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Development of an experimental method to investigate the hydrodynamics in a fluidized bed using PIV and DIA

Roghair, I. (2007) Development of an experimental method to investigate the hydrodynamics in a fluidized bed using PIV and DIA.

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Abstract:An experimental investigation has been performed, studying bubble phase and emulsion phase behavior in a gas-solid fluidized bed using non-invasive optical techniques. The fluidized bed setup, consisting of two pseudo-2D beds, was operated at various conditions, varying both the bed aspect ratio and the superficial gas velocity. The bed consists of Geldart B glass beads. Experiments were performed by recording images of the bed with a high-speed camera. The images were analyzed by commercial (PIV) and in-house developed software (DIA). Particle Image Velocimetry has been used to analyze the behavior of the emulsion phase. A method has been implemented to verify that the image recording scheme yielded reproducible time-averaged flow patterns. Also, a vector field stitching program was delivered. In addition, a method is developed to correct for raining particles through bubbles, which severely influence the time-averaged emulsion phase flow pattern. The correction algorithm showed an obvious upward particle flow, whereas the raw PIV results barely yielded any upflow of particles at all. Even after correction, upflow of particles is less pronounced than the downflow. Adaptations of the correction algorithm have been proposed to solve this issue. Corrected time-averaged emulsion phase flow patterns were obtained at 28 different operating conditions. It was shown that the upflow of particles is found along the bubble path, from the lower wall region to the top-center region in the bed. The velocity of the particles increased severely with increasing gas flow. A Digital Image Analysis (DIA) algorithm has been developed, capable of measuring bubble properties from an image series. The program was validated and yields accurate and reproducible results. The DIA program was used to investigate relations for bubble size, velocity and aspect ratio. A theoretical relation, predicting the bubble diameter in a pseudo-2D bed was adapted to include the bed width. The velocity of the bubbles in a pseudo-2D bed can be described as ub = KB p gdb, in which KB is a value between 0.6 and 0.7. Moreover, a relation between the bubble aspect ratio and the rise velocity has been observed. An attempt has been made to describe the bubble-particle phase interaction. By accounting for the average bubble rise velocity, diameter, aspect ratio and frequency of bubbles, it was shown that the trend of the lateral velocity distribution at a single height of the emulsion phase can be predicted. More studies are required to adapt the proposed correlation to yield the expected absolute emulsion phase velocity.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:35 chemistry
Programme:Chemical Engineering MSc (60437)
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