Bubble Behaviour in Three Phase Capillary Microreactors

Two-phase flow characteristics in vertical capillary downflow were investigated in order to obtain understanding of the behaviour of three-phase monolith reactors. Experiments were conducted using air and dyed water in round and square capillary tubes of 2 mm and 3 mm diameter. The flow regimes and transitions observed were recorded using high speed videography and this data was used to produce flow maps for each tube. The gas and liquid superficial velocities used ranged from 0.001 to 10 m/s and 0.0001 to 1 m/s respectively. The flow regimes and their transitions were found to be a strong function of tube geometry and surface tension effects, and some differences were observed between capillaries of round and square section. This has significant implications for the design of microchannel reactors. Annular, slug-annular, slug, bubbly and churn flow regimes were observed in the round tubes; channelling/irregular flow was observed in the square tubes in place of annular and slug-annular flow.