Re: latent heat of evaporation

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

Ludwik,
When the bubbles form below the surface, you still have a gas-liquid
interface, its just that the gas is essentially all water vapor, and the
pressure is slightly higher because of the depth of the water.  Further
the rate of boiling depends on the character of the nucleation sites.
Rough surfaces have lots of sights so small bubbles are formed.
Chemists use boiling chips to keep the bubbles small.  This is basically
a kinetic effect, not an equilibrium one, so I wouldn't expect the
latent heat to change.  But I wouldn't stake my life on it.

joe

On Sun, 26 Sep
2004, Ludwik Kowalski wrote:

> I suppose that latent heat of evaporation of water,
> L=540 cal/gm, applies to evaporation from the
> surface (to overcome attractive molecular forces).
> What evidence can be found that L remains the
> same during intensive boiling? I am watching a
> heating resistor immersed in a beaker. In this
> case most bubbles are formed below the
> surface, near the heating coil.
> Ludwik Kowalski

Joseph J. Bellina, Jr.               574-284-4662
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556