An investigation of flow boiling with two arrays of microjets with R134a was conducted. Velocities of 4 and 7 m/s, subcoolings of 10, 20, and 30 degrees C, and jet-to-heater area ratios of 8.9% and 21% were employed. Lower subcoolings and lower velocities were found to enhance boiling and reduce the onset of nucleate boiling heat flux. The area ratio did not influence the onset of nucleate boiling but did increase the boiling enhancement of the heat transfer coefficient. Also, a previous hypothesis that nitrogen dissolved into the working fluid prevented premature temperature excursion was tested with controlled mixtures and was not substantiated. (C) 2011 Elsevier Ltd. All rights reserved.