[ethanbond]

> In recent years, some researchers have been puzzled upon finding that water in their experiments, which was held in a sponge-like material known as a hydrogel, was evaporating at a higher rate than could be explained by the amount of heat, or thermal energy, that the water was receiving. And the excess has been significant — a doubling, or even a tripling or more, of the theoretical maximum rate.

Apparently it evaporates much, much more quickly than you'd expect from purely energy per mass.

[pdonis]

> it evaporates much, much more quickly than you'd expect from purely energy per mass

From purely "thermal" energy per unit mass. But the light is delivering energy too; the total energy per unit mass being delivered is still the same, it's just being put in in a different form. Nothing about this changes the bonding energy between water molecules that has to be overcome for evaporation to occur. It's just a different method of delivering that energy.

[elil17]

The paper is accounting for the energy that the light is delivering. The very neat thing about this paper is that it does change the bonding energy between water molecules that has to be overcome for evaporation to occur.

They observed evaporation of clusters of molecules, not individual molecules. Since whole groups of molecules are flung into the air, not all of the intermolecular bonds need to be broken for them to evaporate. Heat from the air is later used to break those clusters apart into individual molecules.

[pdonis]

> They observed evaporation of clusters of molecules, not individual molecules. Since whole groups of molecules are flung into the air, not all of the intermolecular bonds need to be broken for them to evaporate. Heat from the air is later used to break those clusters apart into individual molecules.

This sounds more like the light is making thin fog, not water vapor.

[elil17]

Well, sort of. I’m conceptualizing it as an intermediate state between a vapor and an aerosol. The aerosol would have way more intermolecular bonds per molecule on average since most of its molecules are in the insides of droplets. But these molecule clusters have all or almost all their molecules exposed on the clusters surface, so they have many fewer intermolecular bonds.

[pixl97]

Evaporation should be a function of surface area. In a large pool of water the evaporation should occur primarily in the upwards direction. Any molecular activity that is sideways or downwards will not lead to the molecule escape.

Once a water particle escapes, depending on the clump size it should have more degrees of freedom in evaporation and I would think surface tension would be reduced.

[tzot]

As I understand it, when you heat water, you give energy to all of the water molecules that start moving faster in their random direction. So molecules that were directed towards outside the water mass are “directly” extracted, and the rest will bounce around in the increasing pressure until they are “indirectly” extracted (I used “directly” and “indirectly” non-scientifically here, just to make a distinction.) It takes quite a lot of energy which leads to evaporation over time.

I think what they found is a set of circumstances where the energy of the light “chips off pieces” of water, so the energy needed is much less. A small broken-off “piece” (or cluster of water molecules) has a very large ratio of surface area over volume, so the rest of the evaporation is taken care of by the surrounding environment as-is.