Intermittent dewetting and dryout of annular flows

Flow visualisation of saturated flow boiling of refrigerant R245fa in a silicon parallel multi-microchannel evaporator, at low mass flux and moderate uniform heat flux, has been carried out with a high-speed digital camera. Using the time-strip technique to post-process the recorded image sequences has revealed profound details regarding the intermittent dryout mechanism of annular flows. Features of these observed phenomena have been successfully correlated with the dynamics expected from a ruptured metastable liquid film under shear. These observations can act as a basis for the development of new mechanistic critical heat flux prediction models and the design of future high heat flux devices. This study also reveals details concerning the nature of the droplet entrainment-deposition process and nucleate boiling in very thin annular liquid films.