It
should be noted that the plug flow and slug flow are characterized
by the diameters of elongated bubbles. The diameters of elongated
bubbles which are similar in size to the channel diameter refer to
slug flow, and those which are smaller than the channel diameter
refer to plug flow [22]. Regarding the experimental data, they indicated the channel orientation affecting the flow pattern transition
and the heat transfer coefficient which was found to be compatible
with nucleate boiling mechanism.