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Hydrodynamics of a Counter-current Downer Reactor Using Particle Image Velocimetry and Digital Image Analysis Techniques

During my master's studies at KAUST, I opted to pursue the thesis track. Although a mega-corporate funds my thesis, therefore, is not publishable as of now; I will give glimpses of my work without breaking the contract I signed on. The abstract can be found here.

Downer Reactor

Fluidized bed reactors are used extensively in industry for their enhanced mass and heat transfer; due to the nature of vigorous mixing.

Nevertheless, and for very fast reactions, the selectivity is hampered. Therefore, during my master's thesis, I focused on the newly developed fluidization regime, the downer where the solid moves downward with gravity's assistance. This type of reactor helps to assure a narrow RTD of the solid particles, therefore, better selectivity.

downer.png

Powder Characterization

The most common type of fluidized bed is that of a gas-solid. Therefore, a careful understanding of the solid particles' physical properties, a measurable quantity, is eminent to correlate with the fluidization behavior. The seminal work of Geldart correlating the particles' density and size with the fluidization behavior proves its practicality with roughly 4000 citations [D. Geldart, Powder Technol. 7 (1973) 285].

The primary techniques/experiments in my thesis were:

1- Particle size analysis using Laser Diffraction Analyzer

2- Experimental and theoretical determination of Minimum fluidization velocity and terminal velocity

3- Determination of Hausner index and angle of repose

I used a mini glass reactor to carry out the characterization experiments.

Particle Image Velocimetry

Particle Image Velocimetry (PIV), the most advanced velocity measuring technique was the main tool I used to characterize the solid particles flow behavior quantitatively and qualitatively.

PIV measures the fluid (or in my case the solid particles) velocity based on the displacement correlation between two images taken at a known frequency. The notable thing about PIV is that it takes instantaneously the velocity vector field of the whole imaging area at once, therefore, assuring reproducible results compared with other techniques.

Digital Image Analysis

Based on the PIV images, Digital Image Analysis (DIA), a non-intrusive technique superior in terms of catching the complex gas-solid interactions, was used to measure the solid particles volume fraction in just a matter of seconds with the ability to illustrate the quantity radially. DIA utilizes an in-home developed MATLAB code to read 100s of images and calculate the volume fraction.

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