Enhanced Boiling on Microconfigured Surfaces

New results are presented for pool boiling from vertical, smooth and regularly microconfigured etched silicon surfaces, in saturated water at 1 atm. All specimens were 1.27 cm square and approximately 300 μm thick. The etched microstructures were hexagonal dimples and rectangular trenches. The dimples were 4.1 μm deep and 11.5 μm across, on 22 μm centers. The trenches were 51 μm deep, 12.6 μm wide and 101 μm long, with repeat distances of 22 and 110 μm, in the two directions. The surface densities of the microstructures were 2 × 10⁵ per cm² for the dimples and 0.4 × 10⁵ per cm² for the trenches. Electrical heating was accomplished by applying an electrical potential across the phosphorous doped dry side of the silicon specimen substrate. The hexagonally dimpled specimen in the nominal nucleate pool boiling region had heat transfer increased by a factor of 4.2 over that of the smooth specimens. The heat transfer enhancement was a factor of 3.1 over the smooth specimen data, for the trenched specimen data. In the nominally convective-vaporization regime, both the smooth and microconfigured specimens had as much as 5 times the heat transfer compared to a uniform flux natural convection correlation. Comparable heat transfer measurements in subcooled water verified the experimental procedure and also indicated that only a small fraction of this large enhancement may be explained by edge effects, on these small heaters.