Heating and Evaporation of Sessile Droplets: Simple and Advanced Models

Area of Science:

• Thermodynamics
• Fluid Dynamics
• Heat Transfer

Background:

• Accurate modeling of sessile droplet behavior is crucial for understanding heat and mass transfer processes.
• Existing one-dimensional (1D) models often oversimplify heat distribution within droplets.
• There is a need for more sophisticated models that account for spatial variations in heat transfer.

Purpose of the Study:

• To develop and validate new two-dimensional (2D) models for sessile droplet heating, cooling, and evaporation.
• To compare the predictive capabilities of advanced 2D, simple 2D, and simple 1D models against experimental data.
• To assess the suitability of different models for predicting droplet radius and surface temperature dynamics.

Main Methods:

• Developed an advanced 2D model using numerical solutions of conservation equations (mass, momentum, vapor mass fraction, energy) in COMSOL Multiphysics.
• Created simple 2D and 1D models, assuming truncated spherical droplet shapes and solving heat conduction equations numerically (simple 2D) or analytically implemented numerically (1D).
• Validated model predictions against experimental data from sessile water droplets (2.2–5.2 μL) at 298.15 K and atmospheric pressure.

Main Results:

• All three models (advanced 2D, simple 2D, 1D) showed good agreement with experimental data for normalized droplet radii squared, supporting the use of the simple 1D model for this parameter.
• The advanced 2D model accurately predicted the time dependence of the average surface temperature, closely matching experimental observations.
• Simple 2D and 1D models successfully captured the initial rapid decrease followed by a gradual increase in average surface temperature, consistent with experimental findings.

Conclusions:

• The developed advanced 2D model provides a more accurate representation of sessile droplet heating and evaporation by considering spatial heat distribution.
• The simple 1D model is recommended for predicting droplet radius changes due to its accuracy and simplicity.
• Simple 2D and 1D models offer valuable insights into surface temperature dynamics, particularly the initial cooling and subsequent warming phases.