Firewood

[Christophe]

Yes, seen from above the slot is radial, but it also goes from bottom to top, longitudinally ... but I think we agree ...

I speak of linearity (maybe it is not the appropriate term?) Because each concentric layer of cells sees its number increasing regularly, so the value of the shrinkage also increases (since each cell and intercellular space shrinks identically ). I do not know if it's clear?

Yes it is clearer!

Ok for the slot ... radially longitudinal

A washer is similar to 2D but actually a trunk is in 3D ...

[chatelot16]

for linearity, it's straight like a tree branch

more seriously, wood heating is the oldest form of solar heating!

when the wood is dry, like 20% water, the yield in a simple boiler is not too bad!: 1

there is worse than the energy lost to vaporize the water, there is the formation of bad combustible compound which carry the energy in the smoke when the wood is wet ... triple problem
1) loss of energy
2) fine particle pollution worse than diesel
3) fouling of the smoke pipes up to the chimney fire

a condensing boiler makes it possible to recover the energy wasted to evaporate the water is not as good as one could hope since it does not avoid the loss due to bad combustion

[Christophe]

Uh, do wood condensing boilers exist?

Frankly I have doubts because it will be terrible ... with the risks that we know: heating-insulation / security-of-wood-heating-avoid-fire-of-chimney-t10059.html

Already that for fuel oil it was for a long time not recommended!

[Grelinette]

... Normally dry wood is 4 to 4.5 kw.h per kilo.

The calorific value of firewood depends above all on its moisture content, the essence of the tree from which it comes being less important in this respect30,28. "It is the densest woods, which produce the most heat at equal weight".
The best energy efficiency of a gasoline is obtained at a humidity rate lower than 20%. Indeed, 1 kg of wood at 50% humidity gives off 2 kWh, at 20% 4 kWh.

https://fr.wikipedia.org/wiki/Bois_%C3% ... alorifique

see the table of calorific energies according to species in the link indicated.

I am surprised to see in the Wikipedia table that Pine (4.4 kWh / kg) has a higher calorific value than Oak (4.2 kWh / kg)!

Similarly, Willow (4.1), Work (4.3) and Poplar (4.1), which are very soft and very light woods, seem to me to have very high calorific values, always in comparison with Oak ... How to explain these values ​​?

To return to the questions initiated by Ahmed, I have a question about the concentric rings which indicate the age of the tree, as in the photo of the oak washer posted by Ahmed.
When you cut a tree trunk at the base you can see the concentric circles indicating the age. If we cut the trunk of the tree higher, there are fewer circles ...
First how do these circles form from one year to the next? And where do the circles disappear as you go up the trunk? ...

[Christophe]

Similarly, Willow (4.1), Work (4.3) and Poplar (4.1), which are very soft and very light woods, seem to me to have very high calorific values, always in comparison with Oak ... How to explain these values ​​?

Good note greli!

Willow, work and poplar are very bad firewood! It's well known!

Wiki may give the PCI "0% RH" (ideal therefore accessible only in the laboratory ??)?!?

[Christophe]

When you cut a tree trunk at the base you can see the concentric circles indicating the age. If we cut the trunk of the tree higher, there are fewer circles ...
First how do these circles form from one year to the next? And where do the circles disappear as you go up the trunk? ...

Another good note ... I never asked myself the question!

- For the appearance I think it is linked to the "winter break" quite simply, winter limits growth and the absence of sap must be represented by the dividing line between the years = drier period ... well this theory is only valid when there is a winter and I believe that exotic woods also have these growth circles, right?

- I think it's not that they disappear: it's that they never appeared!

[Grelinette]

... or else a tree trunk grows in the center, like the petals of a flower or an artichoke!
or a bit like a stack of nested funnels ...

[Christophe]

Oh no, we can see that the circles in the center are much smaller and closer together, these are the first years of growth ...

And how would you like the wood in the center to "push and deform" the rest of the trunk ...

or a bit like a stack of nested funnels ...

Ah I understand the idea better ... Yes there why not! It would be logical that there is more energy (sap flow) in the center than in the periphery ...

There is no modeling of the movement of the sap of a tree ??

[Grelinette]

Oh no, we can see that the circles in the center are much smaller and closer together, these are the first years of growth ...

And how would you like the wood in the center to "push and deform" the rest of the trunk ...

Well, it is perhaps the most recent center circles, and those on the outskirts that are the oldest!
Mystery, mystery ...

If we could cut a rose into slices, the first slices at the base would have more petals than higher: https://www.youtube.com/watch?v=dpNj6YsC2G8

[Christophe]

Basically no it is not possible!

On the other hand it is possible that the growth is done "at the top" more by those in the center and that the most recent circles do not appear at the top (they do not end up disappearing as you say on the height) ...

In fact he defrauded cutting a trunk along its length to analyze the behavior of the circles (which in this case will have become lines + or - parallel to the bark) on the height ...