Swirl Bubbles Effects on Hydrodynamic Characteristics of an Air-Water Bubble Column

Ariny, Demong (2020) Swirl Bubbles Effects on Hydrodynamic Characteristics of an Air-Water Bubble Column. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Gas liquid bubbly flow reactors are used in chemical, petrochemical and bioprocess industries to enhance the mass transfer between the gas and liquid phases. The two-phase bubble column has gained huge attention for few decades due to its complex hydrodynamics and its impact on transport characteristics. The gas is dispersed to create a small bubble and disseminate them consistently to maximize the intensity of mass transfer. The motion of bubble’s rise in liquids is fascinating due to the bubble’s ability of adopting a variety of bubble’s motion patterns, which are characterized on the basis of bubble’s wakes, instability and size & velocity. This thesis describes bubble’s swirl effects on hydrodynamic characteristics in an air-water bubbly flow. The experimental set up comprises a cylindrical column, with a ring-cone sparger. The measurement technique contains a digital high-speed camera and image analysis software to track multiple moving bubbles. Bubble’s size, population and radial migration distance have been identified from consecutive pictures as a result of bubble’s edge recognition and projection on the basis of edge recognition for each of the bubble. The results from the experimental works show that by increasing the sparger rotation speed from 30 rpm up to 150 rpm, bubbles size is reduced, but bubble population is increased. Hence, the bubble migration distance is higher when the sparger’s rotating speed increases. Increasing gas flowrate results in larger bubble size, while promoting rotation induced by the sparger decreases the bubble size. As the rotating speed increase, the radial velocity of the water also increases. This is because, at high rotating speed, the velocity is dispersed more to the surrounding. Thus, at the center of the column, the liquid velocity is higher due to the bubble rising velocity is greater. As a conclusion, swirling bubble can enhance the mixing between air and water as well as provide larger migration of bubbles in the air water system. From this study, the efficiencyiv of the air-water mixing is increased, thus gives knowledge that by inducing swirl bubble in the flow, we can enhance the performance of the bubbly flow process.

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