Blade Mixer Research Articles

The effect of primary and secondary flows on the homogenization process in a vertical bladed mixer

This article focuses on numerical simulations of the granular mixing process in a vertical cylindrical mixer with two opposed flat blades with a 45° rake angle. Computer simulations were performed by the discrete element method. The blending was examined for the blades' stirrer speeds in the range from 1.9 to 960 rpm and three different initial spatial configurations. The development of the concentration patterns and the evolution of phase interphase between different types of particles have shown that the homogenization process depends not only on the system's dynamics but also on the initial spatial distribution of particles. The dependence on the initial distribution is provided by involving primary and secondary flows in different time-scale in the homogenization process. This ability of the individual flows to engage in the mixing is granted by the mutual synergy between the direction of movements of particles located on the phase interface and the orientation of the phase interface. Because there is a significant difference between the intensity of primary and secondary flows in most cases, an improperly oriented phase interface will significantly slow down the entire rate of the homogenization process. On the other hand, during the mixing process, the phase interface expands and deforms, which gradually also allows the rest of the flows to get involved in the homogenization process. Based on the results, the basic rules have been identified for effective homogenization. As a mixing index, the relative surface of the phase interface was used. By comparing individual homogenization curves, it follows that the critical factor for the homogenization process is the centrifugal force. When it is in balance with other forces, it encourages homogenization. On the contrary, if it becomes the dominant force in the system, it causes a significant deformation of the surface, and its effect on the homogenization process is destructive.

Numerical study of the mixing process of binary-density particles in a bladed mixer

Discrete element method (DEM) simulations of binary mixing of particles with different densities were conducted to study the influence of density ratio, blade speed, and filling level on the particle dynamics and mixing performance in a bladed mixer. Four particles with different densities at different locations were tagged to discuss the influence of three factors on the particle trajectory and velocity field in the mixer. A method based on cubic polynomial fitting of relative standard deviation was used to determine the critical revolution during the mixing process. It was found that the non-dimensional tangential velocity decreases with the increase of the blade speed and filling level, the fluctuation of vertical velocity increases with the radial location, blade speed, and filling level, and it is more pronounced than the fluctuation of tangential and radial velocity during the mixing process. Results obtained indicate that the mixing performance of particles with different density increases with the decrease of density ratio and filling level, while it increases with the increase of blade speed.

Corrections to: Heat transfer of dry granular materials in a bladed mixer: Effect of thermal properties and agitation rate

Corrections to: Heat transfer of dry granular materials in a bladed mixer: Effect of thermal properties and agitation rate

Scale up of heat transfer for dry granular material in a cylindrical bladed mixer

Heated bladed mixers are widely used to process granular materials. Yet, despite their ubiquity, unanswered questions remain regarding how heat transfer occurs in this system, particularly when scaling up the process. In this work, the discrete element method was coupled with a heat transfer model to investigate how the amount of material and the mixer size influence the particle bed heating time. The findings show that the relationship between the fill level and the heating time depends on the heating area of the mixer relative to the amount of material, the bed compression, and the mixing rate. The results also indicate that the heating time is directly proportional to the mixer diameter. The proportionality constant has an order of magnitude of one and depends on the impeller rotation rate. Overall, this work enhances fundamental understanding of the elements at play during the scale up of granular processes in heated bladed mixers.

The effect of rotation speed and mixer size on granular flow and mixing in bladed mixers

Bladed mixers are widely used in the industry for granular mixing. In the past decades, the mixing of particles in bladed mixers has been extensively investigated experimentally and numerically. Recently, GPU-based DEM has been employed to simulate various industrial-scale applications. This work aims to apply the GPU-based DEM to investigate the effect of rotation speed and mixer size on granular mixing in bladed mixers of different sizes. The simulation in a larger mixer revealed distinct particle flow patterns that well-describe the mixing mechanism which is difficult to observe in a smaller mixer. The Lacey’s mixing index curves revealed a delay in mixing as the mixer size increases. The mixing rate decreases as the mixer size increases and it can be improved with increasing rotation speed. The average particle velocity increase significantly with increasing rotation speed and mixer size.

