue encountered in the manufacturing process of food materials. The advantages of the internal meshing screw mixer have led to its adoption in various manufacturing processes, but it has yet to be implemented in the food industry. The paper presents a design method for an internal meshing screw mixer based on kinematic principles. The mixer features a helical chamber created by alternating volumes formed by the stator and rotor, establishing an extension-dominated environment for mixing high-viscosity fluids. A kinematic model based on the internal cycloid principle was established, providing trajectories and equations for key points on the rotor, simulating both its rotation and revolution processes, and revealing the velocity variations at different points on the rotor. Based on the kinematic analysis results, a stator and rotor design method was developed according to relevant functional divisions. To achieve the desired motion effects, transmission and support devices were designed, and the relationship between the transmission device and the internal cycloid surface of the fixed rotor was established. The mixer’s application and mixing effectiveness in the food industry were validated using corn syrup and flour. Experimental results showed that the extensional mixer described in the paper effectively mixed high-viscosity fluids while also efficiently blending fine powders. Slurry viscosity was tested with a rheometer at different speeds with an eccentric rotor mixer. Results showed that viscosity decreased with increasing shear rate, with a more pronounced decrease at higher shear rates. The apparent viscosity trend remained consistent at different speeds, although variations were observed at lower shear rates, especially concerning speed. The non-Newtonian fluid index exhibited minimal variations at different speeds, while the consistency coefficient showed significant fluctuations. The mixing uniformity index of the slurry was used to evaluate the mixing uniformity and dispersion uniformity of this extensional mixer. At different rotational speeds, the density of the slurry changes little. The uniformity index of mixing decreases gradually with the increase of rotational speed, reaching its maximum at 15 r/min. The overall trend of the uniformity index decreases with increasing rotational speed, indicating a decrease in density uniformity. A peak appears at 45 r/min, possibly due to the maximum values of elongation rate and shear rate at this speed. As the rotational speed increases, the residence time of the material in the mixer decreases, which may be the main reason for the decrease in mixing uniformity. These findings provide valuable insights into the design and utilization of extension-dominated screw mixers within the food industry, laying a solid foundation for future research and practical applications in this field.

Optimization of Pin Type Single Screw Mixer for Fabrication of Functionally Graded Materials

The direct ink writing (DIW) process, used for creating components with functionally graded materials, holds significant promise for advancement in various advanced fields. However, challenges persist in achieving complex gradient variations in small-sized parts. In this study, we have developed a customized pin shape for an active screw mixer using a combination of quadratic B-Spline, the response surface method, and global optimization. This tailored pin design was implemented in a two-material extrusion-based printing system. The primary objective is to facilitate the transformation of material components with shorter transition distances, overcoming size constraints and enhancing both printing flexibility and resolution. Moreover, we characterized the transition delay time for material component changes and the mixing uniformity of the extruded material by constructing a finite element simulation model based on computational fluid dynamics. Additionally, we employed a particle tracking method to obtain the Lyapunov exponent and Poincaré map of the mixing process. We employed these metrics to represent and compare the degree of chaotic mixing and dispersive mixing ability with two other structurally similar mixers. It was found that the optimized pin-type mixer can reduce the transition delay distance by approximately 30% compared to similar structures. Finally, comparative experiments were carried out to verify the printing performance of the optimized pin-type active mixer and the accuracy of the finite element model.

Numerical Simulation and Experimental Research on Heat Transfer Characteristics Based on Internal Meshing Screw

The mixing and processing of high-viscosity materials play a pivotal role in composite material processing. In this context, the internal meshing screw mixer, rooted in volume extensional rheology, offers distinct advantages, including heightened mixing efficiency, exceptional material adaptability, and favorable thermomechanical properties. This research endeavors to advance our understanding of these qualities by presenting an in-depth exploration of internal meshing screw mixing. To facilitate this, an internal meshing screw mixing experimental apparatus was meticulously constructed, accompanied by extensive numerical simulations and experimental investigations into its heat transfer characteristics. Two distinct heat transfer modes are established: Mode 1 entails the transfer of the high temperature from the outer wall of the stator to the interior, while Mode 2 involves the transmission of the high temperature from the inner wall of the rotor to the exterior. The ensuing research yields several notable findings: 1. It is evident that higher rotational speeds lead to enhanced heat transfer efficiency across the board. However, among the three rotational speeds examined, 60 rpm emerges as the optimal parameter for achieving the highest heat transfer efficiency. Furthermore, within this parameter, the heat transfer efficiency is superior in Mode 1 compared to Mode 2. 2. As eccentricity increases, a corresponding decline in comprehensive heat transfer efficiency is observed. Moreover, the impact of eccentricity on heat transfer efficiency becomes increasingly pronounced over time. 3. A lower gap dimension contributes to higher heat transfer within the system. Nevertheless, this heightened heat transfer comes at the expense of reduced stability in the heat transfer process. 4. It is demonstrated that heat transfer in Mode 1 primarily follows a convection heat transfer mechanism, while Mode 2 predominantly exhibits diffusion-based heat transfer. The heat transfer efficiency of Mode 1 significantly surpasses that of Mode 2. This research substantiates its findings with the potential to enhance the heat transfer efficiency of internal meshing screw mixers, thereby making a valuable contribution to the field of polymer engineering and science.

