Stagnation Point of Surface Flow during Drop Evaporation

Area of Science:

• Fluid dynamics
• Surface science
• Evaporation phenomena

Background:

• Evaporating liquid drops exhibit complex flow patterns influenced by surface tension gradients (Marangoni flow) and liquid-solid interactions (capillary flow).
• Understanding these flow dynamics is crucial for applications like inkjet printing, coating, and heat transfer.

Purpose of the Study:

• To investigate the influence of capillary flow on the flow patterns of an evaporating liquid drop.
• To identify and explain the formation of a stagnation point near the contact line.
• To validate numerical findings with experimental observations.

Main Methods:

• Numerical simulations were employed to model the fluid flow within an evaporating liquid drop.
• Lubrication theory was used to provide a theoretical explanation for the observed flow behavior.
• Experimental data was utilized for comparison and validation of the numerical results.

Main Results:

• A stagnation point was identified near the contact line in the numerical simulations.
• The stagnation point arises from the competing effects of Marangoni flow and capillary flow.
• The formation and position of the stagnation point are strongly dependent on the contact angle, becoming more pronounced at smaller angles.

Conclusions:

• Capillary flow plays a significant role in determining the flow patterns of evaporating drops, contrary to the common assumption that Marangoni flow is the sole driver.
• The study confirms the existence of a stagnation point near the contact line, explained by the combined influence of capillary and Marangoni effects.
• Numerical results for the stagnation point's radial position closely matched experimental observations, validating the model.