Liquid-vapour interface behaviours and the pressure drop fluctuation during flow boiling in a single rectangular micro-channel with high aspect ratio were experimentally investigated in the present study. A micro-channel with the hydraulic diameter of 727 μm was chosen, the aspect ratio of which was 10. FC-72 was used as the working liquid. Wide ranges of mass fluxes and heat fluxes were tested to study bubble dynamics and hydraulic instabilities during flow boiling. With the aid of high speed camera, various liquid-vapour interface behaviours during flow boiling were captured, such as bubble nucleation and growth, interface deformation, recoiling and rewetting. Based on the interface movement, the evaporation rate of the liquid was discussed. Evaporation rates of bubble nose and bubble tail at different mass fluxes and heat fluxes were compared. Besides, the effects of thermal and flow conditions on bubble geometry were discussed. Moreover, the pressure fluctuations resulting from boiling instabilities was remarkable. Fluctuation frequency was largely affected by the heat and mass fluxes.

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