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Effect of bubble size on the rising behavior in pure water medium

The phenomenon of rising bubbles in pure water is an important aspect of the bubble and liquid interactions. Due to several forces that act on the bubble accompanied by the pressures inside and outside the bubble, the rising bubble behaviour may vary depending on a few parameters such as the characteristics of the bubble and liquid medium. In general, the bubble increase occurs following the drag motion determined by the bubble drag coefficient but under certain conditions bubble also may move by a rolling pattern. Both drag and rolling are related to other forces that worked on the bubble, particularly the buoyancy force. The velocity of them may be different due to the mechanism types of motions. Rolling motion can be assumed does not occur for a very small bubble so there is only a relation between size and velocity. Several observations of bubble sizes have shown that for a very small bubble there is a linear relationship between size and rising velocity. Meanwhile, for a larger bubble, the rising velocity becomes faster almost seems an exponential relation. The increase of the bubble size results in a higher buoyancy force so that the bubbles rise more easily to reach the water surface. This paper aimed to prove that the small bubble will show linear relation of the rising velocity depending on the size. Our experimental observation has shown that the linearity of velocity only occurred for a very small bubble. This linearity gradient becomes quite important for predicting the rising pattern of other various bubble sizes.