Two-Phase Convection Heat Transfer in Microchannels

Experiments were conducted to investigate two-phase subcooling flow boiling in 75 parallel microchannels (L=30 mm) having 200 mu m (W) x 100 mu m (H) cross-section with/without structured reentrant angle (theta= 180 degrees, 60 degrees, 90 degrees and 120 degrees). Boiling inceptions, flow morphologies, critical heat flux, heat transfer coefficients, and friction factor correlation were obtained for three different working mediums (DI water, DI water-MCNT(1 vol.%) nanofluids and FC-72) and two different heated surface material (Cu and Cu coated with 2 pm diamond film) at G 820 similar to 1600 kg/m(2)s and Delta T(sub) = 20 similar to 85 degrees C. Results were compared to non- reentrant parallel microchannels (theta = 180 degrees) at the same experimental conditions. It was found that the reentrant angle parallel microchannels can significantly decrease the wall superheat and increase the critical heat flux (CHF). Moreover, the working medium (I)l water) with 1 vol.% nanoparticles and heated surface coated with 2 mu m diamond film were also shown to significantly enhanced the heat transfer performance. The maximum CHF was found to be up to 614 W/Cm(2).