A New Mechanism for Heterogeneous Nucleation in Boiling Systems

University Of Florida, Gainesville FL

Investigators

Abstract

0967473 Klausner This proposal addresses the onset of boiling involving surfaces that are extremely smooth, with geometrical features on the order of nanometers. Experimental observation has shown that the onset of boiling using such surfaces occurs at superheats much lower than expected and on the same order as for rough surfaces. This observation of somewhat anomalous behavior calls the traditional view of heterogeneous nucleation as emanating from trapped vapor in small surface crevices and cavities, into question. The proposed research seeks to explain, from a fundamental basis, this apparent anomaly. A combined experimental and analytical approach is taken. Intellectual Merit: It is hypothesized that the high surface energy associated with free electron flow at metallic surfaces contributes to the work of formation of a critical nucleus, thus reducing the thermal energy required to initiate vapor bubble incipience. Density functional theory will be used to develop a mathematical framework to compute the incipient superheat while an experimental facility will be employed to measure incipience phenomena for a variety of atomically smooth surface/fluid combinations. The experimental investigation will be extended to measure the incipient superheat for the same surfaces fabricated with nano-sized features embedded within micron sized cavities. The degree to which these features promote or inhibit incipience will be determined. Once the heterogeneous incipient mechanism for nano-smooth surfaces is well understood, the production and suppression of nucleation sites at low to moderate superheats will be investigated. Finally, a computational platform will be developed to simulate and predict the detailed transient thermal field within the solid heating surface, and the local temperature field will be used in conjunction with the incipience criteria to determine whether nucleation sites are produced or suppressed. Broader Impacts: Boiling is a basic heat transfer process that is ubiquitous across an extremely wide spectrum of manufacturing, energy generation and water production processes. University of Florida electronic education delivery platforms will be used to broadly disseminate new knowledge that evolves from the research via distance learning. Short courses for industry will be offered and the research results will be incorporated into these courses.