Numerical simulation on the mixing behavior of double-wave screw under speed sinusoidal pulsating enhancement induced by differential drive

Abstract A novel speed sinusoidal pulsating system is designed by applying differential drive, which is loaded on the plasticizing screw in an extruder or in an injection molding machine. With the CFD software ANSYS POLYFLOW 19.2, this paper builds simplified physical and mesh models for the double wave screw unit, carries out numerical simulation by using particle tracing manner, and finally analyses comparatively the mixing behavior of the wave screw mixing unit with and without sinusoidal pulsating field. It is found that the mixing screw unit with the superimposed excitation field takes on lower transportation efficiency and a descending melt pressure, while there are different reactions on the various pulsating amplitude and frequency for the max shear rate and mixing index. On the other hand, the introducing pulsating field can strengthen the shear field and gain a higher mixing efficiency. The results are of great importance and reference for improving the plasticizing performance and engineering application of the speed pulsating system.

Prediction and optimization of tower mill grinding power consumption based on GA-BP neural network

Grinding is commonly responsible for the liberation of valuable minerals from host rocks but can entail high costs in terms of energy and medium consumption, but a tower mill is a unique power-saving grinding machine over traditional mills. In a tower mill, many operating parameters affect the grinding performance, such as the amount of slurry with a known solid concentration, screw mixer speed, medium filling rate, material-ball ratio, and medium properties. Thus, 25 groups of grinding tests were conducted to establish the relationship between the grinding power consumption and operating parameters. The prediction model was established based on the backpropagation “BP” neural network, further optimized by the genetic algorithm GA to ensure the accuracy of the model, and verified. The test results show that the relative error of the predicted and actual values of the backpropagation “BP” neural network prediction model within 3% was reduced to within 2% by conducting the generic algorithm backpropagation “GA-BP” neural network. The optimum grinding power consumption of 41.069 kWh/t was obtained at the predicted operating parameters of 66.49% grinding concentration, 301.86 r/min screw speed, 20.47% medium filling rate, 96.61% medium ratio, and 0.1394 material-ball ratio. The verifying laboratory test at the optimum conditions, produced a grinding power consumption of 41.85 kWh/t with a relative error of 1.87%, showing the feasibility of using the genetic algorithm and BP neural network to optimize the grinding power consumption of the tower mill.

Tuning of Mixing Zone Parameters in a Dynamic Mixer and Performance Comparison with Screw-based Mixers

A new dynamic mixer has been designed for the mixing of two incompatible polymer melts. Three main design parameters (number of circles of holes (N), number of holes (M) per circle, and diameter of the holes (d3)) for the mixing zone of the dynamic mixer were selected to study their influences on the pressure drop (Δp) and the segregation scale (S) using Orthogonal tests. The influences of flow rate and rotational speed were also investigated. In addition, the mixing effect was compared with that of screw and slotted-screw mixers. The results showed that the most significant factor influencing S and S∙Δp is N. Both Δp and S increased with increasing flow rate, and decreased with increasing rotational speed. Compared to the screw and slotted-screw mixers, the dynamic mixer had a better mixing effect and shorter length.

