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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]