РАЗРАБОТКА КОНСТРУКТИВНОЙ СХЕМЫ СМЕСИТЕЛЯ БЕЛКОВО-МИНЕРАЛЬНО-ВИТАМИННЫХ ДОБАВОК

To ensure the eff ective use of protein-mineral-vitamin supplements in the diets of dairy cows, a mixer design has been developed for their preliminary mixing before adding to the main mixing process. Based on the structural-morphological analysis, alternative structural elements of the mixer design have been considered and conventional symbols were assigned to them. A morphological matrix of solutions has been compiled to off er a set of alternative options. The mixer drive was chosen by the ability to ensure high speed, rotational speed control, user-friendly operation and cost. The design uses an electromechanical drive combined with a V-belt drive. This solution meets all the specifi ed requirements and allows protecting the drive from possible overloads. The working tool was chosen based on the requirement to contact the material actively throughout the chamber volume and to avoid the formation of stagnant zones. A blade mixer with variable blade positioning was found the most eff ective tool for the high-speed mixing of bulk materials. The designed mixer will be operating at a continuously varying speed in the range from 500 to 1500 min-1. This will off er the advantages of high-speed mixing while reducing the infl uence of negative factors on the fi nal mixture quality. The resulting decision matrix will allow determining the most promising areas for further designing, which makes it possible to improve the quality of the developed technical means.

Polyvinyl Alcohol Fiber Length Optimization for High Ductility Cementitious Composites with Different Compressive Strength Grades

The fiber length has a significant impact on the fiber bridging capacity and the mechanical properties of high ductility cementitious composites (HDCCs), which is related to fiber/matrix interfacial bonding. However, this fundamental knowledge of HDCCs design has rarely been investigated systematically. To this end, this study deeply investigates the effect of the fiber length on the bridging stress and the complementary energy with various fiber/matrix interfacial bonds in theory. Then, the mechanical performances of HDCCs with various fiber lengths and compressive strengths were evaluated experimentally. In micromechanical design, longer fibers can achieve stronger bridging stress and more sufficient complementary energy regardless of the fiber/matrix interfacial bonding properties. However, it should be noted that the increase in bridging capacity was quite slow for the overlong fibers and excessive interfacial bonding. The experiments indicated that overlong fibers (18 mm and 24 mm) easily twined on the mixer blade and were hard to disperse evenly. The HDCCs with shorter fibers displayed better workability. The compressive strength was less affected by the fiber length, and most striking differences were less than 5.0%, while the flexural properties and the tensile properties first increased and then decreased when the fiber length ranged from 6 mm to 24 mm. Consequently, the fibers with lengths of 9 mm and the fibers with lengths of 12 mm were better candidates for the HDCCs with compressive strengths of 30 MPa to 80 MPa, and fibers with lengths of 9 mm caused the HDCCs to exhibit higher ductility properties in general.

Reliability analysis of mixer structure under mixing simulation

When the forced two-horizontal shaft mixer is used to mix concrete, the mixing drum and the mixing components are subjected to random loads of the mixture. Structural static analysis usually ignores the randomness of the load, resulting in a large calculation error. Based on the EDEM software, this paper simulates the mixing process of the mixture, obtains the random load data of the mixture on the mixing drum and the mixing parts, and describes the variation law of the random load with a probability distribution, establishes the stress-strength interference reliability model of the mixer structure, and Monte Carlo simulation method is used to solve the structural reliability of the mixer. The results show that the load distribution of the mixing arm is the same as the mixing blade, the load distribution follows the gamma distribution, and the mixing shaft also follows the gamma distribution; the load distribution of the mixing drum follows the normal distribution. After calculation, the above load probability distribution and its intensity distribution do not interfere, and the structural reliability of the mixer meets the requirements, which can ensure the safe operation of the mixer. This method solves the reliability calculation error caused by random loads.

