An Investigation of Pool Boiling Heat Transfer on Single Crystal Surfaces and a Dense Array of Cylindrical Cavities

Abstract

The pool boiling heat transfer characteristics of smooth single crystal and densely packed cylindrical cavity surfaces were investigated using two highly wetting fluids, perfluoronhexane (FC72) and nhexane. Three single crystal copper surfaces and five undoped single crystal silicon surfaces with different plane orientations were considered. In addition, silicon surfaces with densely packed cylindrical cavities with diameters ranging from 9 to 75 خ¼m, depth ranging from 9 to 20 خ¼m, and spacing ranging from 75 to 600 خ¼m were tested for comparison. It is observed that the copper single crystal surfaces show increasing heat transfer coefficient with decreasing atomic planar density. The single crystal silicon surfaces show increasing heat transfer coefficient with increasing atomic planar density. Plausible molecular scale mechanisms are discussed. In contrast, the silicon surfaces seeded with cylindrical cavities having diameters of 27 خ¼m or less generally yield higher heat transfer coefficients than the single crystal silicon surfaces. A decrease in the cavity spacing results in a larger number of cavities on the surface, and the heat transfer coefficient increases as a result. Cavity depths of 6 and 20 خ¼m result in the same heat transfer coefficient irrespective of cavity diameter. The nucleation site density for the cylindrical cavity surfaces is measured and reported at low superheat using a novel imaging technique.