الفهرس 
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Abstract
This work studies the hydrodynamics of a U-tube reactor using experimental and numerical methods. Different geometrical designs and operating conditions of the column were examined to figure out its performance, optimum design and operation, and effectiveness with respect to other gas-liquid reactors.
In the experimental study, the performance of a U-tube reactor of 50 mm inner-column diameter, 300 mm outer-column diameter and 2000 mm height was examined at a fixed liquid flow rate of 75 LPM, gas flow rate ranging between 5 and 50 LPM and using three different gas spargers. Three main variables were measured, namely the gas hold-up, the gas supply pressure and bubble size distribution. These were measured using manometric and displaced-liquid weight methods, U-tube mercury manometer, and a devised photographic technique, respectively.
In the numerical study, four cases representing different geometrical designs and operational conditions were investigated at four gas flow rates ranging from I to 35 LPM. The Eulerian model was used to simulate the two-phase flow while the k-E model was used to simulate turbulence. Only the drag and virtual mass forces were included in the study. The parameters studied were the gas hold-up, gas and liquid velocity fields, turbulence energy dissipation rate, global gas hold-up, and supply pressure.
The results of the experimental and numerical studies have shown good agreement, especially at low gas flow rates, less than 10 LPM. from the study of the flow structure, it was suggested to use thin-tall columns to enhance gas spread through the outer column. The relations between the superficial gas velocity and the global gas hold-up on one hand and between the superficial gas velocity and supply-pressure on the other hand were found to display linear behavior.
The air-water mixer proposed in this study has shown high ability to produce small bubbles especially in conjunction with streamlined spargers. The development of the bubble size distribution along the flow was obtained and analyzed to plot the coalescence and breakage map through the U-tube reactor. The distribution of the turbulence energy dissipation rate helped discovering the factors affecting turbulence in the column. Also investigating the bubble size distribution in accord with the distribution of the turbulent energy dissipation rate revealed the effect of the latter on the bubble coalescence and breakage processes.
The obtained performance data were used to determine the optimum geometrical design and operational conditions of the U-tube reactor. Finally, the U-tube reactor has shown a higher gas hold-up than the traditional bubble column and air lift reactor.