Numerical and experimental investigation of solid mixing and segregation in tumbling blenders

Tumbling blenders (especially V-blenders and rotating drums) are among the most commonly used equipment for granular mixing purposes. One aspect that must be addressed when designing such mixing devices is low axial mixing efficiency, which can lead to nonhomogeneous mixtures, especially when the physical and flow properties of the particles brought into play are different. Existence of granules with different properties inside tumbling blenders could lead to significant segregation. To overcome these limitations, we recently undertook an interest in the so-called tetrapodal mixing device, patented in 1964 (USA patent office, 3,134,578). This blender can be described as two V-shaped pairs of arms connected at the bottom whereby one is twisted by 90°.;The main objective of this study is to investigate (both numerically and experimentally) solid mixing and segregation in the following tumbling blenders: rotating drum, V-blender and tetrapodal blender. There are several studies in the literature that have been performed to investigate the performance of rotating drums and V-blenders. However, despite the seemingly effective shape of the tetrapodal blender for solid mixing, there have not been any studies to investigate the performance of this blender. Therefore, investing in manufacturing a lab-scale version of such a blender at first step is risky and it is of interest to characterize its efficiency via numerical tools and obtain design parameters. Among the common techniques for simulating granular flow, the discrete element method (DEM) has recently been applied to investigate the granular flow in many applications. This simulation technique has been proven to be efficient in providing insight into phenomena occurring in granular beds as well as details about the flow and mixing of granules. However, this technique suffers from some limitations that one should be vigilant when using the results of this simulation method. Therefore, to offset these limitations the first step of this work was to check the validity of DEM-based model by comparing its results with Lagrangian experimental data. Next, based on the results of first step, appropriate parameters were chosen for DEM-based model to investigate the mixing and segregation of non-adhesive granules inside the tumbling blenders. Finally, the simulation findings of mixing and segregation were validated using experimental data and further investigations were performed to characterize the effect of operating conditions on blender efficiency.;The scientific findings of this work contribute to four categories of applications. Firstly, the deep findings of this work in the case of tumbling blenders may facilitate the design and scale-up of more efficient solid mixing processes. Secondly, the performance of the tetrapodal blender was investigated for the first time. It is recommended to use a tetrapodal blender, where there are issues with conventional mixers regarding mixing time or non-homogenous products that may be a result of less efficient mixing mechanisms or segregation of ingredients. Thirdly, it was originally shown why the DEM-based model yields acceptable results even when wrong physical parameters are used. Lastly, our accurate contact force model could be applied in DEM-based simulations to obtain more reliable results. (Abstract shortened by UMI.).