Retention Forces for Drops on Microstructured Superhydrophobic Surfaces

Area of Science:

• Surface Science
• Fluid Dynamics
• Heat Transfer

Background:

• Accurate modeling of drop retention forces on superhydrophobic (SH) surfaces is crucial for predicting drop dynamics and heat transfer during dropwise condensation.
• Existing models often fail for microstructured SH surfaces, necessitating new approaches that consider surface topography and wetting behavior.

Purpose of the Study:

• To develop and validate accurate models for retention forces between drops and microstructured SH surfaces.
• To investigate the influence of contact angle distribution and base area shape on retention forces.
• To improve the prediction of drop dynamics and heat transfer on SH surfaces.

Main Methods:

• Measurement of contact angle distribution and drop base area shapes for various drop sizes on inclined microstructured SH surfaces.
• Approximation of base area shape using two ellipses and fitting contact angle distribution with a sigmoid function.
• Calculation of retention forces using measured contact angles and base area shapes, validated against drop weight on tilted surfaces.

Main Results:

• Drop base area shape was approximated by two ellipses; contact angle distribution was best fit by a sigmoid function.
• Near roll-off angles, drop base areas were circular for high/low solid fractions but non-circular for intermediate fractions.
• The proposed model, incorporating sigmoid contact angle distribution and modified base area, improved retention force calculations by 50% compared to previous methods.

Conclusions:

• The study provides a more accurate method for calculating retention forces on microstructured SH surfaces by considering specific geometric and wetting properties.
• The findings enhance the ability to predict drop behavior and optimize heat transfer in applications utilizing SH surfaces.
• The developed model offers improved retention force factor values for surfaces with varying solid fractions.