CFD-PBE coupled model for size-driven segregation in polydisperse granular flows

Mixtures of granular materials made of different-sized particles may segregate when subjected to vibration or shear rate and in the presence of a gravitational field. This leads to highly inhomogeneous mixtures, which are undesirable in many industrial processes. This work focuses on size-driven segregation in polydisperse mixtures. We described the evolution of the particle size distribution through a Population Balance Equation (PBE), which we solved numerically with the Direct Quadrature Method of Moments. To allow segregation and micromixing to occur, we closed the size-conditioned velocity of the particles with a segregation- mixing model. The PBE was then included in an Eulerian-Eulerian model and solved in a commercial Computational Fluid Dynamics (CFD) code. We used the model to study granular flows down inclined planes. The numerical results were then compared with those obtained from Discrete Element Method simulations. The CFD-PBE model predicts well segregation and micromixing in packed beds of polydisperse powders

Towards a digital twin for analytical HPLC

Digital twins for industrial process development are quickly gaining popularity in the pharmaceutical industry as an effective alternative to expensive and time-consuming physical experiments. This work describes the digital model element of a digital twin of High-Performance Liquid Chromatography (HPLC). The model is based on a mechanistic model implemented in gPROMS ModelBuilder and integrated into the MATLAB environment. Unlike other models reported in the literature, our model comprises a more accurate prediction of the injection profile and can predict the elution behaviour for a wide range of HPLC conditions given a reduced number of experiments. The model is compared against experimental data performed to separate a mixture of eight small drug molecules on a C18 column, in gradient elution mode, and under nine different operative conditions (i.e. 3 temperatures × 3 solvent gradient). We will show that by considering only two isotherm parameters for each molecule, the digital model can accurately predict the retention behaviour of the eight analytes. Furthermore, it facilitates HPLC in-silico method development, showcased here via method time minimization through a dynamic solvent strength gradient. The proposed model is intended to be integrated into a digital twin architecture for offline decision support and real-time optimization

Dynamic ball indentation for powder flow characterization

In industrial processing and manufacturing, characterizing the flowability of particulate solids is of particular importance both for reliable powder flow and for a consistent production rate. Shear testing is the most widely used method for powders subjected to moderate or high stresses, and under quasi-static conditions. However, this method is not suitable for measuring the powder flow properties occurring in dynamic systems, such as powder mixers and screw conveyors. In this study, the rheological behaviour of powders at high shear rates has been evaluated by the ball indentation method. The technique, which simply consists of dropping a ball onto a cylindrical bed of previously consolidated powder, directly measures the material hardness, which is related to the unconfined yield stress by the constraint factor. The impact of the ball on the bed is recorded with a high-speed camera to determine velocity and penetration depth. The hardness against the strain rate is considered for four different materials. Because of their difference in particle size, and by using a range of drop heights and a range of indenter densities, the intermediate regime of flow has been fully analyzed. Although hardness is constant in the quasi-static condition, it results to be strain rate dependent in the intermediate regime of flow. Finally, a predictive correlation that allows the operator to choose the best operating conditions for achieving the desired flow regime is proposed, and the unconfined yield strength of the materials is inferred

Shear-induced particle segregation in binary mixtures: Verification of a percolation theory

Granular materials composed of different-sized grains may experience undesired segregation. Segregation is detrimental for a lot of industries because it leads to an increase in production costs and wastes. For these reasons, the segregation phenomena have been intensively studied in the last decades, and a lot of models have been provided by many researchers. However, these models are mainly based on empirical relations rather than physical considerations. This paper aims to confirm the main assumptions made by Volpato, Tirapelle, and Santomaso (2020) in their percolation theory by means of DEM simulations. The simulated geometry is a tilting shear box filled with few tracer particles in a bed of coarser sized grains, and simulations are performed for a range of tilting frequencies and size ratios. The results provide meaningful insight on the mathematical model parameters and allow us to say that the percolation theory relies on physically consistent assumptions

Experimental investigation and numerical modelling of density-driven segregation in an annular shear cell

Granular materials segregate spontaneously due to differences in particle size, shape, density and flow behaviour. In this paper we experimentally investigate density-difference-driven segregation for a range of density ratios and a range of heavy particle concentrations. The experiments are conducted in an annular shear cell with rotating bumpy bottom that yields an exponential shear profile. The cell is initially filled with a layer of light particles and an upper layer of heavier grains and, on top, a load provides confinement. The segregation process is filmed through the transparent side-wall with a camera, and the evolution of particle concentration in space and time is evaluated by means of post-processing image analysis. We also propose a continuum-approach to model density-driven segregation. We use a segregation-diffusion transport equation, constitutive relations for effective viscosity and friction coefficient, and a segregation velocity analogous to the Stokes\u2019 law. The model, which is validated by comparison with experimental findings, can successfully predict density-driven segregation at different density ratios and volumetric fraction

Identification of Proteins Associated with Polyhydroxybutyrate Granules from <i>Herbaspirillum seropedicae</i> SmR1 - Old Partners, New Players

<div><p><i>Herbaspirillum seropedicae</i> is a diazotrophic ß-Proteobacterium found associated with important agricultural crops. This bacterium produces polyhydroxybutyrate (PHB), an aliphatic polyester, as a carbon storage and/or source of reducing equivalents. The PHB polymer is stored as intracellular insoluble granules coated mainly with proteins, some of which are directly involved in PHB synthesis, degradation and granule biogenesis. In this work, we have extracted the PHB granules from <i>H. seropedicae</i> and identified their associated-proteins by mass spectrometry. This analysis allowed us to identify the main phasin (PhaP1) coating the PHB granule as well as the PHB synthase (PhbC1) responsible for its synthesis. A <i>phbC1</i> mutant is impaired in PHB synthesis, confirming its role in <i>H. seropedicae.</i> On the other hand, a <i>phaP1</i> mutant produces PHB granules but coated mainly with the secondary phasin (PhaP2). Furthermore, some novel proteins not previously described to be involved with PHB metabolism were also identified, bringing new possibilities to PHB function in <i>H. seropedicae</i>.</p></div

PHB production of <i>Herbaspirillum seropedicae</i> strains SmR1 (wild-type) and Δ<i>phbC1</i>.

<p>The quantity of PHB was determined as described in Material and Methods during different time of cell growth. Numbers in parenthesis indicate the OD₆₀₀ of the cell culture at the indicated time of growth. Data represent the average of two biological replicates.</p

Expression level of genes related to phasins in <i>Herbaspirillum seropedicae</i>.

a<p>the gene identification is the same as deposited in the Genbank (accession number CP002039.1).</p><p>The expression value corresponds to the average of RPKM of two biological replicates. RPKM is defined as RPKM = total gene reads per mapped reads (millions) × gene length (kb).</p

Electrophoretic pattern of PHB granule-associated proteins from <i>Herbaspirillum seropedicae</i> SmR1 and Δ<i>phaP1</i> strains in 10% SDS-PAGE.

<p>Lanes: MW – molecular weight markers; lane 1: granule-associated proteins after granule purification from the wild type strain SmR1; lane 2: granule-associated proteins after granule purification from the Δ<i>phaP1</i> mutant strain. Phasins are indicated on the right. PhaP1was identified in lane 1 whereas PhaP2 and Hsero_2402 were identified in lane 2. Proteins were Coomassie blue R-250 stained.</p