Flow Patterns During Convective Boiling in Microchannels

To develop a flow regime map for convective boiling in microchannels and to propose flow pattern-based models to predict the corresponding heat transfer coefficients, a thorough understanding of the existing flow patterns and their transitions is necessary. In the present study, high-speed photography is employed to observe the flow patterns in flow boiling of a dielectric liquid, FC-77, in parallel silicon microchannels of depth 400 μm and widths ranging from 100 to 5850 μm. In each test, liquid mass flux and inlet subcooling are fixed at 250 kg/m2s and 5°C, respectively, while the heat flux to the bottom of the heat sink is increased form zero to a value near the critical heat flux. Temperature and pressure are measured at several locations. A high-speed digital video camera is used to observe boiling patterns at frame rates ranging from 2000 to 24000 frames per second (fps). The images presented show a top view of the horizontal microchannels, at a location along the heat sink centerline and near the flow exit