Experiments are conducted in subcooled flow boiling for boiling regimes close to the critical heat flux (CHF) and during the CHF transient. Different measuring techniques are applied to create a set of independent results. The techniques include high-speed photography and particle image velocimetry (Ply), digital holographic interferometry (DHI), fiber optical microprobes and heat flux measurements with thermocouple arrays. The experiments are performed in a rectangular channel with a copper heater flush mounted into one of the channel walls. The fluid is 3 M Novec 649, a fluorinated ketone with a low boiling point. Fluid subcoolings range from 5 to 27 K. From the experiments, it can be shown that in regimes close to critical heat flux the void fraction shows a periodic behavior with larger agglomerations passing at constant frequency ranges for all subcoolings. DHI reveals areas of cold liquid to be present between the vapor patches, with PIV showing the movement of the cold liquid towards the heater surface in the wake of the agglomerations, giving strong information about the mechanism of heat transfer at fully developed nucleate boiling. During the CHF transient, the void fraction is observed to concentrate near the heater surface, with bubble size and speed increasing, giving further information about the CHF mechanism. Results are compared to available mechanistic models on CHF transient. (C) 2013 Elsevier Ltd. All rights reserved.