Liquid Mixing on Falling Films: Marker-Free, Molecule-Sensitive 3D Mapping Using Raman Imaging.

Area of Science:

• Chemical Engineering
• Fluid Dynamics
• Surface Science

Background:

• Surface characteristics critically influence mixing in falling liquid films.
• Understanding mixing on different surfaces is crucial for process optimization.
• Previous methods lacked the resolution or non-invasiveness for detailed analysis.

Purpose of the Study:

• To develop and validate a new marker-free, molecule-sensitive method for mixing mapping on falling liquid films.
• To quantify and compare the mixing capabilities of plain versus structured surfaces.
• To demonstrate the utility of Raman imaging for analyzing fluid flow and mixing dynamics.

Main Methods:

• Utilized point-by-point Raman imaging with a specialized high-working-distance, low-depth-of-focus probe.
• Employed cross-section mapping to analyze mixing progression along the falling film.
• Ensured steady-state conditions for reliable, time-independent measurements.

Main Results:

• The novel Raman imaging technique successfully mapped mixing without disturbing the liquid film.
• Significant differences in mixing efficiency were observed between plain and structured (pillow plate) surfaces.
• Detailed insights into liquid flow and component distribution were obtained.

Conclusions:

• Raman imaging is a powerful, non-invasive tool for monitoring mixing in falling liquid films.
• Surface topography plays a key role in enhancing or hindering mixing processes.
• The developed method provides valuable data for designing and improving fluid handling systems.