Solid-Solid Mixing with Static Mixers

The Canadian Journal of Chemical Engineering, 2011

Previous experimental and computational work has demonstrated that the geometry of the impeller has a significant effect on the mixing performance of continuous powder mixers. In particular, different blade patterns using either all blades pushing the powder forward ('forward pattern') are less effective than patterns where some of the blades push the powder backwards ('alternate pattern'). In this article, we use Discrete Element Method to investigate this issue, as well as to examine whether batch mixers can be used to estimate the cross-sectional mixing rate of continuous mixing process. Mixing and flow of particles are examined in simple geometries consisting of a cylindrical cross-section agitated by impellers. In these geometries, blades are designed 'forward' and 'alternate' to study different blade patterns. Periodic boundary conditions are used to approximate an idealised cross-section of a continuous mixer. In addition, to examine whether an experimentally realisable batch system could be used to validate these cross-sectional simulations, we examine mixing in geometries with solid end walls. Performance in these elemental systems is compared qualitatively in terms of radially averaged velocity vectors, and quantitatively in terms of the mixing rate and the fill level profile. Results show that end walls and symmetric blade pairs of the 'alternate' blade patterns lead to faster mixing. Non-symmetric elemental systems display both increased fill level uniformity and similar mixing performance for both blade patterns. Results demonstrate the need for caution when attempting to use batch mixing information to estimate the cross-sectional mixing rate of continuous powder mixers.

Particuology, 2008

The mixing of particulates such as powders is an important process in many industries including pharmaceuticals, plastics, household products (such as detergents) and food processing. The quality of products depends on the degree of mixing of their constituent materials which in turn depends on both geometric design and operating conditions. Unfortunately, due to lack of understanding of the interaction between mixer geometry and the granular material, limited progress has been made in optimizing mixer design. The discrete element method (DEM) is a computational technique that allows particle systems to be simulated and mixing to be predicted. Simulation is an effective way of acquiring information on the performance of different mixers that is difficult and/or expensive to obtain using traditional experimental approaches. Here we demonstrate how DEM can be used to unravel flow dynamics and assess mixing in several different types of devices. These devices used for mixing and/or granulation of particulates, are classified broadly as gravity controlled, bladed and high shear. We also explore the role of particle shape in mixing performance and use DEM to test whether Froude number scaling is suitable for predicting scale performance of rotating mixers.

ASEAN Journal of Scientific and Technological Reports, 2021

Granular mixing process is necessary for operation in many industries such as food, pharmaceutical and cosmetic industries. Although the mixing materials are almost the first stage in the production process, it can affect the quality and cost of the final product. They are choosing a suitable mixer that may reduce cost and energy consumption. A static mixer is a device widely used to mix materials in industries. Because the mixing phenomena are very complex, a proper static mixer design still needs to be studied. In this work, we simulate the mixing pro-cess of granular materials in a conical mixer. We assume the two types of gran-ular solid with the same size flowing in the mixer. The discrete Element Method (DEM) is applied to obtain numerical solutions in the mathematical model. This work aims to use a coordinate mixing index to compare the effectiveness of mixing from the conical mixers with different angles, including 15o, 30o, 45o, and 60o. The results show that the highest co...

