Evaporation Rate of a Sessile Drop

Title: Developing a Diffusion-Limited Evaporation Model for Sessile Drops

Students: Joe Chen and Daniel Villamizar

Advisors: Dr. Peter Kelly- Zion and Dr. Hoa Nguyen

Abstract:

Evaporation is an important phenomenon in a great many applications including cooling, coating and painting, preparing fuel for combustion, and remediating toxic spills. The study of the evaporation of a sessile drop, which is a drop resting on a solid substrate, is important not only because of the important physics that can be learned but also because of the potential for sessile drop evaporation to have a key role in important emerging applications such as DNA stretching and depositing, self-assembly and patterning, and nano-wire fabrication. The interaction of diffusion and convection in the vapor phase and their effects on the evaporation rate are a focus of ongoing research at Trinity. To support this research, a numerical model of the evaporation process will be beneficial. Eventually, all of the important transport processes will be incorporated into the model, but in this project the model contains only diffusive vapor transport. The geometry of the drop is also simplified as a disk for the initial model. The goal for this semester has been to develop the initial, diffusion-limited numerical model and to demonstrate that it can approximate: 1) the overall evaporation rate, 2) the distribution of the evaporative flux along the surface of the drop (disk), and 3) the distribution of the vapor concentration above the drop.

Student Final Presentation: Final_presentation(1)(1).pptx

Student Final Report: final_report.docx, pdetool_documentation_Webers_disc.docx

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Title: Studying the Mass Transport Phenomena Associated with Evaporation

Students: Taylor Piske and Gregory Wassom

Advisors: Dr. Peter Kelly- Zion, Dr. Chris Pursell and Dr. Hoa Nguyen

Abstract:

The subject of our research is evaporation, looking particularly at the two mass transport phenomena of the vapors – diffusion and buoyancy-induced convection. Diffusion is the outward expansion of the evaporated gas driven by a concentration gradient and the tendency of the gas to distribute itself evenly throughout a given space. Convection is the gravitational effect on the gas, which tends to pull the gas down and prevents it from spreading upward freely into the ambient gas (for evaporated gases that are heavier than the ambient gas). Traditionally, mathematical models used to describe the vapor transport of evaporation are diffusion-limited, meaning they do not take into account the effects of convection on evaporation. The purpose of our research is to gain insight into how diffusion and buoyancy-induced convection combine to affect evaporation, as well as how these two vapor transport phenomena are coupled. Several experiments have been carried out. Evaporation rates in air at one atmosphere have been directly determined using a gravimetric technique, while a shadowgraph technique in a pressure chamber has been utilized to measure evaporation rates in a variety of gases at various pressures. In our most recent experiments, the vapor concentration above an evaporating droplet of methanol, hexane, and 3-methylpentane was measured using infrared spectroscopy.

Student Final Presentation: