Double Screw Mixer Research Articles

Геометрическая составляющая технических инноваций

In technical inventions related to innovative developments, the role of one of the main components belongs to geometry. A follow hypothesis has been adopted: in technical inventions the geometrical component is the determining one. This hypothesis applied to technical inventions can be confirmed by any copyright certificate, any patent both in Russia and abroad. In proposed paper this statement is proved by examples developed based on geometry of following inventions. 1. Screen feeder for sticky masses. Screen feeder’s grates are made in pairs, and between grate pairs there are gaps for screening of material’s size-defined fractions. In the screen-feeder has been proposed such geometry of grates that grates of each pair could clean each other, thereby preventing sticking on the surface and destroying the gaps between the pairs, which transforms the usual screen-feeder with cylindrical grates at an ordinary feeder. 2. Double-screw mixer for paste-like masses. The mixer consists of two contiguous worms. Their surfaces are the helical ones, in cross-section consisting of two quarters of circles stacked at the ends. Such cross-section allows homogenize the mixed paste-like material in the best way, and also deliver it under higher pressure in an extrusion head, that improves a final product. 3. Machine for processing of multi-faceted surfaces. This invention serves for manufacture of worms with a cross-section composed of two, three, etc. pieces of circles of the same radius and angle. Worms, made with this machine, are designed for the above mentioned two-screw mixer. 4. Method of mechanical processing. This method is also intended to manufacture of worms for two-screw mixer.

Numerical study of particle mixing in a lab-scale screw mixer using the discrete element method

This study employs the discrete element method (DEM) to simulate particulate flow and investigate mixing performance of a lab-scale double screw mixer. The simulation employs polydispersed biomass and glass bead particles based on experiments conducted in previous studies. Visual examination of particle distribution and statistical analysis of particle residence times of experimental data served as model validation. Statistical analysis indicates a maximum 9.8% difference between the experimental and simulated biomass particle mean residence time, and visual observations suggest the simulation captures the particle mixing trends observed in the experiments. Results indicate that the particle mean mixing time, non-dimensionalized by ideal flow time in the plug flow reactor, varies between 1.008 and 1.172, and it approaches 1 with increasing biomass feed rate. The mixing index profile in the axial direction shows a mixing-demixing-mixing oscillation pattern. Increasing screw pitch length is detrimental to mixing performance; decreasing the solid particle feed rate reduces the mixing degree; and increasing the biomass to glass bead size ratio decreases mixing performance. A comparison of a binary, single-sized biomass and glass particles mixture to a multicomponent mixture indicates that the binary system has similar mixing pattern as a multicomponent system. These findings demonstrate that DEM is a valuable tool for the design and simulation of double screw mixing systems.

Effect of particle size, density, and concentration on granular mixing in a double screw pyrolyzer

Double screw pyrolyzers can be used to convert cellulosic biomass into bio-oil. Bio-oil can then be converted into synthetic gasoline, diesel, and other transportation fuels, or can be converted into bio-based chemicals for a wide range of purposes. One method of industrial bio-oil production is called fast pyrolysis, the fast thermal decomposition of organic material in the absence of oxygen. One type of pyrolyzer, a double screw pyrolyzer, features two intermeshing screws encased in a reactor which mechanically conveys and mixes the biomass and heat carrier media. The mixing effectiveness of the two materials in the pyrolyzer is directly correlated to the bio-oil yield—the better the mixing, the higher the yields. This study investigates the effects of particle size, density, and concentration on mixing effectiveness in a double screw pyrolyzer. Using glass beads as simulated heat carrier media and various organic particles as biomass, a cold-flow double screw mixer with 360° of optical access and full sampling capabilities was used to collect mixing data. Unique optical visualization and composition analysis paired with statistical methods were used to evaluate the effects of varying the biomass particle size and density, the heat carrier particle size, and the biomass particle concentration. Both qualitative and quantitative analysis indicated that reducing the biomass particle size, for counter-rotating down pumping screw rotation orientations, noticeably increased mixing effectiveness. Increasing the heat carrier media particle size showed both increases and decreases in mixing effectiveness depending on operating condition. For all screw rotation orientations, a change in biomass particle density resulted in little change in mixing effectiveness, while reducing the biomass particle concentration reduced the overall mixing effectiveness.

Characterizing 3D granular flow structures in a double screw mixer using X-ray particle tracking velocimetry

Granular flows are commonly encountered in many industrial processes, but are difficult to characterize due to the opaque nature of the flow. For instance, screw pyrolyzers are being developed for the thermochemical conversion of biomass into bio-oil, but the granular flow and mixing process inside the reactor lacks fundamental understanding. In this study, X-ray particle tracking velocimetry (XPTV) is used to qualitatively and quantitatively characterize the three-dimensional (3D) granular flow structures in a double screw mixer, which geometrically replicates double screw pyrolyzers, by visualizing the position and speed profiles and quantifying the dimensionless pathlength and dimensionless residence time of individual tracer particles. The influence of screw rotation speed, dimensionless screw pitch, screw rotation orientation, and material injection configuration are investigated. Certain operating conditions are shown to significantly influence the granular flow structures and, in some instances, cause the double screw mixer to behave similar to two single screw conveyors. Comparisons with previous granular mixing studies are made to provide a link between granular flow behavior and mixing effectiveness.

