1. IntroductionTwo-phase flow studi

1. Introduction
Two-phase flow studies have been carried out extensively over
the years. However, there have been a relatively small amount of
publications dealing with micro-channels when compared with
those for ordinarily sized channels. Capillary force is likely to play
an important role for two-phase flow characteristics in microchannels,
resulting in flow phenomena significantly different from
those observed in ordinarily sized channels. Serizawa et al. [1], for
instance, investigated the visualization of the two-phase flow pattern
in circular micro-channels. The flowing mixture of air and
water in channels of 20, 25 and 100 lm in diameter and that of
steam and water in a channel of 50 lm in diameter were conducted
experimentally. The study confirmed that the surface wettability
had a significant effect on the two-phase flow patterns in
very small channels. The discrepancies between micro-scale and
macro-scale flows have been reported in the literature [2–7].
Two-phase flow in micro-channels has gained significant attention
in engineering due to wide application, extending to such
fields as bioengineering, fuel cells, compact heat exchangers, heat
sinks, and so on. For cooling purposes, various applications of
micro-channels are discussed in detail by Mudawar [8]. Due to