Numerical simulation of five different screw configurations used during the preparation of hot-melt extruded Kollidon® and Soluplus® based amorphous solid dispersions containing indomethacin

This work developed immediate-release hot melt extruded pellets containing the poorly aqueous soluble drug Indomethacin with five different screw configurations for oral application. Moreover, numerical simulation concerning residence time was performed for each configuration to give valuable tools for better process understanding and ease of scale-up. The pellets were prepared using immediate-release matrix-forming polymers such as Kollidon® and Soluplus® by coupling hot melt extrusion (HME) with a die-surface cutting pelletizer. The HME extruded filaments were pelletized with a die-surface cutting pelletizer into 1.5 mm pellets. The extruded pellets were characterized by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), in vitro release testing, drug content, and stability studies. DSC data revealed the formation of the amorphous solid dispersions of Indomethacin in both polymeric blends. FTIR spectra did not reveal any incompatibilities between the drug and the polymers. SEM micrographs revealed a smooth surface without any cracks. In vitro release studies demonstrated that the Indomethacin dissolution rate was significantly improved from both polymeric matrices for all the tested screw configurations compared to the bulk drug. However, the numerical simulation studies showed no significant difference between predicted and experimental extrusion residence time for only four screw configurations. In conclusion, the current investigation revealed the potential use of the continuous hot-melt extrusion technology for large-scale production of Indomethacin pellets with good prediction tools for the experimental extrusion residence time with standard, conveying, distributive, one mixing screw configurations for both polymers.

Особливості конструкцій і технологічного проєктування робочих органів лопатевих гвинтових змішувачів

Blade screw mixers are typical tools for mixing building materials, compound feed, various types of products in the food industry, etc. The principle of their operation uses a combination of the operation of moving multicomponent mixtures with the operation of mixing them. Features of bladed screw working bodies of mixers are the arrangement of blades along a helical line along the axis of the shaft, on which they are, as a rule, immovably fixed. However, separate structures of working bodies can be located on the shaft with the possibility of rotation. The production of the working body of the blade screw mixer in the most technological ways may involve the following sequence of technological operations: 1. Winding a spiral of the appropriate diameter. Drilling holes with a drill head on the end surface of a spiral wound with a dense package on the edge of the spiral, which is installed in the conductor (provided that a mechanical connection will be used in the design of the auger). Calibrating the helix to a given pitch. Installation (screwing) of a spiral on a hollow shaft with a given pitch. Fixation of the spiral on the hollow shaft (welded connection). Production of blade elements of the appropriate profile (stamping, cutting). Drilling of mounting holes on the end surface of the blade elements (provided that a mechanical connection will be used in the design of the auger). Fastening the blade elements on the spiral: option 1: in the holes with a bolt or rivet connection; option 2: using a welded connection. 2. Winding a spiral of the appropriate diameter from a rectangular profile blank. Cutting (cutting) segmental openings (removals) of the appropriate size and profile on the end surface of a dense package wound on the edge of a spiral to form the necessary blade elements on it. Calibrating the helix to a given pitch. Installation (screwing) of a spiral on a hollow shaft with a given pitch. Fixation of the spiral on the hollow shaft (welded connection). 3. The production of an L-shaped bladed spiral involves the cutting (cutting) of segmental holes (removals) of the appropriate size and profile on the end surface of the L-shaped profile workpiece to form the necessary blade elements on it (the operation can also be used for a rectangular workpiece). Winding the L-shaped spiral on the frame with an internal continuous cylindrical part of the corresponding diameter. Calibration of the L-shaped spiral to a given pitch. Drilling of fastening holes at the ends on the end surface of the cylindrical part of the L-shaped spiral. The manufacturing technology of bladed screw working bodies of mixers significantly affects their technical and economic indicators and is ensured by the use of various methods. Technological features of the design parameters of the blade spirals of the mixers, which are made in various ways from rolled sheet, tape or L-shaped profile (angle). The results of calculating the production cost of manufacturing 1 m/p of a bladed spiral using different manufacturing methods showed that the most economically effective method of manufacturing bladed spirals is winding a dense package of spirals along the inner end profile from rectangular blanks followed by cutting (cutting out) segmental holes (removals ) and calibration to a given step, as in general and other methods that use winding. The production of blade spirals by methods using stamping or rolling is many times more expensive.

THE MECHANICAL MIXING EFFICIENCY IMPROVING AT FEED PREPARATION BY MIXERS’ DESIGN PROGRESS

The main directions of mixers’ productivity increasing and shredders-and-feed mixers of continuous and periodic action at small and mediumsized livestock enterprises of APK are considered. One of the ways of feed grinding and mixing’s machines productivity increasing is the working bodies’ design to improve, that includes the working bodies of sharpening angles’ cutting edges so as the gaps between the working bodies optimizing, a constructive possibility of changing the angles at cutting working bodies’ turns inclination creating in the depending on the mixed material resistance. Another direction is the working bodies drive’s improvement -trajectory’s optimization and working bodies’ movement speeds, the hollow shaft’s at drive designs using. As examples of these directions implementation, a vertical screw of shredder-and-mixer feeder designs with a screw working body as an active countercutting element and a planetary screw mixer with a hollow shaft at the working bodies’ drive using, that is the conical gearbox’s body simultaneously, are presented. As a result of the presented machines’ improvement, the energy efficiency and mixing performance by energy losses reducing at the working bodies movement and mixed material’s resistance, as well as the structures’ metal consumption reducing are increased. At the proposed working bodies using, feed mixture quality is also improved by the material mixing’s intensity and uniformity increasing.

