A visualization study of pool boiling at atmospheric pressure from transparent enhanced structures was conducted for a dielectric fluorocarbon liquid (PF 50-60). The single layer enhanced structures studied were fabricated in quartz and had an overall size of 10 mm × 10 mm and were 0.75 mm thick. The parameters investigated in this study were the heat flux and the width of the microchannels. A high-speed camera operated at 1000 frames/s at full resolution with attached magnifying lens allowed precise observation of the evaporation process in the subsurface and top tunnels. Three boiling regimes have been identified: slug formation (in either top or bottom channels), slug migration between the top and bottom channels and slug predominance (most of channels vapor filled). These regimes occurred at q{sup}∥ ≤ 3 W/cm{sup}2, q{sup}∥≈ 3-4 W/cm{sup}2 and q{sup}∥ ≈ 9.5 W/cm{sup}2 respectively (for a 0.285 mm × 0.285 mm pore size) and at q{sup}∥≤ 2 W/cm{sup}2, q{sup}∥ ≈ 2-3 W/cm{sup}2 and q{sup}∥ ≈ 5 W/cm{sup}2 respectively (for a 0.09 mm × 0.09 mm pore size).
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