The effect of channel size on bubble motion characteristics under mini/micro-scale condition is analyzed theoretically.The comparison between channel width and bubble departure diameter indicate that when the former is smaller than the latter

the flow pattern of confined bubbly flow will occur

the flow features of which is further analyzed.On this basis

traditional flow patterns in confined mini/micro-channel are subdivided and flow pattern transition criteria are derived.The prediction of the theoretical model agrees well with corresponding experimental data.The analysis on characteristics of the transition criteria shows an apparent postponement of transition for flow boiling in mini/micro-channel than that under adiabatic conditions.Moreover

for flow boiling under the same heat flux and mass flux conditions

the flow pattern transition may occur earlier with the decrease of channel size.