Analyzing interfacial transport for water evaporating into dry nitrogen. (5th February 2022)

• Record Type: Journal Article
• Authors: Murray, Brandon; Fox, Matthew J.; Narayan, Shankar
• Is Part Of: Applied thermal engineering. Volume 202(2022)
• Publication Date: 2022-02-05
• Subjects: Accommodation coefficient -- Droplet evaporation -- Interfacial transport -- Evaporation kinetics; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2021.117910
• Languages: English
• ISSNs: 1359-4311

Abstract

Graphical abstract: Highlights: The study analyzes water evaporating into a dry nitrogen stream at room temperature. The study analyzes the macroscopic and microscopic factors affecting evaporation. The mass accommodation coefficient of water evaporating in dry nitrogen is 0.001. Kinetic-theory based evaporation flux model for two-component systems was developed. Abstract: Designing air-water systems for industrial applications requires a fundamental understanding of mass accommodation at the liquid-vapor interface, which depends on many factors, including temperature, vapor concentration, and impurities that vary with time. Hence, understanding how mass accommodation changes over a droplet's lifespan is critical for predicting the performance of applications leveraging evaporation. In this study, experimental data of water droplets on a gold-coated surface evaporating into dry nitrogen is coupled with a computational model to measure the accommodation coefficient at the liquid-vapor interface. We conduct this measurement by combining macroscopic observations with the microscopic kinetic theory of gasses. The experiments utilize a sensitive piezoelectric device to determine the droplet radius with high accuracy and imaging to measure the droplet contact angle. This setup also quantifies the trace amounts of non-volatile impurities in the droplet. For water droplets evaporating in a pure nitrogen stream, the accommodation coefficient directly relates to vapor flux over the droplet's surface and is affected by the presence of impurities. We obtained a surface-averaged accommodation coefficient close to 0.001 across multiple water droplets evaporating close to room temperature. This quantification can aid in conducting a more accurate analysis of evaporation, which can assist in the improved design of evaporation-based applications. We believe the modeling approach presented in this work, which integrates the kinetic theory of gases to the macroscale flow behavior, can provide a basis for predicting evaporation kinetics in the presence of extremely dry non-condensable gas streams.