Cинтез гвинтових конвеєрів-змішувачів з обертовим кожухом

Carrying out a structural-schematic synthesis often allows you to obtain a significant range of quite effective constructive solutions of various technical means, which fully also applies to the generation of alternative solutions for screw mixers. Screw conveyors-mixers with a rotating casing (GKZOK) are atypical mechanical means for performing the operation of mixing materials, however, they can become quite widely used in various sectors of the economy by combining the operation of moving loose material with the operation of mixing it. For their creation and further research, it is necessary to develop separate rational structures that would meet the relevant parameters in terms of achieving quality indicators of the mixing process, high performance of the process, as well as acceptable cost of manufacturing, operation and maintenance of such structures. For this reason, it is advisable to use the method of structural-schematic synthesis by the method of hierarchical groups with the help of morphological analysis to obtain appropriate technical solutions. As a result of the analysis of the influence of various factors on the process of mixing materials by screw mechanisms, the characteristics of the structural elements of such mechanisms and their interrelationships were determined, which made it possible to build an appropriate morphological table of these elements for GKZOK, from which a model of the mechanical system was selected. Screw conveyor-mixer with a rotating casing". As a result of the structural and diagrammatic synthesis of GKZOK, the following basic morphological features were selected: drive; screw, which includes a casing (gutter) and a screw working body; bunker; unloading mechanism; locomotor mechanism. The structural and schematic synthesis of screw conveyors-mixers with a rotating casing made it possible to obtain effective design solutions for the screw working bodies of the mixers with the possibility of selecting the necessary gap between the blades of the screw working body for intensifying the process of mixing materials of different fractions, for which Ukrainian patents were obtained, as well as mixer conveyors with a rotating casing without forced rotation of the casing with the possibility of braking and with forced rotation of the casing with the possibility of changing the length of the mixing track and moving materials, for which applications for obtaining patents of Ukraine have been submitted. The developed structures can provide significantly higher productivity and efficiency of the technological process of mixing with screw conveyors-mixers, as well as have extended functional characteristics. A dependency was also developed, according to which the final selection of synthesized constructive solutions of GKZOK is carried out by maximizing the expected positive result, which takes into account the weight of such factors as the total cost, productivity, efficiency of the technological process of mixing and the number of functional characteristics.

Improvement in Injection Molding Quality Performance with Innovative Cyclone Mixers Used in Polypropylene with Spherical Silicon Dioxide Composites.

This research proposes an innovative design of a new cyclone mixer for the quality of polymer materials, and it presents a systematic optimization model of process parameters for plastic injection molding. Thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to determine the appropriate thermal properties of processing in order to select appropriate control factors and level values for a Taguchi orthogonal array. The injection molding machine was used to make sample test pieces for tensile strength, hardness and impact strength. Significant factors were found by the signal-to-noise (S/N) ratio with an analysis of variation (ANOVA), and the single-quality optimal parameter combination was obtained. The reproducibility of the experiment was evaluated, and various quality weights were evaluated by principal components analysis (PCA). The multi-quality optimal parameter combination was found, and the comprehensive scores were compared. Finally, the process capability indices were combined with a multi-process capability analysis chart (MPCAC) to compare the process yields of cyclone mixing and screw mixing. The mechanical properties of products were evaluated to verify the performance of cyclone mixing and to provide perfect information for the injection molding quality performance of cyclone mixing and screw mixing. It was concluded that the overall quality of the cyclone mixing products is 42.72, and the total quality of the screw mixing products is 41.85. The total number of defects for the cyclone mixing is 9659 ppm, and that of the screw mixing is 10688 ppm. It can be seen that, for the overall product quality performance, cyclone mixing can be applied in the plastic injection molding process instead of screw mixing.

