Flow Visualization In Evaporating Liquid Drops And Measurement Of Dynamic Contact Angles And Spreading Rate

Flow Visualization in Evaporating Liquid Drops and Measurement of Dynamic Contact Angles and Spreading Rate

A new hybrid optical system, consisting of reflection-refracted shadowgraphy and top-view photography, is used to visualize flow phenomena and simultaneously measure the spreading and instant dynamic contact angle in a volatile-liquid drop on a nontransparent substrate. Thermocapillary convection in the drop, induced by evaporation, and the drop real-time profile data are synchronously recorded by video recording systems. Experimental results obtained from this unique technique clearly reveal that thermocapillary convection strongly affects the spreading process and the characteristics of dynamic contact angle of the drop. Comprehensive information of a sessile drop, including the local contact angle along the periphery, the instability of the three-phase contact line, and the deformation of the drop shape is obtained and analyzed. Zhang, Neng-Li and Chao, David F. Glenn Research Center NASA/TM-2001-211284, E-13084, NAS 1.15:211284

Flow Visualization in Evaporating Liquid Drops and Measurement of Dynamic Contact Angles and Spreading Rate

FLOW VISUALIZATION IN EVAPORATING LIQUID DROPS, AND MEASUREMENT OF DYNAMIC CONTACT ANGLES AND SPREADING RATE... NASA/TM-2001-211284 ... MAR.