Proper orthogonal decomposition (POD) analysis of flow structure in volatile binary droplets

In the present study we perform an in-depth analysis of the internal flow induced by concentration gradients in an evaporating binary ethanol–water droplet. The flow structure during the first stage of evaporation is characterised using micro particle image velocimetry (PIV) to investigate the flow field and analyse various modes of convection. Although PIV shows convection vortices, it does not help in identifying the various superimposed convection modes present. The proper orthogonal decomposition (POD) method is hence used in conjunction with PIV data to identify and characterise prevailing convection modes. During the first stage of evaporation many modes i.e. flow structures are found to co-exist, however the analysis reveals one dominant mode. In addition to the identification of this new mode of convection, the analysis quantifies the energetic contribution of each of these convection modes. The dominant mode is found to contribute to more than half of the total kinetic energy.