Infrared Evaporative Absorption and Condensative Emission in Water

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

1062361 Brewster Abstract The objective of this project is to investigate infrared radiation emission and absorption associated with first-order, vapor-liquid and vapor-solid phase transitions in water. Water undergoing condensation and evaporation plays a vital role in many engineering systems as well as in the environment. Heat exchangers are pervasive in society and water condensation, vaporization, sublimation and deposition are critically important in the performance of these devices. Drying is another important industrial process involving water vaporization that is very energy intensive. In the environment water plays a crucial thermal regulation role and its phase changes have a significant effect on Earth's energy balance through latent heat effects. It is also well known that water, in all three phases, plays an important role in atmospheric and surface radiative transfer via volumetric (single-phase) emission, absorption, and scattering. What is not well recognized is that vapor-liquid and vapor-solid water phase-transitions also may play a potentially critical role in surface and atmospheric radiative transfer. In spite of extensive knowledge of water's bulk, volumetric infrared properties, surface radiative properties associated with first-order phase transitions are almost unrecognized. In this study both measurements and modeling of phase-change radiation involving vapor and condensed-state transitions will be conducted. A laboratory-scale test chamber will be constructed and used to measure infrared emission and absorption by water droplets tens of microns and smaller in size undergoing vapor-liquid phase transition. The closed chamber will operate isobarically under steady-state and transient heating/cooling conditions. Surface (phase-change) emission/absorption will be delineated from volumetric emission/absorption by analytic data reduction techniques including Monte Carlo methods. A unified molecular model will be developed covering solid-, liquid-, and vapor-states that describes both new surface radiative phase-change properties and volumetric (single-phase) radiative properties. This study has intellectual merits at levels ranging from fundamental, scientifically oriented to engineering oriented. New knowledge will be generated about radiative phase- transitions for one of the most important substances on the planet. The infrared emission measurements will generate new knowledge about liquid-vapor radiative phase transitions of water for both condensation and vaporization. These measurements will be used to develop a model for liquid-water structure. At the engineering level, new data and a mathematical model for infrared emission and absorption by water will be developed. This study will also have broader impacts, ranging from individuals to society at-large. At the individual level this study will most immediately affect the education and career of graduate and undergraduate students. Locally, workshops will be conducted for K-12 students on water properties, phase-change heat transfer, and global climate change. At the engineering level the radiative phase-transition findings obtained herein will allow a better fundamental understanding of energy transfer in heat exchanger and drying equipment. At a larger, societal level, these findings may open a door to improved microphysical modeling of atmospheric energy transfer processes. The ultimate broad impact of this project will be better understanding of the fundamental thermophysical properties of our industrial society's primary thermal regulating fluid and Earth's principal greenhouse gas: water.