Speaker
Description
Drying in porous media holds a great significance across a wide range of natural and engineering processes. Notable applications include food processing, pharmaceutical industries, porous building materials, soil and hydrology. For instance, during CO$_2$ injection, salt precipitation due to drying reduces permeability, posing a threat to sequestration by obstructing pores. In soil, drying and rewetting processes control water and nutrient transport. A comprehensive knowledge of the underlying fluid physics in drying is crucial to modeling, predicting, designing and guiding the aforementioned applications. During this multiphase flow process, the liquid phase vaporizes, causing the originally liquid-saturated pore space to be continuously displaced by the vapor phase, often described as the invasion-percolation process. Currently, drying in a homogeneous porous media is relatively well understood, which is characterized by three periods. However, the drying of porous media can be significantly complicated by the multi-scale structures that exist in many porous media. For instance, in soil, while the pore size in macroaggregates can be on the order of tens or hundreds of micrometers, the microscale pores in the microaggregates can be sub-micrometers. The different pore sizes in the same porous medium causes complex flow interactions between micro- and macro-pores due to their variations in capillary pressure. Our understanding of drying from porous media featuring dual porosity is thus still limited.
To that end, a novel 2D dual-porosity microfluidic device is used to study the multi-phase flow of air and water during drying, emphasizing the multi-scale interaction and role of corner film flows. In particular, the subtle interactions between drying and multiscale transport across micro- and macro-pores are carefully investigated. The microfluidic devices are created to bear the innovative three-layer glass-silicon-glass architecture, providing precise structural control and excellent optical access from both top and bottom. An innovative dual-magnification imaging technique adapted for micro-PIV and epi-fluorescent microscopy, offers insightful information about the flow dynamics at both the micro- and macro-scales concurrently. The results depict the overall drying dynamics in various porous structures and show that the porous geometry and external flow conditions pose a strong control on drying rate and flow patterns.
| Country | United States |
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