Characterizing Effects of Particle Size on Flow Boiling in Sintered Porous- Microchannels

Flow boiling in porous microchannels draws extensive attention recently owing to its great potential in high heat flux applications. Subcooled flow boiling of deionized and degassed water was carried out to characterize transport performance. Porous microchannels were sintered from six-sized copper particles: 10, 30, 50, 90, 120 , and 150 μm with the same layer thickness of 400 μm. The dimensions of 23 parallel porous microchannels are 600 μm × 1200 μm × 2.8 cm (width × depth × length). The inlet subcooling degree and mass flux is maintained at 40 K and 142 kg/m 2 · s, respectively. Experimental results show that particle sizes have great effects on the heat transfer coefficient (HTC) and Critical heat flux (CHF) of flow boiling in porous microchannels. Medium particle size (90 μm or 120 μm) achieve the highest HTC and CHF. The visualization study reveals that the underlying heat transfer mechanism in porous microchannel is dominated by the nucleate boiling in low heat fluxes, and then by the thin film evaporation from moderate to high heat fluxes. Moreover, two types of boiling crisis phenomena have been observed: (a) in microchannels sintered from medium-size particles, the rewetting-dryout cycle could be well established and sustain without being interrupted by explosive boiling, indicating capillary limits; (b) in other samples, high wall superheat in the rear region usually leads to explosive boiling persistently, which interrupts periodic oscillation with heat flux exceeding to moderate level and results in CHF condition . An optimal ratio of bottom wall thickness and particle diameter, δ / d, is found in the range of 3 ~ 5 for the flow boiling in sintered porous microchannels.