Fig. 7 shows the overall two-phase flow regime map developed
for micro-channels by Kawahara et al. [3]. The lines represent the
boundaries at which flow regime transition occurred among the
four flow patterns, i.e., slug–ring, ring–slug, multiple and semiannular
flows. According to the classification given by Kawahara
et al. (2002) semi-annular flow is the one in which the flow alternates
mostly between A1 and A2 regime and the time-averaged
void fraction is greater than 0.8. The present experiments were carried
out under this condition.