Enhanced Boiling Heat Transfer in Second Generation Microchannels: Part B — Sub-Atmospheric Results

Boiling flow of de-ionized water through 227 μm hydraulic diameter microchannels with 7.5 μm wide interconnected reentrant cavities at 47 kPa exit pressure has been investigated. Average two-phase heat transfer coefficients have been obtained over effective heat fluxes ranging from 28 to 445 W/cm² and mass fluxes from 41 to 302 kg/m²s. A map is developed that divides the data into two regions where the heat transfer mechanisms are nucleation or convective boiling dominant. The map is compared to similar atmospheric exit pressure data developed in a previous study. A boiling mechanism transition criterion based on the Reynolds number and the Kandlikar k₁ number is proposed.