Transient flow boiling in a semi-annular duct: From the Onset of Nucleate Boiling to the Fully Developed Nucleate Boiling

•Infra-red (IR) measurements are synchronized with high-speed camera visualizations.•A time scale related to flow dynamics characterizes the transient heat convection.•Space-time diagrams of wall temperature allows a better understanding of the ONB.•A very strong time and space variation of the wall heat flux is observed.•The overheated wall temperature at ONB is well predicted by modified Hsu’s model.