Local mass flux and pinning behavior of an evaporating droplet on heated aluminum surfaces

Abstract

The present study aims to investigate the characteristics of pinning behaviors and local mass flux variations during droplet evaporation at different surface temperatures ranging from 22.5 °C to 80 °C. An evaporating droplet is visualized by a CMOS camera, and the images are analyzed from droplet deposition to completion of evaporation. We measure the contact angle, the contact diameter, the droplet volume, the total evaporation time, and the pinning time during evaporation. The pinning time and Marangoni number increase with surface temperatures in the range from 20 °C to 50 °C; however, they decrease at surface temperatures higher than 50 °C. Moreover, the present study analyzes the local mass flux variation according to the surface temperature, showing the increase in the local mass flux over time. We also consider the change in vapor concentrations for the heated surfaces to estimate the local mass flux. Indeed, the local mass flux at the contact line becomes much higher; it experiences over a 10-fold increase from 0.1tf to 0.9tf.