Huo et al. [4] studied experimentally boiling heat transfer of R-
134a fluid flowing in small vertical tubes of 2.01 and 4.26 mm
internal diameter. In the range of low vapour quality, the heat
transfer coefficient in both tubes increased with increasing heat
flux and saturated pressure but was independent of vapour quality.
These results were attributed to nucleate boiling being the dominant
heat transfer mode. Over other ranges of vapour quality, however,
the dominant heat transfer mode was not addressed as a
result of inconsistency in the experimental data. Under the same
controlled conditions, they found that the nucleate boiling heat
transfer coefficient was higher for the 2.01 mm tube than for the
4.26 mm tube.