and working fluids. The effects of such parameters as mass flux
and heat flux on flow boiling phenomena have been reported in
several publications whereas the important information dealing
with the gravitational aspect is still lacking, especially in the channel
thought to be in the transition range between macro-scale
channel and micro-scale channel [37]. The present experimental
study, which is a continuation of the authors’ previous work, is
therefore carried out to compare the heat transfer results obtained
from the horizontal channel with those from the vertical upward
flow channel under the same test conditions with a channel diameter
of 1.75 mm. The discussions are presented based on twophase
flow pattern and heat transfer coefficient.