Reliability life analysis of blades of twin-shaft mixer based on wear failure

As an important part of mixing material, the study on the reliability life of the blade of mixer is very necessary. According to the Arcard wear formula, the mathematical model expression of the wear amount and the load on the blades of the twin-shaft mixer in a single cycle is established. The discrete element method is used to obtain the load on the blade in the mixing process. The law of load distribution of mixer blades is obtained by Lilliefers method. Furthermore, Lagrange interpolation method is used to analyze the static simulation results of the mixing blade, and the total wear amount when the blade reaches the critical thickness is obtained. By establishing the functional relationship between wear and blade life, Monte Carlo method is used to simulate the load distribution law to predict the reliability life of the mixer blade. The results show that the reliability of the life of the mixer blade is 85.02%.

Improving the efficiency of the process of continuous flow mixing of bulk components

Modern industrial and agricultural processing almost always implies mixing loose material on a variety of equipment. At present, there are known mixers of various designs, principles, and techniques to implement the technological process. One of the existing mixing techniques is a continuous flow method that has significant advantages – reducing energy intensity while improving the quality of the process of the mixture continuous preparation and distribution. However, the continuous-flow technique of mixing loose materials has been paid little attention to. This prevents the application of well-known analytical models of the process of moving loose components to substantiate the structural and technological parameters for the working bodies of a continuous flow mixer. The result of the analytical study of the continuous-flow mixing technique is the constructed system of differential equations of the movement of a bulk material’s components in the airflow under the influence of the working bodies’ surfaces of the designed mixer. The reported system of differential equations underlies the physical-mathematical apparatus for the numerical modeling of the specified process employing the software package StarCCM+ (USA). The result of the numerical modeling is the established dependences of the dynamics of change in the concentration of components in the mixture and the homogeneity of the mixture in the zones of a continuous flow mixer depending on the study factors (the frequency of rotations, the angle of attack of the blade mixer, the performance of feeding the first and second components). The optimal structural and technological parameters for a continuous flow mixer involved in the process of mixing a two-component feed mixture (stem and concentrated feed) have been determined, at which the uniformity of the resulting forage mixture is maximal

GPU-based DEM simulation for scale-up of bladed mixers

GPU-based DEM is used to study large-scale particle mixing in bladed mixers. A bladed mixer is scaled-up to three different sizes by maintaining the geometric similarity. Four Froude numbers are selected as the main operating conditions of bladed mixers with different sizes. The results demonstrated that the mixing quality across different mixer sizes is similar at the same Froude number, but it requires a longer mixing time to achieve similar mixing performances as the mixer becomes larger. Correlations to predict the mixing rate, average particle velocity, average total forces, average contact forces and average blade torque as functions of the scale-up ratio and Froude number (or rotation speed) are proposed. A similarity study shows that maintaining the dynamic or kinematic similarity does not produce a similar mixing performance, while maintaining the mixing rate produces a similar mixing performance across all mixers.

Influence of processing conditions on microstructural, mechanical and tribological properties of graphene nanoplatelet reinforced UHMWPE

Ultra-high molecular weight polyethylene (UHMWPE) is a relevant thermoplastic in industry and a well-proven standard biomaterial in joint replacements. To enhance its tribological properties while preserving its bulk ones, composite coatings on a UHMWPE substrate were prepared using non-functionalised graphene nanoplatelet (GNP) at reinforcement concentration of 0.1–5 wt% and two mechanical mixing techniques (ball mill or blade mixer) with different consolidation temperatures of 175–240 °C. Changes in morphology and size of the UHMWPE particles before hot-pressing were observed in function of the mechanical mixing techniques applied. Wear rate was affected by graphene content, reaching a minimum at 0.5 wt% GNP, with a reduction of 20 and 15%, for ball milling and blade mixer, respectively. However, blade mixer increased the wear rate by around twice respect the ball milling results, for all the studied materials. The coefficient of friction decreased notably, by ~25%, below 3 wt% GNP content, and hardness increased by 24%, regardless of the mechanical mixing process used. Finally, consolidation temperature had a positive influence on wear rate at temperatures of around 195 °C, which could be related to the free radical scavenger effect of the GNP.

