Evaporation in model porous media with transport of particles

Abstract

Using a SUEX resin microchannel, we studied the effect of the presence of particles on the evaporation dynamics in a single channel. The experiments showed that the kinematics is slowed down by the presence of the particles due to their effect on the thickness of the corner films. They are thicker with pure water than in the presence of particles, at small concentrations, which results in smaller vapor partial pressure gradients in the channel entrance region. The work is extended considering a two-dimensional network of interconnected channels as model porous medium. To this end, an experimental set up was
developed to study the effect of the particles presence in the model porous medium and their respective deposit. The constructed network is composed of interconnected throats of rectangular cross section The drying process is analyzed from optical visualizations, while the deposit is observed under the microscope with confocal green light. Different parameters were varied in order to better understand the particles preferential regions of deposit and their relation with the drying pattern. For example, changing the wettability of the chip’s material completely changes the localization of the deposit. The particles concentrate in the channels closest to the top edge of the network (open edge of network), while the concentration is decreasing further away in the network. Two other variables that were changed, was the total pressure and temperature. Using an oven to perform the drying under partial vacuum condition (100mbar) at ambient temperature and at 55◦C, the invasion patterns are very different from the one obtained at the atmospheric pressure under diffusive evaporation condition and the deposits are more homogeneous throughout the micromodel. Furthermore we investigated the role of gravity on the evaporation rate, which was slowed down, and on the final deposit for which it is found out that particles do not tend to accumulate at the bottom of the network, instead the distribution is still homogeneous.