Two dimensional unsteady numerical simulations of flow boiling heat transfer inside a 1 mm and 2 mm smooth horizontal tubes for R32 were conducted utilizing VOF multiphase model

under the condition of a mass flux of 100 kg·m-2·s-1

a heat flux of 12 kW·m-2

a saturation temperature of 15℃. Single phase flow

bubbly flow

slug flow were observed in the simulation results for R32 flow boiling heat transfer inside a 2 mm channel while single phase flow

bubbly flow

confined bubbly flow

slug flow were observed inside a 1 mm channel. Bubble movement characters and influences on flow boiling heat transfer basic patterns exerted by channel diameter during flow boiling heat transfer inside the tubes for R32 were analyzed based on the distributions of gas phase volume fraction and temperature generated by the simulations. A promising consistency was achieved through the comparison between numerical simulation and experimental results.