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Bubble nucleation site distributions based on cross correlation studies of surface temperature fluctuations
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.
"Major subject: Mechanical Engineering."
Includes bibliographical references (leaves 67-73).