Latent Heat of Water Vapor in Flue Gas

[Deleted]

The temperature of flue gas does not tell anything
about the amount of water it may contain,
nor about the amount of water it left behind in the system.

The saturation values in tables for relative humidity
are only valid if there is no temperature gradient to the surface
and they are not valid for surfaces of anything but water.
Contaminants in the water influence saturation values too.

Condensation is the change of the physical state of matter
from gaseous phase into liquid phase.
Initiated by adsorption which is the adhesion to a surface.

Condensation of water vapor starts rarely as adsorption to water,
as it needs a energy gradient delivered by condensing cores.
In experiments water vapor, without condensing cores,
has been freezed to -40°C/-40°F without condensation.
Anything wettable will adsorp vapor stronger than water.
Once the condensing core ( surface ) is completely surrounded by
a water film ( if only one molecule thick )condensation can start.
At this point the amount of water vapor has already been reduced.
Actually there may be no condensation involved in reducing
the amount of water vapor in a gas.

The amount of adsorption/condensation is influenced by:
Temperature
Temperature gradient
Size of the surface and the surface itself.
Turbulence
Pressure

Higher temperatures will weaken the small forces between molecules,
but enhance the probability of contact.
For lower temperatures the reversal of the above is valid.

Porosity can enlarge a surface many times.
Capillarity may move water inside of the material
and thus additionaly enlarge the involved surface many times.
Surfaces with a high surface/ volume ratio can be
significantly enlarged by condensation.

Turbulence enhances the probability of contact
and in case of a liquid it may enhance its surface.

Pressure influences the vapor pressure in the gas and of the liquid.

Precise calculations may need a very powerful number cruncher.

Water molecules will try to occupy any place on wettable surfaces,
and thus wettable surfaces could be almost seen as water surfaces.
But as environments are not static and the laws of physics will enforce
leveled values after disorder there will be dynamic.

Capillary condensation of vapor occurs below the saturation vapor pressure.

[ashbed]

Karl:
A year ago I investigated the ability of adobe to absorb/desorb humidity for temperature control (in hot humid climates).
I found only a few esoteric references, the best confirmation was in Minke.
The effect is real, but the rate is slow and the area required is huge, (ie all walls of house) as it is the skin about 2cm most effective.
Also it is the clay with high specific surface area which is active, not sands etc.
Require about 150m2 of walls to absorb 30 lt moisture over 24 hours from 80%RH air with 1 air change per hour (rough calculation – see Minke).
The effect is insufficient to replace an air-conditioner by maybe an order of magnitude. (but good for keeping inside humidity close to 50%)

Having worked in wildfire suppression I know it takes hours for vegetation moisture levels to respond to changes in air humidity levels, even though the leaves are less than 1mm thick and porous on the microscopic level.

I doubt a kang/bench/bell would be even this effective, with 6 – 8 inch diameter tunnel, only 10 to 30 metre long, say 15 m2 surface.
The residence time for flue gasses would be less than a minute.
I reckon you are three orders of magnitude short of a solution.
Your post is just a thought bubble with no references, no values or calculations.
This in response to my quite specific earlier post mentioning 0.8 kg of water per kg of wood burned, as vapour in 5.3 kg of other flue gasses.
We are dealing with bucket chemistry here, many approximations and heroic assumptions, just a ball-park result expected.
Personally, I was shocked to find the majority of the vapour wouldn't automatically condense out at 99 degrees.
I had no idea air could contain such a large quantity of water, at a temperature as low as 50 Celsius.

Much of the rest of your logic relies on red herrings.
How do you propose to alter the pressure by more than a percent or two?
How much temperature gradient do you expect in the bench-flue?
Turbulence equals resistance, which is to be avoided in the bench flue.
In another post you confuse relative and absolute humidity.
You also claimed 98% efficiency.
Attention to detail doesn't seem as important as shooting from the lip.

Follow the KISS principle.
It is all to chase the last 15 odd % of heat extraction efficiency. Not much really, just nice for a purist if we can get it.
Ianto mentions condensation and low exhaust temperatures, so it cannot be too difficult to just build a longer bench or whatever to drop the exhaust temperature to say 30 degrees C

[Deleted]

Apr 2, 2013 4:58:27 GMT -8 ashbed said:

Karl:
A year ago I investigated the ability of adobe to absorb/desorb humidity for temperature control (in hot humid climates).

Nobody needs stoves in hot humid climates.
Gradients in steam pressure on both sides of a wall have much influence.
Have you ever taken a hot shower in a room with mud walls in a drier climate ?

You will not foster your stance by insulting comments.

I assume I am the only of us both with an professional education in this respect.
I admit I am sometimes sloppy.
You too, were not always careful.

I have put much attention to detail in what I wrote above.

BTW you are wrong with the sand.
Capillary condensation needs sufficiently wide capillars.

If you devide a one cubic meter cube into cubes with one micro meter
and fill them into the same space the total surface will be six million square meter,
but the inner surface will be inaccessible.
If you fill a one cubic meter cube with fine rounded sand there will be a huge
and accessible inner surface, which could maybe take more water than some clays.