Role of CFD techniques in discriminating experimental solids concentration data in stirred suspensions and modelling of the solids concentration profiles in a pilot reactor

In this work, the suitability of an optical probe for studying local solid particle distribution in agitated systems and of Computational Fluid Dynamics (CFD) as a means to discriminate among the experimental data is investigated. Solids concentrations are determined in a high-aspect-ratio baffled tank stirred with three Rushton turbines by means of a fibre-optical probe and by CFD simulations. The local analysis of the simulated liquid flow field allows to better understand the source of differences in the measured solid concentrations that are obtained by changing the angular orientation of the probe in a few specific positions and, therefore, to identify the best operating mode for the measurements. The predicted radial and axial solid concentration profiles are then compared with the experimental data obtained with the most reliable probe orientation and very good agreement is found. This study allows to point out that, once proper computational strategies are selected, the usefulness of CFD simulations is twofold: they can be adopted for obtaining reliable predictions of various parameters in solid-liquid systems and used for gaining a better understanding of the complex fluid flow features of turbulent multiphase flows

Production of L- and D-lactic acid isomers by Lactobacillus casei subsp. casei DSM 20011 and Lactobacillus coryniformis subsp. torquens DSM 20004 in continuous fermentation

With the aim of producing L(+) and D(−) lactic acid to be employed in poly-lactic acid polymer production, for biomedical applications, the strains Lactobacillus casei subsp. casei DSM 20011 and Lactobacillus coryniformis subsp. torquens DSM 20004 were studied in a conventional chemostat mode using various dilution rates. The results obtained showed that the dilution rate influences the fermentation pattern, modifying various fermentation parameters. Nevertheless, the product and biomass yields remained constant and the ratio of the L(+) and D(−) isomers of lactic acid was not affected by the dilution rate. The optimal glucose concentration on inlet feed medium was also determined for the L. coryniformis fermentation

Solids distribution and rising velocity of buoyant solid particles in a tank stirred with multiple turbines: a simplified approach for the study of sparged gas-liquid reactors (Paper 7.4)

The distribution of buoyant solids in agitated suspensions has been studied. The investigation was carried out in a baffled vessel characterised by an aspect ratio equal to four and stirred with four radial impellers. Dilute suspensions of single-sized spherical particles of expanded polystyrene (density equal to 90.7 kg/m3) in water were used. Solid concentration was measured with a non-intrusive optical technique. Measurements were performed along the axis of the reactor to obtain steady-state vertical profiles as well as at fixed elevations to determine the concentration transient after a pulse of solids injected at the bottom. Both the transient concentration curves and the steady-state profiles were interpreted by means of the axial dispersion model with sedimentation. The particle rising velocity in the agitated system was determined by data treatment; it proved to be significantly smaller than the free-rising velocity, i.e. the rising velocity in a still liquid. The ratio of these two velocities is in reasonable agreement with a correlation of the ratio of the settling velocities of heavy particles with the ratio of the Kolmogorov microscale to particle diameter established previously

Solids distribution and rising velocity of buoyant solid particles in a vessel stirred with multiple impellers

The distribution of buoyant solid particles in agitated suspensions has been studied. The investigation was carried out in a baffled vessel characterised by an aspect ratio equal to four and stirred with four radial impellers. Dilute suspensions of single-sized spherical particles of expanded polystyrene (density equal to 90.7 kg/m3) in water were used. Solid concentration was measured with a non-intrusive optical technique. Measurements were performed along the axis of the reactor to obtain steady-state vertical profiles (that increase from the vessel base to the top) as well as at fixed elevations to determine their transient after a pulse of solids injected at the bottom. Both the steady-state profiles and the transient concentration curves were interpreted in terms of the axial dispersion model with sedimentation. By data treatment the rising velocity in the agitated system could be determined, which proved to be significantly smaller than the rising velocity in a still liquid. The ratio of these two velocities is in reasonable agreement with a correlation of the ratio of the settling velocities for heavy particles with the ratio of the Kolmogorov microscale to particle diameter established in the past

The ubiquitin ligase Hecw controls oogenesis and neuronal homeostasis by promoting the liquid state of ribonucleoprotein particles

Specialised ribonucleoprotein (RNP) granules are a hallmark of germ cells. Among their main function is the spatial and temporal modulation ofthe activity of specific mRNA transcripts that allow specification of primary embryonic axes. While RNPs composition and role are well established, their regulation is poorly defined. Here, we demonstrate that Hecw, a newly identified Drosophila ubiquitin ligase, is a key modulator of RNPs in oogenesis. Loss of Hecw activity results in the formation of enlarged granules that transition from a liquid to a gel-like state. At the molecular level, Hecw depletion leads to reduced ubiquitination and activity of the translational repressorFmrp, resultinginprematureOrbexpression/recruitmentinnursecells. In addition to defective oogenesis, flies lacking Hecw show neurodegenerative traits with prematureagingandclimbingdefectsduetoneuronalloss thatarelinkedtoRNPscondensation. Our findings reveal an unprecedented function of ubiquitin in modulating RNP fluidity and activity