Measurement of acetone-vapor concentration field using Background oriented schlieren (BOS)

Droplet evaporation is a simple natural phenomenon, however, associated with complex heat and mass transfer processes and seen in a wide range of applications, e.g. spray cooling, medical treatment, inkjet printing, etc. Therefore, it is important to understand the inherent coupling between the temperature and the vapor concentration to control the evaporation process and develop more accurate heat transfer models to predict evaporation rates. The present work demonstrates the application of background-oriented schlieren (BOS) to measure the transient concentration gradient around the evaporating acetone droplet during its impact on a horizontally placed aluminium surface at room temperature and atmospheric conditions. From the concentration maps retrieved, the droplet evaporation is identified to be primarily driven by the concentration difference. The experiments also revealed the relative dominance of the contact line evaporation process after the initial transients seen in the form of a significant increase in the concentration of acetone vapor in the vicinity of the contact line.