EAGER: Experimental Determination of Non-Evaporating Film Thickness in Pool Boiling

Syracuse University, Syracuse NY

Investigators

Abstract

CBET-1445946 Maroo Boiling is used in domestic and industrial applications, ranging from residential refrigeration systems to power generation systems such as boiling water reactors. For example, about 90% of all electricity generation in the United States is by the use of steam turbines, where a large percentage of systems generate the steam using boilers. Due to its wide applicability, boiling has been researched for over five decades to understand bubble dynamics and attain enhancements in heat transfer; however, a complete knowledge of the bubble growth phenomenon is still lacking. One of the key missing pieces is the nanoscale non-evaporating liquid film (also known as the "adsorbed" film) widely theorized to exist at the base of a bubble. This film is of critical importance in bubble dynamics as it can sustain reduced/negative liquid pressure causing liquid to flow to the surface for evaporation and bubble growth. The non-evaporating film has not yet been directly measured in pool boiling experiments due to complexities associated with its nanoscale thickness and fluidic nature in the turbulent boiling process; the proposed research aims to overcome this shortcoming. The objective of the proposed research is to perform in-situ measurements of the nanoscale non-evaporating film thickness in pool boiling through the use of a novel interdisciplinary approach: application of two independent free-space optical techniques, spectral reflectometry and Michelson-interferometry, in pool boiling experiments of water. These high resolution techniques will enable measurement of the non-evaporating film thickness and its variation during a bubble's life-cycle in the isolated bubble regime at low heat fluxes. The effect of increasing heat flux and surface temperature on the film thickness will also be investigated. The experimental determination of the non-evaporating film thickness will facilitate accurate representation of the evaporation characteristics of the microlayer (region where the film is present) and its contribution to bubble growth, compared to current numerical simulations where the film is treated as a boundary condition with an assumed constant thickness. This work can also act as a basis for enhancing pool boiling heat transfer via novel surface modifications and other techniques aimed at altering the non-evaporating film and contact line region. The proposed research will enable new course materials and lab demonstrations to give students first-hand experience in interdisciplinary visualization techniques. Undergraduate students will also be actively engaged in the proposed research.