Origin, Evolution, and Movement of Microlayer in Pool Boiling

Area of Science:

• Fluid dynamics
• Heat transfer
• Surface science

Background:

• Pool boiling is a crucial heat transfer mechanism.
• Understanding bubble dynamics, including the microlayer thin film, is key to optimizing heat transfer.
• Current models often assume a three-phase contact line dictates bubble origin.

Purpose of the Study:

• To visualize the microlayer thin film in situ during pool boiling.
• To investigate the initial formation of vapor bubbles on different surfaces.
• To characterize the drying process and contact line movement.

Main Methods:

• In situ visualization of the microlayer thin film within vapor bubbles during pool boiling.
• Experimental determination of bubble base behavior on hydrophilic and hydrophobic surfaces.
• Analysis of curvature changes and energy requirements for bubble movement.

Main Results:

• Bubbles originate with a completely wetted base, lacking a three-phase contact line, on both hydrophilic and hydrophobic surfaces.
• The wetted bubble base phenomenon is dependent on liquid-solid interactions.
• A cyclical behavior in microlayer curvature, termed "dryout viscosity," occurs during the drying process.
• The energy required for contact line unpinning and movement was defined.

Conclusions:

• The initial formation of vapor bubbles during pool boiling deviates from established theories.
• Liquid-solid interactions significantly influence the presence of a wetted bubble base.
• The study provides new insights into the complex dynamics of the microlayer during bubble growth and detachment.