Yea, Jason and Bruce are the
Yea, Jason and Bruce are the wine drinkers at ASHRAE. I used to drink Pabst until the hipsters drove the price up, then I switched to Pearl until I moved from Texas to Oklahoma. Now I just drink whatever 3.2 beer is on sale here.

Bill,
Bill,

I am not sure what you mean about capillarity and a contact angle of 90 degrees. My understanding is that hydrophylic surfaces have high attraction of liquid water with contact angles between zero and 90, and hydrophobic surfaces have contact angles between 90 and 180 degrees. On the former, water tends to “wet” the surface, whereas on the latter the water tends to “bead” up. I am guessing that sponges have contact angles less than 90 degrees. But then again, perhaps the sponge is just trapping beads of water in hydrophobic pores?

But I see three different mechanisms for water being discussed here. Condensation is simply water vapor condensing to a liquid because its temperature is lowered to a value below its dewpoint, or correspondingly, the water vapor pressure is higher than the saturation water vapor pressure at that temperature. You don’t even need a surface for this to happen (rain?). Sorption occurs because of molecular attraction that results in water vapor being absorbed or adsorbed from the air onto a hygroscopic material at even lower vapor pressures than those associated with condensation. Capillary action is purely a liquid water (not vapor) and surface material interaction. Sponges can probably exhibit all three depending on the material and temperatures, but I think that capillary action is what makes a sponge useful for cleaning up spills or drying surfaces.

That was probably Jason. I do

That was probably Jason. I do drink wine but I don’t recall having done so with Paul at an ASHRAE meeting. We were drinking beer in Virginia, though, because at a place named Fatback Soul Shack, I trust the quality of the beer a lot more than I trust the wine. Plus, I like good craft beer.

I’m glad Bill Rose caught wind of the discussion and has chimed in here now.

Capillarity depends on the molecular level where the water meets the capillary wall. There would be no capillarity if the contact angle is 90 degrees.

I try to reserve the term “condensation” for where it’s water-to-water, and avoid it with water-to-material. That’s a losing battle.

I do the mirror and sponge routine when I present, and I always credit Paul for the wiping the mirror bit.

RoyC challenges the role of sorption, which he correctly notes occurs at the chemical/molecular level. Water binds to molecules like the molecules of cellulose, and clay, and gypsum. The dry sponge sitting on the counter is not entirely dry–it loses weight with oven-drying. If we pressed out all the pores, there would still would be a small amount of water hugging the surface.

In my book I noted the three classical phases of water, of pure water, then described another “phase” of bound water–dirty water. The classical phases use the textbook values of binding energy for water-to-water. The binding energies to hygroscopic materials vary all over the place.

Take care, y’all. Gotta check on my daughter in Santo Domingo. By the way, I hear all these weatherheads talking about “most violent storm ever recorded” and “highest rainfall ever recorded”, and none of them say that storms will all be milder after this. They will, won’t they?

Allison, I thought that I
Allison, I thought that I always saw you and Paul drinking wine at ASHRAE meetings. Do you switch to beer when you are with the “working” people 😉

I think that the mechanisms of “hygroscopicity” and “capillary action” are quite different in terms of their driving forces and probably can occur simultaneously. I would guess that brick has both, but I don’t know. But I will still claim that water “condenses” on any surface that is colder than the dewpoint of the surrounding air. Hygroscopic materials will absorb water vapor at even lower surrounding humidities, but capillary action (things with pores) need direct contact with liquid water for them to “absorb” water and will eventually dry out if in contact with air that is not saturated.

Tim, you’re right that water

Tim, you’re right that water activity is the relevant measure for understanding moisture content and mold growth. But that’s not the point I’m trying to make here. I was explaining Bill Rose’s reasoning for why the word “condensation” doesn’t apply in many of the building science cases where it’s used. Relative humidity and sorption isotherms are indeed the right track for that discussion. If Roy is correct, though, a sponge may not have been the best material to use to illustrate that.

Roy, I completely disagree

Roy, I completely disagree with you. Paul and I could not have had too much wine because we were drinking beer. But I think I may be in agreement with you about sponges. When Paul told the story, he said Bill Rose used that as an example when he talked about condensation, so I assumed it must be right. I need to ask Bill for his version of the story, though. Maybe something got lost in the translation. Or maybe it depends on the type of sponge.

Then again, I don’t buy your argument about using “sponge material to make an object with no pores.” If you could use brick material to make an object with no pores, it probably wouldn’t be hygroscopic either.

Let me see what I can soak up in my research.