Identification of nucleation site interactions

Simple models of nucleate boiling consider nucleation sites in isolation. In practice, they interact in ways that depend on the distance between them. In this paper, statistical evidence of interactions is obtained for a large number of non-uniformly distributed sites with different activation superheats during pool boiling of water on a thin plate at a heat flux of 51 kW/m2. By analysis of spatio-temporal data for wall temperature obtained by liquid crystal thermography over a period of 30 s, the timing, position, activation superheat and radius of cooled region are obtained for every nucleation event, without need for direct observations of the bubbles. For each event, the number of subsequent events at all other sites during different delayed time intervals is obtained as a function of distance from the original site. The number is compared with a null hypothesis obtained by assigning random times to all events: a higher number indicates promotion, a lower number inhibition. It is found that there is promotion during very short time delays of the order of the bubble growth time at distances less than the bubble radius and inhibition for slightly longer delays and shorter distances. There is no statistically significant effect at distances greater than the bubble radius. This finding may be influenced by the low bubble frequencies characteristic of these particular experiments.