Title: Characterization of Flow Boiling in a Fractal-Like Branching Microchannel Network Abstract approved:

Based on experimental investigations the present study evaluates flow instability and void fraction in a fractal-like branching microchannel network with rectangular cross-section. The hydraulic diameter of the channels ranged from 308μm at the inlet to 143μm at the outlet. The flow network used is characterized by set branching ratios for channel length and width of 2 iL and 2iL ⋅ , respectively, and features 5 branching levels. Test were performed using DI degassed water heated to an 88°C inlet temperature with a mass flow rate of 10g/min. Heat fluxes of 1.76 W/cm2 and 2.64 W/cm2 were applied to the test device for the given flow rate. Finally, a control valve directly upstream of the test device was throttled until the pressure drop across the valve was roughly 100 times larger than the pressure drop across the test device. For the cases with and without throttling at the inlet, results for inlet pressure oscillation and vapor activity at the inlet and exit of the test device are compared. Frequency of inlet pressure oscillations and the upstream flow of vapor are correlated. In addition time averaged void fraction is presented for each branching level for the 10g/min, 1.76 W/cm2 case with and withou