The Coalescence Mechanism of Multiple Slug Bubbles

Abstract

The authors have been investigating geysering, which may appear during start-up of a natural circulation boiling reactor. From the results, it became clear that a large slug bubble covering the entire channel and its condensation in the upper plenum were indispensable for geysering to occur. In this work, an image processing unit has been developed in order to measure the coalescence process of multiple slug bubbles. The proposed system was used to measure the coalescence process of multiple slug bubbles flow in vertical circular channel on air-water system. It was shown that a following slug bubble was influenced by the preceding slug bubble as the distance between the slug bubbles became 5 times inner channel diameter. The rise velocity of the following slug bubble increased due to the pressure drop induced by the wake behind the preceding slug bubble. The bubbles coalesced together in a fraction of a second.

KEYWORDS:

• geysering
• image processing unit
• slug bubbles
• coalescence
• wake flow
• condensation
• pressure drop