In addition to the mechanisms corresponding to nucleate boiling
and convective boiling contributions, recently, a three-zone
flow boiling model based on the elongated bubble flow regime,
was developed by Thome et al. [16] and Dupont et al. [17] to predict
heat transfer characteristics in micro-channels. The point they
make is that heat transfer is controlled primarily by conduction
through the evaporation film trapped between the elongated bubble
and the tube wall.
From the above review of the literature, the characteristics of
flow boiling heat transfer in small channels are not entirely consistent
with those in ordinarily sized channel. Moreover, there is
inconsistency in the micro-scale heat transfer results obtained
from different researchers and, as a result, the major heat transfer
mechanisms behind the phase-change phenomena are still unclear
for small flow passages. Flow patterns have been expected to affect
the heat transfer phenomena. Different flow patterns may give differences
in flow boiling mechanisms. The current work is, therefore,
aimed at examining the three-zone flow boiling model for
various flow patterns observed in R-134a refrigerant flow boiling
through a 1.75 mm tube.