Slug flow, characterized by elongated bubbles flowing in the axial
direction, and gas core flow, which is defined as long gas slug
occupied over a length of channel, were observed. As shown in
Fig. 7a, for the inlet section which led the gas–liquid mixture directly
to the micro-channels, large gas bubbles in the chamber
could expand along the channel length, leading to gas core flow
in most channels. The formation of gas core flow is schematically
depicted in Fig. 8. Comparatively, almost all the channels could
be occupied by slug flow, as seen in Fig. 7b, when a piece of foamed
plastic polymer inserted in the inlet section was used to induce the
discrete bubbles before entering the channels.