Impingement dynamics of droplets on mildly heated walls at initial and later stages

The impingement dynamics of water droplets on a heated wall at initial and later stages are experimentally investigated. First, the effects of the wall temperature and the Weber number on the water droplet spreading characteristics are considered. A constant contact radius evaporation mode is observed during most of the evaporation. The wall temperature has little influence on the spreading characteristics at the initial stages. The Weber number greatly influences the spreading characteristics, such as the spreading dynamic behavior, maximum spreading time, spreading height, diameter, and contact angle, at the initial stages. At the later stages of spreading, the heating temperature has a relatively greater impact on the rate of linear change of the residual volume, whereas the impact of the Weber number on that is relatively small. Subsequently, the effect of evaporation on the impingement dynamics is investigated. The spreading characteristics of the water droplet are compared with those of an ionic liquid droplet (which does not experience evaporation), whereby the spreading factor increases and the volume remains unchanged with the increasing contact time in the absence of the evaporation effect.