Speaker
Description
Evaporation in porous media plays a key role in many natural and industrial processes, such as drying of products, CO2 sequestration, soil remediation and many more. Despite its significance, controlling evaporation at the pore scale remains challenging because it depends on several factors like wettability, pore geometry and fluid distribution. Surfactants are often used to alter liquid-gas interface properties in porous systems; however, their specific influence on evaporation at the pore scale is still not well understood.
We hypothesized that adjusting the surfactant mass fraction, particularly around the critical micelle concentration (CMC), would significantly influence how liquid evaporates in a porous medium. Therefore, we performed microfluidic experiments in a two-dimensional PDMS pore network. We compared pure water to sodium dodecyl sulfate (SDS) surfactant solutions at 0.10 wt.% (below the CMC), 0.23 wt.% (at the CMC), and 0.3 and 0.5 wt.% (above the CMC).
We recorded the evaporation process using an imaging technique (experimental setup shown in Figure 1) and used an image processing algorithm in Python to analyze the snapshots obtained. This allowed us to measure how liquid saturation changed, observe the movement of the liquid-air interfaces, and track how the contact angle changed as evaporation progressed.
Our results showed that surfactant mass fraction significantly influenced the evaporation dynamics. The fastest evaporation occurred at the critical micelle concentration (CMC) of SDS, which is 0.23 wt.%. At this optimum concentration, SDS reduced the surface tension from about 72.01 mN/m to 39.95 mN/m, thereby lowering the capillary pressure required for air entry and accelerating the evaporation process to complete roughly 47% faster than with pure water. Even at 0.10% (below CMC) air invaded pores more easily, speeding up the initial evaporation phase. At higher mass fractions above the CMC (0.30% and 0.50%), increasing the surfactant amount did not speed up the evaporation process; instead, the total evaporation time was slightly longer than at 0.23%. We believe this happened because the excess surfactant formed micelles, which may have slowed vapor transport and reduced the benefit of having a lower surface tension.
Our results demonstrate that adjusting the surfactant concentration is an effective way to control evaporation in porous media. By lowering surface tension and influencing how liquid distributes within the pore space, surfactant addition promoted more efficient liquid removal, confirming our initial hypothesis. These findings provide a foundation for developing more accurate evaporation models in porous materials and can inform the design of improved materials and processes for applications such as industrial drying and enhanced oil recovery.
| Country | Germany |
|---|---|
| Green Housing & Porous Media Focused Abstracts | This abstract is related to Green Housing |
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