BOILING SURFACE TOPOGRAPHY
Recently there have been renewed attempts to unravel the problems posed by the nucleate boiling process. One important area requiring clarification is the mechanism determining the relation-Ship between the active site density na and the surface temperature difference ΔÐ¢.
The first part of this study is essentially an experimental confirmation that the boiling component of the heat flux is directly proportional to both na and ΔÐ¢ in the low heat flux or discrete bubble region. The second part is devoted to an attempt to physically account for the variation of na with ΔÐ¢. A new parameter termed the seeded proportion, s, is defined as the ratio of the density of the seeded or activated cavities of a particular mouth radius to the density of total available sites of the same mouth radius. The seeded proportion is postulated to be a function of the cavity mean depth and the volume of gas required to initiate boiling at the cavity. This allows the possibility of expressing the na − ΔÐ¢ variation for pool boiling in general terms.
For the particular experimental conditions used, allocation of reasonable values to the parameters
concerned leads to a theoretical relationship of
na α ΔT4
which is similar to the experimentally determined variation where the power index was found to be 4.5