Characterization of intruder particle motion in a bladed mixer

Granular mixing is important to many industries, but the mixing process is still poorly understood. In this study, motion of a single intruder particle introduced in a shallow bed of native particles was investigated. A parametric investigation was carried out to quantify the effects of initial intruder particle location, blade speed, and density difference between similarly sized native and intruder particles on the motion of the intruder particle during the mixing process. Intruder particles were color-tagged and videos were obtained from the top free surface of the shallow bed throughout the mixing duration. Additional experiments were performed to investigate the effect of density ratio between the intruder and native particles on the mean radial location (MRL) of the intruder particle. In the shallow bed system, all particles were found to be consistently under the direct influence of the blade and moved in discrete tracks unless randomly excited by the blade or neighboring particles. Intruder particles that were denser than the native particles were found to rotate closer to the hub with a smaller mean radial location, whereas less dense intruders were found to be further away from the mixer center on average. Initial location was important only for the first few rotations, and the blade speed had a negligible impact on the intruder particle flow behavior.

Pengembangan Butiran Premiks untuk Fortifikasi Zat Besi dalam Beras

Iron-fortified rice potentially increases iron consumption in order to overcome anemia in Indonesia. Premix kernel can be applied as a fortificant vehicle being formulated into rice. The premix kernel is processed by mixing rice flour and iron source and extruded to yield rice-like extrudate. This research aimed to develop iron premix kernel using a double screw extruder and evaluate the fortificant homogeneity during mixing and stability due to washing as well as overall sensory acceptability of fortified rice. The premix kernel was made by mixing rice flour (1000 g), pyrophosphate ferries (containing 5,000 mg Fe), and GMS (10 g) for 5, 10, 15, 20, 25, and 30 minutes, added with water (450 mL) and passed into an extruder at 80°C. The dry-mixed for 20 minutes yielded a homogenous premix kernel (6,030±135 mg/kg with RSD of 2.25%). The mixing of premix kernel and Pandanwangi rice (1:100) for 25 minutes using a blade mixer yielded fortified rice with iron content of 39 mg/kg and RSD of 13.56%. The washing process of fortified rice decreased iron content, and the percentage of iron loss was affected by the washing frequency. Raw and cooked fortified rice did not differ organoleptically from those without fortification.
 Keywords: anemia, fortified rice, ferric pyrophospate, homogeneity, premix kernel

DEM study of dry and wet granular flows in a vertical bladed mixer

In this work, numerical simulations of both dry and wet granular flows inside a vertical cylindrical mixer were performed using discrete element method (DEM). Two different cases were considered by using four-bladed and two-bladed mixer setups. Effects of blade rake angle, blade rotational speed and number of blades on mixing characteristics for both dry and wet flows were examined under different conditions. It was found that blade rake angle of 90° produces low velocity but with relatively high time-averaged mean interparticle forces. Moisture content also influences the flow and mixing behavior. It was found that dry particles have higher mixing efficiencies than wet particles but only with higher moisture contents like 4% (vol%) used in this study. The same is not true when lower moisture contents of less than 1% (vol%) are used and show better mixing performance at these low moisture contents. It was also found that a two-bladed mixer is a better choice for mixing at these moisture contents in comparison to a four-bladed mixer. Our results suggest that all these factors must be considered carefully for each specific application.

