Kelvin Effect: Physical Cartoon Equilibrium vapor pressure is higher over a curved surface than a...
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Kelvin Effect: Physical Cartoon Equilibrium vapor pressure is higher over a curved surface than a flat one. Important for nucleation of new particles, lifetime of small droplets.
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Transcript of Kelvin Effect: Physical Cartoon Equilibrium vapor pressure is higher over a curved surface than a...
- Slide 1
- Kelvin Effect: Physical Cartoon Equilibrium vapor pressure is higher over a curved surface than a flat one. Important for nucleation of new particles, lifetime of small droplets.
- Slide 2
- Energy of converting vapor molecules to bulk liquid molecules Energy required to maintain a liquid-gas surface boundary X v X l Kelvin Effect: Energy of Droplet Formation
- Slide 3
- Rp*Rp* Radius at which G maximizes and beyond which droplet formation becomes possible S1 GG S = ratio of eq. vapor pressure around a droplet relative to to above a flat surface For a droplet to exist, S>1. p curved > p flat always How does S vary with R p ?
- Slide 4
- Kelvin Equation Relates molecular properties (molecular weight, surface tension, density) to the degree to which v.p. over curved surface is enhanced
- Slide 5
- Questions 1.Some organic compounds are highly surface active. That is, they prefer to reside at the gas-liquid interface, and lead to a lower surface tension. By how much would S change if the surface tension of a droplet changed from 75 dynes (pure water) to 35 dynes (surfactant coated water)? 2.Do you have a physical explanation to the above answer? 3.What is the surface tension of a cluster of 10 H 2 SO 4 molecules and 10 H 2 O? Is it the same as the surface tension for a 50 wt% H 2 SO 4 bulk solution?
- Slide 6
- RpRp RpRp Free Molecular or Non-continuum Regime Continuum Regime Transition Regime Continuum versus Free Molecular Dynamics
- Slide 7
- Mean Free Path In 1 second: red has swept through a volume For N molecules per cm 3, red-blue collisions per sec ~ The distance traveled between collisions:
- Slide 8
- Mean Free Path Increases with Altitude For 10 nm particle: Kn