A cone-beam compensated back-projection algorithm for X-ray particle tracking velocimetry

Characterizing multiphase or granular flows is difficult due to the opaque nature of the system. While invasive measurement techniques provide detailed information about a single point, assessing the entire system is a laborious task due to the large number of samples required. Therefore, significant work has gone into developing noninvasive methods of measuring these flow systems. In this study, identical pairs of X-ray source/detector systems are used to provide two simultaneous but independent X-ray radiographic projections, which are then coupled together to perform X-ray stereographic imaging of a granular flow. A cone-beam compensated back-projection algorithm is developed for X-ray particle tracking velocimetry (XPTV). This method accurately corrects for the X-ray׳s cone-beam geometry, which is ignored in parallel-beam back-projection methods. To demonstrate the need for the cone-beam compensation, a direct comparison between the cone-beam and parallel-beam back-projection algorithms is used, and significant differences are presented. These methods are then used to perform XPTV in a double screw mixer, allowing the position and velocity of individual tracer particles to be characterized.

Granular mixing optimization and the influence of operating conditions in a double screw mixer

Granular mixing processes often seek a high degree of homogeneity and, in some instances, can influence simultaneous processing, such as chemical reactions and heat and/or mass transfer. However, specific operating conditions and differences in particle size, shape, and/or density lead to segregation and reduce the mixing effectiveness of these processes. In this study, red oak chips and glass beads are mechanically mixed using a laboratory-scale double screw mixer and the mixing effectiveness is evaluated under various operating conditions. Qualitative optical visualization from four spatially aligned and temporally synced projections is combined with quantitative composition and statistical analysis techniques to optimize and investigate the influence of different operating conditions on the mixing effectiveness of the screw mixer. For the parameters considered in this study, the best mixing performance occurs when the screw rotation speed is ω=60rpm, the dimensionless screw pitch is p/D=1.75, the screw rotation orientation is counter-rotating down-pumping, and the material injection configuration features the red oak chips and glass beads injected into port one and two, respectively.

Optical visualization and composition analysis to quantify continuous granular mixing processes

The mixing of granular materials has a significant influence on the yield and/or quality of the desired products in numerous industrial processes including energy generation, food processing, and pharmaceutical production. However, characterizing the mixing effectiveness of systems or processes in granular applications is difficult due to challenging sampling procedures and measurement techniques. In this study, a two-part measurement technique consisting of optical visualization and composition analysis is developed to provide qualitative and quantitative mixing characteristics of continuous granular mixing processes, respectively. Mixing studies are performed in a laboratory-scale double screw mixer using a binary mixture of 500–6350μm red oak chips and 300–500μm glass beads. The effect of screw rotation speed and dimensionless screw pitch on the mixing effectiveness is investigated for ω=20, 40, and 60rpm and p/D=0.75, 1.25, and 1.75, respectively. Optical visualization in terms of video capture is captured across the entire mixing region's periphery, providing extensive qualitative observations. Quantitative composition analysis is performed on samples collected across the screw mixer and a two-way analysis of variance (ANOVA) statistical model is applied. Overall, the mixing effectiveness is maximized at an intermediate screw rotation speed of ω=40rpm and a dimensionless screw pitch of p/D=1.75. The developed measurement techniques and resulting trends are compared to previous granular mixing studies featuring similar mixing equipment found in the literature.

Screw Machines with Longitudinal Circulation of Fluid. Communication 3. Intensification of Mixing Processes

Flow of melts and solutions of polymers with Newton's law of flow was investigated in a double screw mixer with screw channels of different depth and width in the presence of a radial gap on one screw ridge. With the radial gap, the pressure gradients along both channels are the same, the pressure along the entire length of the shallow and deep channels differ by a constant value and the higher pressure is always established in the second channel along the path of movement of the upper plate. By intensive exchange between channels, flow which gives zero flow of fluid in each section in the direction across the channels is organized in the deep and shallow channels of the mixer. The overall pressure differential and output of the mixer do not decrease in the presence of a radial gap on one of the ridges of the screw.

Thermo-mechanical degradation of polypropylene, low-density polyethylene and their 1:1 blend

Thermo-mechanical degradation of isotactic polypropylene (iPP) and low-density polyethylene (LDPE), and the effect of the specific degradation processes of each polymer on the degradation of a 1:1 blend of these polymers, have been studied by using a conrotatory double-screw mixer coupled to a torque rheometer. The products were characterized by Fourier transform infra-red spectroscopy and thermogravimetry under inert and oxidative atmospheres. Data for the blend were compared with curves simulated from a combination of the results for the single polymers. LDPE is shown to form three to four times more carbonyl-containing products than iPP in the processing conditions used to prepare the blend. The main reason for this difference are the stabilizers added to iPP by the producer before its pelletization. Blending with LDPE stabilizes iPP, even at temperatures well above its melting point.

Power consumption in double-screw mixers

The authors conduct an element-by-element calculation of power consumption in mixing by breaking the power down into the individual components that apply to the elements of the mixing process and thereby deriving relatively simple relationships. The geometric parameters of the screws are shown. The authors employ the proposed method to make a theoretical calculation of the power consumed in a double-screw mixer by testing an SN-100 double-screw mixer producing filled polyvinyl chloride to be used in linoleum and floor tile manufacture.