STUDY ON THE PERFORMANCE OF SHALLOW SOIL MIXING WITH CEMENT

Shallow Soil Mixing (SSM) method with a low dosage of cement can be used to create a sufficiently strong platform for quick access onto grounds that have been recently reclaimed with soft clays. The effectiveness of the SSM method is dependent on the type, dosage and dosing method of cement, the mixing blade design, and the mixing sequence. Hence, a laboratory-scale SSM apparatus was developed to simulate SSM in the field. The early strength development and uniformity of Cement Mixed Soil (CMS) were evaluated by taking into consideration (a) Type of cement: CEM I vs CEM III/A, (b) Dosage of cement: 7% vs 3%, (c) Dosing method: 1-layer vs 2-layer mixing, and (d) Mixing blade design: without overlap between mixing blades vs overlapped mixing blades. Shear strength test results demonstrated that the shear strength development of CMS at an early stage is affected by the type, dosage, and dosing method of cement, while the uniformity of the CMS is affected by the dosage and dosing method of cement and the mixing blade design. From the laboratory test results, it is recommended that CEM III/A cement with 7% cement dosage, 2-layer of dosing method and overlapped mixing blades design parameters be used for SSM in the field to achieve high early strength gain and good uniformity cement soil mix.

Abrasive wear and optimal installation angle of concrete double-horizontal shaft mixer stirring blades

The quality of a building desponds directly on the quality of concrete, and mixing is the key process of concrete production. However, a mixing blade is severely worn and has a relatively short life during the mixing process because of severe friction between the concrete material and the double-horizontal shaft mixer stirring blades. This study uses the abrasion mechanism of a mixer and the abrasive wear formula as bases to analyze the theoretical maximum line wear rate $$\eta$$ of an experimental prototype at five blade installation angles, and obtain the optimal installation interval and optimal installation angle. Results indicate that the wear rate of different blade installation angles changes significantly. The wear rate at 45° is the largest, and the corresponding theoretical life is only 125 days. By contrast, the wear rate at 35° is the smallest, and the corresponding theoretical life is 192 days. The change rule of the maximum line wear rate $$\eta$$ of the blade is obtained through the wear line chart, and the performance curve and evaluation function are fitted using MATLAB. The three aspects of stirring quality, energy consumption, and wear loss are quantitatively analyzed. The best installation angle and interval are 31.8° and 30°–34°. This study can provide a reference for the design choice of the installation angle of the mixing blade of concrete mixers.

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

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

Investigation of the Efficiency of Wet Biodiesel Purification

The main research aim is to verify the efficiency of wet methods of biodiesel cleaning and to establish optimal and rational parameters for biodiesel purification and disposing of its cleaning waste. The efficiency of biodiesel washing was studied by means of volumetric, bubble and aerosol washing. Volumetric washing of biodiesel was carried out with the use of a blade mixer with three blades on a shaft and a four-blade agitator with sloping blades. One of the three methods of biodiesel washing studied can be recommended for practical use – aerosol washing with medium- and large-grained washing to be carried out for at least 4-5 hours, while fine-grained – for a longer time. The use of waste from the purification of biodiesel as a cosubstrate in biogas plants will almost double the output of biogas, which will significantly reduce the payback period of biogas plants.

An investigation on the microstructure, wear rate and hardness of Surface alloying Ni-Hard 4 cast iron with Tungsten Using GTA

Ni-Hard 4 cast iron is a special grade alloy and its extensively used in the field of concrete mixer blade, mining, turbine fittings etc. The investigation of surface modification process (SMP) on microstructure, wear rate and hardness of Ni-Hard 4 cast iron alloyed with tungsten was performed using gas Tungsten arc source. The grain structure was refined in the modified layer. The hardness was measured and it was found to be increased from 597 HV for the substrate to 1738 HV in the modified layer. Wear rate was 4.3 x 10 -3 mm 3 /m for the substrate and 0.21 x 10 -3 mm 3 /m in the modified layer. The wear was calculated using the weight loss of the specimen. The phase formation in the modified layer was observed by XRD analysis. From the elemental composition analysis, the presence of tungsten was observed to be 5.21 wt. % on an average. The test was performed in several locations in the modified layer for the elemental composition. So the investigation of this experiment to improve the surface properties of Ni-hard 4 cast iron used in the field of mining area.