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Abstract: Fluidized Bed Membrane Reactors gain worldwide increasing interest for various applications. Nevertheless, fundamental research on the hydrodynamics of these reactors is required in order to improve the predictive capabilities of numerical models and to improve reactor performance. This study comprises an experimental investigation in a pseudo-2D gas–solid fluidized bed containing horizontal submerged membrane tubes, through which gas can be added to – or extracted from – the fluidized suspension. Employing Particle Image Velocimetry (PIV) combined with a novel Digital Image Analysis (DIA) technique, the effect of the presence of, and permeation of gas through the membranes, on both the solids flux profiles as well as the bubble properties has been investigated in great detail for different membrane configurations. It has been shown that merely the presence of the membrane tubes decreases the solid fluxes by about a factor three, but does not significantly change the overall circulation patterns in the bed. The permeation ratio and the membrane tube arrangement (in-line vs. staggered, size and number of membranes) hardly influence the time-averaged solid flux profiles. In addition, it has been found that, compared to a fluidized bed without inserts, the average bubble size with horizontally submerged membrane tubes decreases by a factor of approximately three, but is hardly dependent on the permeation ratio. The average total superficial gas velocity is more important than the permeation ratio. With respect to bubble size and number of bubbles, the staggered membrane arrangement with 9.6mm tubes outperforms the in-line arrangement, the arrangement with smaller tubes and the arrangement with fewer membrane tubes, which is of great benefit to reduce bubble-to-emulsion phase mass transfer limitations in fluidized bed membrane reactors under reactive conditions. [Copyright &y& Elsevier]

Abstract: Particle Image Velocimetry (PIV) is a widely applied non-intrusive, optical experimental technique to measure characteristics of the solids motion in pseudo 2D fluidized beds. However, the majority of the research that concerns the use of PIV on granular systems focused thus far on either particle velocities or on particle fluxes with a very rudimentary implementation for the correction for the presence of bubbles. A reliable correlation between the 2D image intensity and the true 3D solids fraction in fluidized beds is required to obtain more accurate information on the solid particle flux profiles in granular systems. Using only experimental data, it is difficult – if not impossible – to obtain such a correlation, but by using data from Discrete Particle Model (DPM) simulations to create artificial 2D-images, we reconstructed this 2D–3D correlation for the solids fraction correction. In this paper the influence of particle size, fluidization velocity, bed depth and intensity distribution function on the 2D–3D correlation has been investigated, in particular for the application in gas-solid fluidized beds in the bubbling regime. It was found that the particle size and fluidization velocity have no influence on the correlation and the intensity distribution function only slightly affects the results for dilute regions, but the bed depth shows the most prominent effect. A detailed comparison between the DPM velocity field as a reference and the conventional and newly introduced Digital Image Analysis (cDIA/ nDIA) techniques shows that the error in the solids flux decreases from 18.7% to 12.3%. Also, we used PIV software to reconstruct the solids velocity field, based on a pair of artificial images from DPM simulations (as done for experimentally acquired data based on a pair of real images), and showed that the largest error is introduced in the determination (cross-correlation) of the particle velocity field. [Copyright &y& Elsevier]

Abstract: Fluidized bed membrane reactors gain worldwide increasing interest for various applications. Nevertheless, fundamental understanding of the hydrodynamics of these reactors is required in order to improve the future design of these reactors. This study focuses on a pseudo-2D fluidized bed containing flat vertical membranes, through which gas can be added to – or extracted from – the fluidized suspension. By employing Digital Image Analysis (DIA) in combination with Particle Image Velocimetry (PIV), both solids motion as well as bubble properties were investigated in detail. In addition the experimental results were compared to computational results obtained from a Discrete Particle Model (DPM) and a Two-Fluid Model (TFM). Comparison between results obtained from a 4cm wide bed and a (previously used) 30cm bed revealed that the effect of gas addition is qualitatively the same (solids motion inverts and average bubble size decreases). During gas extraction, bubbles (and solids) are forced towards the center, enhancing bubble coalescence compared to the reference condition. Both the DPM and the TFM qualitatively capture these phenomena well. However, these models are not able to predict the experimentally observed solids motion and gas bubbles behavior quantitatively. DPM and TFM simulations for a wider bed reveal that grid dependency and maximum solids fraction play an important role with respect to solids motion. Furthermore, the porosity distribution shows significant differences between the DPM and TFM models. [Copyright &y& Elsevier]

Disruption of the SC3 gene in the basidiomycete Schizophyllum commune affected not only formation of aerial hyphae but also attachment to hydrophobic surfaces. However, these processes were not completely abolished, indicating involvement of other molecules. We here show that the SC15 protein mediates formation of aerial hyphae and attachment in the absence of SC3. SC15 is a secreted protein of 191 aa with a hydrophilic N-terminal half and a highly hydrophobic C-terminal half. It is not a hydrophobin as it lacks the eight conserved cysteine residues found in these proteins. Besides being secreted into the medium, SC15 was localized in the cell wall and the mucilage that binds aerial hyphae together. In a strain in which the SC15 gene was deleted (Δ SC15) formation of aerial hyphae and attachment were not affected. However, these processes were almost completely abolished when the SC15 gene was deleted in the Δ SC3 background. The absence of aerial hyphae in the Δ SC3Δ SC15 strain can be explained by the inability of the strain to lower the water surface tension and to make aerial hyphae hydrophobic. [ABSTRACT FROM AUTHOR]