Interaction of active sites in pool boiling heat transfer

[摘要] Heat transfer studies were performed on saturated carbon tetrachloride under natural convective and nucleate boiling conditions. A flat, polished, stainless steel plate was the heat source; and degassed, spectroscopic grade carbon tetrachloride was the heat transfer fluid. Tests were conducted at both one, and one and one-half atmospheres. Heat flux measurements were made for superheats ranging from 10 to 40°F, with corresponding heat fluxes ranging from 700 to 2500 Btu/hr-ft2. Two runs were performed. In the first run, seven equidistant cylindrical cavities, 0.006 inches in diameter and 0.010 - 0.012 inches deep, were drilled into the central portion of the heat transfer area. In the second run, additional holes with identical geometries were drilled halfway between the cavities studied in the first run. These artificial cavities served as active sites for the boiling studies. The purpose of the study was to investigate the nature of the interaction between these carefully positioned sites under nucleate boiling conditions. However, the drilling procedure created small protrusions around the mouths of the cavities. As a result, the bubbles obtained during nucleate boiling were smaller than would normally be expected, and no significant interaction between active sites was obtained for the site population densities studied. Nonetheless, the results provide useful information about the influence of cavity lip geometry on the heat transfer characteristics of an ebullating site. The boiling results obtained in this study reveal that the local heat transfer coefficient for the protruding lip case is an order of magnitude smaller than those obtained in other studies involving non-protruding lips.

[发布机构] Rice University