Measuring temperature gradients in evaporating multicomponent alcohol/water droplets

Area of Science:

• Physical Chemistry
• Fluid Dynamics
• Spectroscopy

Background:

• Understanding temperature gradients in evaporating droplets is crucial for various scientific and industrial applications.
• Previous methods lacked the precision to accurately characterize these internal temperature variations.
• Volatile droplets present unique challenges due to rapid evaporation and changing conditions.

Purpose of the Study:

• To develop and demonstrate a dual-spectroscopic approach for investigating temperature gradients in evaporating water/alcohol droplets.
• To accurately measure both volume-averaged and near-surface temperatures within these droplets.
• To validate experimental findings against theoretical predictions of droplet evaporation.

Main Methods:

• Volume-averaged temperature determined using laser-induced fluorescence (LIF) of Rhodamine B, achieving +/-1 K accuracy.
• Near-surface temperature measured via cavity-enhanced Raman scattering (CERS) by analyzing the OH stretching band, with +/-4 K accuracy.
• Experimental conditions varied, including evaporation time, buffer gas pressure, droplet size, and composition.

Main Results:

• Successfully measured temperature gradients within evaporating droplets using the combined LIF and CERS techniques.
• Experimental temperature measurements showed consistency with quasi-steady theoretical models of evaporation.
• The accuracy of both techniques allows for detailed characterization of thermal profiles during evaporation.

Conclusions:

• The developed spectroscopic methods provide a robust tool for studying temperature gradients in evaporating droplets.
• This technique enables a deeper understanding of the complex interplay between evaporation dynamics and thermal profiles.
• Findings support theoretical models and offer new avenues for controlling evaporation processes.