Numerical simulation and PEPT measurements of a 3D conical helical‐blade mixer: A high potential solids mixer for solid‐state fermentation

Abstract

Helical-blade solids mixers have a large potential as bioreactors for solid-state fermentation (SSF). Fundamental knowledge of the flow and mixing behavior is required for robust operation of these mixers. In this study predictions of a discrete particle model were compared to experiments with colored wheat grain particles and positron emission particle tracking (PEPT) measurements. In the discrete particle model individual movements of particles were calculated from interaction forces. It was concluded that the predicted overall flow behavior matched well with the PEPT measurements. Differences between the model predictions and the experiments with wheat grains were found to be due to the assumption that substrate particles were spherical, which was in the model. Model simulations and experiments with spherical green peas confirmed this. The mixing in the helical-blade mixer could be attributed to (1) the transport of particles up and down in the interior of the mixer, and (2) dispersion or micro-mixing of particles in the top region of the mixer. It appeared that the mixing rate scaled linearly with the rotation rate of the blade, although the average particle velocity did not scale proportionally. It may be that the flow behavior changes as a function of the rotation rate (e.g., changing thickness of the top region); further study is required to confirm this. To increase the mixing performance of the mixer, a larger blade or a change in the shape of the mixer (larger top surface/volume ratio) is recommended.

Granular flow fields in vertical high shear mixer granulators

“…The formation of this toroidal flow structure is attributed to a combination of two independent trajectories caused by centrifugal forces, impact forces and gravity. Similar flow structure is observed by other investigators in cyclindrical mixers18, 21, 23, 24 and also in a conical frustum‐shaped mixer with helical blade 30. The reversed toroidal flow structure is reported for planetary mixers 27–29.…”

“…The advance in digital imaging technology and the invention of Positron Emission Particle Tracking (PEPT) have permitted more detailed quantitative investigation of granular flow. Many of the investigations have focused on the characterization of granular flow in vertical cylindrical mixers17–26 and there are few studies on more complicated configurations such as the planetary mixers27–29 and the vertical cone shape mixer 30. Ramaker et al,17 Muguruma et al,18 Litster et al,21 Conway et al,22 Nilpawar et al,23, 24 Lekhal et al,25 and Darelius et al26 have used the Particle Imaging Velocimetry (PIV) technique to characterize granular flow near the top surface in vertical cylindrical mixers.…”

Solid state fermentation pilot-scaled plug flow bioreactor, using partial least square regression to predict the residence time in a semicontinuous process

“…In practice, neither of these ideal models can be considered fully accurate and the measurement of residence time distribution (RTD) of the outflowing solid medium in a non-ideal PFB gives a sense of the axial dispersion existing along the bioreactor. With continuous process, it is also difficult to follow a single particle inside the bioreactor, though some models exist [19]. In order to optimize the bioprocess, it is therefore necessary to use models to approximate the residence time of the solid particles all along the bioreactor.…”

Mathematical Development and Comparison of a Hybrid PBM-DEM Description of a Continuous Powder Mixing Process

“…It was coupled with computational �uid dynamics for describing particle-�uid interactions [26,27] and continuum models [27]. Various rotational mixers [28][29][30], helical mixers [31,32] and rotor type mixers [33][34][35] have been studied with the help of DEM. It has been used as an effective tool in order to study various particulate and multiphase systems but it still needs further developments in order to address the current research needs [27,36] which would in turn help to understand the nature of particleparticle or particle-�uid interactions and dynamic behavior of granular materials.…”