Raman mixture composition and flow velocity imaging with high repetition rates

Area of Science:

• Fluid dynamics
• Chemical engineering
• Optical imaging

Background:

• Understanding liquid mixing is crucial for various industrial processes.
• Existing methods often rely on tracers, which can interfere with the mixing dynamics.
• High-resolution imaging is needed to capture transient mixing phenomena.

Purpose of the Study:

• To develop and demonstrate a tracer-free imaging strategy for analyzing liquid mixing.
• To achieve high temporal and spatial resolution for resolving small-scale mixing features.
• To quantitatively measure composition and velocity fields during mixing.

Main Methods:

• Utilized high-repetition rate Raman imaging with a laser cluster and light sheet pulses.
• Employed two high-speed cameras to capture CH-vibration (ethanol) and OH-vibration (water and ethanol) Raman signals.
• Computed mixture composition fields from the ratio of Raman signals.
• Determined dense flow fields using variational optical flow on composition images.

Main Results:

• Successfully imaged composition and velocity fields without tracers.
• Achieved temporal resolution of 30 ns, spatial resolution of 54 x 54 µm², and sampling rate of 10 kHz.
• Resolved Kolmogorov scales and transient mixing phenomena during water-ethanol injection.
• Quantitatively observed the mixing process at high resolution.

Conclusions:

• The developed tracer-free Raman imaging technique is effective for studying liquid mixing.
• The method provides sufficient resolution to capture key mixing dynamics relevant to technical processes.
• This approach offers a new tool for fundamental research and industrial applications in fluid mixing.