Fick diffusion coefficients probed by the shadowgraph method considering confinement and advection.

Area of Science:

• Thermodynamics
• Fluid Dynamics
• Physical Chemistry

Background:

• Accurate determination of the Fick diffusion coefficient (D11) is crucial for understanding binary fluid mixtures.
• Existing methods may face challenges with confinement and advection in thermodiffusion experiments.

Purpose of the Study:

• To develop and validate the shadowgraph method for routine, accurate determination of D11 in binary fluid mixtures.
• To establish measurement and data evaluation strategies for thermodiffusion experiments, accounting for confinement and advection.

Main Methods:

• Utilized the shadowgraph technique to study two binary liquid mixtures: 1,2,3,4-tetrahydronaphthalene/n-dodecane (positive Soret coefficient) and acetone/cyclohexane (negative Soret coefficient).
• Analyzed the dynamics of non-equilibrium concentration fluctuations.
• Applied data evaluation procedures informed by recent theoretical advancements.

Main Results:

• Demonstrated the suitability of the shadowgraph method for accurate D11 determination in binary mixtures.
• Developed robust data evaluation strategies applicable to various experimental configurations, including those with confinement and advection.
• Successfully measured D11 for the selected mixtures, considering their distinct Soret coefficients.

Conclusions:

• The refined shadowgraph method offers a reliable approach for routine D11 measurements.
• The developed strategies enhance the accuracy of thermodiffusion experiments, even under complex conditions.
• This work provides a foundation for more precise studies of diffusion in fluid mixtures.