woodburning safety (avoiding the fireplace)

[aerialcastor]

When you dry in the open air you must not provide the latent heat of vaporization which is enormous in the case of water and which will be pumped into the hearth. It takes more than 500 times more energy to pass 1 g of water from 100 to 101 ° C than from 99 to 100 ° C!

You sure about that?
Even if we are not at 100 ° C, the water must evaporate so it changes phase.

[Christophe]

Yes I think

Drying by hot air does not require going through the latent heat of vaporization: it is the air which tends to always want to saturate itself with humidity, did67 explained it well above. It must have energy exchanged but by far as important as during a vaporization by boiling.

Otherwise any puddle of water that evaporates to the air would require very high energy. I'm going to do some research because it's far ...

Conversely, a petrol carburetor frost because petrol has a lower evaporation temperature than water, this evaporation of petrol (at least partly because 100% is not evaporated) will therefore pump calories until the carburetor frost.

[aerialcastor]

Good after a quick search:

here: http://fr.wikipedia.org/wiki/%C3%89vaporation

We have :

Evaporation requires a significant amount of energy in general (the latent heat of vaporization), which allows for example the temperature regulation in homeotherms by perspiration and evaporation of sweat, or the cooling of a jug in earth, or air by nebulization (water aerosol). The evaporation of a liter of sweat removes 600 kcalories

Where no difference is made between latent heat of vaporization and latent heat of evaporation.

And here : http://fr.wikiversity.org/wiki/Changements_d%27%C3%A9tats/Vaporisation_et_condensation

We have :


Which shows that the higher the temperature, the lower the latent heat of vaporization.


Good after I did not cross the sources, nor too dug, I have a little laziness, and a little job but that is less important
so if someone can confirm.

[Did67]

Yes I think :)


Otherwise any puddle of water that evaporates to the air would require very high energy. I'm going to do some research because it's far ...

Conversely, a petrol carburetor frost because petrol has a lower evaporation temperature than water, this evaporation of petrol (at least partly because 100% is not evaporated) will therefore pump calories until the carburetor frost.

It requires !!! That's why your puddle slowly evaporates!

Like fuel, yes. And like gas from the fridge or the heat pump ...

That's why you're cold when you leave a swimming pool even if it's 30 ° especially if there is a little wind (while dry, you will be hot 5 minutes later) ...

In Africa, in dry climates (Namibia), evaporators are used to air-condition homes. A fan, a large mesh box with fibers between the grids and water running over it and voila. If it's very dry, it's frozen!

And for those who sweat a lot and roll with the window open, torticoli guaranteed because the air flow evaporates the sweat and we end up with a "frozen neck". It took 3 months before I realized that I had to wrap a towel around my neck!

This is also why we "suffocate" under a cumulo-nimbus (storm cloud): thousands of tons of water vapor which condense above your head and which conversely (condensation ) give off a phenomenal heat which is radiated towards the earth ...

This is why 27 ° in Abidjan (saturated air) is pungent while 35 ° in Ouagadougou (dry air) is pleasant: perspiration in Abdijan flows without evaporating, wets your shirt, while in Ouaga , you do not realize that you are sweating: it evaporates, cooling off, instantly ...

Yes, at any temperature, the phase change in the liquid-gas direction "pumps" calories.

And that explains the drop in yield when you burn wet wood (and the difficulty of lighting a fire with wet wood) ...

The curve out of Wikipedia troubles me a little, not on the principle, but on the scale. That said, is it standard in particular pressure conditions so that the water evaporates at 400 °?

[Christophe]

Ok I bow, it's the same then ... so much the better it will be easier to remember

Did, that the evaporation pumps energy whatever the T ° I obviously do not question it but I thought that there were other phenomena below 100 ° C which favored the evaporation of the water and reduced the energy required compared to that of boiling at 100 ° C ... as if the curve found by beaver went through a maximum.

However, this is defined by:

The latent heat of vaporization is the quantity of heat that must be supplied to 1 kg of water (at constant pressure and temperature) to obtain 1 kg of saturated vapor

However in the case of drying below 100 ° C we do not get saturated steam ... but a little more humid air ... hence my perplexity about the equivalence of energies. ..

So please ignore my previous remarks and excuse my ignorance (school is far away).

[Did67]

The curve out of Wikipedia troubles me a little, not on the principle, but on the scale. That said, is it standard in particular pressure conditions so that the water evaporates at 400 °?

While walking, I thought a little and finally, it's pretty obvious!

- the energy is used to "agitate" the molecules, so that they "tear away" from each other ...

- the hotter the water, the more the molecules are already agitated ...

It is therefore obvious that the latent heat decreases markedly as the water temperature rises!

[Christophe]

Yes it makes sense ... in the case of steam.

I would have to walk too because I'm still not 100% convinced that we have saturated steam when drying in dry air ...

Does cycling also work?

ps: like another "problem" of the moment (about VAT, nothing to do I know): https://www.econologie.com/forums/post180507.html#180507

[Did67]

Did, that the evaporation pumps energy whatever the T ° I obviously do not question it but I thought that there were other phenomena below 100 ° C which favored the evaporation of the water and reduced the energy required compared to that of boiling at 100 ° C ... as if the curve found by beaver went through a maximum.

I think you are right: the curve given is that for a saturated vapor, by defeat of the latent heat

Evaporation will probably be facilitated by the fact that the air is not saturated: there is surely a bundle of parallel curves depending on the vapor pressure in the air ... So we can think that it will be necessary slightly less calories.

[Christophe]

Ah well here ...

It remains to be seen "how much a little less calories" ...

I think we have the answer in a mollier diagram (full version) which gives the enthalpy of the following humid air are% humidity and its T °.

I will try to find one.

[Christophe]

I found: https://www.econologie.com/forums/post180536.html#180536

Here are 2 other Mollier diagrams including enthalpy:

"Simple" version:



Full version high resolution in .pdf
https://www.econologie.info/share/partag ... uQHxvN.pdf

usage:

1 kg of air at 20 ° C contains at saturation 15 g of water and 58 kJ.
This means that if we condense 100% of the water contained in the water, we will recover 58 kJ.

Problem: if we condense 1 L of water we would get: 1000/15 * 58 = 3800 kj / kg ... it's much more than latent heat ...

I bug or else?