MRI studies of the evaporation of a single liquid droplet from porous surfaces

A combination of in situ one-dimensional profiling and two-dimensional 1H magnetic resonance imaging has been applied to study the shape and subsequent dynamic evaporation behavior of a single liquid droplet after impact onto a porous surface in a carefully controlled atmosphere. Aspects of the porous media permeability and particle shape are shown to affect considerably the observed drying regime. Variation in the shape, spread ratio, and penetration depth of the liquid droplet following impact are attributed to the different types of porous media used. A comparison of numerical simulations with the MRI data for the droplet shape, spread factor, and penetration depth show good agreement though larger deviations between simulated and experimental results occur in certain cases where the surface of the porous medium is disrupted by the impact of the liquid droplet. Initial results examining the effect of a reduced liquid surface tension show a significantly increased evaporation rate.