Bubble nucleation site distributions based on cross correlation studies of surface temperature fluctuations

Abstract

Experimental work on the nucleate pool boiling of propanol-2 at a pressure -12.25 psig has been conducted. The locations of the bubble nucleation sites, the site density, and the nucleation frequency were studied. These studies were based on a computer analysis of the statistical cross correlation of experimentally acquired heating surface temperature fluctuations. The objectives of this research was to develop a new, relatively simple, experimental technique whereby the surface temperature fluctuations, as indicated by an array of surface temperature sensors, might be used to determine the number of active nucleation sites on a boiling surface as a function of heat flux. Three 0.015 in. diameter type K thermocouples were used as a detecting array. They were installed from the bottom of a stainless steel heating plate with their junctions flush with the heating surface. When a bubble developed and grew from a nucleation site within the area which was defined by the array, it was sequentially detected by the three thermocouples. A Saicor SAI-42 correlation and probability analyzer was utilized to do the cross correlation analysis. A digital computer was used for further analysis of the cross-correlation functions and, eventually, the locations of the nucleation sites on the heating surface were determined using a triangulation scheme. This research confirmed that the product of the average bubble departure diameter, D (subscript d), and its average frequency, f(subscript d), is constant and is independent of heat flux. The density of bubble nucleation sites increases with an increase in the heat flux.