Advanced Powder Technology, 2018

In this study the mixing kinetics and flow patterns of non-cohesive, monodisperse, spherical particles in a horizontal paddle blender were investigated using experiments, statistical analysis and discrete element method (DEM). EDEM 2.7 commercial software was used as the DEM solver. The experiment and simulation results were found to be in a good agreement. The calibrated DEM model was then utilized to examine the effects of the impeller rotational speed, vessel fill level and particle loading arrangement on the overall mixing quality quantified by the relative standard deviation (RSD) mixing index. The simulation results revealed as the impeller rotational speed was increased from 10 RPM to 40 RPM, generally a better degree of mixing was reached for all particle loading arrangements and vessel fill levels. As the impeller rotational speed was increased further from 40 RPM to 70 RPM the mixing quality was affected, for a vessel fill level of 60% and irrespective of the particle loading arrangement. Increasing the vessel fill level from 40% to 60% enhanced the mixing performance when impeller rotational speed of 40 RPM and 70 RPM were used. However, the mixing quality was independent of vessel fill level for almost all simulation cases when 10 RPM was applied, regardless of the particle loading arrangement. Furthermore, it was concluded that the particle loading arrangement did not have a considerable effect on the mixing index. ANOVA showed that impeller rotational speed had the strongest influence on the mixing quality, followed by the quadratic effect of impeller rotational speed, and lastly the vessel fill level. The granular temperature data indicated that increasing the impeller rotational speed from 10 RPM to 70 RPM resulted in higher granular temperature values. By evaluating the diffusivity coefficient and Peclet number, it was concluded that the dominant mixing mechanism in the current mixing system was diffusion.

Volume 1D, Symposia: Transport Phenomena in Mixing; Turbulent Flows; Urban Fluid Mechanics; Fluid Dynamic Behavior of Complex Particles; Analysis of Elementary Processes in Dispersed Multiphase Flows; Multiphase Flow With Heat/Mass Transfer in Process Technology; Fluid Mechanics of Aircraft and R..., 2014

Granular mixing processes are commonly used to increase product homogeneity in many industrial applications involving pharmaceuticals, food processing, and energy conversion. Determining the appropriate granular mixing length is necessary to avoid over/under mixing and unnecessary power consumption. The goal of this study is to experimentally characterize the granular mixing process and determine, under various operating conditions, the needed mixing length to achieve adequate mixing in a laboratory-scale double screw mixer. Nine different combinations of screw rotation speeds and dimensionless screw pitches are used to investigate the rate of mixing at dimensionless mixing lengths of L/D = 2, 5, and 10. Composition and statistical analysis methods are employed to assess mixing effectiveness, and it is determined that the dimensionless mixing length is the most influential parameter in terms increasing granular homogeneity. For all the conditions tested, the granular mixture approaches an acceptable level of mixing for all testing conditions when the dimensionless mixing length is L/D = 10. However, the segregation rate throughout the screw mixer is vastly different for various combinations of screw rotation speed and dimensionless screw pitch, and is partly attributed to the influence of entrance effects caused by the material injection process. This is a proceeding published as Kingston, T.

Powder Technology, 1975

The performance of seven continuous mixers has been assessed using 20 : 1 mixtures of sand and sugar. The particle size of the sand and sugar was selected such that the powder pairs were cohesive/cohesive, cohesive/free-flowing, and free-flowing/free-flowing.

When engineers and scientists encounter the mixing of powders, they enter a subject where it is often difficult to find bearings. This perspective seeks to address this need by setting out the state of practice. It then considers the growing momentum in the area following advances in computation and in measurement that became significant in the 1990s.

Chemical Engineering & Technology, 2018

A simple yet informative model was built to estimate the influence of the initial distribution of dissimilar particulate solids to be mixed on the mixing time and mixture quality, and a way was searched to reduce the negative influence of segregation on the mixing process. The influence of segregation is particularly strong when it is necessary to mix a small amount of a key component with a large amount of a basic one. It is shown that the mixing time and mixture quality can be noticeably improved by introducing a premixing stage that consists in loading the key component in layers distributed over the basic component. A possible technical solution for such loading is also proposed. Experimental tests of such lab-scale vibration mixer proved its efficiency.

Chemical Engineering Science, 2016

AIChE Journal, 1985

pingement of two streams, was developed and successfully tested. It was found that in comparison to other available solid-solid pneumatic mixers, such as the fluidized bed, spouted bed, air mixer, and mixing silo, the new device is very convenient and easy to operate and more energyefficient. This is also true for gas-gas mixing when compared with a fluidized bed. A model for the gas phase behavior in the mixing of two gases was successfully tested, which supplements the picture of the solid particles behavior predicted from a model previously derived by the authors.