Heat transfer of R-134a refrigerant during flow boiling in horizontal
tubes with different diameters including 0.51, 1.12 and
3.1 mm was studied experimentally by Saitoh et al. [7]. Nucleate
boiling was reported in the low vapour quality region whereas convective
evaporation was dominant in the high vapour quality region.
The latter mechanism was found to be less dominant as the
tube diameter decreased. The smaller the tube diameter, the higher
is the effect of saturation temperature on heat transfer coefficient.
Flow instability was also discussed in this work.