Conference Presentation

Well folks, every summer the bees lazily churn their wings for honey, every fall the trees shed their leaves to dance with the winter wind, every winter Christmas lights mimic icicles, and every spring I start anew. It is a beautiful time of rebirth.

I truly feel as if it were my springtime, where life has a deep and flowing purpose, and the love of the Lord abounds like a well-spring in my heart. Several miracles have been in the works, and this little abstract is one of them.

I have submitted this (it's still a rough draft) abstract for consideration to present at the national conference for chemical engineers. I've attended this in the past as a wide-eyed undergraduate, and walked around the poster sessions trying to glean intelligence from the glasses-framed faces of PhD students. It's now my turn to present some of my research. More is yet to come, but, like this new springtime of my life, it's a springboard to starting my studies again.

Efficiency of Interfacial Heat and Mass Transfer

There has been both historic and recent excitement in literature concerning the evaporation (η_ev) and condensation (η_cond) coefficients and their application to mass transfer at liquid-vapor interfaces. Classically defined in the Hertz-Knudsen- Schrage equation [1], η_ev and η_cond represent the molecular emission efficiency from a liquid surface and the accommodation efficiency of an impinging molecule onto a liquid surface. Studies have been conducted which make no separation between these efficiencies, assuming their affects non-distinct or their numerical values synonymous. Other authors define an uptake coefficient (γ_meas) as being similar to η_ev, but including solubility constraints as the liquid species approaches Henry’s law saturation [2]. These definitions of mass transfer efficiencies have numerous application in literature, i.e. experimentation on the uptake of gases by aqueous surfaces [3,4].

The thermal analog of the evaporation coefficient is the thermal (energy) accommodation coefficient (η_therm), defined as the efficiency of heat transfer per molecular collision with the interface. A stream of molecules with velocity modeled by a Maxwellian distribution impinges on a liquid surface with a representative bulk temperature. Complete accommodation would result in a η_therm of unity, where reflected molecules would impart a portion of their energy to the interface, resulting in a η_therm ranging from zero up to unity.

This paper presents a study that incorporates the evaporation, condensation, and thermal accommodation coefficients into an analytic model which predicts mass and heat fluxes as functions of particle and bulk vapor temperatures. The solution for a constant-diameter water droplet undergoing steady state vaporization while suspended in a quiescent, dry nitrogen environment is elucidated.

[1] R. Schrage, A Theoretical Study of Interphase Mass Transfer. Columbia University Press, New York, 1953

[2] Q. Shi, Y. Q. Li, P. Davidovits. Isotope Exchange for Gas-Phase Acetic Acid and Ethanol at Aqueous Interfaces: A Study of Surface Reactions. J. Phys. Chem. B., 103: 2417-2430, 1999

[3] J. T. Jayne, P. Davidovits. Uptake of SO2 (g) by Aqueous Surfaces as a Function of pH: The Effect of Chemical Reaction at the Interface. J. Phys. Chem. 94(6041-6048), 1990

[4] James A. Gardner, Lyn R. Watson, Mark A. Zahniser. Measurement of the Mass Accommodation Coefficient of SO2 (g) on Water Droplets. J. Geophys. Res. 92(D9), 10, 887-10, 95, 2010