Twin-Screw Continuous Mixing Can Produce Dry Powder Inhalation Mixtures for Pulmonary Delivery

The feasibility of twin-screw corotating extruder as a continuous process mixer to prepare dry powder inhalation (DPI) powders was investigated. Interactive mixtures of 1% micronized budesonide, 0.3% magnesium stearate and 98.7% alpha-lactose monohydrate were manufactured using a Leistritz Nano-16 extruder at various processing conditions. One set of GFM (grooved mixing) elements were included in the screw profile to provide distributive mixing of conveyed powders with the goal of resulting in a homogeneous mixture. Residence time in the twin-screw mixer was modelled to quantify mixing efficiency. Comparative powders were also prepared using either low or high-shear batch mixing to compare the effect of mixing methods on the properties of the budesonide dry powder inhalation formulation. Twin screw mixing results in homogeneous mixtures with aerosol performance comparable to that of high-shear batch mixing. Scanning electron microscopy confirmed that twin screw mixing produces particles with morphology like that of low and high-shear batch mixing. X-ray diffraction (XRD) analysis verified that there was no form change of the drug due to twin-screw processing. Statistical regression was used to probe the relationship between twin screw mixing process parameters such as screw speed and feed rate and aerosol performance. The twin screw mixing process was found to be robust, as no significant differences in aerosol performance were found for various processing parameters.

Investigating the effects of material properties on the mixing dynamics of cohesive particles in a twin screw mixer using a discrete element method approach

A discrete element method (DEM) model was developed for a co-rotating twin-screw mixer (TSM) consisting of conveying and kneading elements. This model was used to simulate the mixing of a cohesive binary system of particles (P1 and P2). The particles were calibrated using angle of repose and dynamic yield strength simulations. Properties of P1 were kept constant throughout the study while properties of P2 were varied. The TSM model was used to study the influence of particle size, density, and flowability of P2 on process outputs such as powder holdup, mean residence time (MRT), and degree of mixing along the length of the TSM. All the three particle properties were varied at three-factor levels with flowability ranging from good flow (GF), poor flow (PF), and very very poor flow (VVPF) based on Carr’s classification. The model provides fundamental insights into the differences in mixing in the conveying sections of the mixer for materials with different flowability. Due to the co-rotating nature of the screws, the majority of the material in the conveying sections was carried on one side of the TSM for GF and PF particles, while both the screws carried VVPF particles. The total steady-state holdup and the mean residence time (MRT) of particles inside the TSM were heavily influenced by particle flowability compared to the other two tested particle parameters. The holdup in the conveying compartments ranged from 11%–15% of the total holdup, while the kneading compartment comprised 40% of the total holdup in the mixer. The simulations found that VVPF particles mixed the fastest and that the GF particles had the highest tendency to demix. The model was also used to suggest and test other screw design configurations to improve mixing. A screw design with kneading elements closer to the mixer outlet resulted in better mixing of GF particles. A screw design consisting only of conveying elements achieved the same degree of mixing as the original screw design for VVPF particles. • A model for a co-rotating twin-screw mixer was developed using DEM. • Holdup and mean residence time was influenced by the particle flowability. • Particles were transported mainly on one of the conveying screws. • The model was also used to suggest changes to screw design configurations.

Development of an Injection Molding Process for Long Glass Fiber-Reinforced Phenolic Resins

Glass fiber-reinforced phenolic resins are well suited to substitute aluminum die-cast materials. They meet the high thermomechanical and chemical demands that are typically found in combustion engine and electric drive train applications. An injection molding process development for further improving their mechanical properties by increasing the glass fiber length in the molded part was conducted. A novel screw mixing element was developed to improve the homogenization of the long fibers in the phenolic resin. The process operation with the mixing element is a balance between the desired mixing action, an undesired preliminary curing of the phenolic resin, and the reduction of the fiber length. The highest mixing energy input leads to a reduction of the initial fiber length L0 = 5000 μm to a weighted average fiber length of Lp = 571 μm in the molded part. This is an improvement over Lp = 285 μm for a short fiber-reinforced resin under comparable processing conditions. The mechanical characterization shows that for the long fiber-reinforced materials, the benefit of the increased homogeneity outweighs the disadvantages of the reduced fiber length. This is evident from the increase in tensile strength from σm = 21 MPa to σm = 57 MPa between the lowest and the highest mixing energy input parameter settings.

