Description:

Water-hating (superhydrophobic) and water-loving (superhydrophilic) surfaces have been extensively studied for the past two decades. The early focus in the field was on mimicking nature, e.g., lotus leaves, to make surfaces on which water beads up and rolls off easily. Such surfaces are “self-cleaning.” Through the past decade and a half, the focus in our group has also been on manipulating phase change of water near surfaces. We’ve used thermodynamics and fluid-dynamics to explore possibilities. To elucidate these ideas, four foundational problems will be explored in this talk: 

1. How to stay dry under water? To enable this can we sustain water vapor next to a surface at temperatures below the boiling point? Can we extend this idea to sustain liquid water above its boiling point next to surfaces? Can we also use rough surfaces to do what salt does – sustain supercooled liquid water below the freezing point?

2. How to use dry surfaces or superwetting surfaces to completely change the textbook boiling behavior of water, e.g., no bubbly (nucleate) boiling of water drops? 

3. What non-dimensional number (or physical processes) characterizes the stability of those ultramobile bead-like drops (Leidenfrost drops) you see on a hot kitchen pan? 

4. What is the liquid-vapor interface temperature during boiling – is it always the boiling point?

Neelesh A. Patankar, Professor, Department of Mechanical Engineering, Northwestern University

Host: Anupam Garg