ОПРЕДЕЛЕНИЕ РАЦИОНАЛЬНОГО КОЛИЧЕСТВА ВИТКОВ ШНЕКОВОГО СМЕСИТЕЛЯ С АКТИВНЫМ КАНАЛОМ ОБРАТНОГО ХОДА

The conducted studies have shown that a promising design and technological scheme of the mixer is a low-speed screw mixer of periodic action, the loading and unloading parts of which are connected by an active return channel having areas of interpenetration of feed mixture components.It is established that the cycle time consists of the time of passage of the components of the mixture through the sections of the screw winding, tangential blades and in the return channel under the action of an additional screw. The time spent by the mixture on the screw section and in the return channel is determined by the length of each section, the design parameters of the winding, the angle of installation of the housing to the horizon and the rotation frequency of the working body. When determining the time spent on the interpenetration site of the components of the mixture, it is necessary to take into account the filling factor of the return channel and the physico-mechanical properties of the components of the mixture.The duration of loading and unloading of the mixer is determined from the condition of the axial velocity of movement of the feed mixture components in each of the sections and corresponds to the cycle time.The residence time of the mixture at each of the sites is determined taking into account the design parameters and the rotation speed of each working body. The optimal ratio between the diameters of the auger and the additional auger from the condition of the maximum volumetric capacity of the mixer is revealed. Expressions are obtained for determining the supply of working bodies at each of the sections from the condition of continuity of the flow. Modeling of the volumetric feed allowed us to estimate the effect on the volumetric flow of the mixer depending on the ratio of the pitch of the screw turn to its diameter, the number of screw turns.

Cartesian grid method with a consistent direct discretization approach for numerical simulation of non-Newtonian fluid flow

This paper proposes an extended version of the discretization scheme for a consistent direct discretization approach in a Cartesian grid method for flow simulations of incompressible non-Newtonian fluids. Based on the concept of the original method, which was developed for Newtonian fluid flow, the Navier–Stokes and the pressure Poisson equations are discretized directly in the vicinity of a solid boundary while maintaining the consistency between the velocity and pressure fields. The main difficulty in the discretization arises from the evaluation of the velocity gradients on the fluid–solid interface, which is necessary for handling the viscous term for spatially distributed shear-dependent viscosity. In the extended method, a new procedure for the calculation of the velocity gradient using the relation that holds on a rigidly moving solid surface is proposed. The validity of the method is ascertained in fundamental test problems of non-Newtonian fluids: laminar Poiseuille/Couette flows in a concentric annulus and flows around a circular cylinder. It is found that a second-order spatial accuracy with the desired numerical stability is achieved in both the shear-thinning and shear-thickening viscous properties, and the numerical error is considerably decreased compared with some conventional methods. As a realistic application of the extended method, a polymer mixing simulation inside a co-rotating twin-screw extruder is demonstrated by applying the method to the moving boundary problem. In a screw arrangement with a sequential combination of a kneading disk (KD), a cylindrical ring (CR), and a backward mixing screw (BMS), large- and small-scale structures of bifurcating and converging flows are respectively formed in the KD and BMS zones, whereas elongational flow structures and velocity fluctuations are still maintained in the CR zone due to flow interaction with the upstream and downstream screw elements, which presumably contributes to moderate mixing at low shear stress. • A Cartesian grid method for non-Newtonian fluid flow is developed. • The present method extends a consistent direct discretization approach. • A procedure for evaluating velocity gradients on an immersed boundary is proposed. • Second order spatial accuracies for velocity and its derivatives are ascertained. • A polymer mixing simulation in a co-rotating twin-screw extruder is demonstrated.

Optimization of Screw Mixer to Improve Drying Performance of Livestock Manure Dryer Using CFD Analysis

Scarcity of fossil fuels and their emissions of fossil fuel pollutants, such as carbon dioxide, into the atmosphere, and the resulting consequences, have led energy policymakers to look for alternative renewable and clean energy sources. The use of animal wastes is one of the very promising renewable energy alternatives paving the way for a more sustainable energy network. Animal manure produced by livestock farms has a moisture content of about 80%, and such livestock manure is dehydrated to a moisture content of 20–25% and solidified to be used as biomass and fuel for thermal power plants. Previous studies on manure dryers have been concentrated on convection-type dryers, but this type of dryer has the disadvantage of inadequate processing capacity per hour because it cannot agitate manure. In this study, to deal with the drawbacks of conventional livestock manure drying methods, a screw-type dryer was proposed. CFD analysis of the dryer was performed by selecting the viscosity of livestock manure and design parameters of the screw using Ansys Workbench. Through the response surface method, optimal design of the screw shape for the improvement of drying efficiency and smooth discharge of residual manure was carried out.